class MailManager

class MailManager extends DefaultPluginManager implements MailManagerInterface {
    use MessengerTrait;
    use StringTranslationTrait;
    
    /**
     * The config factory.
     *
     * @var \Drupal\Core\Config\ConfigFactoryInterface
     */
    protected $configFactory;
    
    /**
     * The logger factory.
     *
     * @var \Drupal\Core\Logger\LoggerChannelFactoryInterface
     */
    protected $loggerFactory;
    
    /**
     * The renderer.
     *
     * @var \Drupal\Core\Render\RendererInterface
     */
    protected $renderer;
    
    /**
     * List of already instantiated mail plugins.
     *
     * @var array
     */
    protected $instances = [];
    
    /**
     * Constructs the MailManager object.
     *
     * @param \Traversable $namespaces
     *   An object that implements \Traversable which contains the root paths
     *   keyed by the corresponding namespace to look for plugin implementations.
     * @param \Drupal\Core\Cache\CacheBackendInterface $cache_backend
     *   Cache backend instance to use.
     * @param \Drupal\Core\Extension\ModuleHandlerInterface $module_handler
     *   The module handler to invoke the alter hook with.
     * @param \Drupal\Core\Config\ConfigFactoryInterface $config_factory
     *   The configuration factory.
     * @param \Drupal\Core\Logger\LoggerChannelFactoryInterface $logger_factory
     *   The logger channel factory.
     * @param \Drupal\Core\StringTranslation\TranslationInterface $string_translation
     *   The string translation service.
     * @param \Drupal\Core\Render\RendererInterface $renderer
     *   The renderer.
     */
    public function __construct(\Traversable $namespaces, CacheBackendInterface $cache_backend, ModuleHandlerInterface $module_handler, ConfigFactoryInterface $config_factory, LoggerChannelFactoryInterface $logger_factory, TranslationInterface $string_translation, RendererInterface $renderer) {
        parent::__construct('Plugin/Mail', $namespaces, $module_handler, 'Drupal\\Core\\Mail\\MailInterface', 'Drupal\\Core\\Annotation\\Mail');
        $this->alterInfo('mail_backend_info');
        $this->setCacheBackend($cache_backend, 'mail_backend_plugins');
        $this->configFactory = $config_factory;
        $this->loggerFactory = $logger_factory;
        $this->stringTranslation = $string_translation;
        $this->renderer = $renderer;
    }
    
    /**
     * Overrides PluginManagerBase::getInstance().
     *
     * Returns an instance of the mail plugin to use for a given message ID.
     *
     * The selection of a particular implementation is controlled via the config
     * 'system.mail.interface', which is a keyed array.  The default
     * implementation is the mail plugin whose ID is the value of 'default' key. A
     * more specific match first to key and then to module will be used in
     * preference to the default. To specify a different plugin for all mail sent
     * by one module, set the plugin ID as the value for the key corresponding to
     * the module name. To specify a plugin for a particular message sent by one
     * module, set the plugin ID as the value for the array key that is the
     * message ID, which is "${module}_${key}".
     *
     * For example to debug all mail sent by the user module by logging it to a
     * file, you might set the variable as something like:
     *
     * @code
     * array(
     *   'default' => 'php_mail',
     *   'user' => 'devel_mail_log',
     * );
     * @endcode
     *
     * Finally, a different system can be specified for a specific message ID (see
     * the $key param), such as one of the keys used by the contact module:
     *
     * @code
     * array(
     *   'default' => 'php_mail',
     *   'user' => 'devel_mail_log',
     *   'contact_page_autoreply' => 'null_mail',
     * );
     * @endcode
     *
     * Other possible uses for system include a mail-sending plugin that actually
     * sends (or duplicates) each message to SMS, Twitter, instant message, etc,
     * or a plugin that queues up a large number of messages for more efficient
     * bulk sending or for sending via a remote gateway so as to reduce the load
     * on the local server.
     *
     * @param array $options
     *   An array with the following key/value pairs:
     *   - module: (string) The module name which was used by
     *     \Drupal\Core\Mail\MailManagerInterface->mail() to invoke hook_mail().
     *   - key: (string) A key to identify the email sent. The final message ID
     *     is a string represented as {$module}_{$key}.
     *
     * @return \Drupal\Core\Mail\MailInterface
     *   A mail plugin instance.
     *
     * @throws \Drupal\Component\Plugin\Exception\InvalidPluginDefinitionException
     */
    public function getInstance(array $options) {
        $module = $options['module'];
        $key = $options['key'];
        $message_id = $module . '_' . $key;
        $configuration = $this->configFactory
            ->get('system.mail')
            ->get('interface');
        // Look for overrides for the default mail plugin, starting from the most
        // specific message_id, and falling back to the module name.
        if (isset($configuration[$message_id])) {
            $plugin_id = $configuration[$message_id];
        }
        elseif (isset($configuration[$module])) {
            $plugin_id = $configuration[$module];
        }
        else {
            $plugin_id = $configuration['default'];
        }
        if (empty($this->instances[$plugin_id])) {
            $this->instances[$plugin_id] = $this->createInstance($plugin_id);
        }
        return $this->instances[$plugin_id];
    }
    
