#!/bin/sh
# Replace patch series

usage="$0 branch [base-branch] <patchfile"

if test -d .dotest
then
	echo >&2 "still in the middle of rebase/am"
	exit 1
fi

case "$#,$1" in
1,--continue)
	;;
*)
	rm -f .rp-state
	target_branch="$1"
	case $# in
	1)
		base_branch=master
		;;
	2)
		base_branch=$(git rev-parse --verify "$2") || exit
		;;
	*)
		echo >&2 "$usage"
		exit 1
		;;
	esac

	# find branch point
	branch_point=$(git merge-base "$base_branch" "$target_branch") || {
		echo >&2 "failed to compute the branch point"
		exit 1
	}

	# safety -- never rewind/replace what's merged to next
	in_branch=$(git rev-list $branch_point..$target_branch) &&
	not_in_next=$(git rev-list $branch_point..$target_branch ^next) &&
	test "z$in_branch" = "z$not_in_next" || {
		echo >&2 "should not be rewinding part of $target_branch that is already in next"
		exit 1
	}

	# detach the HEAD
	git checkout "$branch_point" || {
		echo >&2 "detaching the head at $branch_point"
		exit 1
	}

	{
		echo "target_branch=$target_branch"
		echo "branch_point=$branch_point"
	} >.rp-state
	# apply patches
	git am -3 -s -u || {
		echo >&2 "finish the am and say $0 --continue"
		exit 1
	}
	;;
esac

branch_point=$(sed -ne 's/^branch_point=//p' .rp-state) &&
target_branch=$(sed -ne 's/^target_branch=//p' .rp-state) || {
	echo >&2 "no replace-patch session"
	exit 1
}
rm -f .rp-state

git branch -f "$target_branch" HEAD
git checkout "$target_branch"
git -p show-branch "$target_branch@{1}" "$target_branch"
git diff --stat -p "$target_branch@{1}" "$target_branch"