deer-flow/backend/src/gateway/app.py

import logging
from collections.abc import AsyncGenerator
from contextlib import asynccontextmanager

from fastapi import FastAPI
from fastapi.middleware.cors import CORSMiddleware

from src.gateway.config import get_gateway_config
from src.gateway.routers import models, proxy

logger = logging.getLogger(__name__)


@asynccontextmanager
async def lifespan(app: FastAPI) -> AsyncGenerator[None, None]:
    """Application lifespan handler."""
    config = get_gateway_config()
    logger.info(f"Starting API Gateway on {config.host}:{config.port}")
    logger.info(f"Proxying to LangGraph server at {config.langgraph_url}")
    yield
    logger.info("Shutting down API Gateway")


def create_app() -> FastAPI:
    """Create and configure the FastAPI application.

    Returns:
        Configured FastAPI application instance.
    """
    config = get_gateway_config()

    app = FastAPI(
        title="DeerFlow API Gateway",
        description="API Gateway for DeerFlow - proxies to LangGraph Server and provides custom endpoints",
        version="0.1.0",
        lifespan=lifespan,
    )

    # Add CORS middleware
    app.add_middleware(
        CORSMiddleware,
        allow_origins=config.cors_origins,
        allow_credentials=True,
        allow_methods=["*"],
        allow_headers=["*"],
    )

    # Include routers
    # Models API is mounted at /api/models
    app.include_router(models.router)

    # Proxy router handles all LangGraph paths (must be last due to catch-all)
    app.include_router(proxy.router)

    @app.get("/health")
    async def health_check() -> dict:
        """Health check endpoint."""
        return {"status": "healthy", "service": "deer-flow-gateway"}

    return app


# Create app instance for uvicorn
app = create_app()