interface MailManagerInterface

interface MailManagerInterface extends PluginManagerInterface {
    
    /**
     * Composes and optionally sends an email message.
     *
     * Sending an email works with defining an email template (subject, text and
     * possibly email headers) and the replacement values to use in the
     * appropriate places in the template. Processed email templates are requested
     * from hook_mail() from the module sending the email. Any module can modify
     * the composed email message array using hook_mail_alter(). Finally
     * \Drupal::service('plugin.manager.mail')->mail() sends the email, which can
     * be reused if the exact same composed email is to be sent to multiple
     * recipients.
     *
     * Finding out what language to send the email with needs some consideration.
     * If you send email to a user, use
     * \Drupal\Core\Session\AccountInterface::getPreferredAdminLangcode(). If you
     * send email based on form values filled on the page, there are two
     * additional choices if you are not sending the email to a user on the site.
     * You can either use the language used to generate the page or the site
     * default language. See
     * Drupal\Core\Language\LanguageManagerInterface::getDefaultLanguage(). The
     * former is good if sending email to the person filling the form, the later
     * is good if you send email to an address previously set up (like contact
     * addresses in a contact form).
     *
     * Taking care of always using the proper language is even more important when
     * sending emails in a row to multiple users. Hook_mail() abstracts whether
     * the mail text comes from an administrator setting or is static in the
     * source code. It should also deal with common mail tokens, only receiving
     * $params which are unique to the actual email at hand.
     *
     * An example:
     *
     * @code
     *   function example_notify($accounts) {
     *     foreach ($accounts as $account) {
     *       $params['account'] = $account;
     *       // example_mail() will be called based on the first
     *       // MailManagerInterface->mail() parameter.
     *       \Drupal::service('plugin.manager.mail')->mail('example', 'notice', $account->mail, $langcode, $params);
     *     }
     *   }
     *
     *   function example_mail($key, &$message, $params) {
     *     $data['user'] = $params['account'];
     *     $options['langcode'] = $message['langcode'];
     *     user_mail_tokens($variables, $data, $options);
     *     switch($key) {
     *       case 'notice':
     *         // If the recipient can receive such notices by instant-message, do
     *         // not send by email.
     *         if (example_im_send($key, $message, $params)) {
     *           $message['send'] = FALSE;
     *           break;
     *         }
     *         $message['subject'] = t('Notification from @site', $variables, $options);
     *         $message['body'][] = t("Dear @username\n\nThere is new content available on the site.", $variables, $options);
     *         break;
     *     }
     *   }
     * @endcode
     *
     * Another example, which uses MailManagerInterface->mail() to format a
     * message for sending later:
     *
     * @code
     *   $params = array('current_conditions' => $data);
     *   $to = 'user@example.com';
     *   $message = \Drupal::service('plugin.manager.mail')->mail('example', 'notice', $to, $langcode, $params, FALSE);
     *   // Only add to the spool if sending was not canceled.
     *   if ($message['send']) {
     *     example_spool_message($message);
     *   }
     * @endcode
     *
     * @param string $module
     *   A module name to invoke hook_mail() on. The {$module}_mail() hook will be
     *   called to complete the $message structure which will already contain
     *   common defaults.
     * @param string $key
     *   A key to identify the email sent. The final message ID for email altering
     *   will be {$module}_{$key}.
     * @param string $to
     *   The email address or addresses where the message will be sent to. The
     *   formatting of this string will be validated with the
     *   @link http://php.net/manual/filter.filters.validate.php PHP email validation filter. @endlink
     *   Some examples are:
     *   - user@example.com
     *   - user@example.com, anotheruser@example.com
     *   - User <user@example.com>
     *   - User <user@example.com>, Another User <anotheruser@example.com>
     * @param string $langcode
     *   Language code to use to compose the email.
     * @param array $params
     *   (optional) Parameters to build the email. Use the key '_error_message'
     *   to provide translatable markup to display as a message if an error
     *   occurs, or set this to false to disable error display.
     * @param string|null $reply
     *   Optional email address to be used to answer.
     * @param bool $send
     *   If TRUE, call an implementation of
     *   \Drupal\Core\Mail\MailInterface->mail() to deliver the message, and
     *   store the result in $message['result']. Modules implementing
     *   hook_mail_alter() may cancel sending by setting $message['send'] to
     *   FALSE.
     *
     * @return array
     *   The $message array structure containing all details of the message. If
     *   already sent ($send = TRUE), then the 'result' element will contain the
     *   success indicator of the email, failure being already written to the
     *   watchdog. (Success means nothing more than the message being accepted at
     *   php-level, which still doesn't guarantee it to be delivered.)
     */
    public function mail($module, $key, $to, $langcode, $params = [], $reply = NULL, $send = TRUE);

}