<?php

/**
 * See #394445 for an explanation of why this thing even exists.
 *
 * @task recipients   Managing Recipients
 */
final class PhabricatorMetaMTAMail extends PhabricatorMetaMTADAO {

  const STATUS_QUEUE = 'queued';
  const STATUS_SENT  = 'sent';
  const STATUS_FAIL  = 'fail';
  const STATUS_VOID  = 'void';

  const MAX_RETRIES   = 250;
  const RETRY_DELAY   = 5;

  protected $parameters;
  protected $status;
  protected $message;
  protected $retryCount;
  protected $nextRetry;
  protected $relatedPHID;

  private $excludePHIDs = array();
  private $overrideNoSelfMail = false;

  public function __construct() {

    $this->status     = self::STATUS_QUEUE;
    $this->retryCount = 0;
    $this->nextRetry  = time();
    $this->parameters = array();

    parent::__construct();
  }

  public function getConfiguration() {
    return array(
      self::CONFIG_SERIALIZATION => array(
        'parameters'  => self::SERIALIZATION_JSON,
      ),
    ) + parent::getConfiguration();
  }

  protected function setParam($param, $value) {
    $this->parameters[$param] = $value;
    return $this;
  }

  protected function getParam($param, $default = null) {
    return idx($this->parameters, $param, $default);
  }

  /**
   * Set tags (@{class:MetaMTANotificationType} constants) which identify the
   * content of this mail in a general way. These tags are used to allow users
   * to opt out of receiving certain types of mail, like updates when a task's
   * projects change.
   *
   * @param list<const> List of @{class:MetaMTANotificationType} constants.
   * @return this
   */
  public function setMailTags(array $tags) {
    $this->setParam('mailtags', $tags);
    return $this;
  }

  /**
   * In Gmail, conversations will be broken if you reply to a thread and the
   * server sends back a response without referencing your Message-ID, even if
   * it references a Message-ID earlier in the thread. To avoid this, use the
   * parent email's message ID explicitly if it's available. This overwrites the
   * "In-Reply-To" and "References" headers we would otherwise generate. This
   * needs to be set whenever an action is triggered by an email message. See
   * T251 for more details.
   *
   * @param   string The "Message-ID" of the email which precedes this one.
   * @return  this
   */
  public function setParentMessageID($id) {
    $this->setParam('parent-message-id', $id);
    return $this;
  }

  public function getParentMessageID() {
    return $this->getParam('parent-message-id');
  }

  public function getSubject() {
    return $this->getParam('subject');
  }

  public function addTos(array $phids) {
    $phids = array_unique($phids);
    $this->setParam('to', $phids);
    return $this;
  }

  public function addRawTos(array $raw_email) {
    $this->setParam('raw-to', $raw_email);
    return $this;
  }

  public function addCCs(array $phids) {
    $phids = array_unique($phids);
    $this->setParam('cc', $phids);
    return $this;
  }

  public function setExcludeMailRecipientPHIDs($exclude) {
    $this->excludePHIDs = $exclude;
    return $this;
  }
  private function getExcludeMailRecipientPHIDs() {
    return $this->excludePHIDs;
  }

  public function getOverrideNoSelfMailPreference() {
    return $this->overrideNoSelfMail;
  }

  public function setOverrideNoSelfMailPreference($override) {
    $this->overrideNoSelfMail = $override;
    return $this;
  }

  public function getTranslation(array $objects) {
    $default_translation = PhabricatorEnv::getEnvConfig('translation.provider');
    $return = null;
    $recipients = array_merge(
      idx($this->parameters, 'to', array()),
      idx($this->parameters, 'cc', array()));
    foreach (array_select_keys($objects, $recipients) as $object) {
      $translation = null;
      if ($object instanceof PhabricatorUser) {
        $translation = $object->getTranslation();
      }
      if (!$translation) {
        $translation = $default_translation;
      }
      if ($return && $translation != $return) {
        return $default_translation;
      }
      $return = $translation;
    }

