#!/usr/bin/env python
#
# SRC - simple revision control.
#
# Things to know before hacking this:
#
# All the code outside the RCS and SCCS classes (and the RevisionMixin
# helper) is intended to be generic to any file-oriented VCS.
#
# SRC and RCS/SCCS have different goals in managing locks.  RCS/SCCS
# wants to keep the workfile read-only except when it's explicitly
# checked out, SRC wants to leave it writeable all the time.  Thus,
# the checkin sequence is "release lock; check in; assert lock".  If
# this seems confusing, it's because in RCS/SCCS terminology, locked is
# writeable and unlocked is read-only.
#
# Despite appearances, this code does not actually use RCS locks (and
# sets locking to non-strict).  That just happens to be a handy way to
# record which revision the user last checked out, which is significant
# for future checkouts and for branching.
#
# With sufficient cleverness it would be possible to go in a different
# direction - leave the master unlocked at all times except during during
# the commit sequence, intervening with a chmod to turn off write protection
# on the workfile when RCS/SCCS would normally turn it on.  I had this as
# a to-do for a long time but have abandoned the concept; fighting RCS/SCCS's
# notion of when the workfile ought to be write-locked seems too likely to
# lead to weird bugs in unexpected situations.
#
# In an ideal world, we'd get rid of A status. The SCCS back end doesn't
# have it, because the only way to register new content is by "sccs add"
# on an already existing file and that creates a new SCCS master with
# the content checked in as the first commit.  RCS ci works that way as
# well.  On the other hand, if you use rcs -i foo it creates a master foo,v
# but does *not* stuff it with the content of any corresponding foo.  This
# is what A status means.
#
# This code uses magic tags with a 0 in the second-to-last slot to
# designate branches.  It's the same format as CVS sticky tags, for
# the same reason.  They need to be distinguishable from regular tags
# pointing at revisions, and this way the code to transform the sticky
# tag into the branch name is as simple as possible.
#
# Top of the list of things that people will bikeshed about is the
# letter codes returned by 'src status'.  Different VCSes have
# conflicting ideas about this.  The universal ones are 'A' = Added,
# 'M' = Modified, and '?' = Untracked.  Here's a table of the ones
# in dispute.  Entries with '-' mean the VCS does not have a closely
# corresponding status.
#
#                   git     hg     svn      src
# Unmodified        ' '     '='    ' '      '='
# Renamed           'R'      -      -        -
# Deleted           'D'     'R'    'D'       -
# Copied            'C'      -      -        -
# Ignored           '!'     'I'    'I'      'I'
# Updated/unmerged  'U'      -      -        -
# Missing            -      '!'    '!'      '!'
# Locked             -       -     'L'      'L'
#
# (hg used to use 'C' as the code for unmodified status.)
#
# This is a bit oversimplified; it is meant not as a technical
# comparison but rather to illustrate how bad the letter collisions are.
# SRC follows the majority except for absolutely *not* using a space as
# a status code; this makes the reports too hard to machine-parse.
#
# SPDX-License-Identifier: BSD-2-Clause

# This code runs under both Python 2 and Python 3.
# Preserve this property!

from __future__ import print_function

import sys, os, subprocess, datetime, time, calendar, stat, glob
import shutil, difflib, cgi, json, io, re, signal
import tempfile, email.utils
try:
    import curses
except ImportError:
    pass

version="1.20"

CENTURY = "20"	# A Y2.1K problem, but only for SCCS.

# General notes on Python 2/3 compatibility:
#
# SRC uses the following strategy to allow it to run on both Python 2
# and Python 3:
#
# * Use binary I/O to read/write data from/to files and subprocesses;
#   where the exact bytes are important (such as in checking for
#   modified files), use the binary data directly.
#
# * Use latin-1 encoding to transform binary data to/from Unicode when
#   necessary for operations where Python 3 expects Unicode; this will
#   ensure that bytes 0x80..0xff are passed through and not clobbered.
#   The polystr and polybytes functions are used to do this so that when
#   running on Python 2, the byte string data is used unchanged.
#
# * Construct custom stdin, stdout, and stderr streams when running
#   on Python 3 that force ASCII encoding, and wrap them around the
#   underlying binary buffers (in Python 2, the streams are binary and
#   are used unchanged); this ensures that the same transformation is
#   done on data from/to the standard streams, as is done on binary data
#   from/to files and subprocesses; the make_std_wrapper function does
#   this.  Without this change, 0x80..0xff written to stdout will be
#   garbled in unpredictable ways.

master_encoding = 'latin-1'

if str is bytes:  # Python 2

    polystr = str
    polybytes = bytes

else:  # Python 3

    def polystr(obj):
        "Polymorphic string factory function"
        # This is something of a hack: on Python 2, bytes is an alias
        # for str, so this ends up just giving a str back for all
        # inputs; but on Python 3, if fed a byte string, it decodes it
        # to Unicode using the specified master encoding, which should
        # be either 'ascii' if you're sure all data being handled will
        # be ASCII data, or 'latin-1' otherwise; this ensures that the
        # original bytes can be recovered by re-encoding.
        if isinstance(obj, str):
            return obj
        if not isinstance(obj, bytes):
            return str(obj)
        return str(obj, encoding=master_encoding)

    def polybytes(s):
        "Polymorphic string encoding function"
        # This is the reverse of the above hack; on Python 2 it returns
        # all strings unchanged, but on Python 3 it encodes Unicode
        # strings back to bytes using the specified master encoding.
        if isinstance(s, bytes):
            return s
        if not isinstance(s, str):
            return bytes(s)
        return bytes(s, encoding=master_encoding)

    def make_std_wrapper(stream):
        "Standard input/output wrapper factory function"
        # This ensures that the encoding of standard output and standard
        # error on Python 3 matches the master encoding we use to turn
        # bytes to Unicode in polystr above.
        return io.TextIOWrapper(stream.buffer, encoding=master_encoding, newline="\n")

    sys.stdin = make_std_wrapper(sys.stdin)
    sys.stdout = make_std_wrapper(sys.stdout)
    sys.stderr = make_std_wrapper(sys.stderr)

# Note: Avoid using unbolded blue (poor luminance contrast with black
# terminal-emulator background) or bolded yellow (poor contrast with
# white background.)
RESET = BOLD = ''
CBLACK = CBLUE = CGREEN = CCYAN = CRED = CMAGENTA = CYELLOW = CWHITE = ''

def init_colors():
    curses.setupterm()
    global RESET, BOLD
    RESET = polystr(curses.tigetstr('sgr0')) or ''
    BOLD = polystr(curses.tigetstr('bold')) or ''
    colors = {'setaf': [0, 4, 2, 6, 1, 5, 3, 7], # ANSI colors
              'setf': [0, 1, 2, 3, 4, 5, 6, 7]}  # legacy colors
    for (k, v) in colors.items():
        x = curses.tigetstr(k)
        if x:
            for (i, c) in enumerate(['black', 'blue', 'green', 'cyan', 'red',
                                     'magenta', 'yellow', 'white']):
                globals()['C' + c.upper()] = polystr(curses.tparm(x, v[i]))
            break

if 'curses' in sys.modules and sys.stdout.isatty():
    try:
        init_colors()
    except (curses.error, AttributeError):
        pass

def rfc3339(t):
    "RFC3339 string from Unix time."
    return time.strftime("%Y-%m-%dT%H:%M:%SZ", time.gmtime(t))

def announce(msg):
    sys.stdout.write("src: " + msg + "\n")

def croak(msg):
    sys.stdout.flush()
    sys.stderr.write("src: " + msg + "\n")
    sys.exit(1)

debug = 0
DEBUG_COMMANDS  = 1    # Show commands as they are executed
DEBUG_SEQUENCE  = 2    # Sequence debugging
DEBUG_PARSE     = 3    # Debug logfile parse

quiet = False		# option -q: run more quietly
pseudotime = False	# option -T: artificial clock for regression testing

class popen_or_die:
    "Read or write from a subordinate process."
    def __init__(self, command, legend="", mode="r"):
        assert mode in ("r", "w")
        self.command = command
        self.legend = legend
        self.mode = mode
        # Pipe to the correct streams depending on the chosen mode
        self.stdin = (subprocess.PIPE if mode == "w" else None)
        self.stdout = (subprocess.PIPE if mode == "r" else None)
        self.stderr = (subprocess.STDOUT if mode == "r" else None)
        if self.legend:
            self.legend = " "  + self.legend
        self.fp = None
    def __enter__(self):
        if debug >= DEBUG_COMMANDS:
            if self.mode == "r":
                sys.stderr.write("%s: reading from '%s'%s\n" % (rfc3339(time.time()), self.command, self.legend))
            else:
                sys.stderr.write("%s: writing to '%s'%s\n" % (rfc3339(time.time()), self.command, self.legend))
        try:
            # The I/O streams for the subprocess are always bytes; this
            # is what we want for some operations, but we will need
            # to decode to Unicode for others to work in Python 3, as
            # explained in the general notes.
            self.fp = subprocess.Popen(self.command, shell=True,
                                       stdin=self.stdin, stdout=self.stdout, stderr=self.stderr)
            # The Python documentation recommends using communicate() to
            # avoid deadlocks, but this doesn't allow fine control over
            # reading the data; since we are not trying to both read
            # from and write to the same process, this should be OK.
            return self.fp.stdout if self.mode == "r" else self.fp.stdin
        except (OSError, IOError) as oe:
            croak("execution of %s%s failed: %s" \
                                % (self.command, self.legend, oe))
    def __exit__(self, extype, value, traceback_unused):
        if extype:
            if debug > 0:
                raise extype(value)
            croak("fatal exception in popen_or_die.")
        if self.fp.stdout is not None:
            # This avoids a deadlock in wait() below if the OS pipe
            # buffer was filled because we didn't read all of the data
            # before exiting the context mgr (shouldn't happen but this
            # makes sure).
            self.fp.stdout.read()
        self.fp.wait()
        if self.fp.returncode != 0:
            croak("%s%s returned error." % (self.command, self.legend))
        return False

def screenwidth():
    "Return the current width of the terminal window."
    width = 73
    if "COLUMNS" in os.environ:
        return int(os.environ["COLUMNS"])
    if sys.stdin.isatty():
        with popen_or_die('stty size', "rb") as tp:
            # stty returns 0,0 inside Emacs
            width = int(tp.read().split()[1]) or width
    return width

WIDTH = screenwidth() - 1

def is_history(arg):
    "Are we looking at a history file?"
    for vcsb in backends:
        if vcsb.is_history(arg):
            return True
    return False

def modified(workfile, history=None):
    "Has the workfile been modified since it was checked out?"
    # Alas, we can't rely on modification times; it was tried, and
    # os.utime() is flaky from Python - sometimes has no effect.  Where
    # the bug is - Python, glibc, kernel - is unknown.  Even if we
    # could, it's nice to catch the case where an edit was undone.
    #
    # If no revisions, bail out
    if not backend.has_revisions(workfile):
        return False
    if history is None:
        history = History(workfile)
    with backend.lifter(workfile):
        with backend.cat(workfile, history.current().native) as bstream:
            base_content = bstream.read()  # this data will be binary
            with open(workfile, "rb") as fp:
                workfile_content = fp.read()
            # This comparison uses the binary data for maximum accuracy
            return base_content != workfile_content

def do_or_die(dcmd, legend="", mute=True, missing=None):
    "Either execute a command or die."
    if legend:
        legend = " "  + legend
    if debug == 0 and mute:
        muteme = " >/dev/null 2>&1"
    else:
        muteme = ""
    if debug >= DEBUG_COMMANDS:
        sys.stderr.write("executing '%s'%s\n" % (dcmd, legend))
    try:
        retcode = subprocess.call("(" + dcmd + ")" + muteme, shell=True)
        if retcode < 0:
            croak("%s was terminated by signal %d." % (repr(dcmd), -retcode))
        elif retcode != 0:
            errmsg = "%s returned %d." % (repr(dcmd), retcode)
            if retcode == 127:
                if missing is None:
                    missing = backend.__class__.__name__
                errmsg += "\nYou probably need to install %s." % missing
            croak(errmsg)
    except (OSError, IOError) as e:
        croak("execution of %s%s failed: %s" % (repr(dcmd), legend, e))

def capture_or_die(command):
    "Run a specified command, capturing the output."
    if debug >= DEBUG_COMMANDS:
        sys.stderr.write("%s: capturing %s\n" % (rfc3339(time.time()), command))
    try:
        # This will return binary data
        content = subprocess.check_output(command, shell=True)
    except (subprocess.CalledProcessError, OSError) as oe:
        croak("execution of %s failed: %s" % (repr(command), oe))
    if debug >= DEBUG_COMMANDS:
        sys.stderr.write(polystr(content))
    return content

