from typing import Generator
from urllib.parse import urlparse, urlunparse

from sqlalchemy import create_engine
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.orm import sessionmaker

from app.core.config import get_settings

_ASYNC_TO_SYNC_SCHEMES = {
    "postgresql+asyncpg": "postgresql+psycopg2",
}


def _make_sync_db_url(url: str) -> str:
    """Return the synchronous-driver equivalent of *url*.

    Kubernetes and docker-compose deployments sometimes configure DATABASE_URL
    with an async driver scheme (e.g. ``postgresql+asyncpg://``).  Alembic and
    the synchronous SQLAlchemy engine used here require a sync driver, so we
    map known async schemes to their psycopg2 equivalents.

    Only the scheme component of the URL is rewritten; all other parts
    (credentials, host, path, query) are left untouched.
    """
    parsed = urlparse(url)
    sync_scheme = _ASYNC_TO_SYNC_SCHEMES.get(parsed.scheme)
    if sync_scheme is None:
        return url
    return urlunparse(parsed._replace(scheme=sync_scheme))


settings = get_settings()

# Configure SQLAlchemy (normalise async driver schemes to their sync equivalents)
engine = create_engine(_make_sync_db_url(settings.DATABASE_URL), pool_pre_ping=True)
SessionLocal = sessionmaker(autocommit=False, autoflush=False, bind=engine)

# Create base class for SQLAlchemy models
Base = declarative_base()


def get_db() -> Generator:
    """
    Dependency for getting DB sessions
    """
    db = SessionLocal()
    try:
        yield db
    finally:
        db.close()