ExtensionGuesser.php

<?php

/*
 * This file is part of the Symfony package.
 *
 * (c) Fabien Potencier <fabien@symfony.com>
 *
 * For the full copyright and license information, please view the LICENSE
 * file that was distributed with this source code.
 */
namespace Symfony\Component\HttpFoundation\File\MimeType;


/**
 * A singleton mime type to file extension guesser.
 *
 * A default guesser is provided.
 * You can register custom guessers by calling the register()
 * method on the singleton instance.
 *
 * <code>
 * $guesser = ExtensionGuesser::getInstance();
 * $guesser->register(new MyCustomExtensionGuesser());
 * </code>
 *
 * The last registered guesser is preferred over previously registered ones.
 *
 */
class ExtensionGuesser implements ExtensionGuesserInterface {

  /**
   * The singleton instance
   *
   * @var ExtensionGuesser
   */
  private static $instance = null;

  /**
   * All registered ExtensionGuesserInterface instances
   *
   * @var array
   */
  protected $guessers = array();

  /**
   * Returns the singleton instance
   *
   * @return ExtensionGuesser
   */
  public static function getInstance() {
    if (null === self::$instance) {
      self::$instance = new self();
    }
    return self::$instance;
  }

  /**
   * Registers all natively provided extension guessers
   */
  private function __construct() {
    $this
      ->register(new MimeTypeExtensionGuesser());
  }

  /**
   * Registers a new extension guesser
   *
   * When guessing, this guesser is preferred over previously registered ones.
   *
   * @param ExtensionGuesserInterface $guesser
   */
  public function register(ExtensionGuesserInterface $guesser) {
    array_unshift($this->guessers, $guesser);
  }

  /**
   * Tries to guess the extension
   *
   * The mime type is passed to each registered mime type guesser in reverse order
   * of their registration (last registered is queried first). Once a guesser
   * returns a value that is not NULL, this method terminates and returns the
   * value.
   *
   * @param string $mimeType The mime type
   * @return string          The guessed extension or NULL, if none could be guessed
   */
  public function guess($mimeType) {
    foreach ($this->guessers as $guesser) {
      $extension = $guesser
        ->guess($mimeType);
      if (null !== $extension) {
        break;
      }
    }
    return $extension;
  }

}