<?php declare(strict_types=1);

const HEADER = '/^(#+)\s+(.*)/';
const LINK = '/^=&gt;\s+(\S+)\s*(.*)/';
const LIST_ITEM = '/^\*\s+(.*)/';
const PRE = '/^```(.*)?/';
const QUOTE = '/^&gt;\s+(.*)/';

function getPages(string $src, string $output): array
{
    $src = realpath($src);

    $iter = new \RecursiveIteratorIterator(
        new \RecursiveDirectoryIterator($src, \FilesystemIterator::SKIP_DOTS),
        \RecursiveIteratorIterator::SELF_FIRST
    );

    $pages = [];

    foreach ($iter as $fileInfo) {
        if (!is_file($fileInfo->getRealPath())) {
            continue;
        }
        $pages[] = getPageMetaData($fileInfo, $src, $output);
    }

    return $pages;
}

function getPageMetaData(\SplFileInfo $fileInfo, string $src, string $output): array
{
    $input = $fileInfo->getRealPath();

    $pathData = parsePath($input);

    $url = str_replace([$src, '.gmi'], ['', '.html'], $input);

    $contentData = parseContent(file_get_contents($input));

    return [
        'input'  => $input,
        'url'    => $url,
        'date'   => $pathData['date'],
        'tag'    => $pathData['tag'],
        'isPost' => $pathData['isPost'],
        'isTag'  => $pathData['isTag'],
        'title'  => $contentData['title'],
        'author' => $contentData['author'],
        'html'   => gemtext2hmtl(file_get_contents($input)),
        'output' => "$output$url",
    ];
}

function parsePath(string $path): array
{
    $date = null;
    $tag = null;
    $isPost = false;
    $isTag = false;

    /**
     * Assume that only posts have both a date and a tag.
     */
    if (preg_match('/\/posts\/(.+)\/(\d\d\d\d-\d\d-\d\d)\//', $path, $matches) === 1) {
        [, $tag, $date] = $matches;

        $isPost = true;
    }

    /**
     * Assume tags have an index file that contains related posts.
     */
    if (preg_match('/posts\/(?:[^\/]|\/\/)+\/index/', $path, $matches) === 1) {
        $tag = explode('/', $matches[0])[1];
        $isTag = true;
    }

    return [
        'date'   => $date,
        'tag'    => $tag,
        'isPost' => $isPost,
        'isTag'  => $isTag,
    ];
}

function parseContent(string $content): array
{
    $title = null;
    $author = null;

    if (preg_match('/^# (.+)$/m', $content, $matches) === 1) {
        $title = $matches[1];
    }

    if (preg_match('/^> .+ By (.+)$/m', $content, $matches) === 1) {
        $author = $matches[1];
    }

    return [
        'title'  => $title,
        'author' => $author,
    ];
}

function buildWWWSite(array $pages, string $hostname, string $htmlTemplateDiretory, string $output): void
{
    foreach ($pages as $page) {
        $destDirectory = dirname($page['output']);

        if (!file_exists($destDirectory) && !mkdir($destDirectory, 0777, true)) {
            echo "Unable to create WWW site directory $destDirectory.";
            exit(1);
        }

        file_put_contents(
            $page['output'],
            buildHtmlFile(
                $page['title'],
                $page['html'],
                file_get_contents($htmlTemplateDiretory.DIRECTORY_SEPARATOR.'default.html')
            )
        );
    }

    generateAtomFeeds($pages, $hostname);

    generateSiteMap($pages, $hostname, $output);
}

function buildHtmlFile(string $title, string $contents, string $template): string
{
    return str_replace(
        [
            '{{ $title }}',
            '{{ $contents }}'
        ],
        [
            $title,
            $contents,
        ],
        $template
    );
}

function gemtext2hmtl(string $gemtext): string
{
    $html = [];

    $lines = preg_split('/\r?\n/', htmlspecialchars($gemtext));

    $line = fn ($index) => $lines[$index];

    $index = 0;

    $numLines = count($lines);

    while($index < $numLines) {
        if (preg_match(HEADER, $line($index), $matches) === 1) {
            [, $levels, $content] = $matches;

            $level = strlen($levels);

            $html[] = "<h$level>$content</h$level>";
        } elseif (preg_match(LINK, $line($index), $matches) === 1) {
            [, $href, $content] = $matches;

            $content = $content ?: $href;

            $html[] = "<a href=\"$href\">$content</a>";
        } elseif (preg_match(LIST_ITEM, $line($index), $matches) === 1) {
            $items = [];

            while ($index < $numLines) {
                if (preg_match(LIST_ITEM, $line($index), $matches) === 0) {
                    break;
                }

                $items[] = "<li>$matches[1]</li>";

                $index++;
            }

            $index--;

            $html[] =  sprintf("<ul>%s</ul>", implode('', $items));
        } elseif (preg_match(PRE, $line($index), $matches) === 1) {
            [, $alt] = $matches;

            $items = [];

