"""The accounts DB engine layer: dialect selection and the read/read-write split.

These run on the SQLite fallback (no THERMOGRAPH_DATABASE_URL in the test env);
the Postgres path (asyncpg RO/RW engines) is exercised by the docker-compose stack,
not the unit suite, so tests stay Postgres-free and fast."""
import asyncio

from sqlalchemy import select

from accounts import db

# The server-side ceiling these pools spend from, and the deployment shape that
# spends it. Kept here so a pool change that stops fitting is a failing test
# rather than a 2am "sorry, too many clients already". Mirrors max_connections in
# infra/deploy/db/init/20-tuning.sh. ONE Postgres instance serves prod and beta.
MAX_CONNECTIONS = 200
PROD_WEB_WORKERS = 4           # uvicorn workers per prod web replica
BETA_WEB_WORKERS = 2
ASYNC_ENGINES_PER_PROCESS = 2  # RW + RO, both built from _ASYNC_POOL_KWARGS


def _async_ceiling_per_process() -> int:
    """Connections one backend process can hold from its async pools at once."""
    k = db._ASYNC_POOL_KWARGS
    return ASYNC_ENGINES_PER_PROCESS * (k["pool_size"] + k["max_overflow"])


def _sync_ceiling() -> int:
    """The notifier's sync pool. One process holds it cluster-wide (leader flock),
    so it is NOT multiplied by workers or replicas."""
    k = db._SYNC_POOL_KWARGS
    return k["pool_size"] + k["max_overflow"]


def test_defaults_to_sqlite_when_no_database_url():
    assert db.IS_POSTGRES is False
    # Both engines exist; on SQLite the RO engine is an alias of the RW one.
    assert db.async_engine is not None
    assert db.async_engine_ro is db.async_engine


def test_read_and_write_session_makers_are_distinct_dependencies():
    # Distinct FastAPI deps so pure-read endpoints can opt into the RO engine.
    assert db.get_async_session is not db.get_read_session
    assert callable(db.get_async_session) and callable(db.get_read_session)


def test_sync_url_derivation():
    assert db._sync_url("postgresql+asyncpg://u:p@h:5432/d") == "postgresql+psycopg://u:p@h:5432/d"
    assert db._sync_url("sqlite+aiosqlite:////tmp/x.sqlite") == "sqlite:////tmp/x.sqlite"


def test_postgres_pool_sizing_and_sync_timeouts():
    """The Postgres engine-construction kwargs, defined at module scope so they're
    testable without a real Postgres connection (the engines built from them are
    only actually constructed when IS_POSTGRES, exercised by the docker-compose
    stack -- see the module docstring). pool_size=1/max_overflow=1 (the original
    setting) let a 3rd concurrent request per worker wait out pool_timeout for a
    slot, so the steady-state pool needs real headroom; the sync engine (the
    notifier's, driven off-event-loop) must bound connect + statement time so a
    wedged Postgres can't hang it forever under its leader flock."""
    assert db._ASYNC_POOL_KWARGS["pool_size"] >= 5

    # The overflow is the part nobody budgets for -- it is multiplied by two async
    # engines x uvicorn workers x replicas, against a ceiling shared with beta.
    # Prod saturated max_connections on 2026-07-26 with this at 5. Keep it well
    # under pool_size; the budget test below is the real constraint.
    assert db._ASYNC_POOL_KWARGS["max_overflow"] <= 2

    assert db._SYNC_POOL_KWARGS["pool_size"] < db._ASYNC_POOL_KWARGS["pool_size"]
    connect_args = db._SYNC_POOL_KWARGS["connect_args"]
    assert connect_args["connect_timeout"] > 0
    assert "statement_timeout" in connect_args["options"]

    # Build a real (unconnected -- SQLAlchemy engines are lazy) engine from these
    # exact kwargs to confirm they're accepted by the psycopg dialect.
    import sqlalchemy
    engine = sqlalchemy.create_engine("postgresql+psycopg://u:p@h:5432/d", **db._SYNC_POOL_KWARGS)
    assert engine.pool.size() == db._SYNC_POOL_KWARGS["pool_size"]
    engine.dispose()


def test_pool_budget_fits_under_max_connections():
    """At today's replica counts the whole estate's configured worst case must fit
    inside the server's max_connections, with margin -- prod web + prod worker +
    beta web + beta worker all draw on ONE Postgres instance. This is the test
    that would have failed before 2026-07-26, when the configured worst case was
    170 against a ceiling of 100.

    Note this counts *configured maxima*: every pool at full overflow at the same
    instant. Prod web autoscaling to its max of 3 replicas is deliberately NOT in
    this sum -- that peak still does not fit, and closing it needs a connection
    pooler or a lower autoscale ceiling rather than a bigger number here."""
    per_process = _async_ceiling_per_process()
    prod = per_process * PROD_WEB_WORKERS + (per_process + _sync_ceiling())
    beta = per_process * BETA_WEB_WORKERS + (per_process + _sync_ceiling())

    assert prod + beta <= MAX_CONNECTIONS * 0.8, (
        f"configured worst case {prod + beta} leaves too little room under "
        f"max_connections={MAX_CONNECTIONS}"
    )


def test_read_session_yields_a_working_session():
    # On SQLite the read session is fully usable (no read-only enforcement); this
    # just confirms the dependency wiring resolves to a live AsyncSession.
    db.Base.metadata.create_all(db.sync_engine)

    async def _use():
        async for session in db.get_read_session():
            return (await session.execute(select(1))).scalar_one()

    assert asyncio.run(_use()) == 1