from collections.abc import Iterator
from typing import Any

from sqlalchemy import Engine, create_engine, event
from sqlalchemy.orm import DeclarativeBase, Session, sessionmaker
from sqlalchemy.pool import StaticPool

from app.core.config import get_settings


class Base(DeclarativeBase):
    """Single declarative base for the whole application."""


def _build_engine(url: str) -> Engine:
    if url.startswith("sqlite"):
        # Test configuration (pytest runs on SQLite in-memory): a StaticPool
        # shares the single in-memory database across sessions/threads.
        return create_engine(
            url,
            connect_args={"check_same_thread": False},
            poolclass=StaticPool,
        )
    return create_engine(url, pool_pre_ping=True)


engine = _build_engine(get_settings().database_url)

if engine.dialect.name == "sqlite":
    # SQLite does not enforce foreign keys (and thus ON DELETE CASCADE, used by
    # the import rollback) unless the pragma is enabled per connection.
    @event.listens_for(engine, "connect")
    def _enable_sqlite_fks(dbapi_connection: Any, _record: Any) -> None:
        cursor = dbapi_connection.cursor()
        cursor.execute("PRAGMA foreign_keys=ON")
        cursor.close()


SessionLocal = sessionmaker(bind=engine, autoflush=False, expire_on_commit=False)


def get_db() -> Iterator[Session]:
    """FastAPI dependency: one session per request, closed automatically."""
    with SessionLocal() as session:
        yield session