#! /usr/bin/perl
use strict;
use warnings;

use Date::Calc qw(Add_Delta_Days Add_Delta_YM Today);
use File::Spec;
use File::Basename ();
use POSIX;
use FindBin;

my $doDelete = 1;
my $directory = File::Spec->catdir( qw[ / sc backup] );
my $bin = File::Basename::basename( $0 );


my $logfile   = File::Spec->catfile( $FindBin::Bin, "$bin.log" );

my @files = _get_filenames( $directory );

@files    = _clean_list( @files );

getFreeSpace( $logfile );

_delete_files( $directory, $logfile, @files );

getFreeSpace( $logfile );

###
# Subroutines
###

sub _get_filenames{
    my ($dir) = @_;

    opendir my $dirh, $dir or die $!;
    my @files = grep{ /^\w+\_\d{8}-\d{6}\.tar\.gz$/ }readdir $dirh;
    closedir $dirh;

    return @files;
}

sub _clean_list{
    my @files = @_;

    my @dates;

    my @today = Today();

    # keep today's files
    push @dates, sprintf "%04d%02d%02d", @today;

    # keep files of 5 last days
    for (1..4) {
        push @dates, sprintf "%04d%02d%02d", Add_Delta_Days( @today, $_ * -1 );
    }

   # keep files of 11th, 21st of the last 6 months
   for (0..5){
      my ($year,$month,$day) = Add_Delta_YM( @today, 0, $_ * -1 );
      for( 11, 21 ){
         push @dates, sprintf "%04d%02d%02d", $year,$month, $_;
      }
   }

   # filter filenames
   @files = grep{ my ($f) = $_ =~ /^\w+\_(\d{8})/;
                 !( grep{ $f == $_ }@dates or $f =~ /01$/ )
                }@files;
}

sub _delete_files{
   my ($dir,$log,@files) = @_;

   open( my $fh_log, '>>', $log ) or die $!;

   for my $file ( sort @files ){
      my $time = POSIX::strftime( '%Y%m%d-%H%M%S', localtime);
      my $fqfn = File::Spec->catfile( $dir, $file );
      if( $doDelete ) {
          unlink $fqfn and print $fh_log $time,"\t",$file,"\n";
      } # if
      else {
          print "Simulate: file '$file' would have been deleted\n";
      }
   }

   close $fh_log;
} # _delete_files

sub getFreeSpace {
    my( $log ) = @_;

    my @space = `df -k`;

    open( my $fh_log, '>>', $log ) or die $!;
    print $fh_log "\n# Free space:\n";
    foreach my $line ( @space ) {
        print $fh_log "# $line";
    }
    close $fh_log;

} # getFreeSpace