#!/bin/sh

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

case "$generate" in
no)
	accept_rerere () {
		if test -z "$accept_rerere"
		then
			return 1
		fi
		if git diff |
		   grep -e "^.+" -e "^+." |
		   grep -e "^..<<<<<<<" -e "^..=======" -e "^..>>>>>>>" >/dev/null
		then
			return 1
		else
			EDITOR=: git commit -a --no-verify
			echo "Accepted previous resolution"
			return 0
		fi
	}

	while read branch eh
	do
		case "$branch" in '#'*) continue ;; esac
		case "$eh" in
		"")
			save=$(git rev-parse --verify HEAD)

			echo >&2 "* $branch"
			git merge "$branch" || accept_rerere || exit

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

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 --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