autoloader.php

<?php

class Psr4AutoloaderClass
{
    /**
     * An associative array where the key is a namespace prefix and the value
     * is an array of base directories for classes in that namespace.
     *
     * @var array
     */
    protected $prefixes = [];

    /**
     * Register loader with SPL autoloader stack.
     */
    public function register()
    {
        spl_autoload_register([$this, 'loadClass']);
    }

    /**
     * Adds a base directory for a namespace prefix.
     *
     * @param string $prefix   the namespace prefix
     * @param string $base_dir a base directory for class files in the
     *                         namespace
     * @param bool   $prepend  if true, prepend the base directory to the stack
     *                         instead of appending it; this causes it to be searched first rather
     *                         than last
     */
    public function addNamespace($prefix, $base_dir, $prepend = false)
    {
        $prefix = trim($prefix, '\\') . '\\';

        $base_dir = rtrim($base_dir, DIRECTORY_SEPARATOR) . '/';

        if (isset($this->prefixes[$prefix]) === false) {
            $this->prefixes[$prefix] = [];
        }

        if ($prepend) {
            array_unshift($this->prefixes[$prefix], $base_dir);
        } else {
            array_push($this->prefixes[$prefix], $base_dir);
        }
    }

    /**
     * Loads the class file for a given class name.
     *
     * @param string $class the fully-qualified class name
     *
     * @return mixed the mapped file name on success, or boolean false on
     *               failure
     */
    public function loadClass($class)
    {
        $prefix = $class;

        while (false !== $pos = strrpos($prefix, '\\')) {
            $prefix = substr($class, 0, $pos + 1);

            $relative_class = substr($class, $pos + 1);

            $mapped_file = $this->loadMappedFile($prefix, $relative_class);
            if ($mapped_file) {
                return $mapped_file;
            }

            $prefix = rtrim($prefix, '\\');
        }

        return false;
    }

    /**
     * Load the mapped file for a namespace prefix and relative class.
     *
     * @param string $prefix         the namespace prefix
     * @param string $relative_class the relative class name
     *
     * @return mixed boolean false if no mapped file can be loaded, or the
     *               name of the mapped file that was loaded
     */
    protected function loadMappedFile($prefix, $relative_class)
    {
        if (isset($this->prefixes[$prefix]) === false) {
            return false;
        }

        foreach ($this->prefixes[$prefix] as $base_dir) {
            $file = $base_dir
                . str_replace('\\', '/', $relative_class)
                . '.php';

            if ($this->requireFile($file)) {
                return $file;
            }
        }

        // never found it
        return false;
    }

    /**
     * If a file exists, require it from the file system.
     *
     * @param string $file the file to require
     *
     * @return bool true if the file exists, false if not
     */
    protected function requireFile($file)
    {
        if (file_exists($file)) {
            require $file;

            return true;
        }

        return false;
    }
}