#!/usr/bin/env perl
# Copyright (c) 2009 David Aguilar
#
# This is a wrapper around the GIT_EXTERNAL_DIFF-compatible
# git-difftool-helper script.  This script exports
# GIT_EXTERNAL_DIFF and GIT_PAGER for use by git, and
# GIT_NO_PROMPT and GIT_MERGE_TOOL for use by git-difftool-helper.
# Any arguments that are unknown to this script are forwarded to 'git diff'.

use strict;
use warnings;
use Cwd qw(abs_path);
use File::Basename qw(dirname);

my $DIR = abs_path(dirname($0));


sub usage
{
        print << 'USAGE';

usage: git difftool [--no-prompt] [--tool=tool] ["git diff" options]
USAGE
        exit 1;
}

sub setup_environment
{
        $ENV{PATH} = "$DIR:$ENV{PATH}";
        $ENV{GIT_PAGER} = '';
        $ENV{GIT_EXTERNAL_DIFF} = 'git-difftool-helper';
}

sub exe
{
        my $exe = shift;
        return defined $ENV{COMSPEC} ? "$exe.exe" : $exe;
}

sub generate_command
{
        my @command = (exe('git'), 'diff');
        my $skip_next = 0;
        my $idx = -1;
        for my $arg (@ARGV) {
                $idx++;
                if ($skip_next) {
                        $skip_next = 0;
                        next;
                }
                if ($arg eq '-t' or $arg eq '--tool') {
                        usage() if $#ARGV <= $idx;
                        $ENV{GIT_MERGE_TOOL} = $ARGV[$idx + 1];
                        $skip_next = 1;
                        next;
                }
                if ($arg =~ /^--tool=/) {
                        $ENV{GIT_MERGE_TOOL} = substr($arg, 7);
                        next;
                }
                if ($arg eq '--no-prompt') {
                        $ENV{GIT_DIFFTOOL_NO_PROMPT} = 'true';
                        next;
                }
                if ($arg eq '-h' or $arg eq '--help') {
                        usage();
                }
                push @command, $arg;
        }
        return @command
}

setup_environment();
exec(generate_command());