#!/usr/bin/perl -w

=head1 NAME

dh_link - create symlinks in package build directories

=cut

use strict;
use File::Find;
use Debian::Debhelper::Dh_Lib;

=head1 SYNOPSIS

B<dh_link> [S<I<debhelper options>>] [B<-A>] [B<-X>I<item>] [S<I<source destination> ...>]

=head1 DESCRIPTION

B<dh_link> is a debhelper program that creates symlinks in package build
directories.

B<dh_link> accepts a list of pairs of source and destination files. The source
files are the already existing files that will be symlinked from. The
destination files are the symlinks that will be created. There B<must> be
an equal number of source and destination files specified.

Be sure you B<do> specify the full filename to both the source and
destination files (unlike you would do if you were using something like
L<ln(1)>).

B<dh_link> will generate symlinks that comply with Debian policy - absolute
when policy says they should be absolute, and relative links with as short
a path as possible. It will also create any subdirectories it needs to to put
the symlinks in.

B<dh_link> also scans the package build tree for existing symlinks which do not
conform to Debian policy, and corrects them (v4 or later).

=head1 FILES

=over 4

=item debian/I<package>.links

Lists pairs of source and destination files to be symlinked. Each pair
should be put on its own line, with the source and destination separated by
whitespace.

=back

=head1 OPTIONS

=over 4

=item B<-A>, B<--all>

Create any links specified by command line parameters in ALL packages
acted on, not just the first.

=item B<-X>I<item>, B<--exclude=>I<item>

Do not correct symlinks that contain I<item> anywhere in their filename from
being corrected to comply with Debian policy.

=item I<source destination> ...

Create a file named I<destination> as a link to a file named I<source>. Do
this in the package build directory of the first package acted on.
(Or in all packages if B<-A> is specified.)

=back

=head1 EXAMPLES

 dh_link usr/share/man/man1/foo.1 usr/share/man/man1/bar.1

Make F<bar.1> be a symlink to F<foo.1>

 dh_link var/lib/foo usr/lib/foo \
   usr/share/man/man1/foo.1 usr/share/man/man1/bar.1

Make F</usr/lib/foo/> be a link to F</var/lib/foo/>, and F<bar.1> be a symlink to
the F<foo.1>

=cut

# This expand_path expands all path "." and ".." components, but doesn't
# resolve symbolic links.
sub expand_path {
	my $start = @_ ? shift : '.';
	my @pathname = split(m:/+:,$start);

	my $entry;
	my @respath;
	foreach $entry (@pathname) {
		if ($entry eq '.' || $entry eq '') {
			# Do nothing
		}
		elsif ($entry eq '..') {
			if ($#respath == -1) {
				# Do nothing
			}
			else {
				pop @respath;
			}
		}
		else {
			push @respath, $entry;
		}
	}

	my $result;
	foreach $entry (@respath) {
		$result .= '/' . $entry;
	}
	if (! defined $result) {
		$result="/"; # special case
	}
	return $result;
}


init();

foreach my $package (@{$dh{DOPACKAGES}}) {
	my $tmp=tmpdir($package);
	my $file=pkgfile($package,"links");

	my @links;
	if ($file) {
		@links=filearray($file);
	}

	# Make sure it has pairs of symlinks and destinations. If it
	# doesn't, $#links will be _odd_ (not even, -- it's zero-based).
	if (int($#links/2) eq $#links/2) {
		error("$file lists a link without a destination.");
	}

	if (($package eq $dh{FIRSTPACKAGE} || $dh{PARAMS_ALL}) && @ARGV) {
		push @links, @ARGV;
	}

	# Same test as above, including arguments this time.
	if (int($#links/2) eq $#links/2) {
		error("parameters list a link without a destination.");
	}

	# v4 or later and only if there is a temp dir already
	if (! compat(3) && -e $tmp) {
		# Scan for existing links and add them to @links, so they
		# are recreated policy conformant.
		find(
			sub {
				return unless -l;
				return if excludefile($_);
				my $dir=$File::Find::dir;
				$dir=~s/^\Q$tmp\E//;
				my $target = readlink($_);
				if ($target=~/^\//) {
					push @links, $target;
				}
				else {
					push @links, "$dir/$target";
				}
				push @links, "$dir/$_";
				
			},
			$tmp);
	}
	
	while (@links) {
		my $dest=pop @links;
		my $src=expand_path(pop @links);

		$src=~s:^/::;
		$dest=~s:^/::;
		
		if ($src eq $dest) {
			warning("skipping link from $src to self");
			next;
		}

		# Make sure the directory the link will be in exists.
		my $basedir=dirname("$tmp/$dest");
		if (! -e $basedir) {
			doit("install","-d",$basedir);
		}
		
		# Policy says that if the link is all within one toplevel
		# directory, it should be relative. If it's between
		# top level directories, leave it absolute.
		my @src_dirs=split(m:/+:,$src);
		my @dest_dirs=split(m:/+:,$dest);
		if (@src_dirs > 0 && $src_dirs[0] eq $dest_dirs[0]) {
		    	# Figure out how much of a path $src and $dest
			# share in common.
			my $x;
			for ($x=0; $x < @src_dirs && $src_dirs[$x] eq $dest_dirs[$x]; $x++) {}
			# Build up the new src.
			$src="";
			for (1..$#dest_dirs - $x) {
				$src.="../";
			}
			for ($x .. $#src_dirs) {
				$src.=$src_dirs[$_]."/";
			}
			if ($x > $#src_dirs && ! length $src) {
				$src.="."; # special case
			}
			$src=~s:/$::;
		}
		else {
			# Make sure it's properly absolute.
			$src="/$src";
		}

		if (-d "$tmp/$dest" && ! -l "$tmp/$dest") {
			error("link destination $tmp/$dest is a directory");
		}
		doit("rm", "-f", "$tmp/$dest");
		doit("ln","-sf", $src, "$tmp/$dest");
	}
}

=head1 SEE ALSO

L<debhelper(7)>

This program is a part of debhelper.

=head1 AUTHOR

Joey Hess <joeyh@debian.org>

=cut