    if (!$return) {
      $return = $default_translation;
    }

    return $return;
  }

  public function addPHIDHeaders($name, array $phids) {
    foreach ($phids as $phid) {
      $this->addHeader($name, '<'.$phid.'>');
    }
    return $this;
  }

  public function addHeader($name, $value) {
    $this->parameters['headers'][] = array($name, $value);
    return $this;
  }

  public function addAttachment(PhabricatorMetaMTAAttachment $attachment) {
    $this->parameters['attachments'][] = $attachment->toDictionary();
    return $this;
  }

  public function getAttachments() {
    $dicts = $this->getParam('attachments');

    $result = array();
    foreach ($dicts as $dict) {
      $result[] = PhabricatorMetaMTAAttachment::newFromDictionary($dict);
    }
    return $result;
  }

  public function setAttachments(array $attachments) {
    assert_instances_of($attachments, 'PhabricatorMetaMTAAttachment');
    $this->setParam('attachments', mpull($attachments, 'toDictionary'));
    return $this;
  }

  public function setFrom($from) {
    $this->setParam('from', $from);
    return $this;
  }

  public function setReplyTo($reply_to) {
    $this->setParam('reply-to', $reply_to);
    return $this;
  }

  public function setSubject($subject) {
    $this->setParam('subject', $subject);
    return $this;
  }

  public function setSubjectPrefix($prefix) {
    $this->setParam('subject-prefix', $prefix);
    return $this;
  }

  public function setVarySubjectPrefix($prefix) {
    $this->setParam('vary-subject-prefix', $prefix);
    return $this;
  }

  public function setBody($body) {
    $this->setParam('body', $body);
    return $this;
  }

  public function getBody() {
    return $this->getParam('body');
  }

  public function setIsHTML($html) {
    $this->setParam('is-html', $html);
    return $this;
  }

  public function getSimulatedFailureCount() {
    return nonempty($this->getParam('simulated-failures'), 0);
  }

  public function setSimulatedFailureCount($count) {
    $this->setParam('simulated-failures', $count);
    return $this;
  }

  public function getWorkerTaskID() {
    return $this->getParam('worker-task');
  }

  public function setWorkerTaskID($id) {
    $this->setParam('worker-task', $id);
    return $this;
  }

  /**
   * Flag that this is an auto-generated bulk message and should have bulk
   * headers added to it if appropriate. Broadly, this means some flavor of
   * "Precedence: bulk" or similar, but is implementation and configuration
   * dependent.
   *
   * @param bool  True if the mail is automated bulk mail.
   * @return this
   */
  public function setIsBulk($is_bulk) {
    $this->setParam('is-bulk', $is_bulk);
    return $this;
  }

  /**
   * Use this method to set an ID used for message threading. MetaMTA will
   * set appropriate headers (Message-ID, In-Reply-To, References and
   * Thread-Index) based on the capabilities of the underlying mailer.
   *
   * @param string  Unique identifier, appropriate for use in a Message-ID,
   *                In-Reply-To or References headers.
   * @param bool    If true, indicates this is the first message in the thread.
   * @return this
   */
  public function setThreadID($thread_id, $is_first_message = false) {
    $this->setParam('thread-id', $thread_id);
    $this->setParam('is-first-message', $is_first_message);
    return $this;
  }

  /**
   * Save a newly created mail to the database and attempt to send it
   * immediately if the server is configured for immediate sends. When
   * applications generate new mail they should generally use this method to
   * deliver it. If the server doesn't use immediate sends, this has the same
   * effect as calling save(): the mail will eventually be delivered by the
   * MetaMTA daemon.
   *
   * @return this
   */
  public function saveAndSend() {
    $ret = null;

    if (PhabricatorEnv::getEnvConfig('metamta.send-immediately')) {
      $ret = $this->sendNow();
    } else {
      $ret = $this->save();
    }

    return $ret;
  }

  protected function didWriteData() {
    parent::didWriteData();

    if (!$this->getWorkerTaskID()) {
      $mailer_task = PhabricatorWorker::scheduleTask(
        'PhabricatorMetaMTAWorker',
        $this->getID());

