#!/usr/bin/perl
#
# ediff-merge(1) - a frontend command for ediff-merge
#
# Copyright (c) 2012, 2023 Akinori MUSHA
#
# 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.
#
# See https://github.com/knu/emacsc for the latest information.

use Cwd qw(abs_path);
use File::Basename;

main();

sub main {
    my $name = basename($0);

    if (@ARGV < 3 || 4 < @ARGV) {
        print STDERR <<EOF;
usage: $name local remote base merged
       $name local remote merged

This command depends on emacsc(1).  Make sure you require emacsc in
your Emacs initialization file, and put the following lines in your
~/.config/git/config (or ~/.gitconfig).

[merge]
	tool = ediff
[mergetool "ediff"]
	cmd = ediff-merge \\"\$LOCAL\\" \\"\$REMOTE\\" \\"\$BASE\" \\"\$MERGED\\"
	trustExitCode = true
EOF
        exit 64;
    }

    if (@ARGV == 4 && $ARGV[2] eq '') {
        splice(@ARGV, 2, 1);
    }

    my $format;
    if (@ARGV == 4) {
        $format = '(ediff-merge-files-with-ancestor "%s" "%s" "%s" nil "%s")';
    } elsif ($ARGV[1] eq $ARGV[2]) {
        $format = '(ediff "%s" "%s")';
    } else {
        $format = '(ediff-merge-files "%s" "%s" nil "%s")';
    }

    eval {
        my $merged = abs_path(pop @ARGV);
        my @files = map { check_file($_) } @ARGV;
        system qw(emacsc -x),
            sprintf($format,
                    map { elisp_escape($_) } (@files, $merged));
        exec qw(git diff --check), $merged;
    };
    if ($@) {
        print STDERR $name, ": ", $@;
        exit 1;
    }
}

sub check_file {
    my($file) = @_;

    -f $file and return abs_path($file);

    die sprintf("%s: %s\n", $file, $! || 'Not a regular file');
}

sub elisp_escape {
    (local $_) = @_;
    s/[\\"]/\\$1/;
    $_;
}
