from __future__ import annotations

from abc import ABC, abstractmethod
from collections.abc import Sequence
from dataclasses import dataclass


@dataclass(frozen=True)
class Message:
    title: str
    body: str
    link: str | None
    urgent: bool


class NotifierError(Exception):
    pass


class Notifier(ABC):
    @abstractmethod
    def send(self, messages: Sequence[Message]) -> None:
        """Deliver messages. Raise NotifierError if delivery failed."""