app/security/rate_limiter.py

from typing import Callable
from fastapi import Request
from fastapi.responses import JSONResponse
from slowapi import Limiter
from slowapi.util import get_remote_address

# Configure slowapi.Limiter with key_func=get_remote_address.
limiter = Limiter(key_func=get_remote_address)

# Custom handler that returns {"error": "Rate limit exceeded. Try again shortly."}
# with HTTP 429 (not the default slowapi response format).
async def custom_rate_limit_handler(request: Request, exc: Exception) -> JSONResponse:
    return JSONResponse(
        status_code=429,
        content={"error": "Rate limit exceeded. Try again shortly."}
    )

# Decorator factory chat_rate_limit that applies 20/minute limit.
def chat_rate_limit() -> Callable:
    return limiter.limit("20/minute")