      $this->setWorkerTaskID($mailer_task->getID());
      $this->save();
    }
  }


  public function buildDefaultMailer() {
    return PhabricatorEnv::newObjectFromConfig('metamta.mail-adapter');
  }


  /**
   * Attempt to deliver an email immediately, in this process.
   *
   * @param bool  Try to deliver this email even if it has already been
   *              delivered or is in backoff after a failed delivery attempt.
   * @param PhabricatorMailImplementationAdapter Use a specific mail adapter,
   *              instead of the default.
   *
   * @return void
   */
  public function sendNow(
    $force_send = false,
    PhabricatorMailImplementationAdapter $mailer = null) {

    if ($mailer === null) {
      $mailer = $this->buildDefaultMailer();
    }

    if (!$force_send) {
      if ($this->getStatus() != self::STATUS_QUEUE) {
        throw new Exception("Trying to send an already-sent mail!");
      }

      if (time() < $this->getNextRetry()) {
        throw new Exception("Trying to send an email before next retry!");
      }
    }

    try {
      $params = $this->parameters;
      $phids = array();

      foreach ($params as $key => $value) {
        switch ($key) {
          case 'to':
            $params[$key] = $this->buildToList();
            break;
          case 'cc':
            $params[$key] = $this->buildCCList();
            break;
        }
      }

      foreach ($params as $key => $value) {
        switch ($key) {
          case 'from':
            $value = array($value);
            /* fallthrough */
          case 'to':
          case 'cc':
            foreach ($value as $phid) {
              $type = phid_get_type($phid);
              $phids[$phid] = $type;
            }
            break;
        }
      }

      $this->loadEmailAndNameDataFromPHIDs($phids);

      $default = PhabricatorEnv::getEnvConfig('metamta.default-address');
      if (empty($params['from'])) {
        $mailer->setFrom($default);
      } else {
        $from = $params['from'];

        if (!PhabricatorEnv::getEnvConfig('metamta.can-send-as-user')) {
          if (empty($params['reply-to'])) {
            $params['reply-to'] = $phids[$from]['email'];
            $params['reply-to-name'] = $phids[$from]['name'];
          }
          $mailer->setFrom(
            $default,
            $phids[$from]['name']);
          unset($params['from']);
        }
      }

      $is_first = idx($params, 'is-first-message');
      unset($params['is-first-message']);

      $is_threaded = (bool)idx($params, 'thread-id');

      $reply_to_name = idx($params, 'reply-to-name', '');
      unset($params['reply-to-name']);

      $add_cc = array();
      $add_to = array();

      foreach ($params as $key => $value) {
        switch ($key) {
          case 'from':
            $mailer->setFrom($phids[$from]['email']);
            break;
          case 'reply-to':
            $mailer->addReplyTo($value, $reply_to_name);
            break;
          case 'to':
            $to_emails = $this->filterSendable($value, $phids);
            if ($to_emails) {
              $add_to = array_merge($add_to, $to_emails);
            }
            break;
          case 'raw-to':
            $add_to = array_merge($add_to, $value);
            break;
          case 'cc':
            $cc_emails = $this->filterSendable($value, $phids);
            if ($cc_emails) {
              $add_cc = $cc_emails;
            }
            break;
          case 'headers':
            foreach ($value as $pair) {
              list($header_key, $header_value) = $pair;

              // NOTE: If we have \n in a header, SES rejects the email.
              $header_value = str_replace("\n", " ", $header_value);

