Autoloader.php

<?php
/**
 * Autoloader class.
 *
 * @since 0.1
 */

namespace CiviCRM_WP_REST;

class Autoloader {

	/**
	 * Instance.
	 *
	 * @since 0.1
	 * @var string
	 */
	private static $instance = null;

	/**
	 * Namespace.
	 *
	 * @since 0.1
	 * @var string
	 */
	private $namespace = 'CiviCRM_WP_REST';

	/**
	 * Autoloader directory sources.
	 *
	 * @since 0.1
	 * @var array
	 */
	private static $source_directories = [];

	/**
	 * Constructor.
	 *
	 * @since 0.1
	 */
	private function __construct() {

		$this->register_autoloader();

	}

	/**
	 * Creates an instance of this class.
	 *
	 * @since 0.1
	 */
	private static function instance() {

		if ( ! self::$instance ) self::$instance = new self;

	}

	/**
	 * Adds a directory source.
	 *
	 * @since 0.1
	 * @param string $source The source path
	 */
	public static function add_source( string $source_path ) {

		// make sure we have an instance
		self::instance();

		if ( ! is_readable( trailingslashit( $source_path ) ) )
			return \WP_Error( 'civicrm_wp_rest_error', sprintf( __( 'The source %s is not readable.', 'civicrm' ), $source ) );

		self::$source_directories[] = $source_path;

	}

	/**
	 * Registers the autoloader.
	 *
	 * @since 0.1
	 * @return bool Wehather the autoloader has been registered or not
	 */
	private function register_autoloader() {

		return spl_autoload_register( [ $this, 'autoload' ] );

	}

	/**
	 * Loads the classes.
	 *
	 * @since 0.1
	 * @param string $class_name The class name to load
	 */
	private function autoload( $class_name ) {

		if ( false === strpos( $class_name, $this->namespace ) ) return;

		$parts = explode( '\\', $class_name );

		// remove namespace and join class path
		$class_path = str_replace( '_', '-', implode( DIRECTORY_SEPARATOR, array_slice( $parts, 1 ) ) );

		array_map( function( $source_path ) use ( $class_path ) {

			$path = $source_path . $class_path . '.php';

			if ( ! file_exists( $path ) ) return;

			require $path;

		}, static::$source_directories );

	}

}