tatlock/src/main.py

"""
FastAPI application entry point.
Following best practices from github.com/zhanymkanov/fastapi-best-practices

Main responsibilities:
- Application configuration
- Middleware setup
- Exception handlers
- Router registration
- Lifecycle management
"""
from contextlib import asynccontextmanager
from typing import AsyncGenerator

from fastapi import FastAPI, Request, status
from fastapi.exceptions import RequestValidationError
from fastapi.middleware.cors import CORSMiddleware
from fastapi.responses import JSONResponse

from src.chat.router import router as chat_router
from src.core.config import config
from src.core.exceptions import AppException
from src.core.logging_config import get_logger
from src.core.router import router as core_router
from src.core.startup import initialize_application
from src.models.router import router as models_router
from src.responses.router import router as responses_router

# Get structured logger
logger = get_logger(__name__)


@asynccontextmanager
async def lifespan(app: FastAPI) -> AsyncGenerator[None, None]:
    """
    Application lifespan manager.

    Handles startup and shutdown logic.
    """
    # Startup
    logger.info(
        "application_starting",
        app_name=config.APP_NAME,
        version=config.APP_VERSION,
        environment=config.ENVIRONMENT.value,
        ollama_host=str(config.OLLAMA_HOST),
        ollama_model=config.OLLAMA_DEFAULT_MODEL,
        redis_url=config.redis_url,
        log_format=config.log_format,
    )

    # Initialize application (register household members, etc.)
    initialize_application()

    yield

    # Shutdown
    logger.info("application_shutdown")


def create_application() -> FastAPI:
    """
    Application factory.
    
    Creates and configures the FastAPI application.
    Following best practice of using factory pattern.
    """
    # Create app
    application = FastAPI(
        title=config.APP_NAME,
        version=config.APP_VERSION,
        lifespan=lifespan,
        debug=config.DEBUG,
    )
    
    # Add middleware
    application.add_middleware(
        CORSMiddleware,
        allow_origins=config.CORS_ORIGINS,
        allow_credentials=config.CORS_ALLOW_CREDENTIALS,
        allow_methods=config.CORS_ALLOW_METHODS,
        allow_headers=config.CORS_ALLOW_HEADERS,
    )
    
    # Register exception handlers
    register_exception_handlers(application)
    
    # Include routers
    application.include_router(core_router)  # Health and root endpoints
    application.include_router(chat_router, prefix=config.API_PREFIX)
    application.include_router(models_router, prefix=config.API_PREFIX)
    application.include_router(responses_router, prefix=config.API_PREFIX)  # Responses API
    
    return application


def register_exception_handlers(application: FastAPI) -> None:
    """
    Register global exception handlers.
    
    Provides consistent error responses compatible with OpenAI API.
    """
    
    @application.exception_handler(AppException)
    async def app_exception_handler(
        request: Request,
        exc: AppException,
    ) -> JSONResponse:
        """Handle custom application exceptions."""
        logger.error(
            "application_exception",
            error_message=exc.message,
            error_type=exc.__class__.__name__,
            status_code=exc.status_code,
            details=exc.details,
            path=request.url.path,
        )

        return JSONResponse(
            status_code=exc.status_code,
            content={
                "error": {
                    "message": exc.message,
                    "type": exc.__class__.__name__,
                    "details": exc.details,
                }
            },
        )

    @application.exception_handler(RequestValidationError)
    async def validation_exception_handler(
        request: Request,
        exc: RequestValidationError,
    ) -> JSONResponse:
        """Handle Pydantic validation errors."""
        logger.error(
            "validation_error",
            errors=exc.errors(),
            path=request.url.path,
        )

        return JSONResponse(
            status_code=status.HTTP_422_UNPROCESSABLE_ENTITY,
            content={
                "error": {
                    "message": "Invalid request",
                    "type": "invalid_request_error",
                    "details": exc.errors(),
                }
            },
        )

    @application.exception_handler(Exception)
    async def general_exception_handler(
        request: Request,
        exc: Exception,
    ) -> JSONResponse:
        """Handle unexpected exceptions."""
        logger.exception(
            "unexpected_error",
            error_type=type(exc).__name__,
            error_message=str(exc),
            path=request.url.path,
        )

        return JSONResponse(
            status_code=status.HTTP_500_INTERNAL_SERVER_ERROR,
            content={
                "error": {
                    "message": "An internal error occurred",
                    "type": "internal_server_error",
                }
            },
        )


# Create application instance
app = create_application()