"""Tests for the PRAGMA user_version migration runner."""

from __future__ import annotations

from pathlib import Path

import pytest
import sqlalchemy as sa
import sqlalchemy.exc

from cyclone import db_migrate


def _fresh_engine(tmp_path: Path) -> sa.Engine:
    return sa.create_engine(f"sqlite:///{tmp_path}/m.db", future=True)


def _user_version(engine: sa.Engine) -> int:
    with engine.connect() as c:
        return c.exec_driver_sql("PRAGMA user_version").scalar() or 0


def test_run_on_empty_db_bumps_to_latest(tmp_path: Path, monkeypatch: pytest.MonkeyPatch) -> None:
    monkeypatch.setattr(db_migrate, "MIGRATIONS_DIR", tmp_path)
    (tmp_path / "0001_initial.sql").write_text("-- version: 1\nCREATE TABLE t (id INTEGER);\n")

    engine = _fresh_engine(tmp_path)
    db_migrate.run(engine)

    assert _user_version(engine) == 1
    with engine.connect() as c:
        rows = c.exec_driver_sql("SELECT name FROM sqlite_master WHERE type='table' AND name='t'").all()
    assert len(rows) == 1


def test_run_is_idempotent(tmp_path: Path, monkeypatch: pytest.MonkeyPatch) -> None:
    monkeypatch.setattr(db_migrate, "MIGRATIONS_DIR", tmp_path)
    (tmp_path / "0001_initial.sql").write_text("-- version: 1\nCREATE TABLE t (id INTEGER);\n")

    engine = _fresh_engine(tmp_path)
    db_migrate.run(engine)
    db_migrate.run(engine)  # second call should be a no-op

    assert _user_version(engine) == 1


def test_run_skips_already_applied_migrations(tmp_path: Path, monkeypatch: pytest.MonkeyPatch) -> None:
    monkeypatch.setattr(db_migrate, "MIGRATIONS_DIR", tmp_path)
    (tmp_path / "0001_initial.sql").write_text("-- version: 1\nCREATE TABLE t1 (id INTEGER);\n")
    (tmp_path / "0002_add_col.sql").write_text("-- version: 2\nALTER TABLE t1 ADD COLUMN name TEXT;\n")

    engine = _fresh_engine(tmp_path)
    db_migrate.run(engine)
    assert _user_version(engine) == 2

    # Modify 0002 (a no-op for SQLite ALTER, but we want to verify the
    # runner doesn't re-run already-applied migrations).
    db_migrate.run(engine)
    assert _user_version(engine) == 2


def test_run_raises_on_missing_version_header(tmp_path: Path, monkeypatch: pytest.MonkeyPatch) -> None:
    monkeypatch.setattr(db_migrate, "MIGRATIONS_DIR", tmp_path)
    (tmp_path / "0001_bad.sql").write_text("CREATE TABLE t (id INTEGER);\n")  # no header

    engine = _fresh_engine(tmp_path)
    with pytest.raises(RuntimeError, match="missing '-- version"):
        db_migrate.run(engine)


def test_run_rolls_back_version_on_failed_statement(
    tmp_path: Path, monkeypatch: pytest.MonkeyPatch
) -> None:
    """If a DDL statement fails, the version bump must also roll back."""
    monkeypatch.setattr(db_migrate, "MIGRATIONS_DIR", tmp_path)
    (tmp_path / "0001_initial.sql").write_text(
        "-- version: 1\nCREATE TABLE t (id INTEGER);\n"
    )

    engine = _fresh_engine(tmp_path)
    db_migrate.run(engine)  # applies 0001, user_version=1
    assert _user_version(engine) == 1

    # Now drop in a second migration whose DDL conflicts with the first.
    # The runner should apply 0001 and 0002 in one call; 0002 fails, the
    # transaction rolls back, and user_version must stay at 1 (not bump to 2).
    (tmp_path / "0002_bad.sql").write_text(
        "-- version: 2\nCREATE TABLE t (id INTEGER);\n"  # table already exists!
    )

    with pytest.raises(sqlalchemy.exc.SQLAlchemyError):
        db_migrate.run(engine)

    assert _user_version(engine) == 1  # bumped atomically, rolled back on failure


def test_run_ignores_non_sql_files(
    tmp_path: Path, monkeypatch: pytest.MonkeyPatch
) -> None:
    """README.md and similar files in MIGRATIONS_DIR must not be executed."""
    monkeypatch.setattr(db_migrate, "MIGRATIONS_DIR", tmp_path)
    (tmp_path / "0001_initial.sql").write_text(
        "-- version: 1\nCREATE TABLE t (id INTEGER);\n"
    )
    (tmp_path / "README.md").write_text("Don't run me!\nCREATE TABLE should_not_exist (x INT);\n")

    engine = _fresh_engine(tmp_path)
    db_migrate.run(engine)

    with engine.connect() as c:
        rows = c.exec_driver_sql(
            "SELECT name FROM sqlite_master WHERE type='table' AND name='should_not_exist'"
        ).all()
    assert len(rows) == 0
    assert _user_version(engine) == 1