2. Chat App

class UserProfile(models.Model):
    username = models.CharField(
        max_length=70,
        unique=True,
    )

    email = models.EmailField(
        unique=True,
    )

    bio = models.TextField(
        null=True,
        blank=True,
    )


class Message(models.Model):
    sender = models.ForeignKey(
        to=UserProfile,
        related_name="sent_messages",
        on_delete=models.CASCADE,
    )

    receiver = models.ForeignKey(
        to=UserProfile,
        related_name="received_messages",
        on_delete=models.CASCADE,
    )

    content = models.TextField()

    timestamp = models.DateTimeField(
        auto_now_add=True,
    )

    is_read = models.BooleanField(
        default=False,
    )

    def mark_as_read(self) -> None:
        self.is_read = True

    def mark_as_unread(self) -> None:
        self.is_read = False

    def reply_to_message(self, reply_content: str, receiver: UserProfile) -> object:
        return Message(
            sender=self.receiver,
            receiver=receiver,
            content=reply_content
        )

    def forward_message(self, sender: UserProfile, receiver: UserProfile) -> object:
        return Message(
            sender=sender,
            receiver=receiver,
            content=self.content,
        )