# app/core/database.py
"""
Database configuration and session management.

This module provides classes and functions for:
- PostgreSQL database engine creation and configuration
- Session management with connection pooling
- Database dependency for FastAPI routes

Note: This project uses PostgreSQL only. SQLite is not supported.
"""

import logging

from sqlalchemy import create_engine
from sqlalchemy.orm import declarative_base, sessionmaker
from sqlalchemy.pool import QueuePool

from .config import settings, validate_database_url

# Validate database URL on import
validate_database_url()

# Create PostgreSQL engine with connection pooling
engine = create_engine(
    settings.database_url,
    poolclass=QueuePool,
    pool_size=10,
    max_overflow=20,
    pool_pre_ping=True,
    echo=False,
)

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

Base = declarative_base()

logger = logging.getLogger(__name__)


def get_db():
    """
    Database session dependency for FastAPI routes.

    Yields a database session and ensures proper cleanup.
    Handles exceptions and rolls back transactions on error.
    """
    db = SessionLocal()
    try:
        yield db
    except Exception as e:
        logger.error(f"Database session error: {e}")
        db.rollback()
        raise
    finally:
        db.close()