#!/usr/bin/env perl

use strict;
use warnings;
use autodie ':all';
use constant {
    OLD => 0,
    NEW => 1,
};

print "OS: $^O; Perl: $^V\n";

my @filenames = 'a' .. 'd';
my %perms = (
    a => [0644, 0644],
    b => [0644, 0755],
    c => [0644, 0440],
    d => [0644, 07644],
);

print "\n*** Initial permissions (visual check):\n";
list_perms(@filenames);
print "\n*** Initial permissions (program check):\n";
check_perms(\@filenames, \%perms, OLD);

change_perms(\@filenames, \%perms, NEW);

print "\n*** Modified permissions (visual check):\n";
list_perms(@filenames);
print "\n*** Modified permissions (program check):\n";
check_perms(\@filenames, \%perms, NEW);

change_perms(\@filenames, \%perms, OLD);

print "\n*** Restored permissions (visual check):\n";
list_perms(@filenames);
print "\n*** Restored permissions (program check):\n";
check_perms(\@filenames, \%perms, OLD);

sub list_perms {
    my (@files) = @_;
    my @cmd_list = (ls => '-l', @files);
    CORE::system {$cmd_list[0]} @cmd_list;
    return;
}

sub check_perms {
    my ($files, $perms, $oldnew) = @_;

    for my $file (@$files) {
        my $perm = (stat $file)[2] & 07777;
        my $expected
            = sprintf('%#5o', $perms->{$file}[$oldnew]);

        print
            "File: '$file'; Perm: ",
            sprintf('%#5o', $perm),
            '; Check: ',
            (
                $perm == $perms->{$file}[$oldnew]
                ? 'OK' : "WRONG (expected: $expected)"
            ),
            "\n";
    }

    return;
}

sub change_perms {
    my ($files, $perms, $oldnew) = @_;

    for my $file (@$files) {
        chmod $perms->{$file}[$oldnew], $file;
    }

    return;
}