class PhpMail

class PhpMail implements MailInterface {
    
    /**
     * A list of headers that can contain multiple email addresses.
     *
     * @see \Symfony\Component\Mime\Header\Headers::HEADER_CLASS_MAP
     */
    private const MAILBOX_LIST_HEADERS = [
        'from',
        'to',
        'reply-to',
        'cc',
        'bcc',
    ];
    
    /**
     * The configuration factory.
     *
     * @var \Drupal\Core\Config\ConfigFactoryInterface
     */
    protected $configFactory;
    
    /**
     * PhpMail constructor.
     */
    public function __construct() {
        $this->configFactory = \Drupal::configFactory();
    }
    
    /**
     * Concatenates and wraps the email body for plain-text mails.
     *
     * @param array $message
     *   A message array, as described in hook_mail_alter().
     *
     * @return array
     *   The formatted $message.
     */
    public function format(array $message) {
        // Join the body array into one string.
        $message['body'] = implode("\n\n", $message['body']);
        // Convert any HTML to plain-text.
        $message['body'] = MailFormatHelper::htmlToText($message['body']);
        // Wrap the mail body for sending.
        $message['body'] = MailFormatHelper::wrapMail($message['body']);
        return $message;
    }
    
    /**
     * Sends an email message.
     *
     * @param array $message
     *   A message array, as described in hook_mail_alter().
     *
     * @return bool
     *   TRUE if the mail was successfully accepted, otherwise FALSE.
     *
     * @see http://php.net/manual/function.mail.php
     * @see \Drupal\Core\Mail\MailManagerInterface::mail()
     */
    public function mail(array $message) {
        // If 'Return-Path' isn't already set in php.ini, we pass it separately
        // as an additional parameter instead of in the header.
        if (isset($message['headers']['Return-Path'])) {
            $return_path_set = strpos(ini_get('sendmail_path'), ' -f');
            if (!$return_path_set) {
                $message['Return-Path'] = $message['headers']['Return-Path'];
                unset($message['headers']['Return-Path']);
            }
        }
        $headers = new Headers();
        foreach ($message['headers'] as $name => $value) {
            if (in_array(strtolower($name), self::MAILBOX_LIST_HEADERS, TRUE)) {
                // Split values by comma, but ignore commas encapsulated in double
                // quotes.
                $value = str_getcsv($value, ',');
            }
            $headers->addHeader($name, $value);
        }
        $line_endings = Settings::get('mail_line_endings', PHP_EOL);
        // Prepare mail commands.
        $mail_subject = (new UnstructuredHeader('subject', $message['subject']))->getBodyAsString();
        // Note: email uses CRLF for line-endings. PHP's API requires LF
        // on Unix and CRLF on Windows. Drupal automatically guesses the
        // line-ending format appropriate for your system. If you need to
        // override this, adjust $settings['mail_line_endings'] in settings.php.
        $mail_body = preg_replace('@\\r?\\n@', $line_endings, $message['body']);
        $mail_headers = $headers->toString();
        // Since Drupal 10+ does not support PHP < 8, this block is only relevant for Drupal 9.x.
        // See: https://www.drupal.org/node/3270647
        if (version_compare(PHP_VERSION, '8.0.0') < 0) {
            // For headers, PHP's API suggests that we use CRLF normally,
            // but some MTAs incorrectly replace LF with CRLF. See #234403.
            // PHP 8+ requires headers to be separated by CRLF,
            // so we'll replace CRLF by LF only when using PHP < 8. See:
            // - https://bugs.php.net/bug.php?id=81158
            // - https://github.com/php/php-src/commit/6983ae751cd301886c966b84367fc7aaa1273b2d#diff-c6922cd89f6f75912eb377833ca1eddb7dd41de088be821024b8a0e340fed3df
            $mail_headers = str_replace("\r\n", "\n", $mail_headers);
            $mail_subject = str_replace("\r\n", "\n", $mail_subject);
        }
        if (substr(PHP_OS, 0, 3) != 'WIN') {
            // On most non-Windows systems, the "-f" option to the sendmail command
            // is used to set the Return-Path. There is no space between -f and
            // the value of the return path.
            // We validate the return path, unless it is equal to the site mail, which
            // we assume to be safe.
            $site_mail = $this->configFactory
                ->get('system.site')
                ->get('mail');
            $additional_params = isset($message['Return-Path']) && ($site_mail === $message['Return-Path'] || static::_isShellSafe($message['Return-Path'])) ? '-f' . $message['Return-Path'] : '';
            $mail_result = $this->doMail($message['to'], $mail_subject, $mail_body, $mail_headers, $additional_params);
        }
        else {
            // On Windows, PHP will use the value of sendmail_from for the
            // Return-Path header.
            $old_from = ini_get('sendmail_from');
            ini_set('sendmail_from', $message['Return-Path']);
            $mail_result = $this->doMail($message['to'], $mail_subject, $mail_body, $mail_headers);
            ini_set('sendmail_from', $old_from);
        }
        return $mail_result;
    }
    
    /**
     * Wrapper around PHP's mail() function.
     *
     * We suppress warnings and notices from mail() because of issues on some
     * hosts. The return value of this method will still indicate whether mail was
     * sent successfully.
     *
     * @param string $to
     *   Receiver, or receivers of the mail.
     * @param string $subject
     *   Subject of the email to be sent.
     * @param string $message
     *   Message to be sent.
     * @param array $additional_headers
     *   (optional) Array to be inserted at the end of the email header.
     * @param string $additional_params
     *   (optional) Can be used to pass additional flags as command line options.
     *
     * @see mail()
     */
    protected function doMail(string $to, string $subject, string $message, $additional_headers = [], string $additional_params = '') : bool {
        return @mail($to, $subject, $message, $additional_headers, $additional_params);
    }
    
    /**
     * Disallows potentially unsafe shell characters.
     *
     * Functionally similar to PHPMailer::isShellSafe() which resulted from
     * CVE-2016-10045. Note that escapeshellarg and escapeshellcmd are inadequate
     * for this purpose.
     *
     * @param string $string
     *   The string to be validated.
     *
     * @return bool
     *   True if the string is shell-safe.
     *
     * @see https://github.com/PHPMailer/PHPMailer/issues/924
     * @see https://github.com/PHPMailer/PHPMailer/blob/v5.2.21/class.phpmailer.php#L1430
     *
     * @todo Rename to ::isShellSafe() and/or discuss whether this is the correct
     *   location for this helper.
     */
    protected static function _isShellSafe($string) {
        if (escapeshellcmd($string) !== $string || !in_array(escapeshellarg($string), [
            "'{$string}'",
            "\"{$string}\"",
        ])) {
            return FALSE;
        }
        if (preg_match('/[^a-zA-Z0-9@_\\-.]/', $string) !== 0) {
            return FALSE;
        }
        return TRUE;
    }

}