#!/usr/bin/env bash
#
# git-rebase-theirs - Resolve rebase conflicts by favoring 'theirs' version
#
#    Copyright (C) 2012 Rodrigo Silva (MestreLion) <linux@rodrigosilva.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/gpl.html>

#Defaults:
verbose=0
backup=1
inplace=0
ext=".bak"

message() { printf "%s\n" "$1" >&2 ; }
argerr()  { printf "%s: %s\n" "$myname" "${1:-error}" >&2 ; usage 1 ; }
invalid() { argerr "invalid option: $1" ; }
missing() { argerr "missing${1:+ $1} operand." ; }

# Bash 4.4 does not allow 'continue' inside functions to operate on outer loops
# See https://stackoverflow.com/a/52497694/624066
skip()    { message "skipping ${2:-$file}${1:+: $1}"; }

usage() {
	cat <<- USAGE
	Usage: $myname [options] [--] FILE...
	USAGE
	if [[ "$1" ]] ; then
		cat >&2 <<- USAGE
		Try '$myname --help' for more information.
		USAGE
		exit 1
	fi
	cat <<-USAGE

	Resolve git rebase conflicts in FILE(s) by favoring 'theirs' version

	When using git rebase, one may want to automatically resolve conflicts
	by favoring the <working branch> version, which is the branch being
	rebased, 'theirs' side in a rebase, instead of the <upstream> version,
	the base branch, 'ours' side in the rebase.

	The solution is 'git rebase --strategy recursive -X theirs', which is
	only available since git 1.7.3. For older versions, $myname
	solves that problem. And despite its name it's also useful for fixing
	failed cherry-picks.

	It works by discarding all lines between '<<<<<<< ' and '========',
	inclusive, and also the '>>>>>> commit' marker.

	By default it outputs to stdout, but files can be edited in-place
	using --in-place, which, unlike sed, creates a backup by default.

	Options:
	  -h|--help            show this page.
	  -v|--verbose         print more details in stderr.

	  --in-place[=SUFFIX]  edit files in place, creating a backup with
	                       SUFFIX extension. Default if blank is "$ext"

	  --no-backup          disables backup

	Copyright (C) 2012 Rodrigo Silva (MestreLion) <linux@rodrigosilva.com>
	License: GPLv3 or later. See <http://www.gnu.org/licenses/gpl.html>
	USAGE
	exit 0
}
myname="${0##*/}"

# Option handling
files=()
while (( $# )); do
	case "$1" in
	-h|--help     ) usage            ;;
	-v|--verbose  ) verbose=1        ;;
	--no-backup   ) backup=0         ;;
	--in-place    ) inplace=1        ;;
	--in-place=*  ) inplace=1
	                suffix="${1#*=}" ;;
	--            ) shift ; break    ;;
	-*            ) invalid "$1"     ;;
	*             ) files+=( "$1" )  ;;
	esac
	shift
done
files+=( "$@" )

if ! (( "${#files[@]}" )); then missing "FILE"; fi

ext=${suffix:-$ext}

for file in "${files[@]}"; do

	if ! [[ -f "$file" ]]; then skip "not a valid file"; continue; fi

	if ((inplace)); then
		outfile=$(mktemp) ||
			{ skip "could not create temporary file"; continue; }
		# shellcheck disable=SC2064
		trap "rm -f -- '$outfile'" EXIT
		cp "$file" "$outfile" || { skip; continue; }
		exec 3>"$outfile"
	else
		exec 3>&1
	fi

	# Do the magic :)
	awk '/^<<<<<<<+ .+$/,/^=+$/{next} /^>>>>>>>+ /{next} 1' "$file" >&3

	exec 3>&-

	if ! ((inplace)); then continue; fi

	diff "$file" "$outfile" >/dev/null &&
		{ skip "no conflict markers found"; continue; }

	if ((backup)); then
		cp "$file" "$file$ext" || { skip "could not backup"; continue; }
	fi

	cp "$outfile" "$file" || { skip "could not edit in-place"; continue; }
	rm -f -- "$outfile"
	trap - EXIT

	if ((verbose)); then message "resolved ${file}"; fi
done
