Prepend a Taxonomy to the WordPress Permalink Structure

functions.taxonomy.php

<?php

/**
 * @package WordPress
 * @subpackage Prepend a Taxonomy to the WordPress Permalink Structure
 * @author That Stevens Guy
 * @phpcs:disable PSR1.Files.SideEffects
 *
 * wp-config.php:
 *      // Add a main suburb for the homepage to the Suburbs taxonomy,
 *      // define the slug chosen here.
 *      define('MAIN_SUBURB_SLUG', 'suburb');
 *      define('DEBUG_REWRITES', false);
 */

/**
 * Initialise custom suburb permalink.
 * Note: Save permalinks settings page to flush rewrites.
 *
 * @return void
 */
add_action('init', 'tsg_prepare_permalink');
function tsg_prepare_permalink(): void
{
    add_action('parse_request', 'tsg_debug_rewrites');

    tsg_add_rewrites();

    add_filter('rewrite_rules_array', 'tsg_customise_rewrite_rules_array');
    add_filter('request', 'tsg_customise_request_query_vars');
    add_action('template_redirect', 'tsg_verify_query_vars');
    add_filter('query_vars', 'tsg_add_query_var');
    add_filter('available_permalink_structure_tags', 'tsg_add_permalink_structure_tag');

    add_filter('page_link', 'tsg_customise_page_link');
    add_filter('post_link', 'tsg_customise_link');
    add_filter('post_type_link', 'tsg_customise_link');
    add_filter('post_type_archive_link', 'tsg_customise_link');
    add_filter('term_link', 'tsg_customise_link');
    add_filter('author_link', 'tsg_customise_link');
    add_filter('day_link', 'tsg_customise_link');
    add_filter('month_link', 'tsg_customise_link');
    add_filter('year_link', 'tsg_customise_link');
    add_filter('feed_link', 'tsg_customise_link');
    add_filter('attachment_link', '__return_empty_string');
}

/**
 * Add rewrite rules for the query variable %suburb_slug%.
 *
 * @return void
 */
function tsg_add_rewrites(): void
{
    global $wp_rewrite;

    $wp_rewrite->set_permalink_structure('/%suburb_slug%/%year%/%monthnum%/%day%/%postname%/');
    $wp_rewrite->set_category_base('%suburb_slug%/category');
    $wp_rewrite->set_tag_base('%suburb_slug%/tag');
    $wp_rewrite->author_base = '%suburb_slug%/' . $wp_rewrite->author_base;
    $wp_rewrite->comments_base = '%suburb_slug%/' . $wp_rewrite->comments_base;
    $wp_rewrite->date_structure = '%suburb_slug%/%year%/%monthnum%/%day%';
    $wp_rewrite->page_structure = '%suburb_slug%/%pagename%';

    add_rewrite_tag('%suburb_slug%', '([^/]+)', 'suburb_slug=');

    $feedregex = tsg_get_feedregex();
    $feedregex2 = tsg_get_feedregex(2);

    // Fix root rules.
    add_rewrite_rule('^sitemap\.xml$', 'index.php?sitemap=index', 'top');
    add_rewrite_rule('^wp-register\.php$', 'index.php?register=true', 'top');
    add_rewrite_rule('^wp-app\.php(/.*)?$', 'index.php?error=403', 'top');
    add_rewrite_rule('^wp-(atom|rdf|rss|rss2|feed|commentsrss2)\\.php$', 'index.php?feed=old', 'top');
    add_rewrite_rule("^$feedregex", 'index.php?feed=$matches[1]', 'top');
    add_rewrite_rule("^$feedregex2", 'index.php?feed=$matches[1]', 'top');
    add_rewrite_rule("^embed/?$", 'index.php?embed=true', 'top');
    add_rewrite_rule('^page/?([0-9]{1,})/?$', 'index.php?paged=$matches[1]', 'top');
    add_rewrite_rule("^comments/$feedregex", 'index.php?feed=$matches[1]&withcomments=1', 'top');
    add_rewrite_rule("^comments/$feedregex2", 'index.php?feed=$matches[1]&withcomments=1', 'top');
    add_rewrite_rule('^comments/embed/?$', 'index.php?pagename=comments&embed=true', 'top');
    add_rewrite_rule('([^/]+)/trackback/?$', 'index.php?suburb_slug=$matches[1]&tb=1', 'top');
    add_rewrite_rule('([^/]+)(?:/([0-9]+))?/?$', 'index.php?suburb_slug=$matches[1]&page=$matches[2]', 'top');

