rebasebranch

#!/bin/bash

rebasebranch() {
	if [ "" == "${NEW_BASELINE}" ]; then
		return 0
	fi

	local STASH=$(git status -s | grep -v '??')

	if [ "" != "$STASH" ]; then
		git stash
	fi

	if rollbackbranch; then
		if [ "" != "$STASH" ]; then
			git stash pop
		fi

		return 0
	fi

	echo "Rebasing against $SHORT_NAME ($NEW_BASELINE)"

	git rebase $NEW_BASELINE
	EXIT_STATUS=$?

	if [ "" != "$STASH" ]; then
		if [[ 0 -ne $EXIT_STATUS ]]; then
			echo "Failed to rebase against $NEW_BASELINE, restoring git stash"
			git rebase --abort
			git stash pop
		else
			git stash pop
			EXIT_STATUS=$?
		fi
	fi

	return $EXIT_STATUS
}

resetbasebranch() {
	CURRENT_HASH=$(git log -1 --pretty='%H')

	if [ "" == "${NEW_BASELINE}" ]; then
		return 0
	fi

	if git merge-base --is-ancestor $CURRENT_HASH $NEW_BASELINE; then
		git merge --ff-only $NEW_BASELINE
		return $?
	fi

	CLOSEST_ANCESTOR=
	CLOSEST_COUNT=$(git rev-list --count HEAD)

	for remote in $(git remote); do
		local ANCESTOR=$(git for-each-ref --format='%(refname)' refs/remotes/ | grep "/${remote}/${BASE_BRANCH}$" | cut -d'/' -f 3,4)

		if [ "" == "$ANCESTOR" ]; then
			continue
		fi

		local COUNT=$(git log --pretty='%H' ${ANCESTOR}..${CURRENT_HASH} | wc -l)
		echo "$(git rev-parse --abbrev-ref HEAD) differs from ${ANCESTOR} by ${COUNT} commits"

		if [[ $COUNT -lt $CLOSEST_COUNT ]]; then
			CLOSEST_ANCESTOR=$ANCESTOR
			CLOSEST_COUNT=$COUNT
		fi
	done

	if [[ 0 -eq ${CLOSEST_COUNT} ]]; then
		echo "Resetting $(git rev-parse --abbrev-ref HEAD) to ${BASE_BRANCH} baseline because there are no unique commits"
		git reset --hard $NEW_BASELINE
		return $?
	fi

	if ! git merge-base --is-ancestor $NEW_BASELINE $CURRENT_HASH; then
		git rebase $NEW_BASELINE
		return $?
	fi
}

rollbackbranch() {
	CURRENT_HASH=$(git log -1 --pretty='%H')

	if [ "${CURRENT_HASH}" == "${NEW_BASELINE}" ]; then
		return 0
	fi

	git merge-base --is-ancestor $NEW_BASELINE $CURRENT_HASH

	if [[ 0 -ne $? ]]; then
		return 1
	fi

	resetbasebranch

	if [ "$SHORT_NAME" == "$CLOSEST_ANCESTOR" ]; then
		echo "$CURRENT_BRANCH is already rebased against $SHORT_NAME ($NEW_BASELINE)"
		return 0
	fi

	if [ "" == "${CLOSEST_ANCESTOR}" ]; then
		echo "Unable to determine closest ancestor"
		return 1
	fi

	echo "Detected a deviation from the build reference commit ${NEW_BASELINE} due to rebase against ${CLOSEST_ANCESTOR}"
	echo "Saving existing $CURRENT_BRANCH to ${CURRENT_BRANCH}-old in case of failure"

	git branch -m ${CURRENT_BRANCH} ${CURRENT_BRANCH}-old

	echo "Attempting to rollback to reference commit ${NEW_BASELINE}"

	git checkout -b ${CURRENT_BRANCH}
	git format-patch --relative ${CLOSEST_ANCESTOR}
	git reset --hard ${NEW_BASELINE}

	set -o pipefail

	EXIT_STATUS=0

	if [ "" != "$(ls -1 | grep '\.patch$')" ]; then
		ls -1 *.patch | sort | xargs git am
		EXIT_STATUS=$?
		rm -f *.patch
	fi

	set +o pipefail

	if [[ 0 -eq $EXIT_STATUS ]]; then
		echo "Rollback to reference commit succeeded, deleting ${CURRENT_BRANCH}-old"
		git branch -D ${CURRENT_BRANCH}-old
		return 0
	fi

	echo "Rollback to reference commit failed. Build may end up being as slow as a regular ant all!"

	git am --abort
	git checkout -f ${CURRENT_BRANCH}-old
	git branch -D ${CURRENT_BRANCH}
	git branch -m ${CURRENT_BRANCH}-old ${CURRENT_BRANCH}
}

rebasebranch