#!/bin/sh
set -e
fail () { echo >&2 "$0: $*"; exit 1; }

play=.git/tartree-edit-work

git_manip_play () {
	local wd; wd=$(pwd)
	case "$wd" in
	*.edit) fail "bad idea to run gitfetchinfo into a .edit tree!" ;;
	esac
	rm -rf $play
	mkdir $play
}

gitfetchdiff_list () {
	git for-each-ref --format '%(refname) %(objectname)' \
		refs/remotes/"$1" \
	| sed 's/^refs\/remotes\/[^\/]*\///' \
	| sort >"$play/$2"
}

gitfetchdiff () {
	local how="$1"
	local a="$2"
	local b="$3"
	git_manip_play

	rrab=refs/remotes/"$a+$b"

	ulf=\
"delete refs/remotes/$a/%l
delete refs/remotes/$b/%l
"
	case "$how" in
	diff)
		git for-each-ref --format 'delete %(refname)' $rrab \
			| git update-ref --stdin
		;;
	merge)
		ulf=\
"create $rrab/%l
$ulf"
		;;
	*)
		fail "internal error bad how ($how)"
		;;
	esac

	gitfetchdiff_list "$a" a
	gitfetchdiff_list "$b" b

	diff --old-line-format='' --new-line-format='' \
		--unchanged-line-format="$ulf" \
		$play/a $play/b >$play/updates \
	|| test $? = 1

	git update-ref --stdin <$play/updates
	exit 0
}

case "$#.$1" in
2.edit|2.done)	mode="$1"; arg="$2" ;;
3.gitfetchinfo)	mode="$1"; arg="$2"; remote="$3" ;;
3.gitfetchinfo-diff)	gitfetchdiff diff "$2" "$3"	;;
3.gitfetchinfo-merge)	gitfetchdiff merge "$2" "$3"	;;
?.-*)	fail "no options understood"			;;
*)	fail "usage:
    tartree-edit edit|done DIRECTORY|TARBALL
    tartree-edit gitfetchinfo DIRECTORY|TARBALL REMOTE
    tartree-edit gitfetchinfo-merge REMOTE-A REMOTE-B"	;;
    # we don't document gitfetchinfo-diff because it's rather poor
esac

case "$arg" in
*.tar)		base=${arg%.tar}			;;
*.edit)		base=${arg%.edit}			;;
*)		base=${arg}				;;
esac

tryat_pre () {
	local b="$1"
	rm -rf "$b.tmp"
	if test -f "$b.tar" && test -f "$b.edit"; then
		echo "$b.edit exists, deleting possibly-obsolete $b.tar"
		rm "$b.tar"
	fi
}

tryat_edit () {
	local b="$1"
	if test -d "$b.edit"; then
		echo "$b.edit already exists"
		exit 0
	fi
	if test -f "$b.tar"; then
		mkdir "$b.tmp"
		(set -e; cd "$b.tmp"; tar xf "$b.tar")
		mv "$b.tmp" "$b.edit"
		rm "$b.tar"
		echo "$b.edit ready"
		exit 0
	fi
}

gitfetchinfo_perhaps_commit () {
	local m="$1"
	set +e
	git diff --cached --quiet --exit-code HEAD
	local rc=$?
	set -e
	case "$rc" in
	0)   return ;;
	1)   git commit --allow-empty --author='tartree-edit <>' -m "$m" ;;
	*)   fail "git diff failed ($rc)" ;;
	esac
}

tryat_gitfetchinfo () {
	git_manip_play

	if test -d "$b.edit"; then
		cp -a "$b.edit"/. "$play"/.
	else
		exec 3<"$b.tar"
		tar -C $play -f - <&3 -x
		exec 3<&-
	fi

	local innerwd; innerwd="$(echo $play/*)"

	git for-each-ref --format='%(refname)' refs/remotes >$play/l
	perl -w -ne '
	    our %remerge;
	    use strict;
	    chomp;
	    next unless m#^refs/remotes/([^/]+)/#;
	    my $old = $_;
	    my $ab = $1;
	    my $rhs = $'\'';
	    my @ab = split /\+/, $ab;
	    next unless @ab == 2;
	    next unless (grep { $_ eq "'"$remote"'" } @ab) == 1;
	    $remerge{"@ab"} = 1;
	    print "update refs/remotes/$_/$rhs $old\n" or die $! foreach @ab;
	    print "delete $old\n" or die $!;
	    END {
	        open REMERGE, ">&3" or die $!;
		print REMERGE "$_\n" or die $! foreach sort keys %remerge;
		close REMERGE or die $!;
	    }
	' <$play/l >$play/unmerge 3>$play/remerge
	git update-ref --stdin <$play/unmerge

	git remote remove "$remote" 2>/dev/null ||:
	git remote add "$remote" $innerwd
	git fetch --no-tags -p "$remote" \
		+"HEAD:refs/remotes/$remote/TT-HEAD"
	cd $innerwd
	GIT_AUTHOR_DATE=$(git log -n1 --pretty=format:'%ai')
	GIT_COMMITTER_DATE=$GIT_AUTHOR_DATE
	export GIT_COMMITTER_DATE GIT_AUTHOR_DATE
	git checkout -b WORKTREE
	gitfetchinfo_perhaps_commit 'UNCOMMITTED INDEX'
	git add -Af .
	gitfetchinfo_perhaps_commit 'UNCOMMITTED WORKING TREE'
	cd ../../..
	git fetch --no-tags "$remote" --refmap \
		+"refs/*:refs/remotes/$remote/*" \
		+"refs/*:refs/remotes/$remote/*"

	exec 3<$play/remerge
	# $play will be destroyed by what follows, but we have
	# an fd open onto remerge, so this will work
	while read <&3 a b; do
	      echo "Updating gitfetchinfo-merge $a $b"
	      "$0" gitfetchinfo-merge $a $b
	done

	exit 0
}

tryat_done () {
	local b="$1"
	if test -d "$b.edit"; then
		(set -e; cd "$b.edit"; tar cf "$b.tmp" *)
		mv "$b.tmp" "$b.tar"
		mv "$b.edit" "$b.tmp"
		rm -rf "$b.tmp"
		echo "$b.tar regenerated"
		exit 0
	fi
	if test -f "$b.tar"; then
		echo "$b.tar already exists and $b.edit doesn't"
		exit 0
	fi
}

tryat () {
	local b="$1"
	if ! test -f "$b.tar" && ! test -d "$b.edit"; then
		return
	fi
	tryat_pre "$b"
	tryat_$mode "$b"
	fail "unexpected situation in $b.*"
}

case "$arg" in
/*)		tryat "$base"
		;;
*)
		pwd=`pwd`
		tryat "$pwd/$base"
		tryat "$pwd/git-srcs/$base"
		tryat "$pwd/tests/git-srcs/$base"
		fail "could not find $base..."
		;;
esac