#!/bin/sh
#
# Copyright (C) 2017 The Android Open Source Project
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
# --------------------------------------------------------
# Install this hook script as post-receive hook in replicated repositories
# hosted by a gerrit slave which are updated by push replication from the
# corresponding gerrit master.
#
# In the gerrit master configure the replication plugin to push changes from
# refs/changes/ to refs/tmp/changes/
#   remote.NAME.push = +refs/changes/*:refs/tmp/changes/*
#   remote.NAME.push = +refs/heads/*:refs/heads/*
#   remote.NAME.push = +refs/tags/*:refs/tags/*
#
# In the replicated repository in the gerrit slave configure
#    receive.hideRefs = refs/changes/
# in order to not advertise the big number of refs in this namespace when
# the gerrit master's replication plugin is pushing a change
#
# Whenever a ref under refs/tmp/changes/ is arriving this hook will move it
# to refs/changes/. This helps to avoid the large overhead of advertising all
# refs/changes/ refs to the gerrit master when it replicates changes to the
# slave..
#
# Make this script executable then link to it in the repository you would like
# to use it in.
#   cd /path/to/your/repository.git
#   ln -sf <shared hooks directory>/post-receive-move-tmp-refs hooks/post-receive
#
# If you want to use this by default for repositories on the Gerrit slave you
# can set up a git template directory $TEMPLATE_DIR/hooks/post-receive and
# configure init.templateDir in the ~/.gitconfig of the user that receives the
# replication on the mirror host. That way when a new repository is created on
# the master and hence on the mirror (if configured that way) it will
# automatically have the "tmp-refs" commit hook installed.
# See https://git-scm.com/docs/git-init#_template_directory for details.

readonly NULL_SHA1=0000000000000000000000000000000000000000

# move new changes arriving under refs/tmp/changes/ to refs/changes/
mv_tmp_refs()
{
	oldrev=$1
	newrev=$2
	refname=$3
	case "$refname","$oldrev" in
		refs/tmp/changes/*,$NULL_SHA1)
			short_refname=${refname##refs/tmp/changes/}
			$(git update-ref refs/changes/$short_refname $newrev $NULL_SHA1 2>/dev/null)
			$(git update-ref -d $refname $newrev 2>/dev/null)
			echo "moved \"$refname\" to \"refs/changes/$short_refname\""
			;;
	esac
	return 0
}

GIT_DIR=$(git rev-parse --git-dir 2>/dev/null)
if [ -z "$GIT_DIR" ]; then
	echo >&2 "fatal: post-receive: GIT_DIR not set"
	exit 1
fi

# read ref updates passed to post-receive hook
while read oldrev newrev refname
do
	mv_tmp_refs $oldrev $newrev $refname || continue
done