            $index++;

            while ($index < $numLines) {
                $item = $line($index);

                if (preg_match(PRE, $item, $matches) === 1) {
                    break;
                }

                $items[] = $item;

                $index++;
            }

            $items = implode("\n", $items);

            $html[] = $alt ? "<pre><code class=\"$alt\">$items</code></pre>" : "<pre>$items</pre>";
        } elseif (preg_match(QUOTE, $line($index), $matches) === 1) {
            $html[] =  "<blockquote>$matches[1]</blockquote>";
        } else {
            if ($line($index) !== '') {
                $html[] =  "<p>{$line($index)}</p>";
            }
        }

        $index++;
    }

    return implode('', $html);
}

function generateAtomFeeds(array $pages, string $hostname): void
{
    $posts = array_filter($pages, fn ($post) => $post['isPost']);

    $tags = array_filter($pages, fn ($post) => $post['isTag']);

    /**
     * Sort by latest to previous date.
     */
    usort($posts, fn ($a, $b) => $b['date'] <=> $a['date']);

    /**
     * Group posts by tag.
     */
    $groupedPosts = array_reduce($posts, function ($carry, $post) {
        $carry[$post['tag']][] = $post;

        return $carry;
    }, []);

    /**
     * Put posts with their tag page.
     */
    $tags = array_map(function ($tag) use ($groupedPosts) {
        return array_merge($tag, ['posts' => $groupedPosts[$tag['tag']]]);
    }, $tags);

    foreach ($tags as $tag) {
        tagToAtomFeed($tag, $hostname);
    }

    /**
     * Get the page that lists all posts.
     */
    $allPostsIndex = array_values(array_filter($pages, fn ($post) => preg_match('/posts\/index/', $post['url']) == 1))[0];

    $allPostsIndex['posts'] = $posts;

    tagToAtomFeed($allPostsIndex, $hostname);
}

function tagToAtomFeed(array $tag, string $hostname): void
{
    file_put_contents(
        str_replace('index.html', 'atom.xml', $tag['output']),
        buildAtomFeed(
            $tag['title'],
            "https://$hostname".str_replace('index.html', 'atom.xml', $tag['url']),
            "https://$hostname".$tag['url'],
            $tag['posts'][0]['date'].'T12:00:00Z',
            implode('', array_map(fn ($post) => postToAtomEntry($post, $hostname), $tag['posts']))
        )
    );
}

function postToAtomEntry(array $post, string $hostname): string
{
    return buildAtomEntry(
        $post['title'],
        "https://$hostname{$post['url']}",
        $post['author'],
        "{$post['date']}T12:00:00Z",
        htmlspecialchars($post['html']),
    );
}

function buildAtomFeed(string $title, string $href, string $altHref, string $date, string $entries): string
{
    return <<<EOF_STR
<?xml version="1.0" encoding="utf-8"?>
<feed xmlns="http://www.w3.org/2005/Atom">
    <title type="text">$title</title>
    <id>$href</id>
    <link rel="alternate" type="text/html" href="$altHref"/>
    <link rel="self" type="application/atom+xml" href="$href"/>
    <updated>$date</updated>
    $entries
</feed>
EOF_STR;
}

function buildAtomEntry(string $title, string $href, string $author, string $date, string $content): string
{
    return <<<EOF_STR
<entry>
    <title type="text">$title</title>
    <id>$href</id>
    <link rel="alternate" type="text/html" href="$href"/>
    <author><name>$author</name></author>
    <published>$date</published>
    <updated>$date</updated>
    <content type="html">$content</content>
</entry>
EOF_STR;
}

function generateSiteMap(array $pages, string $hostname, $output): void
{
    $posts = array_filter($pages, fn ($post) => $post['isPost']);

    /**
     * Sort by latest to previous date.
     */
    usort($posts, fn ($a, $b) => $b['date'] <=> $a['date']);

    file_put_contents(
        $output.DIRECTORY_SEPARATOR.'sitemap.xml',
        buildSiteMap(
            implode('', array_map(fn ($post) => postToSiteMapUrl($post, $hostname), $posts))
        )
    );

}

function postToSiteMapUrl(array $post, string $hostname): string
{
    return buildSiteMapUrl(
        "https://$hostname{$post['url']}",
        "{$post['date']}T12:00:00Z"
    );
}

function buildSiteMap(string $urls): string
{
    return <<<EOF_STR
<?xml version="1.0" encoding="utf-8"?>
<urlset xmlns="http://www.sitemaps.org/schemas/sitemap/0.9" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.sitemaps.org/schemas/sitemap/0.9 http://www.sitemaps.org/schemas/sitemap/0.9/sitemap.xsd">
    $urls
</urlset>
EOF_STR;
}

function buildSiteMapUrl(string $loc, string $lastmod): string
{
    return <<<EOF_STR
<url>
    <loc>$loc</loc>
    <lastmod>$lastmod</lastmod>
    <changefreq>never</changefreq>
</url>
EOF_STR;
}