"""Unit tests for database wiring helpers."""

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

import pytest
from sqlalchemy.exc import SQLAlchemyError
from sqlalchemy.ext.asyncio import AsyncEngine, AsyncSession

import backend.database as database


@pytest.fixture(autouse=True)
def reset_database_singletons(monkeypatch: pytest.MonkeyPatch) -> None:
    """Reset database singletons before each test."""
    database.reset_runtime_state()


def test_get_database_url_requires_configuration(
    monkeypatch: pytest.MonkeyPatch,
) -> None:
    """Database URL helper should fail when DATABASE_URL is not set."""
    monkeypatch.delenv("DATABASE_URL", raising=False)

    with pytest.raises(database.DatabaseConfigurationError):
        database.get_database_url()


def test_get_database_url_rewrites_postgresql_scheme(
    monkeypatch: pytest.MonkeyPatch,
) -> None:
    """Database URL helper should normalize URLs for SQLAlchemy async psycopg."""
    monkeypatch.setenv("DATABASE_URL", "postgresql://user:pass@db:5432/app")

    assert database.get_database_url() == "postgresql+psycopg://user:pass@db:5432/app"


def test_get_database_url_keeps_existing_scheme(
    monkeypatch: pytest.MonkeyPatch,
) -> None:
    """Database URL helper should keep already-normalized URLs unchanged."""
    monkeypatch.setenv("DATABASE_URL", "postgresql+psycopg://user:pass@db:5432/app")

    assert database.get_database_url() == "postgresql+psycopg://user:pass@db:5432/app"


def test_get_engine_is_singleton(monkeypatch: pytest.MonkeyPatch) -> None:
    """Engine helper should create engine once and reuse it."""
    created: list[tuple[str, bool]] = []
    engine = cast("AsyncEngine", AsyncMock(spec=AsyncEngine))

    def fake_create_async_engine(url: str, *, pool_pre_ping: bool) -> AsyncEngine:
        created.append((url, pool_pre_ping))
        return engine

    monkeypatch.setenv("DATABASE_URL", "postgresql://user:pass@db:5432/app")
    monkeypatch.setattr(database, "create_async_engine", fake_create_async_engine)

    first = database.get_engine()
    second = database.get_engine()

    assert first is engine
    assert second is engine
    assert created == [("postgresql+psycopg://user:pass@db:5432/app", True)]


def test_get_sessionmaker_is_singleton(monkeypatch: pytest.MonkeyPatch) -> None:
    """Sessionmaker helper should create one factory and reuse it."""
    engine = cast("AsyncEngine", AsyncMock(spec=AsyncEngine))
    monkeypatch.setattr(database, "get_engine", lambda: engine)

    first = database.get_sessionmaker()
    second = database.get_sessionmaker()

    assert first is second
    assert first.kw["bind"] is engine
    assert first.kw["expire_on_commit"] is False


@pytest.mark.asyncio
async def test_get_session_raises_database_error_when_db_not_configured(
    monkeypatch: pytest.MonkeyPatch,
) -> None:
    """Session helper should raise a database-layer config error when missing."""

    def raise_config_error() -> Any:
        raise database.DatabaseConfigurationError("missing")

    monkeypatch.setattr(database, "get_sessionmaker", raise_config_error)

    generator = database.get_session()
    with pytest.raises(database.DatabaseConfigurationError):
        await anext(generator)


@pytest.mark.asyncio
async def test_get_session_yields_scoped_session(
    monkeypatch: pytest.MonkeyPatch,
) -> None:
    """Session dependency should yield one session and close context afterwards."""
    fake_session = cast("AsyncSession", AsyncMock(spec=AsyncSession))

    class SessionContextManager:
        """Minimal async context manager used by the fake session factory."""

        exited = False

        async def __aenter__(self) -> AsyncSession:
            return fake_session

        async def __aexit__(self, *args: object) -> None:
            self.exited = True

    context_manager = SessionContextManager()

    class SessionFactory:
        """Callable session factory returning an async context manager."""

        def __call__(self) -> SessionContextManager:
            return context_manager

    monkeypatch.setattr(database, "get_sessionmaker", lambda: SessionFactory())

    generator = database.get_session()
    yielded = await anext(generator)

    assert yielded is fake_session

    with pytest.raises(StopAsyncIteration):
        await anext(generator)

    assert context_manager.exited is True


@pytest.mark.asyncio
async def test_probe_database_success() -> None:
    """Database probe should return True when SELECT 1 succeeds."""
    session = cast("AsyncSession", AsyncMock(spec=AsyncSession))
    session.execute = AsyncMock(return_value=1)

    assert await database.probe_database(session) is True


@pytest.mark.asyncio
async def test_probe_database_failure() -> None:
    """Database probe should return False when SQLAlchemy raises an error."""
    session = cast("AsyncSession", AsyncMock(spec=AsyncSession))
    session.execute = AsyncMock(side_effect=SQLAlchemyError("db unavailable"))

    assert await database.probe_database(session) is False


@pytest.mark.asyncio
async def test_dispose_engine_resets_global_state(
    monkeypatch: pytest.MonkeyPatch,
) -> None:
    """Dispose helper should call engine dispose and reset cached globals."""

    create_calls = 0
    created_engines: list[AsyncEngine] = []

    def fake_create_async_engine(url: str, *, pool_pre_ping: bool) -> AsyncEngine:  # noqa: ARG001
        nonlocal create_calls
        create_calls += 1
        engine = cast("AsyncEngine", AsyncMock(spec=AsyncEngine))
        engine.dispose = AsyncMock()
        created_engines.append(engine)
        return engine

    monkeypatch.setenv("DATABASE_URL", "postgresql://user:pass@db:5432/app")
    monkeypatch.setattr(database, "create_async_engine", fake_create_async_engine)

    first_engine = database.get_engine()
    assert create_calls == 1

    await database.dispose_engine()

    cast("AsyncMock", first_engine.dispose).assert_awaited_once()

    second_engine = database.get_engine()
    assert create_calls == 2
    assert first_engine is not second_engine
    cast("AsyncMock", second_engine.dispose).assert_not_awaited()