Initial commit with Phase 0 Scaffolding

backend/app/db.py

@@ -0,0 +1,58 @@
+"""
+Database engine, session management, and WAL mode setup.
+
+SQLite with WAL mode for single-user concurrent read/write safety.
+"""
+
+from collections.abc import AsyncGenerator
+from contextlib import asynccontextmanager
+from typing import Any
+
+from sqlalchemy import event, create_engine, Engine
+from sqlalchemy.orm import DeclarativeBase, Session, sessionmaker
+
+from app.config import settings
+
+
+class Base(DeclarativeBase):
+    """SQLAlchemy declarative base for all models."""
+    pass
+
+
+def _set_sqlite_wal_mode(dbapi_conn: Any, _connection_record: Any) -> None:
+    """Enable WAL mode and other SQLite performance pragmas on every connection."""
+    cursor = dbapi_conn.cursor()
+    cursor.execute("PRAGMA journal_mode=WAL")
+    cursor.execute("PRAGMA synchronous=NORMAL")
+    cursor.execute("PRAGMA foreign_keys=ON")
+    cursor.close()
+
+
+def create_db_engine() -> Engine:
+    """Create the SQLAlchemy engine with SQLite and WAL mode."""
+    # Ensure the database directory exists
+    settings.DATABASE_PATH.parent.mkdir(parents=True, exist_ok=True)
+
+    engine = create_engine(
+        f"sqlite:///{settings.DATABASE_PATH}",
+        echo=settings.DEBUG,
+        connect_args={"check_same_thread": False},
+    )
+
+    # Register WAL mode on every new connection
+    event.listen(engine, "connect", _set_sqlite_wal_mode)
+
+    return engine
+
+
+engine = create_db_engine()
+SessionLocal = sessionmaker(bind=engine, class_=Session, expire_on_commit=False)
+
+
+def get_db() -> Session:
+    """FastAPI dependency that yields a database session."""
+    db = SessionLocal()
+    try:
+        yield db  # type: ignore[misc]
+    finally:
+        db.close()