#!/bin/sh

# situation: work tree is unknown rev
# arguments: git rev-list arguments
# we now identify the one revision with least differences

usage()
{
	echo "Usage: $0 [--cached] git-rev-list args..."
	echo
	echo "Example: $0 --all"
	echo "Compares current work tree to all revisions, and identifies the"
	echo "closest match."
	echo
	echo "Example: $0 --cached v1.0..HEAD"
	echo "Compares current index to all revisions between v1.0 and HEAD,"
	echo "and identifies the closest match."
}

case "$1" in
	--cached)
		use_worktree=false
		shift
		;;
	--help|-h)
		usage
		exit 0
		;;
	*)
		use_worktree=true
		;;
esac

if [ $# = 0 ]; then
	usage >&2
	exit 1
fi

diffopts="-M -C"

if $use_worktree; then
	echo >&2 "Saving index..."
	oldindex=`git write-tree`
	# set up resetting
	trap 'echo >&2 "Restoring index..."; git reset "$oldindex" .' EXIT
	trap 'exit 1' INT TERM

	echo >&2 "Creating index..."
	git add -A
fi

echo >&2 "Listing candidates..."
allrevs=`git rev-list "$@"`

echo >&2 "Evaluating candidates..."
bestrev=
bestrevscore=
for rev in $allrevs; do
	score=`git diff $diffopts --cached "$rev" | wc -l`
	if [ -z "$bestrevscore" ] || [ "$score" -lt "$bestrevscore" ]; then
		echo >&2 "Improved to $rev (score: $score)"
		bestrev=$rev
		bestrevscore=$score
		if [ $score -eq 0 ]; then
			break
		fi
	fi
done
echo >&2 "Done."

if [ -z "$bestrevscore" ]; then
	exit 1
fi

echo "$bestrev"
git diff $diffopts --cached "$bestrev" >&2