              $mailer->addHeader($header_key, $header_value);
            }
            break;
          case 'attachments':
            $value = $this->getAttachments();
            foreach ($value as $attachment) {
              $mailer->addAttachment(
                $attachment->getData(),
                $attachment->getFilename(),
                $attachment->getMimeType());
            }
            break;
          case 'body':
            $mailer->setBody($value);
            break;
          case 'subject':
            // Only try to use preferences if everything is multiplexed, so we
            // get consistent behavior.
            $use_prefs = self::shouldMultiplexAllMail();

            $prefs = null;
            if ($use_prefs) {

              // If multiplexing is enabled, some recipients will be in "Cc"
              // rather than "To". We'll move them to "To" later (or supply a
              // dummy "To") but need to look for the recipient in either the
              // "To" or "Cc" fields here.
              $target_phid = head(idx($params, 'to', array()));
              if (!$target_phid) {
                $target_phid = head(idx($params, 'cc', array()));
              }

              if ($target_phid) {
                $user = id(new PhabricatorUser())->loadOneWhere(
                  'phid = %s',
                  $target_phid);
                if ($user) {
                  $prefs = $user->loadPreferences();
                }
              }
            }

            $subject = array();

            if ($is_threaded) {
              $add_re = PhabricatorEnv::getEnvConfig('metamta.re-prefix');

              if ($prefs) {
                $add_re = $prefs->getPreference(
                  PhabricatorUserPreferences::PREFERENCE_RE_PREFIX,
                  $add_re);
              }

              if ($add_re) {
                $subject[] = 'Re:';
              }
            }

            $subject[] = trim(idx($params, 'subject-prefix'));

            $vary_prefix = idx($params, 'vary-subject-prefix');
            if ($vary_prefix != '') {
              $use_subject = PhabricatorEnv::getEnvConfig(
                'metamta.vary-subjects');

              if ($prefs) {
                $use_subject = $prefs->getPreference(
                  PhabricatorUserPreferences::PREFERENCE_VARY_SUBJECT,
                  $use_subject);
              }

              if ($use_subject) {
                $subject[] = $vary_prefix;
              }
            }

            $subject[] = $value;

            $mailer->setSubject(implode(' ', array_filter($subject)));
            break;
          case 'is-html':
            if ($value) {
              $mailer->setIsHTML(true);
            }
            break;
          case 'is-bulk':
            if ($value) {
              if (PhabricatorEnv::getEnvConfig('metamta.precedence-bulk')) {
                $mailer->addHeader('Precedence', 'bulk');
              }
            }
            break;
          case 'thread-id':

            // NOTE: Gmail freaks out about In-Reply-To and References which
            // aren't in the form "<string@domain.tld>"; this is also required
            // by RFC 2822, although some clients are more liberal in what they
            // accept.
            $domain = PhabricatorEnv::getEnvConfig('metamta.domain');
            $value = '<'.$value.'@'.$domain.'>';

            if ($is_first && $mailer->supportsMessageIDHeader()) {
              $mailer->addHeader('Message-ID',  $value);
            } else {
              $in_reply_to = $value;
              $references = array($value);
              $parent_id = $this->getParentMessageID();
              if ($parent_id) {
                $in_reply_to = $parent_id;
                // By RFC 2822, the most immediate parent should appear last
                // in the "References" header, so this order is intentional.
                $references[] = $parent_id;
              }
              $references = implode(' ', $references);
              $mailer->addHeader('In-Reply-To', $in_reply_to);
              $mailer->addHeader('References',  $references);
            }
            $thread_index = $this->generateThreadIndex($value, $is_first);
            $mailer->addHeader('Thread-Index', $thread_index);
            break;
          case 'mailtags':
            // Handled below.
            break;
          case 'subject-prefix':
          case 'vary-subject-prefix':
            // Handled above.
            break;
          default:
            // Just discard.
        }
      }

      if (!$add_to && !$add_cc) {
        $this->setStatus(self::STATUS_VOID);
        $this->setMessage(
          "Message has no valid recipients: all To/CC are disabled or ".
          "configured not to receive this mail.");
        return $this->save();
      }

