#!/usr/bin/perl
# Shrink a SAP TYPE-R file by removing common repeating frames (and altering fastplay), and removing trailing zero frames.
# -Don Mahurin
#
# Usage: saprshrink < in.sap > out.sap
#

my $line = <STDIN>;
$line =~ s:\r$::g;
chomp($line);

unless($line eq "SAP")
{
	print STDERR "Not SAP file\n";
	exit 1;
}

my @sap_param_names = ( "SAP" );
my %sap_params;

while($line = <STDIN>)
{
	if($line =~ /\xff/)
	{
		print STDERR "SAP Header not terminated\n";
		exit 1;
	}
	$line =~ s:\r$::g;
	chomp($line);
	last if($line eq '');
	if($line =~ /^([A-Z]+)(\s+(.*))$/)
	{
		my($name) = $1;
		my($value) = '';
		$value = $3 if(defined($2));
		push(@sap_param_names, $name);
		$sap_params{$name} = $value;
	}
}

if($sap_params{TYPE} != "R")
{
	print STDERR "Not SAP Type R\n";
	exit 1;
}

my $data_size = defined($sap_params{"STEREO"}) ? 18: 9;

my $common;
my $last;
my $count = 0;
my @all_data = ();
my $common;

while(read(STDIN, $data, $data_size))
{
	if(defined($last) and $data ne $last)
	{
		$common = gcd($common, $count);
		$count = 0;
	}
	$count++;
	$last = $data;

	push(@all_data, $data);
}

print STDERR "common $common\n";

my(@out_data);

if($common > 1)
{
	while(@all_data)
	{
		push(@out_data, shift(@all_data));
		for($i = 1; $i < $common; $i++)
		{
			shift(@all_data);
		}
	}
	@all_data = @out_data;
	if(defined($sap_params{BPM}))
	{
		$sap_params{FASTPLAY} = 3000 * 312 / $sap_params{BPM};
	}
	elsif(defined($sap_params{FASTPLAY}))
	{
		$sap_params{BPM} = 3000 * 312 / $sap_params{FASTPLAY};
		push(@sap_param_names, "BPM");
	}
	else
	{
		push(@sap_param_names, "FASTPLAY");
		push(@sap_param_names, "BPM");
		$sap_params{FASTPLAY} = 312;
		$sap_params{BPM} = 3000;
	}

	$sap_params{FASTPLAY} *= $common;
	$sap_params{BPM} /= $common;
}


foreach $name (@sap_param_names)
{
	print $name;
	if(defined($sap_params{$name}) and $sap_params{$name} ne '')
	{
		print " " . $sap_params{$name};
	}
	print "\r\n";
}
print "\r\n";

# strip trailing zero data
my $last = $all_data[@all_data -1];
my @last_aud = unpack("C*", $last);
while(@all_data > 1 &&
	$last_aud[0] == 0 &&  $last_aud[2] == 0 && 
	$last_aud[4] == 0 &&  $last_aud[6] == 0 && 
	$all_data[@all_data -2] eq $last
)
{
	print STDERR "striping zero end\n";
	pop(@all_data);
}

foreach $data (@all_data)
{
	print $data;
}

# gcd(x,y) is the greatest common denominator, defined as follows:
#
# gcd(x,0) = x for all x >= 0
# gcd(x,y) = gcd(y,x%y) if x > y > 0
# gcd(x,y) is undef if x<0 or y<0

sub gcd {
  my ($x,$y)=@_;

#  print STDERR "c $x $y\n";
  return undef if $x<0 or $y<0;
  ($x,$y) = ($y,$x) if $x < $y;
  while ($y != 0) {
    ($x,$y) = ($y,$x % $y);
  }
  return $x;
}