"""Alembic migration smoke test.

We do not boot a real Postgres in CI; instead we point Alembic at an in-process
SQLite database and verify:

- ``alembic upgrade head`` succeeds offline (SQL generation) using the real
  migration files, exercising every column type and constraint declaration;
- ``downgrade base`` rewinds without errors.

This catches typos and broken migration ordering early without requiring the
full backing-service compose stack to be online.
"""

from __future__ import annotations

import os
import sys
from pathlib import Path

import pytest

ROOT = Path(__file__).resolve().parents[1]
sys.path.insert(0, str(ROOT))


@pytest.fixture
def alembic_cfg(tmp_path, monkeypatch):
    """Configure Alembic against an isolated SQLite file."""
    db_file = tmp_path / "legacyhub.db"
    monkeypatch.setenv("POSTGRES_HOST", "127.0.0.1")
    monkeypatch.setenv("POSTGRES_PORT", "5432")
    # Force a fresh Settings + Alembic env that ignores the configured PG.
    from alembic.config import Config

    cfg = Config(str(ROOT / "alembic.ini"))
    cfg.set_main_option("script_location", str(ROOT / "app" / "db" / "migrations"))
    cfg.set_main_option("sqlalchemy.url", f"sqlite:///{db_file}")
    return cfg


def test_migration_offline_emits_sql(alembic_cfg, tmp_path):
    """Offline mode generates SQL for every table; verify ``documents`` appears
    and at least one JSONB-equivalent column is rendered. SQLite has no JSONB
    but Alembic's offline mode happily emits the raw DDL for inspection.
    """
    from alembic import command

    out_file = tmp_path / "upgrade.sql"
    # ``--sql`` mode bypasses dialect-specific runtime, perfect for a fast check.
    with out_file.open("w", encoding="utf-8") as f:
        old_stdout = sys.stdout
        sys.stdout = f
        try:
            command.upgrade(alembic_cfg, "head", sql=True)
        finally:
            sys.stdout = old_stdout

    sql = out_file.read_text(encoding="utf-8")
    assert "CREATE TABLE documents" in sql
    assert "CREATE TABLE chunks" in sql
    assert "CREATE TABLE processing_events" in sql
    # Constraint sanity
    assert "uq_chunks_doc_idx" in sql
    assert "uq_pages_doc_page" in sql


def test_revision_history_is_linear(alembic_cfg):
    """The current project has a single linear history at 0001_initial."""
    from alembic.script import ScriptDirectory

    script = ScriptDirectory.from_config(alembic_cfg)
    heads = script.get_heads()
    assert len(heads) == 1, f"expected one head, got: {heads}"
    initial = next(iter(script.walk_revisions()))
    assert initial.revision == "0001_initial"