#!/usr/bin/env bash
#
# Merges a git branch into a another branch.
#
# Author:  Ade Attwood <code@adeattwood.co.uk>
# Created: 2018-11-11
#

set -e

MERGE_BRANCH="$1";

main() {
    local branch=$(git rev-parse --abbrev-ref HEAD);
    echo "Merging $branch with $MERGE_BRANCH";

	#
	# Ensure the target branch is up to date
	#
    git checkout $MERGE_BRANCH
	git pull origin $MERGE_BRANCH
    git checkout $branch

	#
	# Rebase onto branch so we don't create a merge commit
	#
	git rebase $MERGE_BRANCH;

	#
	# Merge into the target branch ensuring its a fast forward merge
	#
    git checkout $MERGE_BRANCH;
    git merge --ff-only --log $branch;
}

if [[ ! -z "$1" ]]; then
    main;
    exit 0;
fi

cat << HELP
Git Merge To

For the reverse of \`git merge\`

The flow for the script is:

- Change to the target branch
- Pull branch for the latest changes
- Merge the previous branch

Usage: $0 <branch_name>

HELP

exit 1;