"""Guard against model/migration drift.

The functional suite builds its schema with ``Base.metadata.create_all`` for speed, so a
column or index added to a model but never written into an Alembic migration would only
surface on the first real deployment. This test runs the migration chain from an empty
database and asserts that Alembic's autogenerate sees nothing left to do.
"""

from __future__ import annotations

from pathlib import Path

import pytest
from alembic.autogenerate import compare_metadata
from alembic.config import Config
from alembic.runtime.migration import MigrationContext
from sqlalchemy import create_engine, text
from sqlalchemy.engine import make_url

from alembic import command
from app.core.config import get_settings
from app.models import Base

BACKEND_DIR = Path(__file__).resolve().parents[1]
SCRATCH_DB = "mobilityops_migration_check"


@pytest.fixture(scope="module")
def migrated_database_url() -> str:
    settings = get_settings()
    base_url = make_url(settings.database_url)
    admin_engine = create_engine(
        base_url.set(database="postgres"), isolation_level="AUTOCOMMIT", poolclass=None
    )
    with admin_engine.connect() as conn:
        conn.execute(text(f'DROP DATABASE IF EXISTS "{SCRATCH_DB}"'))
        conn.execute(text(f'CREATE DATABASE "{SCRATCH_DB}"'))
    scratch_url = base_url.set(database=SCRATCH_DB).render_as_string(hide_password=False)
    try:
        yield scratch_url
    finally:
        admin_engine.dispose()
        admin_engine = create_engine(
            base_url.set(database="postgres"), isolation_level="AUTOCOMMIT", poolclass=None
        )
        with admin_engine.connect() as conn:
            conn.execute(text(f'DROP DATABASE IF EXISTS "{SCRATCH_DB}" WITH (FORCE)'))
        admin_engine.dispose()


def _alembic_config(database_url: str) -> Config:
    config = Config(str(BACKEND_DIR / "alembic.ini"))
    config.set_main_option("script_location", str(BACKEND_DIR / "alembic"))
    config.set_main_option("sqlalchemy.url", database_url)
    return config


def test_migrations_upgrade_from_empty_and_match_models(migrated_database_url: str) -> None:
    config = _alembic_config(migrated_database_url)
    # env.py reads DATABASE_URL from settings; override it for the scratch database.
    import os

    previous = os.environ.get("DATABASE_URL")
    os.environ["DATABASE_URL"] = migrated_database_url
    get_settings.cache_clear()
    try:
        command.upgrade(config, "head")
    finally:
        if previous is None:
            os.environ.pop("DATABASE_URL", None)
        else:
            os.environ["DATABASE_URL"] = previous
        get_settings.cache_clear()

    engine = create_engine(migrated_database_url)
    try:
        with engine.connect() as conn:
            context = MigrationContext.configure(
                conn, opts={"compare_type": True, "compare_server_default": False}
            )
            diff = compare_metadata(context, Base.metadata)
    finally:
        engine.dispose()

    assert diff == [], (
        "Models and Alembic migrations have drifted; write a migration for:\n"
        + "\n".join(repr(entry) for entry in diff)
    )