      $mailer->addHeader('X-Phabricator-Sent-This-Message', 'Yes');
      $mailer->addHeader('X-Mail-Transport-Agent', 'MetaMTA');

      // Some clients respect this to suppress OOF and other auto-responses.
      $mailer->addHeader('X-Auto-Response-Suppress', 'All');

      // If the message has mailtags, filter out any recipients who don't want
      // to receive this type of mail.
      $mailtags = $this->getParam('mailtags');
      if ($mailtags) {
        $tag_header = array();
        foreach ($mailtags as $mailtag) {
          $tag_header[] = '<'.$mailtag.'>';
        }
        $tag_header = implode(', ', $tag_header);
        $mailer->addHeader('X-Phabricator-Mail-Tags', $tag_header);
      }

      // Some mailers require a valid "To:" in order to deliver mail. If we
      // don't have any "To:", try to fill it in with a placeholder "To:".
      // If that also fails, move the "Cc:" line to "To:".
      if (!$add_to) {
        $placeholder_key = 'metamta.placeholder-to-recipient';
        $placeholder = PhabricatorEnv::getEnvConfig($placeholder_key);
        if ($placeholder !== null) {
          $add_to = array($placeholder);
        } else {
          $add_to = $add_cc;
          $add_cc = array();
        }
      }

      $mailer->addTos($add_to);
      if ($add_cc) {
        $mailer->addCCs($add_cc);
      }
    } catch (Exception $ex) {
      $this->setStatus(self::STATUS_FAIL);
      $this->setMessage($ex->getMessage());
      return $this->save();
    }

    if ($this->getRetryCount() < $this->getSimulatedFailureCount()) {
      $ok = false;
      $error = 'Simulated failure.';
    } else {
      try {
        $ok = $mailer->send();
        $error = null;
      } catch (Exception $ex) {
        $ok = false;
        $error = $ex->getMessage()."\n".$ex->getTraceAsString();
      }
    }

    if (!$ok) {
      $this->setMessage($error);
      if ($this->getRetryCount() > self::MAX_RETRIES) {
        $this->setStatus(self::STATUS_FAIL);
      } else {
        $this->setRetryCount($this->getRetryCount() + 1);
        $next_retry = time() + ($this->getRetryCount() * self::RETRY_DELAY);
        $this->setNextRetry($next_retry);
      }
    } else {
      $this->setStatus(self::STATUS_SENT);
    }

    return $this->save();
  }

  public static function getReadableStatus($status_code) {
    static $readable = array(
      self::STATUS_QUEUE => "Queued for Delivery",
      self::STATUS_FAIL  => "Delivery Failed",
      self::STATUS_SENT  => "Sent",
      self::STATUS_VOID  => "Void",
    );
    $status_code = coalesce($status_code, '?');
    return idx($readable, $status_code, $status_code);
  }

  private function generateThreadIndex($seed, $is_first_mail) {
    // When threading, Outlook ignores the 'References' and 'In-Reply-To'
    // headers that most clients use. Instead, it uses a custom 'Thread-Index'
    // header. The format of this header is something like this (from
    // camel-exchange-folder.c in Evolution Exchange):

    /* A new post to a folder gets a 27-byte-long thread index. (The value
     * is apparently unique but meaningless.) Each reply to a post gets a
     * 32-byte-long thread index whose first 27 bytes are the same as the
     * parent's thread index. Each reply to any of those gets a
     * 37-byte-long thread index, etc. The Thread-Index header contains a
     * base64 representation of this value.
     */

    // The specific implementation uses a 27-byte header for the first email
    // a recipient receives, and a random 5-byte suffix (32 bytes total)
    // thereafter. This means that all the replies are (incorrectly) siblings,
    // but it would be very difficult to keep track of the entire tree and this
    // gets us reasonable client behavior.

