ds-chat/backend/app/services/room_service.py

import uuid

from sqlalchemy import delete, func, select
from sqlalchemy.exc import IntegrityError
from sqlalchemy.ext.asyncio import AsyncSession
from sqlalchemy.orm import selectinload

from app.models import Message, MessageMention, Room, RoomMembership, RoomRole, User
from app.schemas.room import RoomCreate, RoomUpdate
from app.services.email_service import send_email


class DuplicateRoomError(Exception):
    pass


class RoomNotFoundError(Exception):
    pass


class RoomIsPrivateError(Exception):
    pass


class MembershipNotFoundError(Exception):
    pass


class CannotRemoveOwnerError(Exception):
    pass


class InsufficientRoleError(Exception):
    pass


class OwnerMustTransferError(Exception):
    pass


class TargetUserNotFoundError(Exception):
    pass


class AlreadyMemberError(Exception):
    pass


async def create_room(db: AsyncSession, owner_id: uuid.UUID, data: RoomCreate) -> Room:
    room = Room(
        name=data.name,
        description=data.description,
        is_private=data.is_private,
        owner_id=owner_id,
    )
    db.add(room)
    try:
        await db.flush()
    except IntegrityError as exc:
        await db.rollback()
        raise DuplicateRoomError() from exc

    db.add(RoomMembership(room_id=room.id, user_id=owner_id, role=RoomRole.owner))
    await db.commit()
    await db.refresh(room)
    return room


async def list_open_rooms(db: AsyncSession, user_id: uuid.UUID) -> list[tuple[Room, bool]]:
    result = await db.execute(
        select(Room)
        .where(Room.is_private.is_(False), Room.is_archived.is_(False))
        .options(selectinload(Room.memberships))
        .order_by(Room.created_at, Room.id)
    )
    rooms = result.scalars().all()
    return [
        (room, any(m.user_id == user_id for m in room.memberships)) for room in rooms
    ]


async def list_member_rooms(
    db: AsyncSession, user_id: uuid.UUID
) -> list[tuple[Room, RoomRole, bool, bool]]:
    last_message_at = (
        select(func.max(Message.created_at))
        .where(Message.room_id == Room.id)
        .correlate(Room)
        .scalar_subquery()
    )
    # Unread AND mentions this user specifically -- a stronger signal than
    # plain has_unread, surfaced as its own field so the sidebar can show a
    # visually distinct badge instead of (not alongside) the plain dot.
    has_unread_mention = (
        select(MessageMention.message_id)
        .join(Message, Message.id == MessageMention.message_id)
        .where(
            MessageMention.user_id == user_id,
            Message.room_id == Room.id,
            Message.created_at > RoomMembership.last_read_at,
        )
        .correlate(Room, RoomMembership)
        .exists()
    )
    result = await db.execute(
        select(
            Room, RoomMembership.role, RoomMembership.last_read_at, last_message_at, has_unread_mention
        )
        .join(RoomMembership, RoomMembership.room_id == Room.id)
        .where(RoomMembership.user_id == user_id)
        # A secondary key on the primary key -- without it, Postgres has no
        # obligation to return two same-instant rooms (a plausible tie:
        # bulk-created/migrated rooms, or just two created in quick
        # succession) in the same order on every call, which without a
        # stable order can visibly reshuffle the sidebar between one
        # device's fetch and another's.
        .order_by(Room.created_at, Room.id)
    )
    return [
        (room, role, last_message_at is not None and last_message_at > last_read_at, has_mention)
        for room, role, last_read_at, last_message_at, has_mention in result.all()
    ]


async def get_room(db: AsyncSession, room_id: uuid.UUID) -> Room:
    room = await db.get(Room, room_id)
    if room is None:
        raise RoomNotFoundError()
    return room


async def join_room(db: AsyncSession, room_id: uuid.UUID, user_id: uuid.UUID) -> RoomMembership:
    room = await get_room(db, room_id)
    if room.is_private:
        raise RoomIsPrivateError()

    result = await db.execute(
        select(RoomMembership).where(
            RoomMembership.room_id == room_id, RoomMembership.user_id == user_id
        )
    )
    membership = result.scalar_one_or_none()
    if membership is not None:
        return membership

    membership = RoomMembership(room_id=room_id, user_id=user_id, role=RoomRole.member)
    db.add(membership)
    await db.commit()
    await db.refresh(membership)
    return membership


async def add_member(
    db: AsyncSession, room: Room, target_user_id: uuid.UUID, base_url: str
) -> RoomMembership:
    target = await db.get(User, target_user_id)
    if target is None:
        raise TargetUserNotFoundError()

