class Message

class Message extends RawMessage {
    private Headers $headers;
    public function __construct(?Headers $headers = null, ?AbstractPart $body = null) {
        $this->headers = $headers ? clone $headers : new Headers();
    }
    public function __clone() {
        $this->headers = clone $this->headers;
        if (null !== $this->body) {
            $this->body = clone $this->body;
        }
    }
    
    /**
     * @return $this
     */
    public function setBody(?AbstractPart $body) : static {
        $this->body = $body;
        return $this;
    }
    public function getBody() : ?AbstractPart {
        return $this->body;
    }
    
    /**
     * @return $this
     */
    public function setHeaders(Headers $headers) : static {
        $this->headers = $headers;
        return $this;
    }
    public function getHeaders() : Headers {
        return $this->headers;
    }
    public function getPreparedHeaders() : Headers {
        $headers = clone $this->headers;
        if (!$headers->has('From')) {
            if (!$headers->has('Sender')) {
                throw new LogicException('An email must have a "From" or a "Sender" header.');
            }
            $headers->addMailboxListHeader('From', [
                $headers->get('Sender')
                    ->getAddress(),
            ]);
        }
        if (!$headers->has('MIME-Version')) {
            $headers->addTextHeader('MIME-Version', '1.0');
        }
        if (!$headers->has('Date')) {
            $headers->addDateHeader('Date', new \DateTimeImmutable());
        }
        // determine the "real" sender
        if (!$headers->has('Sender') && \count($froms = $headers->get('From')
            ->getAddresses()) > 1) {
            $headers->addMailboxHeader('Sender', $froms[0]);
        }
        if (!$headers->has('Message-ID')) {
            $headers->addIdHeader('Message-ID', $this->generateMessageId());
        }
        // remove the Bcc field which should NOT be part of the sent message
        $headers->remove('Bcc');
        return $headers;
    }
    public function toString() : string {
        if (null === ($body = $this->getBody())) {
            $body = new TextPart('');
        }
        return $this->getPreparedHeaders()
            ->toString() . $body->toString();
    }
    public function toIterable() : iterable {
        if (null === ($body = $this->getBody())) {
            $body = new TextPart('');
        }
        (yield $this->getPreparedHeaders()
            ->toString());
        yield from $body->toIterable();
    }
    public function ensureValidity() : void {
        if (!$this->headers
            ->get('To')?->getBody() && !$this->headers
            ->get('Cc')?->getBody() && !$this->headers
            ->get('Bcc')?->getBody()) {
            throw new LogicException('An email must have a "To", "Cc", or "Bcc" header.');
        }
        if (!$this->headers
            ->get('From')?->getBody() && !$this->headers
            ->get('Sender')?->getBody()) {
            throw new LogicException('An email must have a "From" or a "Sender" header.');
        }
        parent::ensureValidity();
    }
    public function generateMessageId() : string {
        if ($this->headers
            ->has('Sender')) {
            $sender = $this->headers
                ->get('Sender')
                ->getAddress();
        }
        elseif ($this->headers
            ->has('From')) {
            if (!($froms = $this->headers
                ->get('From')
                ->getAddresses())) {
                throw new LogicException('A "From" header must have at least one email address.');
            }
            $sender = $froms[0];
        }
        else {
            throw new LogicException('An email must have a "From" or a "Sender" header.');
        }
        return bin2hex(random_bytes(16)) . strstr($sender->getAddress(), '@');
    }
    public function __serialize() : array {
        return [
            $this->headers,
            $this->body,
        ];
    }
    public function __unserialize(array $data) : void {
        [
            $this->headers,
            $this->body,
        ] = $data;
    }

}