<?php
/* This class is part of the XP framework
 *
 * $Id$ 
 */

  uses('util.collections.MD5HashImplementation');

  /**
   * Provides hashing functionality for maps.
   * 
   * Basic usage:
   * <code>
   *   $hashCode= HashProvider::hashOf($string);
   * </code>
   *
   * Uses MD5 as default hashing implementation. To change the hashing
   * implementation to be used, use the following:
   * <code>
   *   HashProvider::getInstance()->setImplementation(new MyHashImplementation());
   * </code>
   * 
   * @see      xp://util.collections.DJBX33AHashImplementation
   * @see      xp://util.collections.MD5HashImplementation
   * @see      xp://util.collections.Map
   * @purpose  Hashing
   */
  class HashProvider extends Object {
    protected static
      $instance = NULL;

    public
      $impl     = NULL;

    static function __static() {
      self::$instance= new self();
      
      // Workaround for bugs in older PHP versions, see MD5HexHashImplementation's
      // class apidoc for an explanation. Earlier versions returned LONG_MAX for
      // hex numbers larger than LONG_MAX. Use 2^64 + 1 as hex literal and see if
      // it's "truncated", using the slower hexdec(md5()) implementation then.
      if (LONG_MAX === @0x20c49ba5e35423) {
        $impl= XPClass::forName('util.collections.MD5HexHashImplementation')->newInstance();
      } else {
        $impl= new MD5HashImplementation();
      }
      self::$instance->setImplementation($impl);
    }

    /**
     * Constructor
     *
     */
    protected function __construct() {
    }
    
    /**
     * Retrieve sole instance of this object
     *
     * @return  util.collections.HashProvider
     */
    public static function getInstance() {
      return self::$instance;
    }
    
    /**
     * Returns hash for a given string
     *
     * @param   string str
     * @return  int
     */
    public static function hashOf($str) {
      return self::getInstance()->impl->hashOf($str);
    }

    /**
     * Set hashing implementation
     * 
     * @param   util.collections.HashImplementation impl
     * @throws  lang.IllegalArgumentException when impl is not a HashImplementation
     */
    public function setImplementation(HashImplementation $impl) {
      $this->impl= $impl;
    }

    /**
     * Get hashing implementation
     * 
     * @return  util.collections.HashImplementation
     */
    public function getImplementation() {
      return $this->impl;
    }
  }
?>