#!/usr/bin/env perl

# Copyright (C) 2024 Ortega Froysa, Nicolás <nicolas@ortegas.org> All rights reserved.
# Author: Ortega Froysa, Nicolás <nicolas@ortegas.org>
#
# This software is provided 'as-is', without any express or implied
# warranty. In no event will the authors be held liable for any damages
# arising from the use of this software.
#
# Permission is granted to anyone to use this software for any purpose,
# including commercial applications, and to alter it and redistribute it
# freely, subject to the following restrictions:
#
# 1. The origin of this software must not be misrepresented; you must not
#    claim that you wrote the original software. If you use this software
#    in a product, an acknowledgment in the product documentation would be
#    appreciated but is not required.
#
# 2. Altered source versions must be plainly marked as such, and must not be
#    misrepresented as being the original software.
#
# 3. This notice may not be removed or altered from any source
#    distribution.

use strict;
use warnings;

use Getopt::Std;
use File::ReadBackwards;

my $VERSION = "1.0";
my $PROG_NAME = "pacundo";

my $r_flag = 0;
my $dry_run = 0;
my $num_txs = 1;

sub print_version {
	print("$PROG_NAME v$VERSION\n");
}

sub print_help {
	&print_version();
	print("A time machine to return your ArchLinux machine back to a working state.\n");
	print("\nUSAGE:
	$PROG_NAME [-i|-r] [-t <num>] [-d]
	$PROG_NAME -h
	$PROG_NAME -v

OPTIONS:
	-i         Enter interactive mode to select packages to downgrade [default behavior]
	-r         Automatically downgrade all packages from last upgrade
	-t <num>   Specify the number of transactions to include for undoing selection [default 1]
	-d         Dry run, i.e. don't actually do anything
	-h         Show this help information
	-v         Print program version\n");
}

getopts("irt:dvh", \my %opts);

if ($opts{'v'}) {
	&print_version();
	exit 0;
} elsif ($opts{'h'}) {
	&print_help();
	exit 0;
} elsif ($opts{'r'} && $opts{'i'}) {
	print("Improper usage. -r and -i cannot be used at the same time.\n");
	print("Use -h for help information.\n");
	exit 1;
} elsif ($opts{'t'} && !($opts{'t'} =~ /[0-9]+/)) {
	print("The argument for -t must be a positive integer.\n");
	exit 1;
}

$r_flag = 1 if ($opts{'r'});
$dry_run = 1 if ($opts{'d'});
$num_txs = $opts{'t'} if ($opts{'t'});

my $pacman_log = File::ReadBackwards->new("/var/log/pacman.log") or
die("Failed to load pacman log file.\n$!");

my $found_txs = 0;
my $in_tx = 0;

my @undo_txs;

while ($found_txs < $num_txs && defined(my $line = $pacman_log->readline)) {
	# Remeber that we're reading this in reverse order
	if (!$in_tx && $line =~ /\[ALPM\] transaction completed/) {
		$in_tx = 1;
	} elsif ($in_tx) {
		if ($line =~ /\[ALPM\] transaction started/) {
			$found_txs++;
			$in_tx = 0;
		} elsif ($line =~ /\[ALPM\] (upgraded|downgraded)/) {
			my ($action, $pkg_name, $oldver, $newver) = $line =~ /\[ALPM\] (upgraded|downgraded) ([^\s]+) \((.*) -> (.*)\)/;
			push(@undo_txs,
				{
					'action' => $action,
					'pkg_name' => $pkg_name,
					'oldver' => $oldver,
					'newver' => $newver,
				}
			);
		} elsif ($line =~ /\[ALPM\] (installed|removed)/) {
			my ($action, $pkg_name) = $line =~ /\[ALPM\] (installed|removed) ([^\s]+)/;
			push(@undo_txs,
				{
					'action' => $action,
					'pkg_name' => $pkg_name,
				}
			);
		}
	}
}