Simple implementation of multi-root class loader for PHP

Loader.php

<?php
/**
 * Created by PhpStorm.
 * @author: Alexey Tishchenko
 * @email: alexey@atishchenko.com
 * @UpWork: https://www.upwork.com/freelancers/~01ad7ed1a6ade4e02e
 * @date: 12.03.16
 */
namespace sjoorm\config;
/**
 * Class Loader is a simple implementation of an autoloader functionality
 */
class Loader {

    const EXTENSION = '.php';

    /** @var static instance */
    protected static $loader;
    /** @var array basic namespace names */
    protected $namespaces;
    /** @var array root directories */
    protected $roots;

    /**
     * Creates Loader class object
     */
    public static function init() {
        if(!static::$loader instanceof static) {
            static::$loader = new static();
        }

        return static::$loader;
    }

    /**
     * Adds classes root directory
     * @param string $root classes root dir
     * @return Loader self reference
     */
    public function addRoot($root) {
        $this->roots[] = $root;

        return $this;
    }

    /**
     * Adds classes basic namespace
     * @param string $namespace classes basic namespace (not presented by a subdirectory)
     * @return Loader self reference
     */
    public function addNamespace($namespace) {
        $this->namespaces[] = $namespace;

        return $this;
    }

    /**
     * Loader constructor
     */
    public function __construct() {
        $this->namespaces = [];
        $this->roots = [];

        spl_autoload_register([
            $this,
            'load',
        ]);
    }

    /**
     * @internal
     * Attempts to load specified class
     * @param string $className class to be registered
     */
    public function load($className) {
        $classNameParts = explode('\\', $className);
        foreach($this->namespaces as $namespace) {
            $namespaceParts = explode('\\', $namespace);
            $found = false;

            foreach($namespaceParts as $index => $part) {
                if($classNameParts[$index] === $part) {
                    unset($classNameParts[$index]);
                    $found = true;
                }
            }

            if($found) {
                break;
            }
        }

        foreach($this->roots as $root) {
            $file = $root . DIRECTORY_SEPARATOR . implode(DIRECTORY_SEPARATOR, $classNameParts) . self::EXTENSION;
            if(is_readable($file)) {
                require($file);

                break;
            }
        }
    }
}