"""
Database Configuration fuer Classroom Engine.

Stellt PostgreSQL-Anbindung fuer Session-Persistenz bereit.
Sessions ueberleben Server-Neustarts (Feature f22).
"""
import os
from sqlalchemy import create_engine
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.orm import sessionmaker

# Database URL from environment (nutzt gleiche DB wie Backend)
# Korrigiert postgres:// zu postgresql:// fuer SQLAlchemy 2.0 Kompatibilitaet
_raw_url = os.getenv(
    "DATABASE_URL",
    "postgresql://breakpilot:breakpilot123@localhost:5432/breakpilot"
)
# SQLAlchemy 2.0 erfordert "postgresql://" statt "postgres://"
DATABASE_URL = _raw_url.replace("postgres://", "postgresql://", 1) if _raw_url.startswith("postgres://") else _raw_url

# Engine configuration
engine = create_engine(
    DATABASE_URL,
    pool_pre_ping=True,
    pool_size=5,
    max_overflow=10,
    echo=os.getenv("SQL_ECHO", "false").lower() == "true"
)

# Declarative Base
Base = declarative_base()

# Session factory
SessionLocal = sessionmaker(autocommit=False, autoflush=False, bind=engine)


def get_db():
    """Database dependency for FastAPI endpoints."""
    db = SessionLocal()
    try:
        yield db
    finally:
        db.close()


def init_db():
    """Erstellt alle Tabellen (fuer Entwicklung)."""
    from . import db_models  # Import models to register them
    Base.metadata.create_all(bind=engine)