#!/usr/bin/perl

use strict;
use warnings;

use File::Slurp;

use GD;
GD::Image->trueColor( 1 );

use Image::Size;
use LWP::Simple;
use Readonly;

Readonly::Scalar my $LIST_URL
    => 'http://data.giss.nasa.gov/gistemp/station_data/station_list.txt';

Readonly::Scalar my $LIST_FILE => 'station_list.txt';

# Map: http://www.evl.uic.edu/pape/data/Earth/
Readonly::Scalar my $MAP_TEMPLATE => 'etopo-landmask.png';
Readonly::Scalar my $MAP_OUTPUT => 'giss-stations-map.png';

unless ( -e $LIST_FILE ) {
    my $station_list = get $LIST_URL;
        
    unless ( (defined $station_list) and length $station_list ) {
        die "Cannot retrieve station list\n"
    }

    write_file $LIST_FILE, \$station_list;
}

my $gd = GD::Image->new( $MAP_TEMPLATE )
    or die "Cannot load map template: '$MAP_TEMPLATE'\n";

my ($lon_mapper, $lat_mapper);

{
    my ($w, $h) = imgsize $MAP_TEMPLATE;
    $lon_mapper = sub ($) { ( $w / 2 ) + $_[0] * ( $w / 360 ) } ;
    $lat_mapper = sub ($) { ( $h / 2 ) - $_[0] * ( $h / 180 ) } ;
}

my $marker_color = $gd->colorAllocate( 0xff, 0x00, 0x00 );
my $circle_color = $gd->colorAllocate( 0xff, 0xff, 0x00 );

open my $list_fh, '<', $LIST_FILE
    or die "Cannot open '$LIST_FILE': $!";

while ( <$list_fh> ) {

#    next unless /cc=425/; # use only U.S. stations

    my $coord_str = substr $_, 58, 12;

    if ( $coord_str =~ /(-?\d+)\s+(-?\d+)/ ) {
        my ($lat, $lon) = ($1, $2);
        $_ /= 10 for $lat, $lon;
        
        my $x = $lon_mapper->( $lon );
        my $y = $lat_mapper->( $lat );
    
        $gd->ellipse( $x, $y, 4, 4, $circle_color );
        $gd->line( $x,     $y - 2, $x, $y + 2, $marker_color );
        $gd->line( $x - 2, $y,     $x + 2, $y, $marker_color );
    }
}

close $list_fh;

write_file $MAP_OUTPUT, { binmode => ':raw' }, \$gd->png;

__END__