"""In-memory sliding window rate limiter.

Note: For multi-instance deployments, swap to Redis-backed implementation.
"""
import asyncio
import time
from collections import defaultdict

from fastapi import Request, HTTPException, status

from app.config import settings

_requests: dict[str, list[float]] = defaultdict(list)
_lock = asyncio.Lock()


async def check_rate_limit(request: Request) -> None:
    """Check if the request IP is within rate limits. Raises 429 if exceeded."""
    client_ip = request.client.host if request.client else "unknown"
    now = time.time()
    window = settings.RATE_LIMIT_WINDOW_SECONDS
    max_requests = settings.RATE_LIMIT_REQUESTS

    async with _lock:
        # Clean old entries
        _requests[client_ip] = [t for t in _requests[client_ip] if t > now - window]

        if len(_requests[client_ip]) >= max_requests:
            raise HTTPException(
                status_code=status.HTTP_429_TOO_MANY_REQUESTS,
                detail="Too many requests. Please try again later.",
            )

        _requests[client_ip].append(now)

        # Evict empty keys to prevent unbounded growth
        stale = [ip for ip, ts in _requests.items() if not ts]
        for ip in stale:
            del _requests[ip]