from sqlalchemy import create_engine
from sqlalchemy.engine import URL
from sqlalchemy.orm import declarative_base, sessionmaker
import os
from dotenv import load_dotenv


load_dotenv()


def _build_database_url() -> str:
    """Construct the SQLAlchemy database URL from granular environment vars.

    Falls back to `DATABASE_URL` for backward compatibility.
    """

    legacy_url = os.environ.get("DATABASE_URL")
    if legacy_url:
        return legacy_url

    driver = os.environ.get("DATABASE_DRIVER", "postgresql")
    host = os.environ.get("DATABASE_HOST")
    port = os.environ.get("DATABASE_PORT", "5432")
    user = os.environ.get("DATABASE_USER")
    password = os.environ.get("DATABASE_PASSWORD")
    database = os.environ.get("DATABASE_NAME")
    schema = os.environ.get("DATABASE_SCHEMA", "public")

    missing = [
        var_name
        for var_name, value in (
            ("DATABASE_HOST", host),
            ("DATABASE_USER", user),
            ("DATABASE_NAME", database),
        )
        if not value
    ]

    if missing:
        raise RuntimeError(
            "Missing database configuration: set DATABASE_URL or provide "
            f"granular variables ({', '.join(missing)})"
        )

    url = URL.create(
        drivername=driver,
        username=user,
        password=password,
        host=host,
        port=int(port) if port else None,
        database=database,
    )

    if schema:
        url = url.set(query={"options": f"-csearch_path={schema}"})

    return str(url)


DATABASE_URL = _build_database_url()

engine = create_engine(DATABASE_URL, echo=True, future=True)
SessionLocal = sessionmaker(autocommit=False, autoflush=False, bind=engine)
Base = declarative_base()