app/core/database.py

# app/core/database.py
"""
Database engine, session factory, and base model.
Supports SQLite (dev) and PostgreSQL (prod) via DATABASE_URL.
Production-hardened: connection pool tuning, pre-ping, recycle.
"""

import logging

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

from app.core.config import settings

logger = logging.getLogger("hale.database")

# ── Connection args ────────────────────────────────────────────────────────
connect_args: dict = {}
pool_kwargs:  dict = {}

if settings.is_sqlite:
    # SQLite: single-thread safety, no connection pool
    connect_args["check_same_thread"] = False
else:
    # PostgreSQL: production-grade connection pooling
    pool_kwargs = {
        "pool_size":    20,    # Base connections kept alive across workers
        "max_overflow": 10,    # Burst connections allowed above pool_size
        "pool_timeout": 30,    # Seconds to wait if pool is exhausted
        "pool_recycle": 1800,  # Recycle connections every 30 min (prevents stale TCP)
    }
    logger.info(
        "PostgreSQL pool: pool_size=%d, max_overflow=%d, recycle=%ds",
        pool_kwargs["pool_size"], pool_kwargs["max_overflow"], pool_kwargs["pool_recycle"],
    )

engine = create_engine(
    settings.DATABASE_URL,
    connect_args=connect_args,
    echo=False,
    pool_pre_ping=True,  # Validates connection before use — handles DB restarts
    **pool_kwargs,
)

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


def init_db() -> None:
    """Create all tables (idempotent — safe for existing tables)."""
    # Import all models so SQLAlchemy registers them before create_all
    from app.models import user, goal, progress  # noqa: F401
    Base.metadata.create_all(bind=engine)


def get_db():
    """FastAPI dependency that yields a database session."""
    db = SessionLocal()
    try:
        yield db
    finally:
        db.close()