#!/usr/bin/perl

use Getopt::Std;

my @splits;
my %args;
getopts('sndh', \%args);

my $usage = <<EOF;
Some PDFs nowadays come with each page constructed from a large
number of partial images that get stacked together. This program
creates TIFFs of the pages from the partial images.

There are two ways to invoke the program.

stitch_pages -n INIT STEP PAGES
	In this case, INIT gives the number of the first image (this
	will usually be 0 or 1); STEP tells how many images are used
	to construct each page; and PAGES tells how many pages we are
	constructing. 
	
Obviously, this assumes that there are the same number of partial 
images for each page. If that is not true, you can use the other
form and specify the "splits" manually.

stitch_pages -s SPLIT1 SPLIT2 ... SPLITn
	In this case, we will stitch together the partial images
	SPLIT1 - (SPLIT2 - 1), etc. The last split given should
	thus be one greater than the last image available.

EOF

if (defined($args{h})) {
	print $usage;
	exit 0;
}

my $debug = defined($args{d});

if (defined($args{s})) {
	@splits = @ARGV;
} 
elsif (defined($args{n})) {
	my $init = $ARGV[0];
	my $step = $ARGV[1];
	my $pags = $ARGV[2];
	push @splits, $init;
	for (my $i = 1; $i <= $pags; ++$i) {
		$init += $step;
		push @splits, $init;
	}
}
else { die("Choose an option!\n"); }

my $start = shift @splits;
my $stop = shift @splits;

sub normalize {
	my $in = shift;
	if ($in < 100) { $in = "0$in"; }
	if ($in < 10) { $in = "0$in"; }
	return $in;
}

my $newpage = 1;
while (1) {
	my @files;
	for (my $i = $start; $i < $stop; $i++) {
		push @files, "*" . normalize($i) . ".pbm";
	}
	
	my $cmd = "convert " . join(" ", @files) . " -append outpage" . normalize($newpage) . ".tiff";
	print "$cmd\n\n";
	system($cmd) unless $debug;

	my $lasttime = scalar @splits;
	last if $lasttime == 0;
	
	$start = $stop;
	$stop = shift @splits;
	$newpage++;
}