WordPress page template from plugin

Page_Templates.php

<?php

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

	/**
	 * Initializes the plugin by setting filters and administration functions.
	 */
	public 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(
			'templates/instantsearch.php' => array(
				'name' 		=> 'Instantsearch',
				'styles' 	=> array( 'algolia-instantsearch' ),
				'scripts'   => array( 'algolia-instantsearch-page' ),
			),
		);
	}

	public function get_template_names() {
		$template_names = array();

		foreach ( $this->templates as $key => $data ) {
			$template_names[ $key ] = $data['name'];
		}

		return $template_names;
	}


	/**
	 * 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->get_template_names() );

		// 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 ( null === $post ) {
			return $template;
		}

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

		$file = plugin_dir_path(__FILE__) . $page_template;

		// Just to be safe, we check if the file exist first
		if ( ! file_exists( $file ) ) {
			return $template;
		}

		$this->enqueue_scripts( $page_template );
		$this->enqueue_styles( $page_template );

		return $file;
	}

	private function enqueue_scripts( $template ) {

		if ( ! isset( $this->templates[ $template ]['scripts'] ) ) {
			return;
		}

		foreach ( $this->templates[ $template ]['scripts'] as $handle ) {
			add_action( 'wp_enqueue_scripts', function() use ( $handle ) {
				wp_enqueue_script( $handle );
			} );
		}
	}

	private function enqueue_styles( $template ) {
		if ( ! isset( $this->templates[ $template ]['styles'] ) ) {
			return;
		}

		foreach ( $this->templates[ $template ]['styles'] as $handle ) {
			add_action( 'wp_enqueue_scripts', function() use ( $handle ) {
				wp_enqueue_style( $handle );
			} );
		}
	}
}