class DelayedEnvelope

final class DelayedEnvelope extends Envelope {
    private bool $senderSet = false;
    private bool $recipientsSet = false;
    public function __construct(Message $message) {
    }
    public function setSender(Address $sender) : void {
        parent::setSender($sender);
        $this->senderSet = true;
    }
    public function getSender() : Address {
        if (!$this->senderSet) {
            parent::setSender(self::getSenderFromHeaders($this->message
                ->getHeaders()));
        }
        return parent::getSender();
    }
    public function setRecipients(array $recipients) : void {
        parent::setRecipients($recipients);
        $this->recipientsSet = (bool) parent::getRecipients();
    }
    
    /**
     * @return Address[]
     */
    public function getRecipients() : array {
        if ($this->recipientsSet) {
            return parent::getRecipients();
        }
        return self::getRecipientsFromHeaders($this->message
            ->getHeaders());
    }
    private static function getRecipientsFromHeaders(Headers $headers) : array {
        $recipients = [];
        foreach ([
            'to',
            'cc',
            'bcc',
        ] as $name) {
            foreach ($headers->all($name) as $header) {
                foreach ($header->getAddresses() as $address) {
                    $recipients[] = $address;
                }
            }
        }
        return $recipients;
    }
    private static function getSenderFromHeaders(Headers $headers) : Address {
        if ($sender = $headers->get('Sender')) {
            return $sender->getAddress();
        }
        if ($return = $headers->get('Return-Path')) {
            return $return->getAddress();
        }
        if ($from = $headers->get('From')) {
            return $from->getAddresses()[0];
        }
        throw new LogicException('Unable to determine the sender of the message.');
    }

}