<?php
/**
 * Copyright 2007 Google Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
/**
 * SessionHandler using App Engine Memcache API.
 *
 * Nb. Does not yet implement session locking, as not available until
 * MemcacheD is available for PHP runtime.
 *
 */

namespace google\appengine\ext\session;

/**
 * Remove direct interaction with Memcache object for ease of mocking in tests.
 */
final class MemcacheContainer {

  private $memcache = null;

  /**
   * Initialises a Memcache instance
   */
  public function __construct() {
    $this->memcache = new \Memcache();
  }

  /**
   * Closes the Memcache instance.
   * @return bool true if successful, false otherwise
   */
  public function close() {
    return $this->memcache->close();
  }

  /**
   * Finds the value associated with input key, from Memcache.
   * @param string $key Input key from which to find value
   * @return string value associated with input key
   */
  public function get($key) {
    return $this->memcache->get($key, null);
  }

  /**
   * Inserts a key value pair, with expiry time, into Memcache.
   * @param string $key Input key to associate with the value
   * @param string $value Input value to be stored
   * @param int $expire Time until the pair can be garbage collected
   * @return bool true if successful, false otherwise
   */
  public function set($key, $value, $expire) {
    return $this->memcache->set($key, $value, null, $expire);
  }

  /**
   * Removes the key value pair, keyed with the input variable.
   * @param string $key Input key to remove key value pair
   * @return bool true if successful, false otherwise
   */
  public function delete($key) {
    return $this->memcache->delete($key);
  }
}

/**
 * A session handler interface using the GAE Memcache API.
 */
final class MemcacheSessionHandler implements \SessionHandlerInterface {

  const SESSION_PREFIX = '_ah_sess_';

  private $expire = null;
  private $memcacheContainer = null;

  /**
   * Constructs the session handler instance.
   * @param MemcacheContainer $memcacheContainer Optional, for mocking in tests
   */
  public function __construct($memcacheContainer = null) {
    if(isset($memcacheContainer)) {
      $this->memcacheContainer = $memcacheContainer;
    }
    else {
      $this->memcacheContainer = new MemcacheContainer();
    }

    // Get session max lifetime to leverage Memcache expire functionality.
    $this->expire = ini_get("session.gc_maxlifetime");
  }

  /**
   * Opens the session handler.
   * @param string $savePath Not used
   * @param string $sessionName Not ued
   * @return bool true if successful, false otherwise
   */
  public function open($savePath, $sessionName) {
    return true;
  }

  /**
   * Closes the session handler.
   * @return bool true if successful, false otherwise
   */
  public function close() {
    return $this->memcacheContainer->close();
  }

  /**
   * Read an element from Memcache with the given ID.
   * @param string $id Session ID associated with the data to be retrieved
   * @return string data associated with that ID or bool false on failure
   */
  public function read($id) {
    // TODO: Implement locking. b/7701850
    return $this->memcacheContainer->get(self::SESSION_PREFIX . $id);
  }

  /**
   * Write an element to Memcache with the given ID and data.
   * @param string $id Session ID associated with the data to be stored
   * @param string $data Data to be stored
   * @return bool true if successful, false otherwise
   */
  public function write($id, $data) {
    // TODO: Implement locking. b/7701850
    return $this->memcacheContainer->set(
        self::SESSION_PREFIX . $id, $data, $this->expire);
  }

  /**
   * Destroy the data associated with a particular session ID.
   * @param string $id Session ID associated with the data to be destroyed
   * @return bool true if successful, false otherwise
   */
  public function destroy($id) {
    return $this->memcacheContainer->delete(
        self::SESSION_PREFIX . $id);
  }

  /**
   * Garbage collection method - always returns true as this is handled by the
   * Memcache expire function.
   * @param int $maxlifetime Not used
   * @return bool true if successful, false otherwise
   */
  public function gc($maxlifetime) {
    // Handled by "expire" in Memcache.
    return true;
  }

  /**
   * Configure the session handler to use the Memcache API.
   * @param MemcacheContainer $memcacheContainer Optional, for mocking in tests
   */
  public static function configure($memcacheContainer = null) {
    $handler = new MemcacheSessionHandler($memcacheContainer);

    session_set_save_handler($handler, true);

    /**
     * Set so that it is clear that Memcache is being used for session handling,
     * as retrieving session.save_handler just returns "user".
     */
    session_save_path("Memcache");
  }
}