#!/usr/bin/perl

# Downloads all beginner exercises and solutions from senseis.xmp.net
# wiki (see http://senseis.xmp.net/?BeginnerExercises); extracts wiki
# topic content and puts it in one big HTML page to make it easy to
# print all of them as one document

#
# Usage: download.pl > output.html
#

use strict;
use warnings;

use LWP::Simple;
use URI;
use XML::LibXML;

my $PARSER = XML::LibXML->new();

my $output = create_output_node();

while (my $topic = next_topic()) {
    my $url = 'http://senseis.xmp.net/?' . $topic;

    print STDERR $topic, "\n\n";

    my @topic_nodes = extract_wiki_topic_content($url);

    links_rel_to_abs($_, $url) for @topic_nodes;

    add_wiki_topic_to_node($output, $topic, @topic_nodes);
}

print $output->ownerDocument->toString;

{
    my $i = 0;
    my $show_solution = 0;

    sub next_topic {
        $i ++;
        if($i > 149) {
            return undef if $show_solution;
            $i = 0; $show_solution = 1;
            return next_topic();
        }

        my $topic = "BeginnerExercise$i";
        $topic .= 'Solution' if $show_solution;

        return $topic;
    }
}

sub create_output_node {
    my $dom = XML::LibXML::Document->new();

    my $root = XML::LibXML::Element->new('html');
    $dom->setDocumentElement($root);

    my $title_text = 'Beginner Exercises and Solutions (senseis.xmp.net)';

    my $title = XML::LibXML::Element->new('title');
    $title->appendText($title_text);
    $root->appendChild($title);

    my $body = XML::LibXML::Element->new('body');
    $root->appendChild($body);

    my $h1 = XML::LibXML::Element->new('h1');
    $h1->appendText($title_text);
    $body->appendChild($h1);

    return $body;
}

sub extract_wiki_topic_content {
    my $url = shift;

    my $dom = $PARSER->parse_html_string(get($url));

    return $dom->findnodes(<<'XPATH');
//td[@valign="top" and @rowspan = 2]
/*[count(preceding-sibling::hr[@noshade]) > 0 and
   count(following-sibling::hr[@noshade]) > 0]
XPATH
}

sub links_rel_to_abs {
    my $node = shift;
    my $base_url = shift;

    for my $link ($node->findnodes('.//@href'), $node->findnodes('.//@src')) {
        $link->setValue(URI->new_abs($link->value, $base_url));
    }
}

sub add_wiki_topic_to_node {
    my $node = shift;
    my $title = shift;
    my @topic_nodes = @_;

    my $h2 = XML::LibXML::Element->new('h2');
    $h2->appendText($title);
    $node->appendChild($h2);

    $node->appendChild($_) for @topic_nodes;
}