<?php

/**
 * @file
 * The Queue Mail module.
 */

/**
 * This is the name of our Drupal queue that stores emails waiting to be sent.
 */
define('QUEUE_MAIL_QUEUE_NAME', 'queue_mail');

/**
 * Get an instance of the mail queue.
 */
function _queue_mail_get_queue() {
  return DrupalQueue::get(QUEUE_MAIL_QUEUE_NAME, TRUE);
}

/**
 * Implements hook_menu().
 */
function queue_mail_menu() {
  $items = array();

  $items['admin/config/system/queue_mail'] = array(
    'title' => 'Queue Mail',
    'description' => 'Configure mails that should be queued for sending on cron instead of immediately.',
    'page callback' => 'drupal_get_form',
    'page arguments' => array('queue_mail_settings_form'),
    'access arguments' => array('administer site configuration'),
    'file' => 'queue_mail.admin.inc',
  );

  return $items;
}

/**
 * Implements hook_cron_queue_info().
 */
function queue_mail_cron_queue_info() {
  $queues[QUEUE_MAIL_QUEUE_NAME] = array(
    'worker callback' => 'queue_mail_send',
    'time' => variable_get('queue_mail_queue_time', 15),
    'skip on cron' => !variable_get('queue_mail_send_on_cron', TRUE),
  );
  return $queues;
}

/**
 * Implements hook_mail_alter().
 */
function queue_mail_mail_alter(&$message) {
  $mail_keys = variable_get('queue_mail_keys', '');

  if (drupal_match_path($message['id'], $mail_keys)) {
    // Store the message for sending on cron.
    _queue_mail_get_queue()->createItem($message);
    // And prevent the message from being sent instantly.
    $message['send'] = FALSE;
  }
}

/**
 * Implements hook_module_implements_alter().
 */
function queue_mail_module_implements_alter(&$implementations, $hook) {
  if ($hook == 'mail_alter') {
    // Ensure that our hook_mail_alter implementation is always called last.
    if (isset($implementations['queue_mail'])) {
      $group = $implementations['queue_mail'];
      unset($implementations['queue_mail']);
      // Now add it back, which will ensure we are called last.
      $implementations['queue_mail'] = $group;
    }
  }
}

/**
 * Email sending function, called via Drupal's queue processing.
 *
 * The body of this function is basically the latter half of drupal_mail(),
 * after the call to allow other modules to alter the message, at which point
 * queue_mail_mail_alter() popped the $message into the queue which is being
 * processed now.
 *
 * @param $message
 *   The message, as built and altered by drupal_mail().
 *
 * @see drupal_mail()
 * @see queue_mail_mail_alter()
 */
function queue_mail_send($message = array()) {

  // Invoke hook_queue_mail_send_alter() to allow all modules to alter the
  // queued e-mail.
  drupal_alter('queue_mail_send', $message);

  // Retrieve the responsible implementation for this message.
  $system = drupal_mail_system($message['module'], $message['key']);

  // Format the message body.
  $message = $system->format($message);

  // The original caller requested sending. Sending was canceled by one or
  // more hook_mail_alter() implementations. We set 'result' to NULL, because
  // FALSE indicates an error in sending.
  if (empty($message['send'])) {
    $message['result'] = NULL;
  }
  // Sending was originally requested and was not canceled.
  else {
    $message['result'] = $system->mail($message);
    // Log errors.
    if (!$message['result']) {
      watchdog('mail', 'Error sending e-mail (from %from to %to).', array('%from' => $message['from'], '%to' => $message['to']), WATCHDOG_ERROR);
    }
  }

  return $message;
}