    existing = await db.execute(
        select(RoomMembership).where(
            RoomMembership.room_id == room.id, RoomMembership.user_id == target_user_id
        )
    )
    if existing.scalar_one_or_none() is not None:
        raise AlreadyMemberError()

    membership = RoomMembership(room_id=room.id, user_id=target_user_id, role=RoomRole.member)
    db.add(membership)
    await db.commit()

    await send_email(
        db,
        target.email,
        f"You've been added to #{room.name}",
        f"You've been added to the #{room.name} room on DS Chat.\n\n"
        f"Open the app: {base_url.rstrip('/')}",
    )

    result = await db.execute(
        select(RoomMembership)
        .where(RoomMembership.room_id == room.id, RoomMembership.user_id == target_user_id)
        .options(selectinload(RoomMembership.user))
    )
    return result.scalar_one()


async def update_room(db: AsyncSession, room: Room, data: RoomUpdate) -> Room:
    if data.name is not None:
        room.name = data.name
    if data.description is not None:
        room.description = data.description
    if data.is_private is not None:
        room.is_private = data.is_private
    try:
        await db.commit()
    except IntegrityError as exc:
        await db.rollback()
        raise DuplicateRoomError() from exc
    await db.refresh(room)
    return room


async def delete_room(db: AsyncSession, room: Room) -> None:
    # Explicit deletes rather than relying on ORM cascade + eager-loading —
    # simpler and more predictable in async code.
    await db.execute(delete(Message).where(Message.room_id == room.id))
    await db.execute(delete(RoomMembership).where(RoomMembership.room_id == room.id))
    await db.delete(room)
    await db.commit()


async def list_room_members(db: AsyncSession, room_id: uuid.UUID) -> list[RoomMembership]:
    result = await db.execute(
        select(RoomMembership)
        .where(RoomMembership.room_id == room_id)
        .options(selectinload(RoomMembership.user))
        .order_by(RoomMembership.joined_at)
    )
    return list(result.scalars().all())


async def _get_membership(
    db: AsyncSession, room_id: uuid.UUID, user_id: uuid.UUID
) -> RoomMembership:
    result = await db.execute(
        select(RoomMembership).where(
            RoomMembership.room_id == room_id, RoomMembership.user_id == user_id
        )
    )
    membership = result.scalar_one_or_none()
    if membership is None:
        raise MembershipNotFoundError()
    return membership


async def remove_member(
    db: AsyncSession, room_id: uuid.UUID, target_user_id: uuid.UUID, acting_role: RoomRole
) -> None:
    membership = await _get_membership(db, room_id, target_user_id)
    if membership.role == RoomRole.owner:
        raise CannotRemoveOwnerError()
    if membership.role == RoomRole.admin and acting_role != RoomRole.owner:
        raise InsufficientRoleError()

    await db.delete(membership)
    await db.commit()


async def change_member_role(
    db: AsyncSession, room_id: uuid.UUID, target_user_id: uuid.UUID, new_role: RoomRole
) -> RoomMembership:
    membership = await _get_membership(db, room_id, target_user_id)
    if membership.role == RoomRole.owner or new_role == RoomRole.owner:
        # Ownership changes only happen through transfer_ownership.
        raise InsufficientRoleError()

    membership.role = new_role
    await db.commit()
    result = await db.execute(
        select(RoomMembership)
        .where(RoomMembership.room_id == room_id, RoomMembership.user_id == target_user_id)
        .options(selectinload(RoomMembership.user))
    )
    return result.scalar_one()


async def transfer_ownership(
    db: AsyncSession, room: Room, current_owner_id: uuid.UUID, new_owner_user_id: uuid.UUID
) -> Room:
    new_owner_membership = await _get_membership(db, room.id, new_owner_user_id)
    current_owner_membership = await _get_membership(db, room.id, current_owner_id)

    new_owner_membership.role = RoomRole.owner
    current_owner_membership.role = RoomRole.admin
    room.owner_id = new_owner_user_id
    await db.commit()
    await db.refresh(room)
    return room


async def mark_room_read(db: AsyncSession, room_id: uuid.UUID, user_id: uuid.UUID) -> None:
    membership = await _get_membership(db, room_id, user_id)
    membership.last_read_at = func.now()
    await db.commit()


async def leave_room(db: AsyncSession, room_id: uuid.UUID, user_id: uuid.UUID) -> None:
    membership = await _get_membership(db, room_id, user_id)
    if membership.role == RoomRole.owner:
        raise OwnerMustTransferError()

    await db.delete(membership)
    await db.commit()