Autoload theme-specific controllers

ThemeAutoloader.php

<?php

namespace frontend\components;

use Yii;

/**
 * Class ThemeAutoloader
 *
 * @package frontend\components
 * @author Arleigh Dickerson
 */
class ThemeAutoloader {
    private $_themeName;
    private $_namespace;
    private $_themeDir;

    private function __construct($themeName, $namespace, $themeDir) {
        $this->_themeName = $themeName;
        $this->_namespace = ltrim($namespace, '\\');
        $this->_themeDir = Yii::getAlias($themeDir);
    }

    public function __invoke($className) {
        if (!$this->startsWith($className, $this->_namespace)) {
            return;
        }
        $themePath = $this->_themeDir . "/" . $this->_themeName;
        $classPath = substr(ltrim(str_replace('\\', '/', $className), '/'), strlen($this->_namespace . '\\'));
        $classFile = Yii::getAlias($themePath . '/' . $classPath . '.php', false);
        if ($classFile === false || !is_file($classFile)) {
            return;
        }
        include($classFile);
    }

    /**
     * Call this in bootstrap
     *
     * @param string $themeName
     * @param string $namespace
     * @param string $themeDir
     */
    public static function register($themeName, $namespace = null, $themeDir = null) {
        if ($namespace === null) {
            $namespace = basename(dirname(__DIR__));
        }
        if ($themeDir === null) {
            $themeDir = dirname(__DIR__) . '/themes';
        }
        spl_autoload_register(new static($themeName, $namespace, $themeDir), true, true);
    }

    private static function startsWith($str, $with) {
        return substr($str, 0, strlen($with)) == $with;
    }
}