    // Fix %suburb_slug% rules.
    add_rewrite_rule('([^/]+)/comments/?$', 'index.php?suburb_slug=$matches[1]&pagename=comments', 'bottom');
    add_rewrite_rule('([^/]+)/comments/embed/?$', 'index.php?suburb_slug=$matches[1]&pagename=comments&embed=true', 'bottom');
    add_rewrite_rule('([^/]+)/author/?$', 'index.php?suburb_slug=$matches[1]&pagename=author', 'bottom');
    add_rewrite_rule('([^/]+)/tag/?$', 'index.php?suburb_slug=$matches[1]&pagename=tag', 'bottom');
    add_rewrite_rule('([^/]+)/category/?$', 'index.php?suburb_slug=$matches[1]&pagename=category', 'bottom');
}

/**
 * Customise rewrite rules.
 *
 * @param array $rules
 * @return array
 */
function tsg_customise_rewrite_rules_array(array $rules): array
{
    $post_types = get_post_types([
        'has_archive' => true,
        '_builtin' => false
    ]);

    // Custom post types don't apply the filter to replace structure tags
    // with regex for the array keys. Substitute our own,
    // without changing the array key position.
    $is_wrong = false;
    foreach ($post_types as $post_type) {
        foreach ($rules as $rule => $query) {
            if (strpos($rule, "%suburb_slug%/$post_type") !== false) {
                $is_wrong = true;
                $new_rule = str_replace('%suburb_slug%', '([^/]+)', $rule);
                $rules = tsg_replace_key($rules, $rule, $new_rule);
            }
        }
    }

    // After the above fix, the queries are messed up, correct them.
    if ($is_wrong) {
        foreach ($post_types as $post_type) {
            foreach ($rules as $rule => $query) {
                if (
                    strpos($rule, "([^/]+)/$post_type") !== false &&
                    strpos($rule, "([^/]+)/$post_type/category") === false &&
                    strpos($rule, "([^/]+)/$post_type/([^/]+)") === false &&
                    strpos($rule, "([^/]+)/$post_type/page/?") === false
                ) {
                    if (strpos($rule, $post_type . '/?$') !== false) {
                        $rules[$rule] =
                            'index.php?suburb_slug=$matches[1]&post_type=' . $post_type;
                    } elseif (strpos($rule, '/feed') !== false || strpos($rule, '/(feed') !== false) {
                        $rules[$rule] =
                            'index.php?suburb_slug=$matches[1]&post_type=' . $post_type . '&feed=$matches[2]';
                    } elseif (strpos($rule, '/page') !== false) {
                        $rules[$rule] =
                            'index.php?suburb_slug=$matches[1]&post_type=' . $post_type . '&paged=$matches[2]';
                    }
                }
            }
        }
    }

    // Remove rewrite rules that don't work,
    // or that we can't be bothered dealing with.
    $remove_by_rule = [
        'amp_',
        'type',
        'search',
        '.*wp-(atom|rdf|rss|rss2|feed|commentsrss2)\\.php$',
        '.*wp-app\\.php(/.*)?$',
        '.*wp-register.php$'
    ];
    $remove_by_query = [
        'attachment',
        '?&'
    ];
    foreach ($rules as $rule => $query) {
        foreach ($remove_by_rule as $match) {
            if (strpos($rule, $match) !== false) {
                unset($rules[$rule]);
            }
        }
        foreach ($remove_by_query as $match) {
            if (strpos($query, $match) !== false) {
                unset($rules[$rule]);
            }
        }
    }

    return $rules;
}

/**
 * Fix request query variables.
 *
 * @param array $query_vars
 * @return array
 */
function tsg_customise_request_query_vars(array $query_vars): array
{
    // Fix canonical redirect and allow root pages.
    if (
        isset($query_vars['suburb_slug']) &&
        !array_key_exists($query_vars['suburb_slug'], tsg_get_all_suburbs_by_slug())
    ) {
        $query_vars['pagename'] = $query_vars['suburb_slug'];
        unset($query_vars['suburb_slug']);
    }

    return $query_vars;
}

/**
 * The %suburb_slug%/%pagename% query variable has no effect on the
 * 404 status of posts for some reason.
 *
 * @return void
 */
function tsg_verify_query_vars(): void
{
    global $wp_query;

