Wordpress admin custom filter

twr-admin-post-filter.php

<?php 
/**
 * @author : Bhaskar K C
 * generic class for admin posts custom filters **dropdown filter on admin listing pages
 * Assuming column values are to be stored in post meta 
 */

if( ! class_exists('TWR_admin_post_filter') ) {

	class TWR_admin_post_filter {

		private $post_type;
		private $filter_options;
		private $filter_name;

		function __construct( $post_type, $filter_name, $filter_options ) {

			if( ! is_admin() ) {
				return false;
			}
			
			if( empty( $post_type ) || empty( $filter_options ) ) { 
				return true;
			}

			global $pagenow;

			$current_screen_post_type	= ( !empty( $_GET['post_type'] )? $_GET['post_type'] : null );

			if( $post_type != $current_screen_post_type && 'edit' != $pagenow ) return;

			$this->post_type 		= $post_type;
			$this->filter_name		= strtolower( $filter_name );
			$this->filter_options 	= $filter_options;

			add_action( 'admin_enqueue_scripts', array( &$this, 'twr_admin_filter_enqueue_script' ) );
			add_action( 'restrict_manage_posts', array ( &$this, 'twr_custom_admin_posts_filter' ) );
			add_action( 'pre_get_posts', array( &$this, 'twr_custom_pre_get_posts' ) );
		}

		function twr_admin_filter_enqueue_script() {
			// https://codex.wordpress.org/Function_Reference/wp_script_is
			if( wp_script_is( 'select2', 'enqueued' ) ) return;

			wp_enqueue_script( 'select2', trailingslashit( get_stylesheet_directory_uri() ) . 'admin-helper/script/inc/select2/select2.min.js', array('jquery') );

			wp_enqueue_style( 'select2', trailingslashit( get_stylesheet_directory_uri() ) . 'admin-helper/script/inc/select2/select2.css' );

			wp_localize_script( 'select2', 'select2_loaded', 'loaded' );
		}

		function twr_custom_admin_posts_filter () {
			
			if( empty( $this->filter_options ) && $this->post_type ) return;

			$filter_label = ucfirst( $this->filter_name );

			printf( "<label class='screen-reader-text' for='%s'> %s </label>", $this->filter_name, "Filter by {$filter_label}" );

			printf( "<select name='%s' id='%s' class='twr_admin_filter'>", $this->filter_name, $filter_label );
			
			foreach( $this->filter_options as $option_key => $option_title ) {
				printf( "<option name='%s'>%s</option>", wp_strip_all_tags( $option_key ), wp_strip_all_tags( $option_title ) );
			}

			printf( '</select>' );
		}

		function twr_custom_pre_get_posts( $query ) {
			
			global $pagenow;
			
			if( is_admin() && 'edit' == $pagenow && ! empty( $_GET[$this->filter_name] ) ) {

				$meta_query_args = array(
									'relation' => 'AND',
										array(
											'key'     => $this->filter_name,
											'value'   => $_GET[$this->filter_name],
											'compare' => '='
										)
									);

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

			}

		}
	}
}