#!/usr/bin/env perl

use strict;
use warnings;

use Gzip::Faster;
use  Math::Random::MT;

my $DATA_LENGTH ||=100000;
my $NUM_REPEATS ||=100;

my ($quant, $got, $expected);
my $MTgen = Math::Random::MT->new();

sub     perls_rand { int(rand(1000000)) }
sub     mt_rand { int($MTgen->rand(1000000)) }

my %results = ();
my $best_results = [ undef, undef ];
foreach( 
        (["Gzip compression test : Perl's rand()", \&perls_rand, $NUM_REPEATS, $DATA_LENGTH],
         ["Gzip compression test : Math::Random::MT's rand()", \&mt_rand, $NUM_REPEATS, $DATA_LENGTH],
        )
){
        my $aresult = do_a_test(@$_);
        $results{$aresult->[1]} = $aresult; # key is the label
        print $aresult->[0]."\n\n"; # the report
        if( ! defined($best_results->[0]) or $best_results->[0] < $aresult->[4] ){
                $best_results->[0] = $aresult->[4]; # mean perc diff
                $best_results->[1] = $_->[0]; # the label
        }
}
print "\n\n$0 : done, here is a summary:\n";
foreach(values %results){
        print "$0 : ".$_->[1]." with mean %diff from expected to be ".sprintf("%.3f",$_->[4])." %\n";
}
print "\n\n$0 : best results for ".$best_results->[1]." with mean %diff from expected to be ".sprintf("%.3f",$best_results->[0])." %\n";
print "$0 : end.\n";
exit(0);

# Does a test given
# a test label (string)
# a sub ref to a rand()
# the number of repeats
# the string length to produce for compression
# see http://search.cpan.org/dist/Statistics-Test-RandomWalk/lib/Statistics/Test/RandomWalk.pm
# returns an arrayref with a report, mean percentage difference and change
# and iters and nbins (see the return statement below)
sub     do_a_test {
        my ($test_label, $rand_sub, $nrepeats, $slength) = @_;
        my @compression_totals = (0,0,0,0);

        my ($a);
        print "$test_label : doing $nrepeats repeats and using random strings of length $slength :\n";
        for(1..$nrepeats){
                my $random_str_to_compress = "";
                for(1..$slength){
                        $random_str_to_compress .= $rand_sub->();
                }
                my $gzipped_str = Gzip::Faster::gzip($random_str_to_compress);
                my $length_gzipped_str = length($gzipped_str);
                my $length_random_str_to_compress = length($random_str_to_compress);
                $compression_totals[0] += $length_random_str_to_compress;
                $compression_totals[1] += $length_gzipped_str;
                $compression_totals[2] += percentage_difference($length_random_str_to_compress, $length_gzipped_str);
                $compression_totals[3] += percentage_change($length_random_str_to_compress, $length_gzipped_str);
                print "repeat $_ / $nrepeats:\n"
                        . "  length of random string: ".$length_random_str_to_compress."\n"
                        . "  length of compressed string: ".$length_gzipped_str."\n"
                        . "  compression ratio as percentage change: ".percentage_difference($length_random_str_to_compress, $length_gzipped_str)."\n"
                        . "  compression ratio as percentage difference: ".percentage_change($length_random_str_to_compress, $length_gzipped_str)."\n"

        }
        $_/=$nrepeats foreach(@compression_totals);
        my $report = "$test_label\n           after $nrepeats repeats and using random strings of length $slength :\n"
                . "mean length of random string: ".$compression_totals[0]."\n"
                . "mean length of compressed string: ".$compression_totals[1]."\n"
                . "mean compression ratio as percentage change: ".$compression_totals[2]."\n"
                . "mean compression ratio as percentage difference: ".$compression_totals[3]
        ;

        return [
                $report,
                $test_label,
                @compression_totals
        ]
}
sub     percentage_difference {
        my ($a, $b) = @_;
        return 200 * abs($a-$b) / ($a+$b)
}
sub     percentage_change {
        my ($a, $b) = @_;
        return 100 - 100 * $a / $b
}