Clarify settings and app wiring

app/backend/core/config.py

@@ -1,13 +1,17 @@
 """Environment configuration derived from environment variables."""
 
 from functools import lru_cache
+from pydantic import SecretStr # Import SecretStr for sensitive data
 from pydantic_settings import BaseSettings, SettingsConfigDict
 
 class Settings(BaseSettings):
-    """Application settings."""
+    """
+    Application settings class using Pydantic BaseSettings.
+    Settings are loaded from environment variables and have default values defined here.
+    """
 
-    service_name: str = "avaaz-backend" # Used as a functional ID
-    environment: str = "development"
+    service_name: str = "avaaz-backend" # A unique functional identifier for the microservice
+    environment: str = "development" # Defines the current deployment stage (e.g., 'development', 'staging', 'production')
 
     title: str = "Avaaz Language Tutoring API"
     description: str = """
@@ -22,14 +26,24 @@ class Settings(BaseSettings):
         *   **Cross-Platform Sync:** Ensures seamless learning continuity and progress synchronization across all user devices.
         """
     
-    version: str = "0.1.0" 
+    version: str = "0.1.0" # The current semantic version of the API application
     
-    database_url: str = "postgresql+psycopg://postgres:postgres@postgres:5432/avaaz"
-
-    model_config = SettingsConfigDict(env_prefix="", case_sensitive=False)
+    # Use SecretStr to prevent accidental logging of credentials.
+    # Access the actual value using settings.database_url.get_secret_value()
+    database_url: SecretStr = SecretStr("postgresql+psycopg://postgres:postgres@postgres:5432/avaaz")
 
+    model_config = SettingsConfigDict(
+        env_prefix="",  # Load variables without a specific prefix (e.g., `DATABASE_URL` instead of `APP_DATABASE_URL`)
+        case_sensitive=False # Environment variable names are treated as case-insensitive during loading
+    )
 
 @lru_cache(maxsize=1)
 def get_settings() -> Settings:
-    """Return cached settings instance."""
+    """
+    Return a cached singleton instance of the application settings.
+    
+    This function leverages functools.lru_cache to ensure that environment variables
+    are read only once during the application's lifecycle, improving performance
+    and ensuring consistency across requests.
+    """
     return Settings()

app/backend/main.py

@@ -1,19 +1,28 @@
-"""Application entrypoint and router wiring."""
+"""
+API Application Entrypoint and Router Wiring.
+
+This module initializes the core FastAPI application instance, loads
+configuration, applies middleware, and wires up all defined API routers.
+"""
 
 from fastapi import FastAPI
 from fastapi.middleware.cors import CORSMiddleware
-
+from typing import List
 
 from api.v1.router import router as api_v1_router
 from operations.health.router import router as health_router
+from core.config import get_settings, Settings # Import Settings type for clarity
 
-from core.config import get_settings
+def create_app(settings: Settings = get_settings()) -> FastAPI:
+    """
+    Create and configure the FastAPI application instance.
 
-def create_app() -> FastAPI:
-    """Create and configure the FastAPI application."""
-
-    settings = get_settings()
+    Args:
+        settings: Configuration object from core.config. Defaults to current settings.
 
+    Returns:
+        A configured FastAPI application instance.
+    """
     app = FastAPI(
         title=settings.title,
         description=settings.description,
@@ -23,19 +32,25 @@ def create_app() -> FastAPI:
         openapi_url="/openapi.json",
     )
 
-    # CORS for local dev (frontend on 3000). Tighten/override in prod.
+    # Define allowed origins dynamically based on local dev environment needs
+    # In a production setting, this list would typically be sourced from environment variables.
+    allowed_origins: List[str] = ["http://localhost:3000", "http://127.0.0.1:3000"]
+    
+    # Configure CORS middleware
+    # TODO: Tightly restrict origins in production deployment.
     app.add_middleware(
         CORSMiddleware,
-        allow_origins=["http://localhost:3000", "http://127.0.0.1:3000"],
+        allow_origins=allowed_origins,
         allow_credentials=True,
         allow_methods=["*"],
         allow_headers=["*"],
     )
 
+    # Include API routers
     app.include_router(health_router)
     app.include_router(api_v1_router, prefix="/api/v1")
 
     return app
 
-
+# Main entry point for services like Uvicorn (e.g., `uvicorn main:app --reload`)
 app = create_app()