#!/bin/sh
#
#  Copyright (c) 2016 Baptiste Daroussin
#  All rights reserved.
#
#  Redistribution and use in source and binary forms, with or without
#  modification, are permitted provided that the following conditions
#  are met:
#  1. Redistributions of source code must retain the above copyright
#     notice, this list of conditions and the following disclaimer.
#  2. Redistributions in binary form must reproduce the above copyright
#     notice, this list of conditions and the following disclaimer in the
#     documentation and/or other materials provided with the distribution.
#
#  THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
#  ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
#  IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
#  ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
#  FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
#  DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
#  OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
#  HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
#  LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
#  OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
#  SUCH DAMAGE.
#
# $FreeBSD$

set -e

rc=0
quiet=0
A_flag=0
E_flag=0
e_flag=0
labelcount=0

usage() {
	echo "$0: usage $0 [-AEpq] [-L label [ -L label [-L label]]] file1 file2 file3" >&2
}

clean_tmp() {
	if [ "${output}" != "/dev/stdout" ]; then
		rm -f "${output}"
	fi
}

while getopts 'AEeL:pq' opt; do
	case "${opt}" in
	A) A_flag=1 ;;
	E) E_flag=1 ;;
	L)
		labelcount=$(( labelcount  + 1))
		if [ ${labelcount} -gt 3 ]; then
			echo "$0: too many -L options" >&2
			echo "$0 aborted" >&2
			exit 2
		fi
		labels="${labels} -L ${OPTARG}"
		;;
	p) output=/dev/stdout ;;
	q) quiet=1 ;;
	*)
		usage
		exit 2
		;;
	esac
done
shift $(( ${OPTIND} -1 ))

case "${A_flag}${E_flag}" in
11)
	echo "$0: -A and -E are incompatible" >&2
	exit 2
	;;
10)
	diff3_args="-A"
	;;
01)
	diff3_args="-E"
	;;
00)
	diff3_args="-E"
	;;
esac

if [ $# -ne 3 ]; then
	echo "$0: not enough arguments" >&2
	usage
	exit 2
fi

trap clean_tmp EXIT

if [ -z "${output}" ]; then
	output=$(mktemp -t merge)
fi

diff3 ${diff3_args} -m ${labels} "$1" "$2" "$3" >"${output}" || rc=$?
if [ "${output}" != "/dev/stdout" ]; then
	if [ -w "$1" ]; then
		mv -f "${output}" "$1"
	else
		echo "$0: $1 permission denied" >&2
	fi
fi
if [ ${rc} -eq 1 ]; then
	if [ ${quiet} -eq 0 ]; then
		echo "$0: warning: conflict during merge" >&2
	fi
	exit 1
fi
exit 0