WP: All Post Filters Class

all-post-filters.php

<?php

/**
 * Add custom post filters on the All Posts page. This is best used with an Elastic
 * Search powered site since this can create a very expensive query.
 *
 * Simple Example:
 *
 * add_filter( 'all_post_filters', function ( $filters, $post_type ) {
 *     // Perform post type validiation.
 *     if ( ! in_array( $post_type, [ 'post' ], true ) ) {
 *         return $filters;
 *     }
 *
 *     // Custom field.
 *     $custom_field_options = [
 *         'key' => 'value',
 *         'key' => 'value',
 *         'key' => 'value',
 *     ];
 *
 *     $filters[] = array(
 *         'id' => 'custom_field',
 *         'name' => __( 'Custom field' ),
 *         'field' => 'meta',
 *         'no_option' => __( 'Any field' ),
 *         'options' => $custom_field_options,
 *     );
 *
 *     return $filters;
 * }, 10, 2 );
 */
class All_Post_Filters {

	/**
	 * The filters.
	 *
	 * @var array
	 */
	private $_filters = array();

	/**
	 * Instances of child classes.
	 *
	 * @var array
	 */
	protected static $instances = array();

	/**
	 * Initialization typically happens via get_instance() method.
	 */
	public function __construct() {}

	/**
	 * Return an instance of a child class.
	 *
	 * @return All_Post_Filters
	 */
	public static function get_instance() {
		$class = get_called_class();
		if ( ! isset( self::$instances[ $class ] ) ) {
			self::$instances[ $class ] = new static;
			self::$instances[ $class ]->setup();
		}
		return self::$instances[ $class ];
	}

	/**
	 * Perform initial setup.
	 */
	public function setup() {
		// Get the current filters.
		add_action( 'admin_init', array( $this, 'get_filters' ) );

		add_action( 'restrict_manage_posts', array( $this, 'add_filters' ) );
		add_action( 'pre_get_posts', array( $this, 'filter_posts' ) );
		add_action( 'parse_query', array( $this, 'parse_query' ) );
		add_filter( 'disable_months_dropdown', '__return_true' );
		add_filter( 'disable_categories_dropdown', '__return_true' );
	}

	/**
	 * Add all of our custom filters.
	 *
	 * @param string $post_type The post type slug.
	 */
	public function add_filters( $post_type ) {
		// Check to see if we have any filters to add.
		$filters = $this->_filters;
		if ( empty( $filters ) ) {
			return;
		}

		foreach ( $filters as $filter ) {
			$this->_the_screen_reader_label( $filter );
			$this->_the_select_dropdown( $filter );
		}
	}

	/**
	 * Get the filters at the proper time.
	 */
	public function get_filters() {
		$this->_filters = $this->_get_filters();
	}

	/**
	 * Parse the query to remove the empty search param.
	 *
	 * @param WP_Query &$this The WP_Query instance (passed by reference).
	 */
	public function parse_query( $query ) {
		// Remove the search param if it is not set.
		if ( isset( $query->query['s'] ) && empty( $query->query['s'] ) ) {
			unset( $query->query['s'] );
			$query->is_search = false;
		}
	}

	/**
	 * Filter the admin All posts page based on the custom filters.
	 *
	 * @param WP_Query $query The current query object.
	 */
	public function filter_posts( $query ) {
		// Check to see if we have any filters to add.
		$filters = $this->_filters;
		if ( empty( $filters ) ) {
			return;
		}

		global $pagenow;

		// Make sure we are only modifing the All posts page query.
		if (
			is_admin()
			&& in_array( $query->get( 'post_type' ), $this->post_types(), true )
			&& 'edit.php' === $pagenow
		) {
			foreach ( $filters as $filter ) {
				// Skip this filter is no value is passed.
				if ( empty( $_GET[ $filter['id'] ] ) ) { // WPCS: input var okay. CSRF okay.
					continue;
				}

				// Skip this filter is no field type is passed.
				if ( empty( $filter['field'] ) ) {
					continue;
				}

				// Suppress Filters
				$query->set( 'suppress_filters', true );

				// Get value.
				$value = $this->get_sanitized_value( $filter['id'], 0 );

				// Meta query
				if ( 'meta' === $filter['field'] ) {
					/**
					 * Filter the meta query.
					 *
					 * @param array  The meta query.
					 * @param string The field ID.
					 */
					$meta_query = apply_filters( 'all_posts_filter_meta_query', array(
						'key' => $filter['id'],
						'compare' => ! empty( $filter['multiple'] ) ? 'IN' : '=',
						'value' => $value,
					), $filter['id'] );

					if ( is_array( $query->get( 'meta_query' ) ) ) {
						$meta_query = array_merge( $query->get( 'meta_query' ), array(
							$meta_query,
						) );
					} else {
						$meta_query = array( $meta_query );
					}

