[Wordpress] Create page template from plugin

class.page-template.php

<?php
/**
 * Plugin Name: MHT Domain Search
 * Description: Page template domain registration for mega high tech.
 * Author: Lafif Astahdziq
 * Author URI: http://astahdziq.in/
 * Version: 1.0
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program. If not, see <http://www.gnu.org/licenses/>.
 *
 */
class PageTemplater {

		/**
         * A Unique Identifier
         */
		 protected $plugin_slug;

        /**
         * A reference to an instance of this class.
         */
        private static $instance;

        /**
         * The array of templates that this plugin tracks.
         */
        protected $templates;


        /**
         * Returns an instance of this class. 
         */
        public static function get_instance() {

        if( null == self::$instance ) {
                self::$instance = new PageTemplater();
        } 

        return self::$instance;

        } 

        /**
         * Initializes the plugin by setting filters and administration functions.
         */
        private function __construct() {

            $this->templates = array();


            // Add a filter to the attributes metabox to inject template into the cache.
            add_filter(
				'page_attributes_dropdown_pages_args',
				 array( $this, 'register_project_templates' ) 
			);


            // Add a filter to the save post to inject out template into the page cache
            add_filter(
				'wp_insert_post_data', 
				array( $this, 'register_project_templates' ) 
			);


            // Add a filter to the template include to determine if the page has our 
			// template assigned and return it's path
            add_filter(
				'template_include', 
				array( $this, 'view_project_template') 
			);


            // Add your templates to this array.
            $this->templates = array(
                    'domain-search.php'     => 'Domain Search',
            );
				
        } 


        /**
         * Adds our template to the pages cache in order to trick WordPress
         * into thinking the template file exists where it doens't really exist.
         *
         */

        public function register_project_templates( $atts ) {

            // Create the key used for the themes cache
            $cache_key = 'page_templates-' . md5( get_theme_root() . '/' . get_stylesheet() );

            // Retrieve the cache list. 
			// If it doesn't exist, or it's empty prepare an array
			$templates = wp_get_theme()->get_page_templates();
            if ( empty( $templates ) ) {
                    $templates = array();
            } 

            // New cache, therefore remove the old one
            wp_cache_delete( $cache_key , 'themes');

            // Now add our template to the list of templates by merging our templates
            // with the existing templates array from the cache.
            $templates = array_merge( $templates, $this->templates );

            // Add the modified cache to allow WordPress to pick it up for listing
            // available templates
            wp_cache_add( $cache_key, $templates, 'themes', 1800 );

            return $atts;

        } 

        /**
         * Checks if the template is assigned to the page
         */
        public function view_project_template( $template ) {

            global $post;

            if (!isset($this->templates[get_post_meta( 
				$post->ID, '_wp_page_template', true 
			)] ) ) {
				
                    return $template;
					
            } 

            $file = plugin_dir_path(__FILE__). get_post_meta( 
				$post->ID, '_wp_page_template', true 
			);
			
            // Just to be safe, we check if the file exist first
            if( file_exists( $file ) ) {
                return $file;
            } 
			else { 
                echo $file; 
            }

            return $template;

        } 


} 

add_action( 'plugins_loaded', array( 'PageTemplater', 'get_instance' ) );

?>