#!/usr/bin/perl
use strict;

sub create_map($$) {
    my($width, $height) = @_;
    my($data) = [];
    print "Creating map...";
    for(my $r=0; $r < $height; $r++) {
	$data->[$r] = [];
    }
    print "\n";
    { width => $width,
      height => $height,
      data => $data }
}

sub merge_hgt($$$$$$) {
    my($map, $filename, $x, $y, $width, $height) = @_;
    my($mapdata) = $map->{'data'};
    print "Merging $filename...";
    if(open(HGT, "unzip -p $filename.zip $filename|")) {
	my($length) = $width * 2; # size of signed short
	my($r2) = $y;
	for(my $r=0; $r < $height; $r++) {
	    my($buffer);
	    my($offset) = 0;
	    while ($offset < $length) {
		my($nread) = sysread HGT, $buffer, $length - $offset, $offset;
		if(defined $nread) {
		    $offset += $nread;
		} else {
		    print "(problem reading data: $!)";
		}
	    }
	    my(@row) = unpack("n$width", $buffer);
	    my($c2) = $x;
	    for(my $c=0; $c < $width; $c++) {
		$row[$c] = -1 - ($row[$c] ^ 0xffff) if $row[$c] & 0x8000;
		$mapdata->[$r2]->[$c2] = $row[$c];
		$c2++;
	    }
	    $r2++;
	}
	close HGT;
	print "\n";
    } else {
	print STDERR "Couldn't open $filename\n";
    }
}

sub save_map($$$$$$$) {
    my($map, $filename, $base, $x, $y, $width, $height) = @_;
    $width = $map->{'width'} unless defined $width;
    $height = $map->{'height'} unless defined $height;
    print "Saving map to $filename...";
    open(TGA, ">$filename") or die "Error opening $filename for write: $!";
    my($tgaheader)="\x00\x00\x02\x00\x00\x00\x00\x00\x00\x00\x00\x00" . pack('v2', $width, $height) . "\x18\x20";
    print TGA $tgaheader;
    foreach my $r (@{$map->{'data'}}[$y..$y+$map->{'height'}-1]) {
	foreach my $c (@{$r}[$x..$x+$map->{'width'}-1]) {
	    my($v) = $c < -32700 ? 0 : $c - $base;
	    print STDERR "\$base too high for $filename, should be less than $c\n" if $v < 0;
   	    print TGA pack('Cv', 0, $v);
        }
    }
    close TGA;
    print "\n";
}

my($map) = create_map(2401, 2401);
merge_hgt($map, 'N44W002.hgt', 0, 1200, 1201, 1201);
merge_hgt($map, 'N45W002.hgt', 0, 0, 1201, 1201);
merge_hgt($map, 'N44W001.hgt', 1200, 1200, 1201, 1201);
merge_hgt($map, 'N45W001.hgt', 1200, 0, 1201, 1201);
save_map($map, 'bordeaux.tga', -70, 0, 0, undef, undef);