"""The mail interface the outbox uses (AD-1, AD-11)."""

from __future__ import annotations

from dataclasses import dataclass
from typing import Protocol


class MailError(Exception):
    """Base class. Messages never contain the recipient or the text of the e-mail."""


class MailUnavailable(MailError):
    """The server could not take the message right now; trying again later may work."""


class MailRejected(MailError):
    """The server refused the message for good (for example an unknown recipient)."""


@dataclass(frozen=True)
class MailMessage:
    sender: str
    recipient: str
    subject: str
    body_text: str


class Mailer(Protocol):
    def send(self, message: MailMessage) -> None:
        """Hand the message to the mail server, or raise MailUnavailable or MailRejected."""
        ...