Create Template from WP Plugin

<?php

if(!class_exists('HRXPageTemplater')):
class HRXPageTemplater {

    /*
     * 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 HRXPageTemplater();
        }

        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.
        if ( version_compare( floatval( get_bloginfo( 'version' ) ), '4.7', '<' ) ) {

            // 4.6 and older
            add_filter(
                'page_attributes_dropdown_pages_args',
                array( $this, 'register_project_templates' )
            );

        } else {

            // Add a filter to the wp 4.7 version attributes metabox
            add_filter(
                'theme_page_templates', array( $this, 'add_new_template' )
            );

        }

        // 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(
            'templates/postal-code.php' => 'Postal Code',
            'templates/driveway-form.php' => 'Driveway Form',
        );

    }

    /**
     * Adds our template to the page dropdown for v4.7+
     *
     */
    public function add_new_template( $posts_templates ) {
        $posts_templates = array_merge( $posts_templates, $this->templates );
        return $posts_templates;
    }

    /**
     * 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 ) {

        // Get global post
        global $post;

        // Return template if post is empty
        if ( ! $post ) {
            return $template;
        }

        // Return default template if we don't have a custom one defined
        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
        return $template;

    }

}
add_action( 'plugins_loaded', array( 'HRXPageTemplater', 'get_instance' ) );
endif;