class HistoryEntry:
    "Capture the state of a native revision item in the log."
    def __init__(self, history):
        self.history = history
        self.revno = None
        self.native = None	# magic cookie only interpreted by back end
        self.headers = None
        self.log = ""
        self.date = None
        self.parent = None	# Another HistoryEntry
        self.child = None	# Another HistoryEntry
        self.branches = set([])
        self.branch = None
    def selected(self):
        return self == self.history.current()
    def getdate(self, who):
        if self.headers and not pseudotime:
            return self.headers.get(who + "-date") or self.date
        return self.date
    def unixtime(self, who):
        date = self.getdate(who)
        try:
            t = calendar.timegm(time.strptime(date, "%Y-%m-%dT%H:%M:%SZ"))
            offset = 0
            if self.headers and not pseudotime:
                offset = self.headers.get(who + "-date-offset") or 0
            return t, offset
        except (TypeError, ValueError):
            croak("garbled date %s" % date)
    def __str__(self):
        return "<%s = %s>" % (self.revno, self.native)

def registered(workfile):
    "Is this a workfile for a registered history?"
    return os.path.exists(backend.history(workfile))

class History:
    "Encapsulate a revision list and some methods on it"
    def __init__(self, name):
        self.name = name
        self.revlist = []
        self.symbols = {}
        self.branch = "trunk"
        self.lockrevs = []
        self.description = ""
        self.annotations = {}
        if not registered(self.name):
            croak("%s is not registered" % self.name)
        self.by_revno_d = {}
        self.by_native_d = {}
        self.branches = set([])
        backend.parse(self)
        self.lift_headers()
        self.normalize_header_dates()
    def build_indices(self):
        for item in self.revlist:
            self.by_revno_d[item.revno] = item
            self.by_native_d[item.native] = item
        for item in self.revlist:
            item.parent = self.by_native_d.get(backend.pred(item.native))
            item.child  = self.by_native_d.get(backend.succ(item.native))
            if item.parent and item.parent.child != item:
                item.parent.branches.add(item)
        #sys.stderr.write("Symbols: %s\n" % self.symbols)
        #for item in self.revlist:
        #    sys.stderr.write("Item %s\n" % item)
        #sys.stderr.write("By revision: %s\n" % self.by_revno_d.keys())
        if self.revlist:
            for (name, rev) in list(self.symbols.items()):
                if backend.isbranch(rev):
                    base = backend.branch_to_base(rev, self)
                    tip = backend.branch_to_tip(rev, self)
                    while True:
                        self.by_native_d[base].branch = name
                        if base == tip:
                            break
                        base = backend.succ(base)
        # Digest JSON from the description field
        if not self.description.strip():
            self.annotations = {}
        else:
            try:
                # The JSON loader returns Unicode, so this is one place
                # where internal data will be Unicode even in Python 2;
                # since ASCII data will be inter-converted between byte
                # string and Unicode whenever needed in Python 2, this
                # is not an issue.
                self.annotations = json.loads(self.description.strip())
            except ValueError as _e:
                croak("legacy data %s in description field" % self.description)
    def lift_headers(self):
        valid = ('author', 'author-date', 'committer', 'committer-date',
                 'mark', 'parents')
        for item in self.revlist:
            headers = {}
            i = 0
            while True:
                n = item.log.find('\n', i)
                if n < 0:
                    break
                header = item.log[i:n].split(':', 1)
                if len(header) != 2:
                    break
                key = header[0].lower()
                if key not in valid:
                    break
                headers[key] = header[1].strip()
                i = n + 1
            # eat blank line between headers and body
            while item.log[i] == '\n':
                i += 1
            item.log = item.log[i:]
            if headers:
                item.headers = headers
    def normalize_header_dates(self):
        for item in self.revlist:
            if item.headers:
                for k in tuple(item.headers):
                    if k.endswith("-date"):
                        d = email.utils.parsedate_tz(item.headers[k])
                        if d:
                            u = email.utils.mktime_tz(d)
                            u = datetime.datetime.utcfromtimestamp(u)
                            item.headers[k] = u.isoformat() + "Z"
                            item.headers[k + "-offset"] = d[9] if d[9] else 0
    def __len__(self):
        return len(self.revlist)
    def current(self):
        "Return the revision currently checked out."
        # Yes, this looks weird.  The idea is: Try to return the locked
        # revision.  If that blows up, try to return the tip revision of
        # the current branch.  If that blows up, return None.
        try:
            return self.by_native_d[self.lockrevs[0]]
        except (IndexError, KeyError):
            try:
                return self.by_native_d[backend.branch_to_tip(self.symbols[self.branch], self)]
            except (IndexError, KeyError):
                return None
    def current_branch(self, backwards=False):
        "Return a list of items that are descendants or ancestors of current."
        if debug >= DEBUG_SEQUENCE:
            sys.stdout.write(("current_branch(%s)" % self.current()))
        selection = []
        p = self.current()
        if p is not None:
            selection = [p]
            while True:
                if p.parent is None:
                    break
                else:
                    p = p.parent
                selection = [p] + selection
            s = self.current()
            while True:
                s = s.child
                if s is None:
                    break
                selection.append(s)
            if backwards:
                selection.reverse()
        return selection
    def tip(self, rev=None):
        "Return the tip revision of the branch of the given native revision."
        if rev is None:
            rev = self.current().native
        s = self.by_native_d[rev]
        while True:
            if s.child is None:
                return s
            else:
                s = s.child
    def native_to_revno(self, revision):
        "Map a native ID to a revno"
        item = self.by_native_d.get(revision)
        return item and item.revno
    def by_revno(self, revno):
        "Map a revno to a revision item."
        try:
            return self.by_revno_d[revno]
        except KeyError:
            if revno == 0:
                # This case comes up if we try to select the tip
                # revision of a history without revisions.
                croak("{0} has no revisions".format(self.name))
            else:
                croak("{0} has no revno {1}".format(self.name, revno))
    def revno_to_native(self, revno):
        "Map a revno to a native ID"
        return self.by_revno(revno).native
    def set_annotations(self):
        "Write auxilary symbols as JSON."
        backend.write_description(json.dumps(self.annotations), self)

help_topics = {
    "topics": """
The following help topics are available:

intro       -- Basic concepts: commits, tags, branches.  The form of commands.
revisions   -- How to specify ranges of commits to operate on.
commands    -- a summary of the commands.
commit      -- the commit command: how to commit changes to a file.
amend       -- the amend command: editing stored change comments.
checkout    -- the checkout command: retrieving historical versions of files.
cat         -- the cat command: dumping revisions to standard output.
status      -- the status command: more details and unusual status codes.
log         -- the log command: dump commit log information to standard output.
list        -- the list command: dump commit summaries to standard output.
diff        -- the diff command: dump revision differences to standard output.
fast-export -- the fast-export command: export history to other systems.
fast-import -- the fast-import command: import history from other systems.
ignores     -- .srcignore files and their uses.

The 'help', 'rename', 'ls', 'move', 'copy', 'visualize', and 'version'
commands are completely described in the command summary.
""",
    "intro": """
SRC Introduction

    SRC (or src) is designed for version control on single-file
    projects.

    A SRC history is a sequence of commits numbered in strict time order
    starting from 1.  Each holds a modification to the file, a comment,
    and the date-time of the commit.

    The sequence also has a branch structure.  By default there is
    just one branch named 'trunk'.  You can start a new named branch
    at any commit.  Branches can later be renamed or deleted.  Because
    of branching, parent and child commits do not necessarily have
    consecutive numbers.

    Commits will always be be added to the tip of the current branch.
    You can change the current branch by either checking out a revision
    that is on that branch, or using a 'src branch' command to
    explicitly change the current branch.

    You can assign tags (names) to point to commits.  They too can be
    renamed later or deleted.

    The general form of a SRC command is

        src verb [switches] [revision-spec] [files...]

    That is, a command verb is followed by optional switches, which are
    (sometimes) optionally followed by a range of commits to operate
    on, which is optionally followed by a list of files to operate on.
    Usually you will specify either a revision range or multiple files,
    but not both.

    The token '--' tells the command-line interpreter that subcommands,
    switches, and revision-specs are done - everything after it is a
    filename, even if it looks like a subcommand or revision number.

    If you do not specify any files, SRC will operate sequentially on
    each individual file in the current directory with a history.

    A good help topics to read after this one would be 'revisions'.
""",
    "revisions": """
SRC Revisions

    A 'revision' is a 1-origin integer, or a tag name designating an
    integer revision, or a branch name designating the tip revision of
    its branch, or '@' meaning the currently fetched revision.  Revision
    numbers always increase in commit-date order.

    A revision range is a single revision, or a pair of revisions 'M-N'
    (all revisions numerically from M to N) or 'M..N' (all revisions
    that are branch ancestors of N and branch successors of M).  If N is
    less than M, the range is generated as if N >= M then reversed.

    If SRC complains that your revision spec looks like a nonexistent
    filename, you can prefix it with '@' (this is always allowed).

    Some commands (help, commit, status, delete/rename commands for tags
    and branches, ls, move, copy, fast-import, release, version) don't
    take a revision spec at all and will abort if you give one.

    Some commands (amend, checkout, cat, tag and branch creation)
    optionally take a singleton revision spec.

    Some commands (log, list, diff, fast-export) accept a range or a
    singleton.

    Unless otherwise noted under individual commands, the default
    revision is the tip revision on the current branch.

    A good topic to read next would be 'commands'.
""",
    "commands": """
SRC Commands Summary

src help [command]
    Displays help for commands.

src commit [-|-m 'string'|-f 'file'|-e] ['file'...]
    Enters a commit for specified files, separately to each one.
    A history is created for the file if it does not already exist.
    With '-', take comment text from stdin; with '-m' use the following
    string as the comment; with '-f' take from a file.  With '-e', edit
    even after '-', '-f' or '-m'. 'ci' is a synonym for 'commit'.

src amend [-|-m 'string'|-f 'file'|-e] ['revision'] ['file'...]
    Amends the stored comment for a specified revision, defaulting to
    the latest revision on the current branch.  Flags are as for commit.

src checkout ['revision'] ['file'...]
    Refresh the working copies of the file(s) from their history files.
    'co' is a synonym for 'checkout'.

src cat ['revision'] ['file'...]
    Send the specified revisions of the files to standard output.

src status [-a] ['file'...]
    '=' = unmodified,   'M' = modified, '!' = missing,
    '?' = not tracked,  'I' = ignored,  'A' = added,
    'L' = locked (recover with 'src checkout').
    Find more details under 'help status'. 'st' is a synonym for
    'status'.

src tag [list|-l|create|-c|delete|del|-d] ['name'] ['revision'] ['file'...]
    List tags, create tags, or delete tags.  Create/delete takes a
    singleton revision, defaulting to the current branch tip.  List
    defaults to all revisions.

src branch [list|-l|create|-c|delete|del|-d] ['name'] ['file'...]
    List, create, or delete branches.  When listing, the active branch
    is first in the list.  The default branch is 'trunk'.  Create/delete
    takes a singleton revision, defaulting to the current branch tip.
    List defaults to all revisions, including 0 (the trunk root phantom
    revision).

src rename ['tag'|'branch'] ['oldname'] ['newname']  ['file'...]
    Rename a tag or branch.  Refuses to step on an existing symbol or
    rename a nonexistent one. 'rn' is a synonym for 'rename'.

src list [(-<n>|-l <n>)] [-f 'fmt'] ['revision-range'] ['file'...]
    Sends summary information about the specified commits to standard
    output.  The summary line tagged with '*' is the state that the file
    would return to on checkout without a revision-spec.  See 'help
    list' for information about custom formats.  Use '-<n>' or '-l <n>',
    where <n> is a number, to limit the listing length.  Default range is
    the current branch, reversed.

src log [-v] [(-<n>|-l <n>)] [(-p|-u|-c) [-b|-w]] ['revision-range'] ['file'...]
    Sends log information about the specified commits to standard
    output.  Use '-<n>' or '-l <n>', where <n> is a number, to limit the
    listing length.  Default range is the current branch, reversed.
    Use '--patch', '-p' or '-u' to also send a unified format diff
    listing to standard output for each revision against its immediate
    ancestor revision; '-c' emits a context diff instead. When generating
    a diff, '-b' ignores changes in the amount of whitespace, and '-w'
    ignores all whitespace.  Histories imported via 'fast-import' (when
    not using its '-p' option) have RFC-822-style headers inserted into
    the log comment to preserve metadata not otherwise representable in
    SRC, such as distinct author and committer identifications and
    dates.  These headers are normally suppressed by 'log', however,
    '-v' shows a summarized view of important headers; '-v -v' shows
    all headers as-is.

