#!/bin/bash
# Copyright (C) 2015-2020 Miquel Sabaté Solà <mikisabate@gmail.com>
#
# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program.  If not, see <http://www.gnu.org/licenses/>.

set -e

# This script adds the `fork` subcommand to git. This subcommand helps to keep
# a forked project updated with upstream. So, in a forked repository you would
# do:
#
#  $ git fork
#
# The previous command will fetch the upstream remote and merge the master
# branch. You can change the remote and the branch to be picked like this:
#
#  $ git fork branch
#  $ git fork remote branch
#
# Finally, if the given remote does not exist, the user will be prompted to
# provide the URL to the remote, so it can be created.

# Configurable values: the name of the branch to be picked and the name of the
# upstream remote.
branch='master'
upstream='upstream'

if [ ! -z "$1" ]; then
    upstream="$1"
fi
if [ ! -z "$2" ]; then
    branch="$2"
fi

# Check whether the given upstream remote really exists. If it doesn't it will
# ask the user for a remote URL.
if [[ $(git remote show | xargs -0 | grep -Fxq "$upstream") -eq 1 ]]; then
    echo "The given upstream '$upstream' remote does not exist"
    echo -n "Provide one: "
    read -ra url
    git remote add $upstream $url
fi

git fetch $upstream && git merge $upstream/$branch