from dataclasses import dataclass, field
from datetime import datetime
from typing import List, Set

from mail_intake.models.message import MailIntakeMessage


@dataclass
class MailIntakeThread:
    """
    Canonical internal representation of an email thread.

    Threads are the primary unit of reasoning for correspondence
    workflows (job applications, interviews, follow-ups, etc.).
    """

    thread_id: str
    normalized_subject: str

    participants: Set[str] = field(default_factory=set)
    messages: List[MailIntakeMessage] = field(default_factory=list)

    last_activity_at: datetime | None = None

    def add_message(self, message: MailIntakeMessage) -> None:
        """
        Add a message to the thread and update derived fields.
        """
        self.messages.append(message)

        if message.from_email:
            self.participants.add(message.from_email)

        if self.last_activity_at is None or message.timestamp > self.last_activity_at:
            self.last_activity_at = message.timestamp