src diff [(-u|-c) [-b|-w]] ['revision-range'] ['file'...]
    Sends a diff listing to standard output.  With no revision spec,
    diffs the working copy against the last version checked in.  With
    one revno, diffs the working copy against that stored revision; with
    a range, diff between the beginning and end of the range. 'di' is a
    synonym for 'diff'.

src ls
    List all registered files.

src visualize
    Emit a DOT visualization of repository structures.  To use this,
    install the graphviz package and pipe the output to something like
    'dot -Tpng | display -'. 'vis' is a synonym for 'visualize'.

src move 'old' 'new'
    Rename a workfile and its history.  Refuses to step on existing
    workfiles or histories. 'mv' is a synonym for 'move'.

src copy 'old' 'new'
    Copy a workfile and its history.  Refuses to step on existing files
    or histories. 'cp' is a synonym for 'copy'.

src fast-export ['revision-range'] ['file'...]
    Export one or more projects to standard output as a Git fast-import
    stream.  For a history originally imported from elsewhere, author
    and committer identification is gleaned from the RFC-822-style
    headers inserted into the commit comment by 'fast-import' (if its
    '-p' option was not used).  Otherwise, this information is copied
    from your Git configuration.  The default range is all commits.

src fast-import [-p] ['file'...]
    Parse a git-fast-import stream from standard input.  The
    modifications for each individual file become separate SRC
    histories.  Mark, committer and author data, and mark cross-
    references to parent commits, are preserved in RFC-822-style headers
    on log comments unless the '-p' (plain) option is given, in which
    case this metadata is discarded.  Give arguments to restrict the
    files imported.

src release ['file'...]
    Release locks on files.  This is never necessary in a normal
    workflow, which will be repeated edit-commit cycles, but it may be
    handy if you have to interoperate with other tools that expect RCS
    masters to be in their normal (unlocked/unwritable) state.

src version
    Report the versions of SRC, the underlying Python, and the back end.

The omission of 'src remove' is a deliberate speed bump.
""",
    "status": """
src status [-a] ['file'...]

    The status command shows you the version-control status of files.
    It is designed to be useful for both humans and software front ends
    such as Emacs VC mode.

    The status codes, in roughly most common to rarest, are:

    = - Unmodified.  File is the same as the latest stored revision.
    M - Modified.  File has been changed since the latest stored revision.
    ? - Not tracked.  SRC does not keep a history for this file.
    I - ignored.  This file matches the patterns in '.srcignore'.
    ! - Missing.  There is a history for this file but the workfile is missing.
    A - The file has been registered into SRC but has no commits.
    L - The file is locked/writable.

    Modification status is by content (using a SHA1 hash) rather than
    the filesystem's last-modified date.  Thus, if you make changes to a
    work file in your editor, then undo them, the file's status returns
    to '='.

    You can usually recover a file from 'A', 'L', and '!' status with
    'src checkout'.  'A' and 'L' statuses should only occur if you have
    used RCS directly on a file, or if you have called 'src commit' with
    the deliberately undocumented '-a' option meant for Emacs VC's use.

    If you give 'src status' no filename arguments, it surveys all files
    in the current directory but untracked and ignored files are not
    listed.  If you give it filename arguments, status is listed for all
    of them.

    The '-a' option forces status listing of all files.  This differs
    from 'src status *' because the latter will not see dotfiles and
    thus not list the status of them.
""",
    "commit":"""
src commit [-|-m 'string'|-f 'file'| -e] ['file'...]

    The commit command is how you add revisions to your file history.
    It always adds the contents of the workfile as a revision to the tip
    of the current branch.

    You also use commit on files that have not been registered to start
    an SRC history for them.

    When you commit, you must specify a change comment to go with the
    revision.  There are several ways to do this.

    The '-m' option to the command takes the following string argument
    as the comment.  The '-' option takes the comment text from standard
    input.  The '-f' option takes the comment from a named file.

    If you use none of these, or if you use one of them and the '-e'
    option, SRC will start an editor in which you can compose the
    comment.  Text specified via '-m', '-f', or '-' becomes the initial
    contents of the comment.

    SRC respects the EDITOR variable and calls it on a temporary file to
    create your comment.  Th file will have a footer including its name
    and revision which will be discarded when you finish editing.

    If you leave the comment empty (except for the generated footer)
    or consisting only of whitespace, the commit will be aborted.  The
    commit will also be aborted if your editor returns a failure status.

    If you commit to multiple files at once, separate changes will be
    registered for each one, and you may get a separate edit session for
    each (if you have not set the comment text with options, or have
    forced editing with '-e').  This is a major difference from other
    VCSes, which are usually designed to create changesets common to
    multiple files.

    'ci' is a synonym for 'commit'.
""",
    "amend" : """
src amend [-|-m 'string'|-f 'file'| -e] ['revision'] ['file'...]

    Use this command to amend (modify) the change comment in a saved
    revision.  The commit date is not changed.

    Takes a singleton revision number, tag, or branch, defaulting to the
    latest revision on the current branch.

    The edit flags and EDITOR variable are interpreted are as for
    commit.  The only difference is that existing change comment is
    appended to any text you specify with switches as the initial
    comment passed to your editor.

    'am' is a synonym for 'amend'
""",
    "checkout":"""
src checkout ['revision'] ['file'...]

    Refresh the working copies of the file(s) from their history files.

    Takes a single revision number, tag, or branch name.  The default if
    you give none is the tip revision of the current branch.

    This command is how you discard the contents of a modified workfile.

    You can also use it to revert the workfile to match a previous
    stored revision.  Doing do may, as a side effect, change your
    current branch.

    'co' is a synonym for 'checkout'.
""",
   "cat" : """
src cat ['revision'] ['file'...]

    Send the specified revision of each file to standard output.  This
    is not normally very useful with more than one file argument, but
    SRC does not prevent that.

    Takes a single revision number, tag, or branch name.  The default if
    you give none is the tip revision of the current branch.

    This command is mainly intended for use in scripts.
""",
   "tag" : """
src tag [list|-l|create|-c|delete|del|-d] ['name'] ['revision'] ['file'...]

    List tags (with '-l'), create tags (with '-c'), or delete tags (with
    '-d').

    Takes at most a singleton revision; the default is the current
    branch tip.

    Tag creation and deletion require a following name argument.  Tag
    creation will not step on an existing tag name, and a nonexistent
    branch cannot be deleted.
""",
   "branch" : """
src branch [list|-l|create|-c|delete|del|-d] ['name'] ['file'...]

    List branches (with '-l'), create branches (with '-c'), or delete
    branches (with '-d').

    In the list produced by '-', the active branch is first in the list.

    Branch creation and deletion require a following name argument.
    Branch creation will not step on an existing branch name, and a
    nonexistent branch cannot be deleted.
""",
   "log" : """
src log [-v] [(-<n>|-l <n>)] [(-p|-u|-c) [-b|-w]] ['revision-range'] ['file'...]

    Sends log information about the specified commits of each file to
    standard output.  The log information includes the revision number,
    the date, and the log comment.

    With no revision, dumps a log of the entire current branch.

    The '--patch', '-p' or '-u' option additionally sends a unified
    format diff listing to standard output for each revision against its
    immediate ancestor revision; '-c' emits a context diff instead. When
    generating a diff, '-b' ignores changes in the amount of whitespace,
    and '-w' ignores all whitespace.

    The '-<n>' or '-l <n>' option, where <n> is a number, can be used to
    limit the listing length.

    Histories imported via 'fast-import' (when not using its '-p' option)
    have RFC-822-style headers inserted into the log comment to preserve
    metadata not otherwise representable in SRC, such as distinct author
    and committer identifications and dates.  These headers are normally
    suppressed by 'log', however, '-v' shows a summarized view of
    important headers; '-v -v' shows all headers as-is.
""",
   "list" : """
src list [(-<n>|-l <n>)] [-f 'fmt'] ['revision-range'] ['file'...]

    Sends summary information about the specified commits of each file
    to standard output.  The summary information includes the revision
    number, the date, and the first line of the log comment.

    This command is provided assuming you will use the good practice of
    beginning each commit with a self-contained summary line.

    With no revision, dumps a log of the entire current branch.

    The '-f' option allows you to set a custom format string.  Available
    substitutions are:

    {0} - the file name
    {1} - the revision number
    {2} - the mark '*' if this is the currently checked out revision, else '-'.
    {3} - the date in RFC3339 format
    {4} - the summary line

    The '-<n>' or '-l <n>' option, where <n> is a number, can be used to
    limit the listing length.

    'li' is a synonym for 'list'.
""",
   "diff" : """
src diff [(-u|-c) [-b|-w]] ['revision-range'] ['file'...]

    Sends a diff listing to standard output.

    With no revision spec, diffs the working copy against the last
    version checked in.  With one revno, diffs the working copy against
    that stored revision; with a range, diff between the beginning and
    end of the range.

    The actual difference generation is done with diff(1).  The default
    diff format is '-u' (unified), but if you specify a '-c' option
    after the verb a context diff will be emitted. '-b' ignores changes
    in the amount of whitespace, and '-w' ignores all whitespace.

    'di' is a synonym for 'diff'.
""",
   "fast-export" : """
src fast-export ['revision-range'] ['file'...]

    Export one or more projects to standard output as a git fast-import
    stream.  This can be consumed by 'git fast-import' to create a Git
    repository containing the project history.

    It is possible (though probably not very useful) to fast-export a
    limited range of commits, producing an incremental dump.  In this
    case branch joins are done with the magic ^0 suffix.

    Fast-exporting multiple files produces a single stream with a joint
    history.

    For a history originally imported from elsewhere, author and
    committer identification is gleaned from the RFC-822-style headers
    inserted into the commit comment by 'fast-import' (if its '-p'
    option was not used).  Otherwise, this information is copied from
    your Git configuration.

    The default range is all commits.
""",
   "fast-import" : """
src fast-import [-p] ['file'...]

    Parse a git-fast-import stream from standard input.  The
    modifications for each individual file become separate SRC
    histories.  Give arguments to restrict the files imported.

    The import is actually done with the rcs-fast-import(1) tool, which
    must be on your $PATH for this command to work.

    Some gitspace metadata cannot be represented in the SRC/RCS
    model of version control.  Mark, committer and author data, and
    mark cross-references to parent commits.  These are preserved in
    RFC-822-style headers on log comments unless the '-p' (plain) option
    is given, in which case this metadata is discarded.
""",
   "ignores" : """
Making SRC Ignore Certain Files

    You can have a file named '.srcignore' containing the names of files
    that SRC should ignore, or more commonly patterns describing files
    to ignore.

    When SRC is told to ignore a file, it won't show up in 'src status'
    listings unless the '-a' (all) flag is used or you give it as an
    explicit argument.  It will also be ignored when commands that
    expect a list of registered files see it (which could easily happen
    when you use shell wildcards in SRC commands).

    Other version-control systems have these too.  The classic example
    of how to do this is using the pattern '*.o' to ignore C object
    files.  But if you need to do that, you should probably be using a
    multi-file VCS with changesets, not this one.

    Patterns that might be useful with single-file projects include
    '*~' to ignore editor backup files, or '*.html' if you're writing
    documents that render to HTML but aren't sourced in it.

    The repo subdirectory - normally '.src' - is always ignored, but
    '.srcignore' itself is not automatically ignored.

    SRC's pattern syntax is that of Unix glob(3), with initial '!'
    treated as a negation operator.  This is forward-compatible to Git's
    ignore syntax.

