"""Database connection and session management.

T06: Database connection & session management
"""
from sqlalchemy import create_engine
from sqlalchemy.orm import sessionmaker, Session, declarative_base
from typing import Generator

from openrouter_monitor.config import get_settings


# Create declarative base for models (SQLAlchemy 2.0 style)
Base = declarative_base()

# Get settings
settings = get_settings()

# Create engine with SQLite configuration
# check_same_thread=False is required for SQLite with async/threads
engine = create_engine(
    settings.database_url,
    connect_args={"check_same_thread": False}
)

# Create session maker with expire_on_commit=False
# This prevents attributes from being expired after commit
SessionLocal = sessionmaker(
    autocommit=False,
    autoflush=False,
    bind=engine,
    expire_on_commit=False
)


def get_db() -> Generator[Session, None, None]:
    """Get database session for FastAPI dependency injection.
    
    This function creates a new database session and yields it.
    The session is automatically closed when the request is done.
    
    Yields:
        Session: SQLAlchemy database session
        
    Example:
        >>> from fastapi import Depends
        >>> @app.get("/items/")
        >>> def read_items(db: Session = Depends(get_db)):
        ...     return db.query(Item).all()
    """
    db = SessionLocal()
    try:
        yield db
    finally:
        db.close()


def init_db() -> None:
    """Initialize database by creating all tables.
    
    This function creates all tables registered with Base.metadata.
    Should be called at application startup.
    
    Example:
        >>> from openrouter_monitor.database import init_db
        >>> init_db()  # Creates all tables
    """
    Base.metadata.create_all(bind=engine)