    $slug = get_query_var('pagename');
    if (
        $slug &&
        is_single() &&
        !array_key_exists($slug, tsg_get_all_suburbs_by_slug())
    ) {
        $wp_query->set_404();
        status_header(404);
        nocache_headers();
    }
}

/**
 * Add query variable %suburb_slug%.
 *
 * @param array $public_query_vars
 * @return array
 */
function tsg_add_query_var(array $public_query_vars): array
{
    $public_query_vars[] = 'suburb_slug';
    return $public_query_vars;
}

/**
 * Add the permalink structure tag %suburb_slug% to the admin page.
 *
 * @param array $tags
 * @return array
 */
function tsg_add_permalink_structure_tag(array $tags): array
{
    $tags['suburb_slug'] = __('%s (The slug of the Suburb.)');
    return $tags;
}

/**
 * Replace %suburb_slug% with the current suburb slug.
 *
 * @param string $link
 * @return string
 */
function tsg_customise_link(string $link): string
{
    return str_replace('%suburb_slug%', tsg_get_current_suburb_slug(), $link);
}

/**
 * Replace main suburb slug with root, or alternate slug if provided.
 *
 * @param string $link
 * @param string $slug
 * @return string
 */
function tsg_customise_link_slug(string $link, string $slug = '/'): string
{
    $slug = $slug !== '/' ? "/$slug/" : $slug;
    return str_replace('/' . MAIN_SUBURB_SLUG . '/', $slug, $link);
}

/**
 * Replace %suburb_slug% and main suburb slug in page links.
 *
 * @param string $link
 * @return string
 */
function tsg_customise_page_link(string $link): string
{
    return tsg_customise_link_slug(tsg_customise_link($link));
}

/**
 * Grab the slug of the current suburb.
 *
 * @param bool $echo
 * @return string|void
 */
function tsg_get_current_suburb_slug(bool $echo = false)
{
    $slug = MAIN_SUBURB_SLUG;

    $query_var = get_query_var('suburb_slug');
    if (!empty($query_var) && array_key_exists($query_var, tsg_get_all_suburbs_by_slug())) {
        $slug = $query_var;
    }

    if ($echo) {
        echo $slug;
    } else {
        return $slug;
    }
}

/**
 * Are we on the main suburb?
 *
 * @param string $slug
 * @return bool
 */
function tsg_is_main_suburb(string $slug = ''): bool
{
    if ($slug) {
        return $slug === MAIN_SUBURB_SLUG;
    }

    return tsg_get_current_suburb_slug() === MAIN_SUBURB_SLUG;
}

/**
 * Return the current suburb.
 *
 * @return WP_Term object or false on failure
 */
function tsg_get_current_suburb()
{
    return tsg_get_suburb_by_slug(tsg_get_current_suburb_slug());
}

/**
 * Retrieve a suburb object by slug.
 *
 * @param string $slug
 * @return WP_Term object or false on failure
 */
function tsg_get_suburb_by_slug(string $slug)
{
    $terms = tsg_get_all_suburbs_by_slug();

    if (isset($terms[ $slug ])) {
        return $terms[ $slug ];
    }

    return false;
}

/**
 * Returns a list of Suburbs in the form of
 * [
 *     term_id => WP_Term {},
 *     ...
 * ]
 *
 * @return array
 */
function tsg_get_all_suburbs(): array
{
    $result = get_option('tsg_suburbs');

    if (!$result) {
        $terms = get_terms('suburb', [ 'hide_empty' => false ]);
        
        if (empty($terms) && defined('MAIN_SUBURB_SLUG')) {
            wp_insert_term(MAIN_SUBURB_SLUG, 'suburb');

            $terms = get_terms([
                'taxonomy' => 'suburb',
                'hide_empty' => false
            ]);
        }

        $result = [];
        foreach ($terms as $term) {
            $result[ $term->term_id ] = $term;
        }

        update_option('tsg_suburbs', $result, false);
    }

    return $result;
}

/**
 * Returns a list of Suburbs in the form of
 * [
 *     term_slug => WP_Term {},
 *     ...
 * ]
 *
 * @return array
 */
function tsg_get_all_suburbs_by_slug(): array
{
    $result = get_option('tsg_suburbs_by_slug');

    if (!$result) {
        $terms = tsg_get_all_suburbs();