    *   matches any string of characters.
    ?   matches any single character.
    []  brackets a character class; it matches any character in the
        class.  So, for example, [0123456789] would match any decimal
        digit.
    [!] brackets a negated character class; [!0123456789] would match
        any character not a decimal digit.
""",
    }

def help_method(*args):
    "Summarize src commands, or (with argument) show help for a single command."
    if not args:
        sys.stdout.write(help_topics['topics'])
    for arg in args:
        if arg in args:
            if arg in help_topics:
                sys.stdout.write(help_topics[arg])
            else:
                croak("%s is not a known help topic.\n%s" % (arg, help_topics['topics']))

def parse_as_revspec(token):
    "Does this look like something that should be parsed as a revision spec?"
    if "/" in token:
        return False
    elif ".." in token:
        return True
    elif token.count("-") == 1 and '.' not in token:
        return True
    elif token.isdigit():
        return True
    elif token.startswith("@"):	# Escape clause for tags that look like files
        return True
    else:
        return False

ignorable = None

def ignore(filename):
    "Should the specified file be ignored?"
    global ignorable
    if ignorable is None:
        ignorable = set([])
        ignorable = set()
        if os.path.exists(".srcignore"):
            with open(".srcignore", "rb") as fp:
                for line in fp:
                    # Use polystr to ensure internal data is Unicode in Python 3
                    line = polystr(line)
                    if line.startswith("#") or not line.strip():
                        continue
                    elif line.startswith("!"):
                        ignorable -= set(glob.glob(line[1:].strip()))
                    else:
                        ignorable |= set(glob.glob(line.strip()))
    return (filename == repodir) or (filename in ignorable)

class CommandContext:
    "Consume a revision specification or range from an argument list"
    def __init__(self, cmd, args,
                 require_empty=False,
                 default_to=None,
                 parse_revspec=True):
        if not os.path.exists(repodir):
            croak("repository subdirectory %s does not exist" % repodir)
        self.start = self.end = None
        self.seq = None
        self.branchwise = None
        if type(args) == type(()):
            args = list(args)
        self.args = list(args)
        self.default_to = default_to
        self.lo = self.start
        self.hi = self.end
        revspec = None
        if self.args:
            if self.args[0] == "--":
                self.args.pop(0)
            elif parse_revspec and parse_as_revspec(args[0]):
                revspec = self.args.pop(0)
                if revspec.startswith("@"):
                    revspec = revspec[1:]
                try:
                    if "-" in revspec or ".." in revspec:
                        self.branchwise = ".." in revspec
                        try:
                            (self.start, self.end) = revspec.split("-")
                        except ValueError:
                            try:
                                (self.start, self.end) = revspec.split("..")
                            except ValueError:
                                croak("internal error - argument parser is confused")
                        try:
                            self.start = int(self.start)
                        except ValueError:
                            pass
                        try:
                            self.end = int(self.end)
                        except ValueError:
                            pass
                    else:
                        try:
                            self.end = self.start = int(revspec)
                        except ValueError:
                            self.end = self.start = revspec
                except ValueError:
                    croak("malformed revision spec: %s" % revspec)
        if require_empty and not self.is_empty():
            croak("%s doesn't take a revision spec" % cmd)
        if not self.args:
            try:
                masters = [fn for fn in os.listdir(repodir) if is_history(fn)]
                masters.sort()
            except OSError:
                croak("repo directory %s does not exist" % repodir)
            if masters:
                self.args += [backend.workfile(master) for master in masters]
            else:
                croak("%s requires at least one file argument" % cmd)
    def is_empty(self):
        "Is the spec empty?"
        return self.start is None
    def is_singleton(self):
        "Is the spec a singleton?"
        return self.start is not None and self.start == self.end
    def is_range(self):
        "Is the spec a range?"
        return self.start is not None and self.start != self.end
    def select_all(self, metadata):
        "Set the range to all revisions."
        self.lo = 1
        self.hi = len(metadata)
        self.seq = [metadata.by_revno(i) for i in range(self.lo, self.hi+1)]
    def select_tip(self, metadata):
        "Set the range to the tip revision."
        self.lo = len(metadata)
        self.hi = None
        self.seq = [metadata.by_revno(self.lo)]
    def __contains__(self, i):
        "Does the spec contain the given revno?"
        if self.seq is None:
            croak("revision spec hasn't been resolved")
        return i in self.seq
    def resolve(self, metadata):
        "Resolve a revision spec that may contain tags into revnos."
        if debug >= DEBUG_SEQUENCE:
            sys.stderr.write("Entering resolve with start=%s, end=%s\n" % (self.start, self.end))
        if self.is_empty():
            if self.default_to == "branch":
                self.seq = metadata.current_branch(backwards=False)
            elif self.default_to == "branch_reversed":
                self.seq = metadata.current_branch(backwards=True)
            else:
                self.seq = []
            return self.seq
        def subresolve(token):
            part = token
            if type(part) == type(0):
                return part
            if token == '':	# User specified @
                current = metadata.current()
                if current is None:
                    croak("in {0}, no current revision".format(metadata.name))
                return current.revno
            if part not in metadata.symbols:
                croak("in {0}, can't resolve symbol {1}".format(metadata.name,token))
            else:
                part = metadata.symbols[part]
            if backend.isbranch(part):
                part = backend.branch_to_tip(part, metadata)
            return metadata.native_to_revno(part)
        self.lo = subresolve(self.start)
        self.hi = subresolve(self.end)
        mreversed = (self.lo > self.hi)
        if mreversed:
            swapme = self.hi
            self.hi = self.lo
            self.lo = swapme
        if self.hi > len(metadata):
            croak("{0} has no {1} revision".format(metadata.name, self.hi))
        if not self.branchwise:
            self.seq = [metadata.by_revno(i) for i in range(self.lo, self.hi+1)]
        else:
            self.seq = []
            e = metadata.by_revno(self.hi)
            while True:
                self.seq.append(e)
                if e.revno == self.lo:
                    break
                if e.parent is None:
                    croak("%s is not an ancestor of %s" % (self.lo, self.hi))
                else:
                    e = e.parent
        if debug >= DEBUG_SEQUENCE:
            sys.stderr.write("selection: %s, branchwise is %s\n" % ([x.revno for x in self.seq], "on" if self.branchwise else "off"))
            for item in metadata.revlist:
                sys.stdout.write("%s\t%s\t%s\n" % (item.revno, item.date, item.native))
        # Because in the branchwise case the sequence is generated in reverse
        if self.branchwise:
            self.seq.reverse()
        # Range might have been reversed
        if mreversed:
            self.seq.reverse()
        return self.seq

class CommentContext:
    COMMENT_CUTLINE = """\
.............................................................................
"""
    COMMENT_EXPLANATION = """\
The cut line and things below it will not become part of the comment text.
"""
    def __init__(self, legend, args):
        "Attempt to collect a comment from command line args."
        self.leader = ""
        self.comment = None
        self.force_edit = False
        self.parse_revspec = True
        if args:
            if args[0] == '--':
                self.parse_revspec = False
                args.pop(0)
            elif args[0] == "-":
                self.leader = sys.stdin.read()
                args.pop(0)
            elif args[0] == "-e":
                self.force_edit = True
            elif args[0] == "-m":
                args.pop(0)
                try:
                    self.leader = args[0]
                    args.pop(0)
                except IndexError:
                    croak("%s -m requires a following string" % legend)
            elif args[0].startswith("-m"):
                self.leader = args[2:]
                args.pop(0)
            elif args[0] == "-f":
                args.pop(0)
                try:
                    # Read filesystem data as binary for robustness, but
                    # decode to Unicode for internal use
                    with open(args[0], "rb") as fp:
                        self.leader = polystr(fp.read())
                    args.pop(0)
                except IndexError:
                    croak("%s -f requires a following filename argument" % legend)
                except OSError:
                    croak("couldn't open %s." % args[1])
            elif args[0].startswith("-"):
                croak("unexpected %s option" % args[0])
    def edit(self, content="", trailer="", diff=None):
        "Interactively edit a comment if required, then prepare for handoff."
        if self.leader and not self.force_edit:
            self.comment = self.leader
        else:
            orig_content = content
            if self.leader:
                content = self.leader + content
            if trailer or diff:
                content += "\n" + CommentContext.COMMENT_CUTLINE + CommentContext.COMMENT_EXPLANATION + trailer
            editor = os.getenv("EDITOR") or "emacsclient"
            try:
                # Use polybytes to ensure that binary data is written
                # on Python 3
                with tempfile.NamedTemporaryFile(prefix = "src", suffix = "tmp", delete = False) as fp:
                    commentfile = fp.name
                    fp.write(polybytes(content))
                    if diff:
                        fp.write(b"\nChanges to be committed:\n")
                        for s in diff:
                            fp.write(polybytes(s))
                            fp.write(b"\n")
                do_or_die(editor + " " + commentfile, mute=False)
                # Use polystr to ensure that incoming data is decoded
                # to Unicode on Python 3
                with open(commentfile, "rb") as fp:
                    self.comment = polystr(fp.read())
                    os.unlink(commentfile)
            except IOError:
                croak("edit aborted.")
            where = self.comment.find(CommentContext.COMMENT_CUTLINE)
            if where != -1:
                self.comment = self.comment[:where]
            self.comment = self.comment.strip()
            if self.comment == orig_content.strip() or not self.comment:
                return False
            # Can be removed if we ever parse RCS/SCCS files directly
            for badnews in backend.delimiters:
                if badnews in self.comment:
                    croak("malformed comment")
        if not self.comment.endswith("\n"):
            self.comment += "\n"
        return True
    def content(self):
        "Return the edited comment."
        return self.comment

def external_diff(file0, s0, file1, s1, unified=True, ignore_ws=None):
    "Compute diff using external program."
    def writetmp(s):
        with tempfile.NamedTemporaryFile(prefix = "src", suffix = "tmp", delete = False) as fp:
            fp.write(polybytes(s))
            return fp.name
    if unified:
        opts, tok0, tok1 = '-u', '-', '+'
    else:
        opts, tok0, tok1 = '-c', '*', '-'
    if ignore_ws:
        opts += ' ' + ignore_ws
    tmp0 = writetmp(s0)
    tmp1 = writetmp(s1)
    with popen_or_die('diff %s "%s" "%s" || :' % (opts, tmp0, tmp1)) as fp:
        diff = polystr(fp.read())
    os.unlink(tmp0)
    os.unlink(tmp1)
    diff = re.sub(r"(?m)^([%s]{3} ).+$" % tok0, r"\1" + file0, diff, 1)
    diff = re.sub(r"(?m)^([%s]{3} ).+$" % tok1, r"\1" + file1, diff, 1)
    return diff.split('\n')

def compute_diff(metadata, lo, hi, differ, ignore_ws=None):
    """Compute diff between two revs of a file.
    If 'lo' is None, then this is a "creation event" in which 'hi'
    materializes fully formed from nothing.
    If 'hi' is None, then diff 'lo' against the working file.
    File must already have been "lifted"."""
    name = metadata.name
    if lo is None:
        file0 = '/dev/null'
        old_content = ''
    else:
        file0 = name + ' (r' + str(lo) + ')'
        with backend.cat(name, metadata.revno_to_native(lo)) as fp:
            old_content = fp.read()  # this data will be binary
    if hi is None:
        file1 = name + ' (workfile)'
        with open(name, "rb") as fp:
            new_content = fp.read()
    else:
        file1 = name + ' (r' + str(hi) + ')'
        with backend.cat(name, metadata.revno_to_native(hi)) as fp:
            new_content = fp.read()  # this data will be binary
    # Don't list identical files (comparison uses binary data
    # for maximum accuracy).
    if old_content == new_content:
        return ()
    # All operations here will need Unicode in Python 3
    if ignore_ws:
        return external_diff(file0, old_content, file1, new_content,
                             differ == difflib.unified_diff, ignore_ws)
    lines0 = polystr(old_content).split('\n')
    lines1 = polystr(new_content).split('\n')
    return differ(lines0, lines1,
                  fromfile=file0,
                  tofile=file1,
                  lineterm="")

def colorize_unified(s):
    for x in colorize_unified.colors:
        if s.startswith(x[0]):
            return x[1] + s + RESET
    return s

colorize_unified.colors = (('+++ ', BOLD), ('--- ', BOLD), ('@@ ', CCYAN),
                           ('+', CGREEN), ('-', CRED))

def print_diff(metadata, lo, hi, differ, ignore_ws=None):
    "Dump diff between revisions to standard output."
    if differ == difflib.unified_diff:
        colorizer = colorize_unified
    else:
        colorizer = lambda x: x
    with backend.lifter(metadata.name):
        for line in compute_diff(metadata, lo, hi, differ, ignore_ws):
            sys.stdout.write(colorizer(line) + "\n")