					$query->set( 'meta_query', $meta_query );
				}

				// Date query
				if ( 'date' === $filter['field'] ) {
					/**
					 * Filter the date query.
					 *
					 * @param array  The date query.
					 * @param string The field ID.
					 */
					$date_query = apply_filters( 'all_posts_filter_date_query', array(
						'after' => $value,
					), $filter['id'] );

					if ( is_array( $query->get( 'date_query' ) ) ) {
						$date_query = array_merge( $query->get( 'date_query' ), array(
							$date_query,
						) );
					} else {
						$date_query = array( $date_query );
					}

					$query->set( 'date_query', $date_query );
				}

				// Tax query
				if ( 'tax' === $filter['field'] ) {
					/**
					 * Filter the tax query.
					 *
					 * @param array  The date query.
					 * @param string The field ID.
					 */
					$tax_query = apply_filters( 'all_posts_filter_tax_query', array(
						'taxonomy' => $filter['tax'],
						'terms'    => $value,
					), $filter['id'] );

					if ( is_array( $query->get( 'tax_query' ) ) ) {
						$tax_query = array_merge( $query->get( 'tax_query' ), array(
							$tax_query,
						) );
					} else {
						$tax_query = array( $tax_query );
					}

					$query->set( 'tax_query', $tax_query );
				}

				// Post
				if ( 'post' === $filter['field'] ) {
					/**
					 * Filter the post query.
					 *
					 * @param array  The post query.
					 * @param string The field ID.
					 */
					$post_query = apply_filters(
						'all_posts_filter_post_query',
						$value,
						$filter['id']
					);

					$query->set( $filter['id'], $post_query );
				}

				/**
				 * Alter the actual query.
				 *
				 * @param string The field ID.
				 */
				$query = apply_filters( 'all_posts_filter_query', $query, $filter['id'] );
			} // End foreach().
		} // End if().
	}

	/**
	 * Get the current filters.
	 *
	 * @return array Filtered list of post filters.
	 */
	private function _get_filters() {
		$post_type = 'post';

		if ( isset( $_GET['post_type'] ) ) { // WPCS: input var okay.
			$post_type = sanitize_text_field( wp_unslash( $_GET['post_type'] ) ); // WPCS: input var okay.
		}

		/**
		 * Allow other parts of the site to add filters.
		 *
		 * @param array  $this->_filters List of filters.
		 * @param string $post_type      The current post type.
		 */
		return apply_filters( 'all_post_filters', $this->_filters, $post_type );
	}

	/**
	 * Output the filter's screen reader text.
	 *
	 * @param  array $filter The current filter.
	 * @return string        HTML string.
	 */
	private function _the_screen_reader_label( $filter ) {
		echo '<label class="screen-reader-text" for="' . esc_attr( $filter['id'] ) . '">' .
			esc_html__( 'Filter by' ) . ' ' . esc_attr( $filter['name'] ) .
		'</label>';
	}

	/**
	 * Output the filter's select dropdown.
	 *
	 * @param  array $filter The current filter.
	 * @return string        HTML string.
	 */
	private function _the_select_dropdown( $filter ) {
		// Custom HTML.
		if ( ! empty( $filter['html'] ) ) {
			echo $filter['html'];
			return;
		}

		// Get the currently selected value.
		$current_selection = $this->get_sanitized_value( $filter['id'], 0 );

		// Output the setting.
		echo '<select name="' . esc_attr( $filter['id'] ) . '" id="' . esc_attr( $filter['id'] ) . '" class="postform">';

		// Add a default option
		if ( false !== $filter['no_option'] ) {
			echo '<option value>' . esc_html( $filter['no_option'] ) . '</option>';
		}

		// Add options
		foreach ( $filter['options'] as $value => $name ) {
			echo '<option value="' . esc_attr( $value ) . '" ' . $this->selected( $current_selection, $value ) . '>' . esc_html( $name ) . '</option>';
		}
		echo '</select>';
	}

	/**
	 * Get sanitized value based on value type.
	 *
	 * @param  string $id The filter id.
	 * @return mixed      The sanitized value.
	 */
	public function get_sanitized_value( string $id, $default = null ) {
		if ( empty( $_GET[ $id ] ) ) {
			return $default;
		}

		if ( is_array( $_GET[ $id ] ) ) {
			$santizied_value = array_map( 'sanitize_text_field', wp_unslash( $_GET[ $id ] ) );
		} else {
			$santizied_value = sanitize_text_field( wp_unslash( $_GET[ $id ] ) );
		}

		return $santizied_value;
	}

	/**
	 * Determine the selection of a select field.
	 *
	 * @param  mixed  $current The current value.
	 * @param  string $value   The option value.
	 * @return string          HTML string.
	 */
	public function selected( $current, $value ) {
		if ( is_array( $current ) ) {
			return in_array( $value, $current ) ? 'selected="selected"' : '';
		}

		return selected( $current, $value, false );
	}

	/**
	 * The valid pst types to display the filters on.
	 *
	 * @return array Valid post types.
	 */
	public function post_types() {
		return [ 'post' ];
	}
}

All_Post_Filters::get_instance();