        $result = [];
        foreach ($terms as $term) {
            $result[ $term->slug ] = $term;
        }

        update_option('tsg_suburbs_by_slug', $result, false);
    }

    return $result;
}

/**
 * Clear cached suburb lists.
 *
 * @return void
 */
add_action('edited_suburb', 'tsg_update_suburb', 11);
add_action('create_suburb', 'tsg_update_suburb', 11);
function tsg_update_suburb(): void
{
    delete_option('tsg_suburbs');
    delete_option('tsg_suburbs_by_slug');

    if (function_exists('w3tc_flush_all')) {
        w3tc_flush_all();
    }
}

/**
 * Register Suburbs taxonomy.
 *
 * @return @void
 */
add_action('after_setup_theme', function (): void {
    register_taxonomy(
        'suburb',
        [ 'post' ],
        [
            'label' => 'Suburbs',
            'labels' => [
                'name' => 'Suburbs',
                'singular_name' => 'Suburb',
                'add_new' => 'Add New',
                'add_new_item' => 'Add New Suburb',
                'edit_item' => 'Edit Suburb',
                'new_item' => 'New Suburb',
                'view_item' => 'View Suburb',
                'search_items' => 'Search Suburbs',
                'not_found' =>  'Nothing Found',
                'not_found_in_trash' => 'Nothing found in the Trash',
                'parent_item_colon' => ''
            ],
            'publicly_queryable' => false,
            'has_archive' => false,
            'rewrite' => false,
            'hierarchical' => true,
            'show_in_nav_menus' => false,
            'show_tagcloud' => false,
            'show_admin_column' => false,
            'capabilities' => [ 'assign_terms' => 'edit_posts' ],
            'show_in_rest' => true
        ]
    );
});

/**
 * Limit posts to just those for the current suburb.
 *
 * @param WP_Query $query Query object before WP_Query is called.
 * @return WP_Query
 */
add_action('pre_get_posts', 'tsg_pre_get_posts');
function tsg_pre_get_posts(WP_Query $query): WP_Query
{
    if ($query->is_admin) {
        return $query;
    }

    // Bypass this entirely for menus.
    if (
        isset($query->query[ 'post_type' ]) &&
        $query->query[ 'post_type' ] === 'nav_menu_item'
    ) {
        return $query;
    }

    $suburb = tsg_get_current_suburb();

    if (empty($suburb)) {
        $query->set('pagename', '');
        $query->set_404();
        status_header(404);
        nocache_headers();

        return $query;
    }

    // Main suburb sees all posts.
    if (tsg_is_main_suburb($suburb->slug)) {
        return $query;
    }

    // Apply the tax query.
    $query->set('tax_query', [
        'relation' => 'AND',
        [
            'taxonomy' => 'suburbs',
            'field' => 'slug',
            'include_children' => false,
            'terms' => [ tsg_get_current_suburb_slug() ],
            'operator' => 'IN'
        ]
    ]);

    return $query;
}

/**
 * Debug rewrite rules.
 * Based on: https://gist.github.com/adamrosloniec/e34fcc7a0743769c75db1b072d677946
 *
 * @param WP $query
 * @return void
 */
function tsg_debug_rewrites(WP $query): void
{
    global $wp_rewrite, $wp_post_types, $wp_taxonomies;

    if (empty(DEBUG_REWRITES)) {
        return;
    }

    if (is_admin() || !is_user_logged_in()) {
        return;
    }

    echo '<p><strong>--- START REWRITE DEBUG ---</strong></p>';

    echo '<h2>Rewrite Rules</h2><table style="font-size:1em;">' .
        '<tr><th align="left">Rule</th><th align="left">Query</th></tr>';
    foreach ($wp_rewrite->wp_rewrite_rules() as $rule => $match) {
        $rewrite_bg = $rule === $query->matched_rule ? 'style="background:yellow;"' : '';
        echo "<tr $rewrite_bg><td>" .
            var_export($rule, true) . "</td><td>$match</td></tr>";
    }
    echo '</table>';

