#!/usr/bin/env perl
# ABSTRACT: compute cosine similarity between two documents
# PODNAME: cosine_cmp
use autodie;
use strict;
use utf8;
use warnings;

our $VERSION = '0.013'; # TRIAL VERSION


use Getopt::Long;
use Pod::Usage;
use Text::SpeedyFx;

GetOptions(
    q(help)             => \my $help,
    q(length=i)         => \my $length,
    q(seed=i)           => \my $seed,
    q(bits=i)           => \my $bits,
) or pod2usage(-verbose => 1);
pod2usage(-verbose => 2)
    if $help or $#ARGV != 1;

$length = 10
    unless $length;
$length *= 2 ** 10 << 3;

$seed = 0x4c53_4820
    unless $seed;
$bits = 8
    unless $bits;

my $sfx = Text::SpeedyFx->new($seed, $bits);
my @fv = map {
    sub {
        open my $fh, q(<:mmap), shift;
        local $/ = undef;
        my $data = <$fh>;
        close $fh;

        return $sfx->hash_fv($data, $length);
    }->($_)
} @ARGV;

printf qq(similarity=%0.5f\n), cosine_similarity(@fv);

sub cosine_similarity {
    my ($a, $b) = @_;

    my $nbits_a = unpack(q(%32b*) => $a);
    my $nbits_b = unpack(q(%32b*) => $b);

    return $nbits_a * $nbits_b
        ? unpack(q(%32b*) => $a & $b) / sqrt $nbits_a * $nbits_b
        : 0;
}

__END__

=pod

=encoding UTF-8

=head1 NAME

cosine_cmp - compute cosine similarity between two documents

=head1 VERSION

version 0.013

=head1 SYNOPSIS

    cosine_cmp [options] FILE1 FILE2

=head1 DESCRIPTION

Cosine similarity is a measure of similarity between two vectors of an inner product space that measures the cosine of the angle between them.
The cosine of 0 is 1, and less than 1 for any other angle; the lowest value of the cosine is -1.
The cosine of the angle between two vectors thus determines whether two vectors are pointing in roughly the same direction.
This is often used to compare documents in text mining.
In addition, it is used to measure cohesion within clusters in the field of data mining.

(L<source|https://en.wikipedia.org/wiki/Cosine_similarity>)

=head1 OPTIONS

=over 4

=item --help

This.

=item --length

Feature vector length (in KB, default: 10).

=item --seed

Custom seed (integer).

=item --bits

How many bits do represent one character.
The default value, 8, sacrifices Unicode handling but is fast and low on memory footprint.
The value of 18 encompasses I<Basic Multilingual>, I<Supplementary Multilingual> and I<Supplementary Ideographic> planes.

=back

=head1 SEE ALSO

=over 4

=item *

L<Text::SpeedyFx>

=item *

L<Tiny & fast document similarity estimation|https://coderwall.com/p/284hja>

=item *

L<Cosine similarity|https://en.wikipedia.org/wiki/Cosine_similarity>

=back

=head1 AUTHOR

Stanislaw Pusep <stas@sysd.org>

=head1 COPYRIGHT AND LICENSE

This software is copyright (c) 2021 by Stanislaw Pusep.

This is free software; you can redistribute it and/or modify it under
the same terms as the Perl 5 programming language system itself.

=cut