"""Whose conversation this is.

A conversation is private to the user who started it — there is no sharing and
no admin view. One gate, used by every endpoint in the package, so the rule
cannot quietly differ between reading and writing.
"""

import uuid

from sqlalchemy import select
from sqlalchemy.ext.asyncio import AsyncSession
from sqlalchemy.orm import selectinload

from app.errors import ApiError
from app.models import Conversation, User


async def own_conversation(
    db: AsyncSession,
    conversation_id: uuid.UUID,
    user: User,
    *,
    with_messages: bool = False,
) -> Conversation:
    stmt = select(Conversation).where(
        Conversation.id == conversation_id, Conversation.user_id == user.id
    )
    if with_messages:
        stmt = stmt.options(selectinload(Conversation.messages))
    conversation = (await db.execute(stmt)).scalar_one_or_none()
    if conversation is None:
        # 404 rather than 403: someone else's conversation must not be
        # confirmed to exist.
        raise ApiError(404, "Conversation not found.", "not_found")
    return conversation