    echo '<h2>Permalink Structure</h2><table style="font-size:1em;">' .
        '<tr><th align="left" colspan="2">Post Type</th></tr>' .
        '<tr><td>Page</td><td>' . $wp_rewrite->get_page_permastruct() . '</td></tr>' .
        "<tr><td>Post</td><td>$wp_rewrite->permalink_structure</td></tr>";
    foreach ($wp_post_types as $post_type) {
        if (
            !empty($post_type->name) &&
            !empty($post_type->label) &&
            // @phpstan-ignore-next-line
            !empty($post_type->rewrite['slug'])
        ) {
            $post_type_bg = !empty($query->query_vars['post_type']) &&
                $post_type->name === $query->query_vars['post_type']
                ? 'style="background:yellow;"'
                : '';
            echo "<tr $post_type_bg><td>$post_type->label</td><td>" .
                $post_type->rewrite['slug'] . '</td></tr>';
        }
    }
    echo '<tr><th align="left" colspan="2">Taxonomy</th></tr>';
    foreach ($wp_taxonomies as $taxonomy) {
        if (
            !empty($taxonomy->name) &&
            // @phpstan-ignore-next-line
            !empty($taxonomy->labels->singular_name) &&
            // @phpstan-ignore-next-line
            !empty($taxonomy->rewrite['slug'])
        ) {
            $taxonomy_bg = !empty($query->query_vars[$taxonomy->name])
                ? 'style="background:yellow;"'
                : '';
            echo "<tr $taxonomy_bg><td>{$taxonomy->labels->singular_name}</td><td>" .
                $wp_rewrite->get_extra_permastruct($taxonomy->name) . '</td></tr>';
        }
    }
    echo '<tr><th align="left" colspan="2">Archive</th></tr>';
    $author_bg = !empty($query->query_vars['author_name']) ? 'style="background:yellow;"' : '';
    echo "<tr $author_bg><td>Author</td><td>" .
            $wp_rewrite->get_author_permastruct() . '</td></tr>';
    $date_bg = !empty($query->query_vars['author_name']) ? 'style="background:yellow;"' : '';
    echo "<tr $date_bg><td>Date</td><td>" .
            $wp_rewrite->get_date_permastruct() . '</td></tr>';
    echo '<tr><th align="left" colspan="2">Feed</th></tr>';
    echo "<tr><td>Feed</td><td>" .
            $wp_rewrite->get_feed_permastruct() . '</td></tr>';
    echo "<tr><td>Comments</td><td>" .
            $wp_rewrite->get_comment_feed_permastruct() . '</td></tr>';
    echo '</table>';

    echo '<h2>Request</h2><p>' .
        var_export($query->request, true) . '</p>';

    $matched_bg = !empty($query->matched_rule) ? 'style="background:yellow;"' : '';
    echo "<h2>Matched Rewrite Rule</h2><p $matched_bg>" .
        var_export($query->matched_rule, true) . '</p>';

    echo '<h2>Matched Query</h2><p>' .
        var_export($query->matched_query, true) . '</p>';

    echo '<h2>Query Variables</h2><p>' .
        var_export($query->query_vars, true) . '</p>';

    echo '<p><strong>--- END REWRITE DEBUG ---</strong></p>';
}

/**
 * Build a regex to match the feed section of URLs, something like (feed|atom|rss|rss2)/?
 * Based on: https://github.com/WordPress/WordPress/blob/master/wp-includes/class-wp-rewrite.php#L873
 *
 * @param int $version
 * @return string
 */
function tsg_get_feedregex(int $version = 1): string
{
    global $wp_rewrite;

    $feedregex2 = '';
    foreach ((array)$wp_rewrite->feeds as $feed_name) {
        $feedregex2 .= $feed_name . '|';
    }
    $feedregex2 = '(' . trim($feedregex2, '|') . ')/?$';

    if ($version === 2) {
        return $feedregex2;
    }

    /*
     * $feedregex is identical but with /feed/ added on as well, so URLs like <permalink>/feed/atom
     * and <permalink>/atom are both possible
     */
    return $wp_rewrite->feed_base . '/' . $feedregex2;
}

/**
 * Replace an array key without changing the array key position.
 * Based on: https://stackoverflow.com/a/8884153
 *
 * @param array $array
 * @return array
 */
function tsg_replace_key(array $array, $old_key, $new_key): array
{
    $keys = array_keys($array);
    $index = array_search($old_key, $keys, true);

    if ($index === false) {
        return $array;
    }

    $keys[$index] = $new_key;

    return array_combine($keys, array_values($array));
}