def commit_method(*args):
    "Commit changes to files."
    if not os.path.exists(repodir):
        try:
            os.mkdir(repodir)
        except OSError:
            croak(" %s creation failed, check directory permissions." % repodir)
    args = list(args)
    register_only = False
    parse_revspec = True
    differ = difflib.unified_diff
    while args:
        if args[0] == '--':
            args.pop(0)
            parse_revspec = False
            break
        elif args[0] == '-a':
            # The Emacs VC-mode support for SRC was written early,
            # before 1.0, when I hadn't quite figured out what the
            # most efficient method for file reigstration would be.
            # VC-mode wants to have a registration as well as a
            # checkin method. This is no longer needed for normal SRC
            # operation, but it's better to leave this in place than
            # risk causing hassles for people running old Enacs versions.
            register_only = True
            parse_revspec = False
            args.pop(0)
        else:
            break
    if not register_only:
        comment = CommentContext("commit", args)
    ctx = CommandContext("commit", args,
                         require_empty=True,
                         parse_revspec=parse_revspec and comment.parse_revspec)
    for arg in ctx.args:
        if not os.path.exists(arg):
            croak("I see no '%s' here." % arg)
        if os.path.isdir(arg):
            croak("cannot commit directory '%s'" % arg)
    for arg in ctx.args:
        if not registered(arg):
            trailer = "Committing initial revision of {0}.\n".format(arg)
            revcount = 0
            metadata = None
            diff = compute_diff(type('', (), {'name':arg}), None, None, differ)
        elif register_only:
            croak("attempt to re-add a registered file failed")
        else:
            metadata = History(arg)
            ctx.resolve(metadata)
            if metadata and ctx.is_empty():
                ctx.select_tip(metadata)
            revcount = len(metadata)
            trailer = "Committing {0} revision {1}.\n".format(arg, revcount+1)
            with backend.lifter(arg):
                diff = compute_diff(metadata, ctx.lo, None, differ)
        if not register_only and not diff:
            announce("in %s, no changes to commit" % arg)
            continue
        if not register_only and not comment.edit('', trailer, diff):
            announce("in %s, commit cancelled" % arg)
        else:
            if not registered(arg):
                backend.register(arg)
            if not register_only:
                with backend.lifter(arg):
                    # If the user changed the executable bit while
                    # modifying the workfile, propagate this change to
                    # the master.  Without this hack, the sequence (1)
                    # Commit workfile (2) Make workfile executable, (3)
                    # checkin workfile fails to work as expected because
                    # the VCS doesn't propagate the changed executable
                    # bit to the master, leading to misbehavior on the
                    # next checkout.
                    master = os.path.basename(backend.history(arg))
                    if os.path.exists(master):
                        oldmastermode = newmastermode = os.stat(master).st_mode
                        userworkmode = os.stat(arg).st_mode
                        for bitmask in (stat.S_IXUSR, stat.S_IXGRP, stat.S_IXOTH):
                           if bitmask & userworkmode:
                               newmastermode |= bitmask
                           else:
                               newmastermode &=~ bitmask
                        if newmastermode != oldmastermode:
                            os.chmod(master, newmastermode)
                    backend.checkin(arg, comment.content())
            if metadata is None:
                metadata = History(arg)
            modified(arg, metadata)
            if not quiet and len(args) > 1:
                announce("%s -> %d" % (arg, revcount))

def add_method(*args):
    "For Emacs VC compatibility."
    commit_method("-a", *args)

def amend_method(*args):
    "Amend comments in stored revisions."
    if not os.path.exists(repodir):
        croak("repository subdirectory %s does not exist" % repodir)
    args = list(args)
    differ = difflib.unified_diff
    comment = CommentContext("amend", args)
    ctx = CommandContext("amend", args, parse_revspec=comment.parse_revspec)
    if ctx.is_range():
        croak("amend cannot take a range")
    for arg in ctx.args:
       if not os.path.exists(arg):
           croak("I see no '%s' here." % arg)
       elif not registered(arg):
           croak("%s is not registered." % arg)
    for arg in ctx.args:
        metadata = History(arg)
        ctx.resolve(metadata)
        if ctx.is_empty():
            ctx.lo = metadata.tip().revno
        trailer ="Amending {0} revision {1}.\n".format(arg, ctx.lo)
        item = metadata.by_revno(ctx.lo)
        parent = item.parent.revno if item.parent else None
        with backend.lifter(arg):
            diff = compute_diff(metadata, parent, ctx.lo, differ)
        if not comment.edit(metadata.by_revno(ctx.lo).log, trailer, diff):
            announce("in %s, amend cancelled" % arg)
        else:
            with backend.lifter(arg):
                backend.amend(arg,
                          metadata.revno_to_native(ctx.lo),
                          comment.content())
    if not quiet and len(args) > 1:
        announce("%s : %d" % (arg, ctx.lo))

def list_method(*args):
    "Generate a summary listing of commits, one line per commit."
    args = list(args)
    custom = None
    limit = None
    parse_revspec = True
    while args and args[0].startswith("-"):
        if args[0] == '--':
            parse_revspec = False
            args.pop(0)
            break
        elif args[0] == "-f":
            args.pop(0)
            try:
                custom = args[0]
                args.pop(0)
            except IndexError:
                croak("list -f requires a following string")
        elif args[0].startswith("-f"):
            custom = args[0][2:]
            args.pop(0)
        elif args[0] == "-l":
            args.pop(0)
            try:
                limit = args[0]
                args.pop(0)
                limit = int(limit)
            except IndexError:
                croak("list -l requires a following integer")
            except ValueError:
                croak("%s is not an integer" % limit)
        elif args[0][1:].isdigit():
            limit = int(args.pop(0)[1:]) # it's all digits, so no ValueError
        else:
            croak("unexpected %s option" % args[0])
    ctx = CommandContext("list", args,
                         default_to="branch_reversed",
                         parse_revspec=parse_revspec)
    for arg in ctx.args:
        if ignore(arg) or os.path.isdir(arg) or not registered(arg):
            continue
        if custom is None:
            sys.stdout.write("= %s %s\n" % (arg, ((WIDTH - len(arg) - 3) * "=")))
        for item in ctx.resolve(History(arg)):
            # Must allow enough room for revno and date
            if item.selected():
                mark = "*"
            else:
                mark = "-"
            summary = item.log.split('\n')[0]
            if custom is None:
                summary = summary[:WIDTH - 34]
                sys.stdout.write("%-4d  %s %s %s\n" \
                             % (item.revno, mark, item.getdate('author'), summary))
            else:
                sys.stdout.write(custom.format(arg, item.revno, mark, item.getdate('author'), summary))
            if limit is not None:
                limit -= 1
                if limit <= 0:
                    break

def log_method(*args):
    "Report revision logs"
    limit = None
    args = list(args)
    parse_revspec = True
    differ = None
    ignore_ws = None
    verbose = 0
    while args and args[0].startswith("-"):
        if args[0] == '--':
            parse_revspec = False
            args.pop(0)
            break
        elif args[0] == "-l":
            args.pop(0)
            try:
                limit = args[0]
                args.pop(0)
                limit = int(limit)
            except IndexError:
                croak("list -l requires a following integer")
            except ValueError:
                croak("%s is not an integer" % limit)
        elif args[0][1:].isdigit():
            limit = int(args.pop(0)[1:]) # it's all digits, so no ValueError
        elif args[0] in ('--patch', '-p', '-u'):
            differ = difflib.unified_diff
            args.pop(0)
        elif args[0] == '-c':
            differ = difflib.context_diff
            args.pop(0)
        elif args[0] in ('-b', '-w'):
            ignore_ws = args.pop(0)
        elif args[0] == '-v':
            verbose += 1
            args.pop(0)
        else:
            croak("unexpected %s option" % args[0])
    ctx = CommandContext("log", args,
                         default_to="branch_reversed",
                         parse_revspec=parse_revspec)
    for arg in ctx.args:
        if ignore(arg) or os.path.isdir(arg) or not registered(arg):
            continue
        sys.stdout.write("= %s %s\n" % (arg, ((WIDTH - len(arg) - 3) * "=")))
        metadata = History(arg)
        for item in ctx.resolve(metadata):
            sys.stdout.write("%s%-4d%s | %s%s%s | %s%s%s\n" \
                             % (BOLD + CCYAN, item.revno, RESET,
                                CYELLOW, item.getdate('author'), RESET,
                                BOLD + CGREEN, item.branch, RESET))
            if verbose and item.headers:
                headers = item.headers
                if verbose == 1:
                    headers = {}
                    for k in ('author', 'committer'):
                        if k in item.headers:
                            v = item.headers[k]
                            if k + "-date" in item.headers:
                                v += " " + item.headers[k + "-date"]
                            headers[k] = v
                for k in sorted(headers.keys()):
                    sys.stdout.write("%s%s%s: %s\n" %
                                     (BOLD, k.title(), RESET, headers[k]))
                sys.stdout.write("\n")
            sys.stdout.write("%s" % item.log)
            if differ:
                if item.parent:
                    parent = item.parent.revno
                    pdesc = 'r%d/%s' % (parent, arg)
                else:
                    parent = None
                    pdesc = '/dev/null'
                sys.stdout.write("\n%sdiff %s r%s/%s%s\n" %
                                 (BOLD, pdesc, item.revno, arg, RESET))
                print_diff(metadata, parent, item.revno, differ, ignore_ws)
            sys.stdout.write(("-" * WIDTH) + "\n")
            if limit is not None:
                limit -= 1
                if limit <= 0:
                    break

def checkout_method(*args):
    "Refresh the working copy from the history file."
    ctx = CommandContext("checkout", args)
    if ctx.is_range():
        croak("checkout needs an empty or singleton revision spec")
    for arg in ctx.args:
        metadata = History(arg)
        ctx.resolve(metadata)
        if ctx.is_empty():
            ctx.select_tip(metadata)
            revision = ""
        elif ctx.lo > len(metadata):
            croak("%s has only %d revisions" % (arg, len(metadata)))
        else:
            revision = metadata.revno_to_native(ctx.lo)
        with backend.lifter(arg):
            backend.checkout(arg, revision)
        if not quiet and len(args) > 1:
            announce("%s <- %d" % (arg, ctx.lo))

def status_method(*args):
    "Get status of some or all files."
    try:
        managed = [fn for fn in os.listdir(repodir) if is_history(fn)]
    except OSError:
        croak("repo directory %s does not exist" % repodir)
    args = list(args)
    allflag = False
    if args:
        if args[0] == '--':
            args.pop(0)
        elif args[0] == '-a':
            allflag = True
            args.pop(0)
    if args:
        candidates = args
    else:
        candidates = [f for f in os.listdir(".") if f != repodir]
    pairs = []
    for fn in candidates:
        if ignore(fn):
            if allflag or fn in args:
                pairs.append((fn, "I"))
            continue
        masterbase = os.path.basename(backend.history(fn))
        if masterbase not in managed:
            if allflag or fn in args:
                if not os.access(fn, os.R_OK):
                    croak("%s does not exist or is unreadable." % fn)
                else:
                    pairs.append((fn, "?"))
        elif not os.path.exists(fn):
            pairs.append((fn, "!"))
        elif modified(fn):
            pairs.append((fn, "M"))
        elif not os.access(fn, os.W_OK):
            pairs.append((fn, "L"))
        elif not backend.has_revisions(fn):
            pairs.append((fn, "A"))
        else:
            pairs.append((fn, "="))
    if not args:
        for m in managed:
            if backend.workfile(m) not in candidates:
                pairs.append((m, "!"))
    pairs.sort()
    for (fn, status) in pairs:
        sys.stdout.write(status + "\t" + fn + "\n")

def cat_method(*args):
    "Dump revision content to standard output."
    ctx = CommandContext("cat", args)
    if ctx.is_range():
        croak("cat refuses to cough up a hairball")
    elif ctx.args[0] == '--':
            ctx.args.pop(0)
    for arg in ctx.args:
        metadata = History(arg)
        ctx.resolve(metadata)
        if ctx.is_empty():
            ctx.select_tip(metadata)
        with backend.lifter(arg):
            for item in ctx.seq:
                with backend.cat(arg, item.native) as fp:
                    # Use polystr to ensure that sys.stdout gets Unicode
                    # in Python 3.
                    sys.stdout.write(polystr(fp.read()))

def diff_method(*args):
    "Dump diffs between revisions to standard output."
    if type(args) == type(()):
        args = list(args)
    differ = difflib.unified_diff
    ignore_ws = None
    while args and args[0] != '--' and args[0].startswith("-"):
        if args[0] == '-u':
            differ = difflib.unified_diff
            args.pop(0)
        elif args[0] == '-c':
            differ = difflib.context_diff
            args.pop(0)
        elif args[0] in ('-b', '-w'):
            ignore_ws = args.pop(0)
        else:
            croak("unexpected %s option" % args[0])
    ctx = CommandContext("diff", args)
    for arg in ctx.args:
        metadata = History(arg)
        ctx.resolve(metadata)
        if ctx.is_empty():
            ctx.select_tip(metadata)
        print_diff(metadata, ctx.lo, ctx.hi, differ, ignore_ws)