    $base = substr(md5($seed), 0, 27);
    if (!$is_first_mail) {
      // Not totally sure, but it seems like outlook orders replies by
      // thread-index rather than timestamp, so to get these to show up in the
      // right order we use the time as the last 4 bytes.
      $base .= ' '.pack('N', time());
    }

    return base64_encode($base);
  }

  private function loadEmailAndNameDataFromPHIDs(array &$phids) {
    $users = array();
    $xusrs = array();
    $mlsts = array();
    // first iteration - group by types to do data fetches
    foreach ($phids as $phid => $type) {
      switch ($type) {
        case PhabricatorPHIDConstants::PHID_TYPE_USER:
          $users[] = $phid;
          break;
        case PhabricatorPHIDConstants::PHID_TYPE_XUSR:
          $xusrs[] = $phid;
          break;
        case PhabricatorPHIDConstants::PHID_TYPE_MLST:
          $mlsts[] = $phid;
          break;
      }
    }

    $user_emails = array();
    if ($users) {
      $user_emails = id(new PhabricatorUserEmail())->loadAllWhere(
        'userPHID IN (%Ls) AND isPrimary = 1', $users);
      $users = id(new PhabricatorUser())->loadAllWhere(
        'phid IN (%Ls)', $users);
      $user_emails = mpull($user_emails, null, 'getUserPHID');
      $users = mpull($users, null, 'getPHID');
    }

    if ($xusrs) {
      $xusrs = id(new PhabricatorExternalAccount())->loadAllWhere(
        'phid IN (%Ls)', $xusrs);
      $xusrs = mpull($xusrs, null, 'getPHID');
    }

    if ($mlsts) {
      $mlsts = id(new PhabricatorMetaMTAMailingList())->loadAllWhere(
        'phid IN (%Ls)', $mlsts);
      $mlsts = mpull($mlsts, null, 'getPHID');
    }

    // second iteration - create entries for each phid
    $default = PhabricatorEnv::getEnvConfig('metamta.default-address');
    foreach ($phids as $phid => &$value) {
      $name = '';
      $email = $default;
      $is_mailable = false;
      switch ($value) {
        case PhabricatorPHIDConstants::PHID_TYPE_USER:
          $user = idx($users, $phid);
          if ($user) {
            $name = $this->getUserName($user);
            $is_mailable = !$user->getIsDisabled()
                        && !$user->getIsSystemAgent();
          }
          $email = isset($user_emails[$phid]) ?
                   $user_emails[$phid]->getAddress() :
                   $default;
          break;
        case PhabricatorPHIDConstants::PHID_TYPE_XUSR:
          $xusr = $xusrs[$phid];
          if ($xusr) {
            $name = $xusr->getDisplayName();
            $email = $xusr->getAccountID();
            $accountType = $xusr->getAccountType();
            if ($accountType == 'email') {
              $is_mailable = true;
            }
          }
          break;
        case PhabricatorPHIDConstants::PHID_TYPE_MLST:
          $mlst = $mlsts[$phid];
          if ($mlst) {
            $name = $mlst->getName();
            $email = $mlst->getEmail();
            $is_mailable = true;
          }
          break;
      }
      $value = array(
        'name' => $name,
        'email' => $email,
        'mailable' => $is_mailable,
      );
    }
  }

  /**
   * Small helper function to make sure we format the username properly as
   * specified by the `metamta.user-address-format` configuration value.
   */
  private function getUserName($user) {
    $format = PhabricatorEnv::getEnvConfig('metamta.user-address-format');

    switch ($format) {
      case 'short':
        $name = $user->getUserName();
        break;
      case 'real':
        $name = $user->getRealName();
        break;
      case 'full':
      default:
        $name = $user->getFullName();
        break;
    }

    return $name;
  }

  private function filterSendable($value, $phids) {
    $result = array();
    foreach ($value as $phid) {
      if (isset($phids[$phid]) && $phids[$phid]['mailable']) {
        $result[$phid] = $phids[$phid]['email'];
      }
    }
    return $result;
  }

  public static function shouldMultiplexAllMail() {
    return PhabricatorEnv::getEnvConfig('metamta.one-mail-per-recipient');
  }


