WordPress: Taxonomy Top Level URL

class-taxonomy-top-level-url.php

<?php
/**
 * The class used to make certain taxonomies have a top level URL.
 */

/**
 * The Taxonomy_Top_Level_URL class.
 */
class Taxonomy_Top_Level_URL {
	/**
	 * Existing instance.
	 *
	 * @var array
	 */
	protected static $instance;
	
	/**
	 * The array holding all of the taxonomies that need top level URLs.
	 *
	 * @var array
	 */
	private $_taxonomies = [];

	/**
	 * Get class instance.
	 *
	 * @return object
	 */
	public static function instance() {
		if ( ! isset( static::$instance ) ) {
			static::$instance = new static();
			static::$instance->setup();
		}
		return static::$instance;
	}

	/**
	 * Setup the singleton.
	 */
	public function setup() {
		// Add the new top level rewrite rules.
		add_filter( 'rewrite_rules_array', array( $this, 'rewrite_rules_array' ), 10, 1 );

		// Setup the taxonomy URL link.
		add_filter( 'term_link', array( $this, 'custom_term_permalink' ), 10, 3 );

		// Flush rewrite rules whenever any term in the taxonomies is saved.
		add_filter( 'created_term', array( $this, 'term_flush_rewrite_rules' ), 10, 3 );
		add_filter( 'edited_term', array( $this, 'term_flush_rewrite_rules' ), 10, 3 );
		add_filter( 'delete_term', array( $this, 'term_flush_rewrite_rules' ), 10, 3 );
	}

	/**
	 * Adding assorted rewrite rules.
	 *
	 * @param  array $rules The current rules.
	 * @return array $rules The new rules.
	 */
	public function rewrite_rules_array( $rules ) {
		// Move all terms to the top level if in our taxonomy.
		$taxonomies = $this->get_taxonomies();
		$all_term_names = [];

		if ( ! empty( $taxonomies ) ) {
			foreach ( $taxonomies as $taxonomy ) {
				$term_names = [];
				if ( taxonomy_exists( $taxonomy ) ) {
					$terms = get_terms(
						$taxonomy,
						[
							'hide_empty' => false,
						]
					);

					// Get all term slugs.
					$term_slugs = [];
					foreach ( $terms as $term ) {
						$term_slugs[] = $this->get_term_slug( $term );
					}

					$term_names = array_map( 'preg_quote', $term_slugs );

					// Remove any terms that have already been added.
					foreach ( $term_names as $key => $term_name ) {
						if ( in_array( $term_name, $all_term_names, true ) ) {
							unset( $term_names[ $key ] );
						}
					}

					// Add the new terms to the all terms array.
					$all_term_names = array_merge( $all_term_names, $term_names );

					if ( ! empty( $term_names ) ) {
						$rules = array_merge( $this->rewrite_term_rules( $term_names, $taxonomy, $rules ), $rules );
					}
				}
			}
		}

		return $rules;
	}


	/**
	 * Create the rules necessary to move a taxonomy term to a top level URL
	 *
	 * @param  array  $term_names The term names to add to the top level.
	 * @param  string $taxonomy   The taxonomy of the terms.
	 * @param  array  $rules      The current rules.
	 * @return array  $rules      The new rules.
	 */
	public function rewrite_term_rules( $term_names, $taxonomy, $rules ) {
		$term_regex = implode( '|', $term_names );

		$taxonomy_name = $taxonomy;
		if ( 'category' === $taxonomy ) {
			$taxonomy_name = 'category_name';
		}

		$new_term_rules = [
			'^(' . $term_regex . ')/?$' => 'index.php?' . $taxonomy_name . '=$matches[1]',
			'(' . $term_regex . ')/page/?([0-9]{1,})/?' => 'index.php?' . $taxonomy_name . '=$matches[1]&paged=$matches[2]',
			'(' . $term_regex . ')/feed/(feed|rdf|rss|rss2|atom|json)/?$' => 'index.php?' . $taxonomy_name . '=$matches[1]&feed=$matches[2]',
			'(' . $term_regex . ')/(feed|rdf|rss|rss2|atom|json)/?$' => 'index.php?' . $taxonomy_name . '=$matches[1]&feed=$matches[2]',
			'(' . $term_regex . ')/(feed|rdf|rss|rss2|atom|json)/(article|gallery)/?$' => 'index.php?' . $taxonomy_name . '=$matches[1]&feed=$matches[2]&post_type=$matches[3]',
		];

		// Append the new rules to the beginning of the array so that they are matched first.
		$rules = $new_term_rules + $rules;

		return $rules;
	}

	/**
	 * Update all terms for a specfic taxonomy to the top level URL.
	 *
	 * @param  string  $termlink The current term link.
	 * @param  WP_Term $term     The current term.
	 * @param  string  $taxonomy The term taxonomy.
	 * @return string  $termlink The new term link.
	 */
	public function custom_term_permalink( $termlink, $term, $taxonomy ) {
		if ( in_array( $taxonomy, $this->get_taxonomies(), true ) ) {
			return trailingslashit( '/' . $this->get_term_slug( $term ) );
		}

		return $termlink;
	}

	/**
	 * Flush rewrite rules when a term is created, edited or deleted.
	 *
	 * @param int    $term_id  Term ID.
	 * @param int    $tt_id    Term taxonomy ID.
	 * @param string $taxonomy Taxonomy slug.
	 */
	public function term_flush_rewrite_rules( $term_id, $tt_id, $taxonomy ) {
		if ( in_array( $taxonomy, $this->get_taxonomies(), true ) ) {
			flush_rewrite_rules( false );
		}
	}

	/**
	 * Get the term slug to use in the URL.
	 *
	 * @param \WP_Term $term The term object.
	 * @return string $term_slug The term slug.
	 */
	public function get_term_slug( \WP_Term $term ) {
		$term_slug = $term->slug;

		// Sub-categories should have their parent category slug prepended to the URL.
		if ( 'category' === $term->taxonomy && 0 !== $term->parent ) {
			$parent_term = get_term( $term->parent );

			if ( $parent_term instanceof \WP_Term ) {
				$term_slug = $parent_term->slug . '/' . $term_slug;
			}
		}

		return $term_slug;
	}

	/**
	 * Get the taxonomies.
	 *
	 * @return array $taxonomies The taxonomies.
	 */
	public function get_taxonomies() {
		return $this->_taxonomies;
	}

	/**
	 * Set the taxonomies.
	 *
	 * @param array $new_taxonomies The new taxonomies.
	 */
	public function set_taxonomies( $new_taxonomies ) {
		$this->_taxonomies = $new_taxonomies;
	}
}

/**
 * Get the singleton instance.
 *
 * @return Taxonomy_Top_Level_URL
 */
function taxonomy_top_level_url() {
	$instance = Taxonomy_Top_Level_URL::instance();
	
	// Add the taxonomies here.
	$instance->set_taxonomies( [
		// 'category',
	] );

	return $instance;
}
add_action( 'after_setup_theme', 'taxonomy_top_level_url' );