def tag_helper(args, legend, validation_hook, delete_method, set_method):
    "Dispatch to handlers for tag and branch manipulation."
    if not os.path.exists(repodir):
        croak("repository subdirectory %s does not exist" % repodir)
    args = list(args)
    if not args:
        args = ["list"] + args
    if args[0] == '--':
        args.pop(0)
    else:
        if args[0] in ("-d", "del", "delete"):
            args.pop(0)
            if not args:
                croak("%s deletion requires a name argument" % legend)
            name = args.pop(0)
            ctx = CommandContext(legend, args)
            if not ctx.is_empty():
                croak("can't accept a revision-spec when deleting a %s." % legend)
            for arg in ctx.args:
                metadata = History(arg)
                if name not in metadata.symbols:
                    croak("in %s, %s is not a symbol" % (arg, name))
                elif backend.isbranch(metadata.symbols[name]) != (legend  == "branch"):
                    croak("in %s, %s is not a %s" % (arg, name, legend))
                else:
                    with backend.lifter(arg):
                        delete_method(name, metadata)
                    if not quiet and len(args) > 1:
                        announce("in %s, %s %s removed" % (arg, legend, name))
                return
        if args[0] in ("-l", "list"):
            args.pop(0)
            ctx = CommandContext(legend + " listing", args, require_empty=True)
            for arg in ctx.args:
                metadata = History(arg)
                ctx.resolve(metadata)
                if ctx.is_empty():
                    prepend = [0]
                    ctx.select_all(metadata)
                else:
                    prepend = []
                revisions = prepend + [item.revno for item in ctx.seq]
                sys.stdout.write("= %s %s\n" \
                                 % (arg, ((WIDTH - len(arg) - 5) * "=")))
                keys = list(metadata.symbols.keys())
                if metadata.branch in keys:
                    keys.remove(metadata.branch)
                    keys.sort()
                    keys = [metadata.branch] + keys
                for key in keys:
                    value = metadata.symbols[key]
                    if legend == "branch":
                        # Note!  This code relies on
                        # backend.branch_to_parent() returning an empty
                        # string when called on a trunk revision.
                        displaystr = backend.branch_to_parent(value)
                        if not displaystr:
                            display = 0
                        else:
                            display = metadata.native_to_revno(displaystr)
                    else:
                        display = metadata.native_to_revno(value)
                    if display in revisions and backend.isbranch(value) == (legend == "branch"):
                        sys.stdout.write("%4s\t%s\n" % (display,key))
            return
        if args[0] in ("-c", "create"):
            args.pop(0)
            if not args:
                croak("%s setting requires a name argument" % legend)
            name = args.pop(0)
            ctx = CommandContext(legend, args)
            if ctx.is_range():
                croak("can't accept a range when setting a %s" % legend)
            for arg in ctx.args:
                metadata = History(arg)
                revision = validation_hook(ctx, metadata, name)
                with backend.lifter(arg):
                    set_method(name, revision, metadata)
                    if not quiet and len(args) > 1:
                        announce("in %s, %s %s = %s" % (arg, legend, name, ctx.start))
            return
        else:
            croak("%s requires a list, create, or delete modifier" % legend)

def tag_method(*args):
    "Inspect, create, and delete tags."
    def tag_set_validate(ctx, metadata, name):
        ctx.resolve(metadata)
        if name in metadata.symbols:
            croak("tag %s already set." % name)
        if ctx.is_empty():
            ctx.select_tip(metadata)
        return metadata.revno_to_native(ctx.lo)
    tag_helper(args, "tag",
               tag_set_validate,
               backend.delete_tag, backend.set_tag)

def branch_method(*args):
    "Inspect, create, and delete branches."
    def branch_set_validate(ctx, _metadata, _name):
        if not ctx.is_empty():
            croak("cannot accept a revision after a branch name")
    tag_helper(args, "branch",
               branch_set_validate,
               backend.delete_branch, backend.set_branch)

def rename_method(*args):
    "Rename a branch or tag."
    args = list(args)
    if not args or args[0] not in ("tag", "branch"):
        croak("rename requires a following 'tag' or 'branch'")
    legend = args.pop(0)
    if not args:
         croak("rename requires a source name argument")
    name = args.pop(0)
    if not args:
        croak("rename requires a target name argument")
    newname = args.pop(0)
    ctx = CommandContext(legend + " renaming", args, require_empty=True)
    for arg in ctx.args:
        metadata = History(arg)
        if name not in metadata.symbols:
            croak("in %s, cannot rename nonexistent %s %s" % (arg, legend, name))
        if newname in metadata.symbols:
            croak("in %s, cannot rename to existing %s %s" % (arg, legend, name))
        ctx = CommandContext(legend, args)
        if not ctx.is_empty():
            croak("can't accept a revision-spec when renaming a %s." \
                  % legend)
        # In the case of a branch, we want to change only the
        # tag reference.
        with backend.lifter(arg):
            backend.set_tag(newname, metadata.symbols[name], metadata)
            backend.delete_tag(name, metadata)
        if not quiet and len(args) > 1:
            announce("in %s, %s -> %s" % (arg, name, newname))

def filecmd(legend, hook, args):
    CommandContext(legend, args, require_empty=True)
    if len(args) != 2:
        croak("%s requires exactly two arguments" % legend)
    (source, target) = args
    if not os.path.exists(source):
        croak("I see no '%s' here." % source)
    elif os.sep in target and not os.path.exists(os.path.dirname(target)):
        croak("directory '%s' does not exist." % target)
    elif not registered(source):
        croak("%s is not registered" % source)
    elif registered(target):
        croak("%s is registered, I won't step on it" % source)
    elif os.path.exists(target):
        croak("%s exists, please delete manually if you want it gone" % target)
    else:
        hook(source, target)

def move_method(*args):
    "Move a file and its history."
    filecmd("move", backend.move, args)

def copy_method(*args):
    "Copy a file and its history."
    filecmd("copy", backend.copy, args)

def release_method(*args):
    "Release locks."
    ctx = CommandContext("release", args, require_empty=True)
    for arg in ctx.args:
        if not os.path.exists(arg):
            croak("I see no '%s' here." % arg)
        elif not registered(arg):
            croak("%s is not registered, skipping" % arg)
        else:
            with backend.lifter(arg):
                backend.release(arg)

def ls_method(*args):
    "List registered files."
    if args:
        croak("ls cannot accept arguments")
    try:
        masters = [fn for fn in os.listdir(repodir) if is_history(fn)]
    except OSError:
        croak("repo directory %s does not exist" % repodir)
    masters.sort()
    for master in masters:
        sys.stdout.write(backend.workfile(master) + "\n")

def visualize_method(*args):
    "Generate (and possibly display) a DOT visualization of repo structure."
    if not os.path.exists(repodir):
        croak("repository subdirectory %s does not exist" % repodir)
    args = list(args)
    comment = CommentContext("visualize", args)
    ctx = CommandContext("visualize", args, parse_revspec=comment.parse_revspec)
    for arg in ctx.args:
       #if not os.path.exists(arg):
       #    croak("I see no '%s' here." % arg)
       if not registered(arg):
           croak("%s is not registered." % arg)
    for arg in ctx.args:
        metadata = History(arg)
        ctx.resolve(metadata)
        if ctx.is_empty():
            ctx.select_all(metadata)
        sys.stdout.write("digraph {\n")
        if len(ctx.args) > 1:
            pref = arg + ":"
        else:
            pref = ""
        for item in ctx.seq:
            if item.parent:
                sys.stdout.write('\t%s%d -> %s%d;\n' \
                                 % (pref, item.parent.revno, pref, item.revno))
            summary = cgi.escape(item.log.split('\n')[0][:42])
            sys.stdout.write('\t%s%s [shape=box,width=5,label=<<table cellspacing="0" border="0" cellborder="0"><tr><td><font color="blue">%s%s</font></td><td>%s</td></tr></table>>];\n' \
                             % (pref, item.revno, pref, item.revno, summary))
            if metadata.tip(item.native) == item:
                    sys.stdout.write('\t"%s%s" [shape=oval,width=2];\n' \
                                     % (pref, item.branch))
                    sys.stdout.write('\t"%s%s" -> "%s%s" [style=dotted];\n' \
                                     % (pref, item.revno, pref, item.branch))
        keys = sorted(metadata.symbols.keys())
        for name in keys:
            native = metadata.symbols[name]
            branch_label = backend.isbranch(native)
            if branch_label:
                native = backend.branch_to_tip(native, metadata)
            revno = metadata.native_to_revno(native)
            if not branch_label:
                sys.stdout.write('\t{rank=same; "%s%s"; "%s%s"}\n' \
                                 % (pref, name, pref, revno))
                sys.stdout.write('\t"%s%s" -> "%s%s" [style=dotted];\n' \
                                 % (pref, name, pref, revno))
        sys.stdout.write("}\n")

def fast_export_method(*args):
    "Dump revision content to standard output."
    def attribute(item, who, fallback):
        s = fallback
        if item.headers and who in item.headers:
            s = item.headers[who]
        t, o = item.unixtime(who)
        return "%s %s %d %s%02d%02d\n" % \
            ((who, s, t, "-" if o < 0 else "+") + divmod(abs(o), 3600))
    ctx = CommandContext("fast-export", args)
    mark = 0
    if pseudotime:
        username = "J. Random Hacker"
        useremail = "jrh@nowhere.man"
    else:
        # Use polystr to ensure that data is decoded to Unicode on
        # Python 3.
        username = polystr(capture_or_die("git config --get user.name")).strip()
        useremail = polystr(capture_or_die("git config --get user.email")).strip()
    attribution = "%s <%s>" % (username, useremail)
    for arg in ctx.args:
        if not registered(arg):
            croak("%s is not registered" % arg)
        executable = os.stat(backend.history(arg)).st_mode & stat.S_IXUSR
        if executable:
            perms = "100755"
        else:
            perms = "100644"
        metadata = History(arg)
        ctx.resolve(metadata)
        if ctx.is_empty():
            ctx.select_all(metadata)
        with backend.lifter(arg):
            markmap = {}
            last_commit_mark = 0
            if len(ctx.args) == 1:
                branch = "master"
            else:
                # FIXME: Make this canonical even with tags
                branch = arg + "/master"
                oldbranch = branch
                for c in "~^\\*?":
                    branch = branch.replace(c, "")
                if not branch:
                    croak("branch name %s is ill-formed" % oldbranch)
                elif branch != oldbranch:
                    announce("branch name %s sanitized to %s" % (oldbranch, branch))
            for i in range(ctx.lo, ctx.hi+1):
                item = metadata.by_revno(i)
                with backend.cat(arg, item.native) as fp:
                    content = fp.read()  # this data will be binary
                size = len(content)  # size will be # of bytes, as desired
                mark += 1
                markmap[item.revno] = mark
                sys.stdout.write("blob\nmark :%d\ndata %d\n" % (mark, size))
                # Use polystr to ensure sys.stdout gets Unicode in Python 3
                sys.stdout.write(polystr(content) + "\n")
                if item.revno == ctx.lo:
                    if ctx.lo == 1:
                        sys.stdout.write("reset refs/heads/%s\n" % branch)
                    else:
                        sys.stdout.write("from refs/heads/%s^0\n" % branch)
                sys.stdout.write("commit refs/heads/%s\n" % branch)
                sys.stdout.write("mark :%d\n" % (mark + 1))
                sys.stdout.write(attribute(item, "author", attribution))
                sys.stdout.write(attribute(item, "committer", attribution))
                sys.stdout.write("data %s\n%s" % (len(item.log), item.log))
                if last_commit_mark:
                    sys.stdout.write("from :%d\n" % last_commit_mark)
                if len(arg.split()) > 1:
                    arg = '"' + arg + '"'
                sys.stdout.write("M %s :%d %s\n\n" % (perms, mark, arg))
                mark += 1
                last_commit_mark = mark
                markmap[item.revno] = mark
            sys.stdout.write("reset refs/heads/%s\nfrom :%d\n\n" % (branch, mark))
            for (key, val) in list(metadata.symbols.items()):
                val = metadata.native_to_revno(val)
                if val in ctx:
                    sys.stdout.write("reset refs/tags/%s\nfrom :%d\n\n" % (key, markmap[val]))

def fast_import_method(*args):
    "Accept a git fast-import stream on stdin, turn it into file histories."
    if not isinstance(backend, RCS):
        croak("fast-import is only supported with the RCS backend")
    if os.path.exists("RCS"):
        croak("refusing to unpack into existing RCS directory!")
    # Force -l to fit SRC's lockless interface.
    do_or_die(r"rcs-fast-import -l " +" ".join(args), missing="rcs-fast-import")
    try:
        os.makedirs(repodir)
    except OSError:
        pass
    for fn in os.listdir("RCS"):
        corresponding = os.path.join("RCS", os.path.basename(fn))
        fn = os.path.join(repodir, os.path.basename(fn))
        if os.path.exists(fn):
            croak("%s exists, aborting leaving RCS in place!" % corresponding)
        os.rename(corresponding, fn)
    shutil.rmtree("RCS")


