#!/bin/sh

accept_rerere="--rerere-autoupdate" generate=no update= diff= edit= stop_at_cut=
while case "$#,$1" in 0,*) break;; *,-*) ;; esac
do
	case "$1" in
	-n)	accept_rerere= ;;
	-e)	edit=t ;;
	-c)	stop_at_cut=1 ;;
	-c?*)	stop_at_cut=${1#-c} ;;
	-d)	update=${2?"diff with what?"}
		diff=yes
		generate=yes
		shift ;;
	-u)	update=${2?"update what?"}
		generate=yes
		shift ;;
	*)	generate=yes
		break ;;
	esac
	shift
done

annotate_merge () {
	test -f Meta/whats-cooking.txt || return 0

	perl -e '
		my ($branch) = $ARGV[0];
		my ($in_section, $in_desc);
		my @msg = ();
		while (<STDIN>) {
			chomp;
			if (/^\* $branch /) {
				$in_section = 1;
				next;
			}
			last if (/^[-*\[]/ && $in_section);
			next unless $in_section;
			s/^\s+//;
			if (/^$/) {
				$in_desc = 1;
			}
			next unless ($in_section && $in_desc);
			push @msg, "$_\n";
		}

		if ($in_section && @msg) {
			open(my $fh, "-|", qw(git cat-file commit HEAD));
			my @original = (<$fh>);
			my @final;
			$in_section = 0;
			for (@original) {
				if (!$in_section) {
					$in_section = 1 if (/^$/);
					next;
				}
				push @final, $_;
				if (/^$/ && $in_section == 1) {
					push @final, @msg;
					push @final, "\n";
					$in_section = 2;
				}
			}
			close $fh;
			open($fh, "|-", qw(git commit --amend -F -));
			print $fh @final;
			close $fh;
		}
	' <Meta/whats-cooking.txt "$1"
}

case "$generate" in
no)
	accept_rerere () {
		if ! git write-tree 2>/dev/null >/dev/null
		then
			git rerere remaining
			return 1
		else
			EDITOR=: git commit --no-verify
			echo "Accepted previous resolution"
			return 0
		fi
	}

	mark_cut () {
		test -n "$stop_at_cut" && return

		count_since_last_cut=$(( $count_since_last_cut + 1 ))
		test -z "$prev_cut" && return
		git commit --allow-empty -m "$prev_cut"
		prev_cut=
	}

	cut_seen=0 prev_cut= count_since_last_cut=0
	while read branch eh
	do
		case "$branch" in '###') cut_seen=$(( $cut_seen + 1 )) ;; esac
		if test -n "$stop_at_cut" && test $stop_at_cut -le $cut_seen
		then
			continue ;# slurp the remainder and skip
		fi

		case "$branch" in
		'###')
			if test "$count_since_last_cut" = 0
			then
				prev_cut=
			else
				echo >&2 "$branch $eh"
				prev_cut="$branch $eh"
				count_since_last_cut=0
			fi
			continue ;;
		'#'* | '')
			continue ;;
		esac

		case "$eh" in
		"" | "#"*)
			echo >&2 "* $branch"

			save=$(git rev-parse --verify HEAD)
			tip=$(git rev-parse --verify "$branch^0")
			mb=$(git merge-base "$tip" "$save")
			test "$mb" = "$tip" && continue

			mark_cut

			EDITOR=: git merge $accept_rerere --edit "$branch" ||
			accept_rerere ||
			exit

			annotate_merge "$branch" || exit
			test -z "$edit" ||
			git commit --amend || exit

			this=$(git rev-parse --verify HEAD)
			if test "$this" = "$save"
			then
				:
			elif git show-ref -q --verify "refs/merge-fix/$branch"
			then
				echo >&2 "Fixing up the merge"
				git cherry-pick --no-commit "refs/merge-fix/$branch" &&
				EDITOR=: git commit --amend -a || exit
			fi
			;;
		pick" "*)
			echo >&2 "* $eh"

			mark_cut

			git cherry-pick "$branch" || exit ;;
		*) echo >&2 "Eh? $branch $eh"; exit ;;
		esac
	done
	exit
esac

if test -n "$update" && test $# = 0
then
	set x $(sed -n -e '2s/^# //p' <"$update") &&
	shift
fi

# Generation (or updating)

x40='[0-9a-f][0-9a-f][0-9a-f][0-9a-f][0-9a-f]'
x40="$x40$x40$x40$x40$x40$x40$x40$x40"
LF='
'

show_merge () {
	case "$msg" in
	"Merge branch '"*"'"*)
		branch=$(expr "$msg" : "Merge branch '\(.*\)'")
		merge_hier=heads/
		;;
	"Merge remote branch '"*"'"*)
		branch=$(expr "$msg" : "Merge remote branch '\(.*\)'")
		merge_hier=
		;;
	*)
		echo 2>&1 "Huh?: $msg"
		return
		;;
	esac &&
	tip=$(git rev-parse --verify "refs/$merge_hier$branch" 2>/dev/null) &&
	merged=$(git name-rev --refs="refs/$merge_hier$branch" "$other" 2>/dev/null) &&
	merged=$(expr "$merged" : "$x40 \(.*\)") &&
	test "$merged" != undefined || {
		other=$(git log -1 --pretty='format:%s' $other) &&
		merged="$branch :rebased? $other"
	}
}

show_pick () {
	case "$msg" in
	"### "* | "###")
		merged="$msg"
		;;
	*)
		merged="$(git rev-parse --verify "$commit") pick $msg"
		;;
	esac

}

generate () {
	PROGRAM=$1
	shift
	echo '#!/bin/sh'
	echo "# $1"
	echo 'case "$#,$1" in'
	echo '1,-u|1,-d)'
	echo "	exec $PROGRAM" '"$1" "$0"'
	echo 'esac'
	echo "$PROGRAM" '"$@" <<\EOF'
	git log --no-decorate --pretty=oneline --first-parent "$1" |
	{
		series=
		while read commit msg
		do
			if other=$(git rev-parse -q --verify "$commit^2")
			then
				show_merge
			else
				show_pick
			fi

			if test -z "$series"
			then
				series="$merged"
			else
				series="$merged$LF$series"
			fi
		done
		echo "$series"
	}
	echo EOF
}

if test -z "$update"
then
	generate "$0" "$@"
elif test -z "$diff"
then
	generate "$0" "$@" | diff -u "$update" -
	if test $? = 0
	then
		echo >&2 "No changes."
	else
		echo >&2 -n "Update [y/N]? "
		read yesno
		case "$yesno" in
		[Yy]*)
			generate "$0" "$@" |
			sed -e 's/ :rebased?.*//' >"$update" ;;
		*)
			echo >&2 "No update then." ;;
		esac
	fi
else
	generate "$0" "$@" | diff -u "$update" -
fi