    /**
     * {@inheritdoc}
     */
    public function mail($module, $key, $to, $langcode, $params = [], $reply = NULL, $send = TRUE) {
        // Mailing can invoke rendering (e.g., generating URLs, replacing tokens),
        // but e-mails are not HTTP responses: they're not cached, they don't have
        // attachments. Therefore we perform mailing inside its own render context,
        // to ensure it doesn't leak into the render context for the HTTP response
        // to the current request.
        return $this->renderer
            ->executeInRenderContext(new RenderContext(), function () use ($module, $key, $to, $langcode, $params, $reply, $send) {
            return $this->doMail($module, $key, $to, $langcode, $params, $reply, $send);
        });
    }
    
    /**
     * Composes and optionally sends an email message.
     *
     * @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.)
     *
     * @see \Drupal\Core\Mail\MailManagerInterface::mail()
     */
    public function doMail($module, $key, $to, $langcode, $params = [], $reply = NULL, $send = TRUE) {
        $site_config = $this->configFactory
            ->get('system.site');
        $site_mail = $site_config->get('mail');
        if (empty($site_mail)) {
            $site_mail = ini_get('sendmail_from');
        }
        // Bundle up the variables into a structured array for altering.
        $message = [
            'id' => $module . '_' . $key,
            'module' => $module,
            'key' => $key,
            'to' => $to,
            'from' => $site_mail,
            'reply-to' => $reply,
            'langcode' => $langcode,
            'params' => $params,
            'send' => TRUE,
            'subject' => '',
            'body' => [],
        ];
        // Build the default headers.
        $headers = [
            'MIME-Version' => '1.0',
            'Content-Type' => 'text/plain; charset=UTF-8; format=flowed; delsp=yes',
            'Content-Transfer-Encoding' => '8Bit',
            'X-Mailer' => 'Drupal',
        ];
        // To prevent email from looking like spam, the addresses in the Sender and
        // Return-Path headers should have a domain authorized to use the
        // originating SMTP server.
        $headers['Sender'] = $headers['Return-Path'] = $site_mail;
        // Make sure the site-name is a RFC-2822 compliant 'display-name'.
        $headers['From'] = MailHelper::formatDisplayName($site_config->get('name')) . ' <' . $site_mail . '>';
        if ($reply) {
            $headers['Reply-to'] = $reply;
        }
        $message['headers'] = $headers;
        // Build the email (get subject and body, allow additional headers) by
        // invoking hook_mail() on this module. We cannot use
        // moduleHandler()->invoke() as we need to have $message by reference in
        // hook_mail().
        if (function_exists($function = $module . '_mail')) {
            $function($key, $message, $params);
        }
        // Invoke hook_mail_alter() to allow all modules to alter the resulting
        // email.
        $this->moduleHandler
            ->alter('mail', $message);
        // Retrieve the responsible implementation for this message.
        $system = $this->getInstance([
            'module' => $module,
            'key' => $key,
        ]);
        // Attempt to convert relative URLs to absolute.
        foreach ($message['body'] as &$body_part) {
            if ($body_part instanceof MarkupInterface) {
                $body_part = Markup::create(Html::transformRootRelativeUrlsToAbsolute((string) $body_part, \Drupal::request()->getSchemeAndHttpHost()));
            }
        }
        // Format the message body.
        $message = $system->format($message);
        // Optionally send email.
        if ($send) {
            // The original caller requested sending. Sending was canceled by one or
            // more hook_mail_alter() implementations. We set 'result' to NULL,
            // because FALSE indicates an error in sending.
            if (empty($message['send'])) {
                $message['result'] = NULL;
            }
            else {
                // Ensure that subject is plain text. By default translated and
                // formatted strings are prepared for the HTML context and email
                // subjects are plain strings.
                if ($message['subject']) {
                    $message['subject'] = PlainTextOutput::renderFromHtml($message['subject']);
                }
                $message['result'] = $system->mail($message);
                // Log errors.
                if (!$message['result']) {
                    $this->loggerFactory
                        ->get('mail')
                        ->error('Error sending email (from %from to %to with reply-to %reply).', [
                        '%from' => $message['from'],
                        '%to' => $message['to'],
                        '%reply' => $message['reply-to'] ? $message['reply-to'] : $this->t('not set'),
                    ]);
                    $error_message = $params['_error_message'] ?? $this->t('Unable to send email. Contact the site administrator if the problem persists.');
                    if ($error_message) {
                        $this->messenger()
                            ->addError($error_message);
                    }
                }
            }
        }
        return $message;
    }

}