def version_method(*args):
    "Report SRC's version"
    sys.stdout.write("src: %s\n" % version)
    (major, minor, micro, _releaselevel, _serial) = sys.version_info
    sys.stdout.write("python: %s.%s.%s\n" % (major, minor, micro))
    sys.stdout.write("%s: %s\n" % (backend.__class__.__name__,backend.version()))
    sys.stdout.write("platform: %s\n" % sys.platform)

dispatch = {
    "help":        help_method,
    "commit":      commit_method,
    "ci":          commit_method,
    "add":         add_method,
    "amend":       amend_method,
    "am":          amend_method,
    "list":        list_method,
    "li":          list_method,
    "log":         log_method,
    "checkout":    checkout_method,
    "co":          checkout_method,
    "status":      status_method,
    "st":          status_method,
    "cat":         cat_method,
    "diff":        diff_method,
    "di":          diff_method,
    "tag":         tag_method,
    "branch":      branch_method,
    "rn":          rename_method,
    "rename":      rename_method,
    "ls":          ls_method,
    "move":        move_method,
    "mv":          move_method,
    "copy":        copy_method,
    "cp":          copy_method,
    "visualize":   visualize_method,
    "vis":         visualize_method,
    "fast-export": fast_export_method,
    "fast-import": fast_import_method,
    "release":     release_method,
    "version":     version_method,
}

class RevisionMixin:
    "Express common operations on RCS and SCCS revisions."
    def splitrev(self, rev):
        "RCS revision to numeric tuple."
        return [int(d) for d in rev.split(".")]
    def joinrev(self, rev):
        "Numeric tuple to RCS revision."
        return ".".join([str(d) for d in rev])
    def pred(self, rev):
        "Our predecessor. Walks up parent branch."
        n = self.splitrev(rev)
        if n[-1] > 1:
            n[-1] -= 1
            rev = self.joinrev(n)
        else:
            rev = self.joinrev(n[:-2])
        return rev
    def succ(self, rev):
        "Our successor."
        if rev:
            n = self.splitrev(rev)
            n[-1] += 1
            return self.joinrev(n)
        else:
            return "1.1"
    def isbranch(self, symbol):
        "Is this a branch symbol?"
        # RCS convention - this could work for SCCS too, if we simulated
        # RCS symbols in some way.
        return "0." in symbol
    def branch_to_parent(self, revid):
        "Go from a branch ID sticky tag to the revision it was based on."
        # Must return an empty string for the fake root sticky tag.
        return self.joinrev(self.splitrev(revid)[:-2])
    def branch_to_base(self, revid, metadata):
        "Go from a branch ID sticky tag to the first revision of its branch."
        rev = self.branch_to_parent(revid)
        if rev:
            rev += ".1.1"
        else:
            rev = "1.1"
        return rev
    def branch_to_tip(self, revid, metadata):
        "Go from a branch ID sticky tag to the tip revision of its branch."
        rev = self.branch_to_base(revid, metadata)
        while True:
            nxt = self.succ(rev)
            if metadata.native_to_revno(nxt) is None:
                return rev
            else:
                rev = nxt
        croak("internal error: couldn't find branch tip of %s" % rev)
    def branch_stickybase(self, name, revision, metadata):
        "Compute a base and tip revision for a named branch."
        if name in metadata.symbols:
            # Must unstickify...
            base = metadata.symbols[name].split(".")
            base = base[:-2] + base[-1:]
            base = ".".join(base)
            return(None, base)
        else:
            def branchfrom(c, p):
                "Is c a branch child (not direct descendant) of parent p?"
                c = c.split(".")
                p = p.split(".")
                return len(c) == len(p) + 2 and c[len(p):] == p
            baserev = metadata.current()
            newsib = len([item for item in metadata.revlist \
                         if branchfrom(item.native, baserev)])
            newsib += 1
            base = baserev + "." + str(newsib)
            sticky = baserev + ".0." + str(newsib)
            return (sticky, base)
    def branch_initial(self, branchname, metadata):
        "Return initial commit of a named branch (the child of the root)."
        # What we need to do is find the branch tip, then walk back to
        # just after the first point where it joins another branch, then
        # do a delete to end of branch from there.
        base = self.branch_to_tip(metadata.symbols[branchname], metadata)
        while True:
            if base is not None and metadata.by_native_d[base].branches:
                break
            else:
                base = self.pred(base)
        return self.succ(base)

class RCS(RevisionMixin):
    "Encapsulate RCS back end methods."
    delimiters = ('----------------------------',
                  '=============================================================================')
    class RCSLifter:
        "Temporarily lift a master to the working directory."
        def __init__(self, name):
            self.name = name
            self.where = os.getcwd()
            self.deferred = []
            self.previous_handlers = {}
        def defer_signal(self, sig_num, stack_frame):
            self.deferred.append(sig_num)
        def __enter__(self):
            # Replace existing signal handlers with deferred handler
            for sig_num in (signal.SIGHUP, signal.SIGINT, signal.SIGTERM):
                # signal.signal returns None when no handler has been
                # set in Python, which is the same as the default
                # handler (SIG_DFL) being set
                self.previous_handlers[sig_num] = (
                    signal.signal(sig_num, self.defer_signal) or signal.SIG_DFL)
            if os.path.dirname(self.name):
                os.chdir(os.path.dirname(self.name))
            do_or_die("mv '{0}'/'{1},v' .".format(repodir, self.name))
        def __exit__(self, extype, value, traceback_unused):
            os.chdir(self.where)
            if extype and debug > 0:
                raise extype(value)
            do_or_die("mv '{0},v' '{1}'".format(self.name, repodir))
            # Restore handlers
            for sig_num, handler in self.previous_handlers.items():
                signal.signal(sig_num, handler)
            # Send deferred signals
            while self.deferred:
                sig_num = self.deferred.pop(0)
                os.kill(os.getpid(), sig_num)
            return True
    def lifter(self, name):
        return RCS.RCSLifter(name)
    def history(self, arg):
        return os.path.join(os.path.dirname(arg),
                            repodir,
                            os.path.basename(arg) + ",v")
    @staticmethod
    def is_history(path):
        return path.endswith(",v")
    def has_revisions(self, arg):
        "Does the master for this file have any revisions"
        # The magic number 105 is the size of an empty RCS file (no
        # metadata, no revisions) at 76 bytes, plus 29 bytes.  We assume
        # that this size has stayed constant or increased since ancient
        # times.  In fact the size of an RCS file with revisions goes up
        # more - by the 78 bytes for the final, fixed line of the log
        # display.  This gives us plenty of slack to cope with minor
        # format differences.
        #
        # The motivation here is to make "src status" faster by avoiding
        # the need for an entire log parse when checking for "A" status.
        return os.path.getsize(self.history(arg)) > 105
    def workfile(self, arg):
        "Workfile corresponding to an RCS master"
        return arg[:-2]
    def register(self, arg):
        "Register a file"
        # Key choices here: -b suppresses all keyword expansion, -U sets
        # non-strict locking (which makes branch appends less painful).
        do_or_die("rcs -q -U -kb -i '{0}' </dev/null && mv '{0},v' '{1}'".format(arg, repodir))
    def checkin(self, arg, comment):
        "Check in a commit, with comment."
        comment = "'" + comment.replace("'", r"'\''") + "'"
        # By unlocking the file before checkin we invoke the following
        # property described on the rcs(1) manual page: "If rev is
        # omitted and the caller has no lock, but owns the file and
        # locking is not set to strict, then the revision is appended to
        # the default branch (normally the trunk; see the -b option of
        # rcs(1))."  This is the behavior we want and why locking is set
        # to non-strict.
        do_or_die("rcs -q -U -u '{0},v' && ci -l -m{1} '{0}'".format(arg, comment))
    def checkout(self, arg, revision):
        "Check out a revision. Leaves it writeable."
        do_or_die("rm -f '{0}' && rcs -q -u '{0},v' && co -q -l{1} '{0}'".format(arg, revision))
    def amend(self, arg, rev, comment):
        "Amend a commit comment."
        # Relies on caller to escape comment string
        comment = "'" + comment.replace("'", r"'\''") + "'"
        do_or_die("rcs -m{0}:{1} '{2}'".format(rev, comment, arg))
    def cat(self, arg, revision):
        "Ship the contents of a revision to stdout or a named file."
        return popen_or_die("co -q -p -r{1} '{0}'".format(arg, revision), "r")
    def delete_tag(self, tagname, metadata):
        "Delete a specified tag."
        do_or_die("rcs -n{0} '{1}'".format(tagname, metadata.name))
    def set_tag(self, tagname, revision, metadata):
        "Set a specified tag."
        do_or_die("rcs -n{0}:{1} '{2}'".format(tagname, revision, metadata.name))
    def delete_branch(self, branchname, metadata):
        "Delete a specified branch."
        # From rcs(1): -orange deletes ("outdates") the revisions given
        # by range.  A range consisting of a single revision number
        # means that revision.  A range consisting of a branch number
        # means the latest revision on that branch.  A range of the form
        # rev1:rev2 means revisions rev1 to rev2 on the same branch,
        # :rev means from the beginning of the branch containing rev
        # up to and including rev, and rev: means from revision rev to
        # the end of the branch containing rev.  None of the outdated
        # revisions can have branches or locks.
        do_or_die("rcs -o{0}: '{1}'".format(self.branch_initial(branchname, metadata), metadata.name))
        self.delete_tag(branchname, metadata)
    def set_branch(self, name, revision, metadata):
        "Set the specified branch to be default, creating it if required."
        (sticky, base) = self.branch_stickybase(name, revision, metadata)
        if sticky:
            do_or_die("rcs -n{0}:{1} '{2}'".format(name, sticky, metadata.name))
        do_or_die("rcs -b%s %s" % (base, metadata.name))
    def move(self, source, target):
        "Move a file and its history."
        do_or_die("mv '{0}' '{1}' && mv '{2}' '{3}'".format(source, target,
                                                    self.history(source),
                                                    self.history(target)))
    def copy(self, source, target):
        "Copy a file and its history."
        do_or_die("cp '{0}' '{1}' && cp '{2}' '{3}'".format(source, target,
                                                    self.history(source),
                                                    self.history(target)))
    def release(self, arg):
        "Release locks."
        do_or_die("rcs -q -u '{0},v'".format(arg))
    def write_description(self, text, metadata):
        "Write description field. If text is empty, clear the field."
        text = "'" + text.replace("'", r"'\''") + "'"
        do_or_die("rcs -t-{1} '{0}'".format(metadata.name, text))
    def version(self):
        rawversion = capture_or_die("rcs --version")
        m = re.search(r"[0-9]+\.[0-9]+\.[0-9]+".encode('ascii'),rawversion)
        return m and polystr(m.group(0))
    def parse(self, metadata):
        "Get and parse the RCS log output for this file."
        def sortkey(rev):
            return rev.date + \
                '.'.join('%010d' % int(n) for n in rev.native.split('.'))
        metadata.symbols["trunk"] = "0.1"
        with popen_or_die("cd %s >/dev/null; rlog %s 2>/dev/null; cd ..>/dev/null" % (repodir, metadata.name)) as fp:
            if debug >= DEBUG_PARSE:
                sys.stderr.write("\t-> init\n")
            state = "init"
            for line in fp:
                # All operations here will need Unicode in Python 3
                line = polystr(line)
                if debug >= DEBUG_PARSE:
                    sys.stderr.write("in: %s\n" % repr(line))
                if state == "init":
                    if line.startswith("locks:"):
                        if debug >= DEBUG_PARSE:
                            sys.stderr.write("\t-> locks\n")
                        state = "locks"
                    elif line.startswith("symbolic names:"):
                        if debug >= DEBUG_PARSE:
                            sys.stderr.write("\t-> symbols\n")
                        state = "symbols"
                    elif line.startswith("branch:"):
                        branch = line.split(":")[1].strip()
                        # Undocumented fact about RCS: The branch "1"
                        # is the same as the blank branch.  Significant
                        # because you can't reset to the blank branch
                        # using rcs -b, that resets to the dynamically
                        # highest branch.
                        if not branch or branch == "1":
                            metadata.branch = "trunk"
                    elif line.startswith("description:"):
                        state = "description"
                elif state == "description":
                    if line.startswith("============================"):
                        break
                    elif line.startswith("----------------------------"):
                        if debug >= DEBUG_PARSE:
                            sys.stderr.write("\t-> logheader\n")
                        state = "logheader"
                        metadata.revlist.append(HistoryEntry(metadata))
                        metadata.description = metadata.description[:-1]
                    else:
                        metadata.description += line
                elif state == "locks":
                    if not line[0].isspace():
                        if debug >= DEBUG_PARSE:
                            sys.stderr.write("\t-> init\n")
                        state = "init"
                    else:
                        fields = line.strip().split()
                        metadata.lockrevs.append(fields[1])
                elif state == "symbols":
                    if not line[0].isspace():
                        if debug >= DEBUG_PARSE:
                            sys.stderr.write("\t-> init\n")
                        state = "init"
                    else:
                        fields = line.strip().split()
                        name = fields[0]
                        if name.endswith(":"):
                            name = name[:-1]
                        rev = fields[1]
                        metadata.symbols[name] = rev
                elif state == "logheader":
                    if line.startswith("revision "):
                        fields = line.split()
                        metadata.revlist[-1].native = fields[1]
                    elif line.startswith("----------------------------"):
                        metadata.revlist.append(HistoryEntry(metadata))
                    elif line.startswith("date: "):
                        fields = line.split()
                        date = fields[1] + " " + fields[2]
                        if date.endswith(";"):
                            date = date[:-1]
                        date = date.replace("/","-").replace(" ","T") + "Z"
                        metadata.revlist[-1].date = date
                    elif line.startswith("branches:"):
                        continue
                    elif line.startswith("======================="):
                        # This deals with RCS v5.7 issuing a log header
                        # divider just before the terminator, something
                        # v5.8 does not do.
                        if not metadata.revlist[-1].native:
                            metadata.revlist.pop()
                        elif not metadata.revlist[-1].log.endswith("\n"):
                            metadata.revlist[-1].log += "\n"
                        break
                    elif line.strip() == "*** empty log message ***":
                        continue
                    elif metadata.revlist:
                        metadata.revlist[-1].log += line
            # Now that we have the symbol table...
            if metadata.branch != "trunk":
                for (k, v) in list(metadata.symbols.items()):
                    if v == metadata.branch:
                        metadata.branch = k
                        break
                else:
                    croak("unrecognized branch ID '%s'" % branch)
            metadata.revlist.sort(key=sortkey)
            for (i, item) in enumerate(metadata.revlist):
                if pseudotime:
                    # Artificial date one day after the epoch
                    # to avoid timezone issues.
                    item.date = rfc3339(86400 + i * 60)
                item.revno = i + 1
            metadata.revlist.reverse()
            if debug >= DEBUG_PARSE:
                #sys.stdout.write("\t%d revisions\n" % len(metadata.revlist)
                sys.stdout.write("\tlockrevs: %s\n" % metadata.lockrevs)
                sys.stdout.write("\tsymbols: %s\n" % metadata.symbols)
            metadata.build_indices()

