"""Schema-drift guard: the DB-vs-code head check behind /health/ready and the
startup log. Regression cover for the outage where the backend image shipped
ahead of an un-applied migration and every trees query 500'd."""

from sqlalchemy import text

from app.core.schema_version import db_heads, expected_heads, schema_is_current


def test_expected_heads_is_a_single_known_head():
    heads = expected_heads()
    # Linear migration history → exactly one head, and it's a real revision id.
    assert len(heads) == 1
    assert all(h and isinstance(h, str) for h in heads)


async def test_schema_is_current_detects_drift(db_session):
    conn = await db_session.connection()

    # The test DB is built from create_all (no alembic_version table), so it is
    # not Alembic-managed and the check stays quiet — treated as current.
    await conn.execute(text("DROP TABLE IF EXISTS alembic_version"))
    assert await db_heads(conn) is None
    ok, _, _ = await schema_is_current(conn)
    assert ok is True

    # Stamp an old/wrong revision → drift detected.
    await conn.execute(text("CREATE TABLE alembic_version (version_num varchar(32) NOT NULL)"))
    await conn.execute(text("INSERT INTO alembic_version (version_num) VALUES ('0000deadbeef')"))
    ok, db, expected = await schema_is_current(conn)
    assert ok is False
    assert db == frozenset({"0000deadbeef"})

    # Stamp the code's real head → current again.
    head = next(iter(expected))
    await conn.execute(text("DELETE FROM alembic_version"))
    await conn.execute(text("INSERT INTO alembic_version (version_num) VALUES (:h)"), {"h": head})
    ok, _, _ = await schema_is_current(conn)
    assert ok is True

    # Leave no alembic_version behind for other tests.
    await conn.execute(text("DROP TABLE IF EXISTS alembic_version"))