#!/usr/bin/perl
use Time::HiRes qw/gettimeofday tv_interval/;
use File::Find;
use strict;

=pod

So it turns out the Weissman Score is a real formula.  Who knew?

                 r     log T_bar
   W = alpha * ----- * ---------
               r_bar     log T

Where r and T are the compression ratio of the target algorithm, and r_bar
and T_bar are the same for a reference compressor (in our case, PNG).  Alpha
is a constant scaling factor.

http://spectrum.ieee.org/view-from-the-valley/computing/software/a-madefortv-compression-metric-moves-to-the-real-world

=cut

my ($bs_total, $png_total, $uncompressed_total, $bs_time, $png_time, $t0);

find({
    wanted => sub {
        next unless -f && /\.png$/;

        $t0 = [gettimeofday];
        my $bs_size = qx!$ENV{HOME}/go/bin/bitsmash $_ | wc -c!;
        $bs_time += tv_interval($t0);

        $uncompressed_total += qx!convert $_ rgb:- | wc -c!;

        my $png_size = -s;
        # So... we're being a bit shifty here by actually decoding a PNG and
        # then encoding it again.  We really should be working from an
        # uncompressed source, but PNGs are handy (and bitsmash is decoding a PNG, too, so it's not unfair).

        $t0 = [gettimeofday];
        system qq!convert $_ png:- >/dev/null!;
        $png_time += tv_interval($t0);

        printf("%4.1f%%   %-6d %-6d %s\n", ($bs_size / $png_size) * 100, $bs_size, $png_size, $_);
        $bs_total += $bs_size;
        $png_total += $png_size;
    },
    no_chdir => 1,
}, @ARGV);

printf("$uncompressed_total uncompressed bytes\n");
printf("$bs_total bitsmash bytes, %.2f seconds\n", $bs_time);
printf("$png_total PNG bytes, %.2f seconds\n", $png_time);
printf("%.1f%% of PNG\n", ($bs_total/$png_total) * 100);

my $r = $uncompressed_total / $bs_total;
my $r_bar = $uncompressed_total / $png_total;
my $alpha = 1.0;
printf("Weissman score: %.2f\n", $alpha * ($r / $r_bar) * (log($png_time) / log($bs_time)));