# SCCS branch numbering (not supported yet) works differently from RCS
# branch numbering.  Node IDs have at most 4 parts in the form R.B.L.S
# (release, level, branch, sequence):
#
# 1.0 - initial trunk version
# 1.1 - next checkin on trunk
# 1.1.1.0 - First branch from trunk v1.1
# 1.1.1.1 - Next checkin on that branch
# 1.1.2.0 - Second branch from v1.1
# 1.2 - next checkin on trunk.
#
# The main difference is that you cannot branch from a branch, only from
# trunk.

class SCCS(RevisionMixin):
    "Encapsulate SCCS back end methods."
    delimiters = ("-X-X-X-X-X--X-X-X-X-X--X-X-X-X-X-",)
    class SCCSLifter:
        "Temporarily lift a master to the working directory."
        def __init__(self, name):
            self.name = name
            self.where = os.getcwd()
            if not os.path.isdir("SCCS"):
                croak("no SCCS directory.")
            self.deferred = []
            self.previous_handlers = {}
        def defer_signal(self, sig_num, stack_frame):
            self.deferred.append(sig_num)
        def __enter__(self):
            # Replace existing signal handlers with deferred handler
            for sig_num in (signal.SIGHUP, signal.SIGINT, signal.SIGTERM):
                # signal.signal returns None when no handler has been
                # set in Python, which is the same as the default
                # handler (SIG_DFL) being set
                self.previous_handlers[sig_num] = (
                    signal.signal(sig_num, self.defer_signal) or signal.SIG_DFL)
        def __exit__(self, extype, value, traceback_unused):
            # Restore handlers
            for sig_num, handler in self.previous_handlers.items():
                signal.signal(sig_num, handler)
            # Send deferred signals
            while self.deferred:
                sig_num = self.deferred.pop(0)
                os.kill(os.getpid(), sig_num)
            return True
    def lifter(self, name):
        return SCCS.SCCSLifter(name)
    def __sccsfile(self, arg, pref):
        return os.path.join(os.path.dirname(arg),
                            "SCCS",
                            pref + "." + os.path.basename(arg))
    def history(self, arg):
        return self.__sccsfile(arg, "s")
    @staticmethod
    def is_history(path):
        return path.startswith("s.")
    def has_revisions(self, arg):
        "Does the master for this file have any revisions"
        # It's not possible to create an SCCS file without at least one
        # revision.
        return True
    def workfile(self, arg):
        "Workfile corresponding to an SCCS master"
        return arg[2:]
    def register(self, arg):
        "Register a file"
        if not os.path.isdir("SCCS"):
            os.mkdir("SCCS")
    def checkin(self, arg, comment):
        "Check in a commit, with comment."
        comment = "'" + comment.replace("'", r"'\''") + "'"
        if os.path.exists(self.history(arg)):
            cmd = "delta -s -y{1} {0}".format(arg, comment)
        else:
            # Yuck - 2>/dev/null is required to banish the message
            # admin: warning: SCCS/XXXXX: No id keywords.
            cmd = "admin -fb -i '{0}' -y{1} <'{0}' 2>/dev/null".format(arg, comment)
        do_or_die("TZ=UTC sccs " + cmd)
        do_or_die("rm -f {0} && sccs get -e -s '{0}' >/dev/null".format(arg))
    def checkout(self, arg, revision):
        "Check out a revision. Leaves it writeable."
        do_or_die("rm -f SCCS/p.{0}".format(arg))
        if revision:
            do_or_die("rm -f '{0}' && sccs get -s -e -r{1} '{0}' >/dev/null".format(arg, revision))
        else:
            do_or_die("rm -f '{0}' && sccs get -s -e '{0}' >/dev/null".format(arg))
    def amend(self, arg, rev, comment):
        "Amend a commit comment."
        comment = "'" + comment.replace("'", r"'\''") + "'"
        do_or_die("sccs cdc -r{1} -y{2} '{0}'".format(arg, rev, comment))
    def cat(self, arg, revision):
        "Ship the contents of a revision to stdout or a named file."
        if revision:
            return popen_or_die("sccs get -s -p -r{1} '{0}' 2>/dev/null".format(arg, revision), "r")
        else:
            return popen_or_die("sccs get -p {0}".format(arg), "r")
    def delete_tag(self, tagname, metadata):
        "Delete a specified tag."
        croak("tags are not supported in the SCCS back end")
    def set_tag(self, tagname, revision, metadata):
        "Set a specified tag."
        croak("tags are not supported in the SCCS back end")
    def delete_branch(self, branchname, metadata):
        "Delete a specified branch."
        croak("branches are not supported in the SCCS back end")
    def set_branch(self, name, revision, metadata):
        "Set the specified branch to be default, creating it if required."
        croak("branches are not supported in the SCCS back end")
    def move(self, source, target):
        "Move a file and its history."
        do_or_die("mv '{0}' '{1}' && mv '{2}' '{3}'".format(source, target,
                                                    self.history(source),
                                                    self.history(target)))
    def copy(self, source, target):
        "Copy a file and its history."
        do_or_die("cp '{0}' '{1}' && cp '{2}' '{3}'".format(source, target,
                                                    self.history(source),
                                                    self.history(target)))
    def release(self, arg):
        "Release locks."
        do_or_die("cssc admin -dla '{0}'".format(arg))
    def write_description(self, text, metadata):
        "Write description field. If text is empty, clear the field."
        if text:
            scribblefile = os.path.join(os.path.dirname(metadata.name),"SCCS",".scribble")
            # Write to filesystem as binary ASCII data for robustness
            with open(scribblefile, "wb") as wfp:
                wfp.write(polybytes(text) + b"\n")
        else:
            scribblefile = ''
        do_or_die("sccs admin -t{0} {1} 2>/dev/null".format(scribblefile, metadata.name))
        if text:
            os.remove(scribblefile)
    def version(self):
        rawversion = capture_or_die("sccs --version 2>&1")
        m = re.search(r"[0-9]+\.[0-9]+\.[0-9]+".encode('ascii'), rawversion)
        return m and polystr(m.group(0))
    def parse(self, metadata):
        "Get and parse the SCCS log output for this file."
        metadata.symbols["trunk"] = "0.1"
        with popen_or_die("sccs prs -e -d':FD::Dt:\n:C:{1}' {0} 2>/dev/null".format(metadata.name, SCCS.delimiters[0])) as fp:
            if debug >= DEBUG_PARSE:
                sys.stderr.write("\t-> init\n")
            state = "init"
            for line in fp:
                # All operations here will need Unicode in Python 3
                line = polystr(line)
                if debug >= DEBUG_PARSE:
                    sys.stderr.write("in %s: %s\n" % (state, repr(line)))
                if state == 'init':
                    if line == 'none\n':
                        line = ''
                    metadata.description = line
                    state = 'header'
                elif state == "header":
                    comment = ""
                    if line.startswith("D "):
                        try:
                            (_, rev, yymmdd, hhmmss) = line.split()[:4]
                            metadata.revlist.append(HistoryEntry(metadata))
                            metadata.revlist[-1].native = rev
                            yymmdd = CENTURY + yymmdd.replace('/','-')
                            metadata.revlist[-1].date = yymmdd+"T"+hhmmss+"Z"
                        except ValueError:
                            croak("ill-formed delta line")
                        if debug >= DEBUG_PARSE:
                            sys.stderr.write("\t-> header\n")
                        state = "comment"
                elif state == "comment":
                    if line == SCCS.delimiters[0] + "\n":
                        metadata.revlist[-1].log = comment.rstrip() + "\n"
                        if debug >= DEBUG_PARSE:
                            sys.stderr.write("\t-> init\n")
                        state = "header"
                    else:
                        comment += line
            metadata.revlist.sort(key=lambda x: x.date)
            for (i, item) in enumerate(metadata.revlist):
                if pseudotime:
                    # Artificial date one day after the epoch
                    # to avoid timezone issues.
                    item.date = rfc3339(86400 + i * 60)
                item.revno = i + 1
            metadata.revlist.reverse()
            try:
                with open(self.__sccsfile(metadata.name, "p"), "rb") as fp:
                    for line in fp:
                        metadata.lockrevs.append(polystr(line).split()[0])
            except IOError:
                pass
            metadata.build_indices()

backends = (RCS, SCCS)

if __name__ == "__main__":
    try:
        commandline = list(sys.argv[1:])
        explicit = False
        repodir = ".src"
        backend = RCS

        if not os.path.exists(".src"):
            for vcs in backends:
                if os.path.exists(vcs.__name__):
                    repodir = vcs.__name__
                    backend = vcs
                    break

        while commandline and commandline[0].startswith("-"):
            if commandline[0] == '-d':
                debug += 1
            elif commandline[0] == '-q':
                quiet = True
            elif commandline[0] == '-T':
                pseudotime = True
            elif commandline[0] == '-S':
                repodir = commandline[1]
                explicit = True
                commandline.pop(0)
            else:
                croak("unknown option %s before command verb" % commandline[0])
            commandline.pop(0)

        if not commandline:
            help_method()
            raise SystemExit(0)

        # User might want to force the back end
        for vcs in backends:
            if commandline[0] == vcs.__name__.lower():
                backend = vcs
                commandline.pop(0)
                break

        # Ugly constraint...
        if backend.__name__ == 'SCCS':
            repodir = "SCCS"

        backend = backend()

        if not commandline:
            help_method()
            raise SystemExit(0)

        if commandline[0] in dispatch:
            dispatch[commandline[0]](*commandline[1:])
        else:
            croak("no such command as '%s'.  Try 'src help'" \
                           % commandline[0])
    except KeyboardInterrupt:
        pass

# The following sets edit modes for GNU EMACS
# Local Variables:
# mode:python
# End: