/sitemap.xml
// ============================================================
require_once __DIR__ . '/includes/config.php';

$type   = $_GET['type'] ?? 'index';
$page   = max(0, (int)($_GET['page'] ?? 0));
$per    = 10000; // Google's max per sitemap

header('Content-Type: application/xml; charset=utf-8');
header('X-Robots-Tag: noindex');

if ($type === 'index') {
    // Sitemap index
    $total = (int)db()->query("SELECT COUNT(*) FROM solutions")->fetchColumn();
    $pages = (int)ceil($total / $per);
    echo '<?xml version="1.0" encoding="UTF-8"?>' . "\n";
    echo '<sitemapindex xmlns="http://www.sitemaps.org/schemas/sitemap/0.9">' . "\n";
    echo "<sitemap><loc>" . SITE_URL . "/sitemap.xml?type=static</loc><lastmod>" . date('Y-m-d') . "</lastmod></sitemap>\n";
    for ($i = 0; $i < $pages; $i++) {
        echo "<sitemap><loc>" . SITE_URL . "/sitemap.xml?type=solutions&amp;page={$i}</loc><lastmod>" . date('Y-m-d') . "</lastmod></sitemap>\n";
    }
    echo '</sitemapindex>';
    exit;
}

if ($type === 'static') {
    echo '<?xml version="1.0" encoding="UTF-8"?>' . "\n";
    echo '<urlset xmlns="http://www.sitemaps.org/schemas/sitemap/0.9">' . "\n";
    $static = [['/', '1.0', 'daily'], ['/categories.php', '0.9', 'daily'], ['/search.php', '0.7', 'weekly']];
    foreach ($static as [$path, $pri, $freq]) {
        echo "<url><loc>" . SITE_URL . $path . "</loc><changefreq>{$freq}</changefreq><priority>{$pri}</priority></url>\n";
    }
    foreach (db()->query("SELECT slug, updated_at FROM categories") as $cat) {
        echo "<url><loc>" . SITE_URL . "/category.php?slug=" . urlencode($cat['slug']) . "</loc><changefreq>hourly</changefreq><priority>0.8</priority><lastmod>" . substr($cat['updated_at'] ?? date('Y-m-d'), 0, 10) . "</lastmod></url>\n";
    }
    echo '</urlset>';
    exit;
}

if ($type === 'solutions') {
    $offset = $page * $per;
    $rows = db()->prepare("SELECT slug, updated_at FROM solutions ORDER BY id LIMIT {$per} OFFSET {$offset}");
    $rows->execute();
    echo '<?xml version="1.0" encoding="UTF-8"?>' . "\n";
    echo '<urlset xmlns="http://www.sitemaps.org/schemas/sitemap/0.9">' . "\n";
    foreach ($rows as $row) {
        echo "<url><loc>" . SITE_URL . "/solution.php?slug=" . urlencode($row['slug']) . "</loc><lastmod>" . substr($row['updated_at'], 0, 10) . "</lastmod><changefreq>monthly</changefreq><priority>0.6</priority></url>\n";
    }
    echo '</urlset>';
    exit;
}