use strict;
use warnings;
use Audio::Wav;

# ** 2 / sqrt formula taken from http://www.fourelectronics.com/Can-you-calculate-a-44-1k-wav-streams-volume-by-looking-at-the-si-2830944.html

my ($chapter, $read, $array_slice_length);
my $slices_per_second = 100; #how many slices to take per second; check beforehand to make sure it works out to a whole number
my $in_folder = 'mp3s';
my $out_folder = 'wav';
my $wav = new Audio::Wav;

$chapter = '40001';
convert_to_wav();
get_wav_info();
get_slices();

sub get_slices
{
	print "Getting slices...\n";
	my @values;
	my $length = $read->length();
	while ($read->position() < $length)
	{
		my ($value) = $read->read(); #it's mono, so don't need both channels
		push @values, $value;
		if (scalar @values == $array_slice_length)
		{
			my $amplitude = get_slice_value(@values);
		}
	}
}

sub get_slice_value
{
	my $out = 0;
	foreach my $value (@_)
	{
		$out += $value ** 2;
	}
	return sqrt $out;
}

sub get_wav_info
{
	print "Getting wav info...\n";
	$read = $wav->read("$out_folder/$chapter.wav");
	my $ref = $read->details();
	die "Uneven slice length ($ref->{sample_rate} % $slices_per_second)" if ($ref->{sample_rate} % $slices_per_second);
	$array_slice_length = $ref->{sample_rate} / $slices_per_second;
}

sub convert_to_wav
{
	print "Converting to wav...\n";
	my $in = $in_folder;
	`lame --decode "$in_folder\\$chapter.mp3" "$out_folder\\$chapter.wav"`;
}