Psr4Autoloader.php

<?php
/**
 * A general-purpose implementation that includes the optional functionality
 * of allowing multiple base directories for a single namespace prefix.
 */
class Psr4Autoloader
{
    const EXTENSION = '.php';
    /**
     * 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.
     * 
     * @param bool $prepend If true, will prepend the autoloader on
     * the autoload queue instead of appending it.
     * @return $this
     */
    public function register($prepend = false)
    {
        spl_autoload_register([$this, 'loadClass'], true, $prepend);
        return $this;
    }

    /**
     * Unregister loader with SPL autoloader stack.
     * 
     * @return void
     */
    public function unregister()
    {
        spl_autoload_unregister([$this, 'loadClass']);
    }
    
    /**
     * Adds a base directory for a namespace prefix.
     *
     * @param string $prefix The namespace prefix.
     * @param string $baseDir A base directory for class files in the namespace.
     * @param bool $prepend If true, prepend the base directory to the stack.
     * instead of appending it, this causes it to be searched first rather than
     * last.
     * @return this
     */
    public function addPrefix($prefix, $baseDir, $prepend = false)
    {
        // Normalize namespace prefix.
        $prefix = trim($prefix, '\\') . '\\';
        // Normalize the base directory with a trailing separator.
        $baseDir = realpath($baseDir) . DIRECTORY_SEPARATOR;
        // Initialize the namespace prefix array.
        if (!isset($this->prefixes[$prefix])) {
            $this->prefixes[$prefix] = [];
        }
        // Retain the base directory for the namespace prefix.
        if ($prepend) {
            array_unshift($this->prefixes[$prefix], $baseDir);
        } else {
            array_push($this->prefixes[$prefix], $baseDir);
        }
        return $this;
    }
    
    /**
     * Loads the class file for a given class name.
     *
     * @param string $class The fully-qualified class name.
     * @return bool
     */
    public function loadClass($class)
    {
        if (strpos($class, '\\') !== false) {
            foreach ($this->prefixes as $namespace => $baseDirs) {
                if (strpos($class, $namespace) === 0) {
                    $path = substr($class, strlen($namespace));
                    $path = str_replace('\\', DIRECTORY_SEPARATOR, $path) . self::EXTENSION;
                    foreach ($baseDirs as $baseDir) {
                        $file = $baseDir . $path;
                        // If the mapped file exists, require it
                        if ($this->requireFile($file)) {
                            return $file;
                        }
                    }
                }
            }
        }
        // Never found a mapped file
        return false;
    }

    /**
     * If a file exists, require it from the file system.
     * 
     * @param string $file The file to require.
     * @return bool
     */
    protected function requireFile($file)
    {
        if (file_exists($file)) {
            require $file;
            return true;
        }
        return false;
    }
}