"""F056: ``create_session`` (and its delegate ``get_or_create_active_session``,
plus the L1868 channel-post adapter that routes through it) must not orphan an
ACTIVE session under concurrent posts.

``create_session`` does a plain check-then-create: read ``group.active_session_id``,
reuse if ACTIVE, else INSERT a new ACTIVE session and point the group at it.
Two concurrent posts can both miss the active session, both INSERT, and the
second ``flush`` overwrites ``group.active_session_id`` — the first session
stays ACTIVE but unreferenced (orphaned) forever. There is no DB uniqueness on
``(group_id, status='active')`` (tables.py:1121-1125 only carries indexes), so
nothing stops the double-insert.

The fix: lock the group row (``SELECT ... FOR UPDATE``) and re-read
``active_session_id`` under the lock before deciding to create, so concurrent
callers serialize per group and the loser reuses the winner's session.
"""

from __future__ import annotations

from typing import Any
from unittest.mock import AsyncMock, MagicMock

import pytest
from roboco.db.tables import SessionTable
from roboco.models.base import SessionStatus
from roboco.models.messaging import SessionCreateRequest
from roboco.services.messaging import MessagingService
from sqlalchemy.dialects import postgresql

_GROUP_ID = MagicMock(name="group-id")
_WINNER_SESSION_ID = MagicMock(name="winner-session-id")


@pytest.mark.asyncio
async def test_lock_group_emits_for_update() -> None:
    """``_lock_group`` must issue ``SELECT ... FOR UPDATE`` (the row lock that
    serializes concurrent session creation per group)."""
    session = AsyncMock()
    captured: list[Any] = []
    result_mock = MagicMock()
    result_mock.scalar_one_or_none.return_value = MagicMock(active_session_id=None)

    async def _exec(stmt: Any) -> Any:
        captured.append(stmt)
        return result_mock

    session.execute = AsyncMock(side_effect=_exec)
    svc = MessagingService(session)

    await svc._lock_group(_GROUP_ID)

    sql = str(
        captured[0].compile(
            dialect=postgresql.dialect(), compile_kwargs={"literal_binds": True}
        )
    )
    assert "FOR UPDATE" in sql


@pytest.mark.asyncio
async def test_create_session_race_loser_reuses_winner_under_lock() -> None:
    """Concurrent posts: caller A wins the race and links its session while
    caller B is between the check and the create. Caller B locks the group,
    re-reads ``active_session_id`` (now A's session), and reuses it — no second
    ACTIVE session is created (no orphan)."""
    session = AsyncMock()
    session.add = MagicMock()
    session.flush = AsyncMock()
    svc = MessagingService(session)

    winner = MagicMock(name="winner-session", status=SessionStatus.ACTIVE)
    svc.get_group = AsyncMock(return_value=MagicMock(active_session_id=None))
    # Under the lock, the group now reflects the winner's link.
    svc._lock_group = AsyncMock(
        return_value=MagicMock(active_session_id=_WINNER_SESSION_ID)
    )
    svc.get_session = AsyncMock(return_value=winner)

    result = await svc.create_session(SessionCreateRequest(group_id=_GROUP_ID))

    assert result is winner
    svc._lock_group.assert_awaited_once()
    svc.get_session.assert_awaited_once()
    session.add.assert_not_called()  # no orphaning INSERT
    session.flush.assert_not_awaited()


@pytest.mark.asyncio
async def test_create_session_creates_when_no_active_under_lock() -> None:
    """No race: under the lock there is still no active session, so create a
    new ACTIVE session and link it on the group (regression guard — the lock
    must not break the happy path)."""
    session = AsyncMock()
    session.add = MagicMock()
    session.flush = AsyncMock()
    svc = MessagingService(session)

    locked_group = MagicMock(active_session_id=None)
    svc.get_group = AsyncMock(return_value=MagicMock(active_session_id=None))
    svc._lock_group = AsyncMock(return_value=locked_group)
    svc.get_session = AsyncMock()  # should NOT be called (no active id)

    result = await svc.create_session(SessionCreateRequest(group_id=_GROUP_ID))

    assert isinstance(result, SessionTable)
    assert result.status == SessionStatus.ACTIVE
    svc._lock_group.assert_awaited_once()
    svc.get_session.assert_not_awaited()
    session.add.assert_called_once()
    assert session.flush.await_count >= 1