/* -(  Managing Recipients  )------------------------------------------------ */


  /**
   * Get all of the recipients for this mail, after preference filters are
   * applied. This list has all objects to whom delivery will be attempted, but
   * does not exclude recipeints two whom delivery may be impossible.
   *
   * @return  list<phid>  A list of all recipients to whom delivery will be
   *                      attempted.
   * @task recipients
   */
  public function buildRecipientList() {
    return $this->resolveRecipients(
      array_merge(
        $this->getRawToPHIDs(),
        $this->getRawCCPHIDs()));
  }


  /**
   * Filter out duplicate, invalid, or excluded recipients from a PHID list.
   *
   * @param   list<phid>  Unfiltered recipients.
   * @return  list<phid>  Filtered recipients.
   *
   * @task recipients
   */
  private function resolveRecipients(array $phids) {
    if (!$phids) {
      return array();
    }

    $phids = array_fuse($phids);


    // Exclude PHIDs explicitly marked for exclusion. We use this to prevent
    // recipients of an accidental "Reply All" from receiving the followup
    // mail from Phabricator.
    $exclude = $this->getExcludeMailRecipientPHIDs();
    $exclude = array_fill_keys($exclude, true);
    $phids = array_diff_key($phids, $exclude);


    // If the actor is a recipient and has configured their preferences not to
    // send them mail about their own actions, drop them from the recipient
    // list.
    $from = $this->getParam('from');
    if (isset($phids[$from])) {
      $from_user = id(new PhabricatorUser())->loadOneWhere(
        'phid = %s',
        $from);
      if ($from_user && !$this->getOverrideNoSelfMailPreference()) {
        $pref_key = PhabricatorUserPreferences::PREFERENCE_NO_SELF_MAIL;
        $exclude_self = $from_user
          ->loadPreferences()
          ->getPreference($pref_key);
        if ($exclude_self) {
          unset($phids[$from]);
        }
      }
    }


    // Exclude all recipients who have set preferences to not receive this type
    // of email (for example, a user who says they don't want emails about task
    // CC changes).
    $tags = $this->getParam('mailtags');
    if ($tags && $phids) {
      $all_prefs = id(new PhabricatorUserPreferences())->loadAllWhere(
        'userPHID in (%Ls)',
        $phids);
      $all_prefs = mpull($all_prefs, null, 'getUserPHID');

      foreach ($phids as $phid) {
        $prefs = idx($all_prefs, $phid);
        if (!$prefs) {
          continue;
        }

        $user_mailtags = $prefs->getPreference(
          PhabricatorUserPreferences::PREFERENCE_MAILTAGS,
          array());

        // The user must have elected to receive mail for at least one
        // of the mailtags.
        $send = false;
        foreach ($tags as $tag) {
          if (idx($user_mailtags, $tag, true)) {
            $send = true;
            break;
          }
        }

        if (!$send) {
          unset($phids[$phid]);
        }
      }
    }

    return array_keys($phids);
  }


  /**
   * @task recipients
   */
  private function buildToList() {
    return $this->resolveRecipients($this->getRawToPHIDs());
  }


  /**
   * @task recipients
   */
  private function buildCCList() {
    return $this->resolveRecipients($this->getRawCCPHIDs());
  }


  /**
   * @task recipients
   */
  private function getRawToPHIDs() {
    $to = $this->getParam('to', array());
    return $this->filterRawPHIDList($to);
  }


  /**
   * @task recipients
   */
  private function getRawCCPHIDs() {
    $cc = $this->getParam('cc', array());
    return $this->filterRawPHIDList($cc);
  }


  /**
   * @task recipients
   */
  private function filterRawPHIDList(array $list) {
    $list = array_filter($list);
    $list = array_unique($list);
    return array_values($list);
  }

}