const SECOND = 1_000;
const FIVE_HOURS = 5 * 60 * 60 * 1_000;

export const RATE_LIMITS = {
  requestsPerSecond: 2,
  requestsPerFiveHours: 100,
  spendPerFiveHours: 10,
};

function prune(timestamps, now, window) {
  return timestamps.filter((timestamp) => timestamp > now - window);
}

export function clientIp(request) {
  const railwayIp = request.get('x-real-ip');
  return railwayIp?.split(',')[0].trim() || request.ip || request.socket.remoteAddress || 'unknown';
}

export function createRateLimiter({ now = () => Date.now() } = {}) {
  const clients = new Map();

  function stateFor(ip, timestamp) {
    let state = clients.get(ip);
    if (!state) {
      state = { requests: [], spend: [] };
      clients.set(ip, state);
    }
    state.requests = prune(state.requests, timestamp, FIVE_HOURS);
    state.spend = state.spend.filter(({ timestamp: spentAt }) => spentAt > timestamp - FIVE_HOURS);
    return state;
  }

  return {
    check(ip) {
      const timestamp = now();
      const state = stateFor(ip, timestamp);
      const recentRequests = state.requests.filter((requestAt) => requestAt > timestamp - SECOND);
      const spend = state.spend.reduce((total, entry) => total + entry.amount, 0);
      if (recentRequests.length >= RATE_LIMITS.requestsPerSecond) {
        return { allowed: false, retryAfter: Math.max(1, Math.ceil((recentRequests[0] + SECOND - timestamp) / 1_000)), reason: 'rate' };
      }
      if (state.requests.length >= RATE_LIMITS.requestsPerFiveHours) {
        return { allowed: false, retryAfter: Math.max(1, Math.ceil((state.requests[0] + FIVE_HOURS - timestamp) / 1_000)), reason: 'rate' };
      }
      if (spend >= RATE_LIMITS.spendPerFiveHours) {
        const firstSpend = state.spend[0];
        return { allowed: false, retryAfter: Math.max(1, Math.ceil((firstSpend.timestamp + FIVE_HOURS - timestamp) / 1_000)), reason: 'spend' };
      }
      state.requests.push(timestamp);
      return { allowed: true };
    },

    recordCost(ip, amount) {
      if (!Number.isFinite(amount) || amount < 0) return;
      const timestamp = now();
      const state = stateFor(ip, timestamp);
      state.spend.push({ timestamp, amount });
    },
  };
}

export function numericCost(payload) {
  const cost = payload?.cost ?? payload?.usage?.cost;
  return typeof cost === 'number' && Number.isFinite(cost) ? cost : null;
}

export function rateLimitError(response, anthropic = false, result) {
  response.set('retry-after', String(result.retryAfter));
  if (anthropic) {
    return response.status(429).json({ type: 'error', error: { type: 'rate_limit_error', message: `Rate limit exceeded (${result.reason === 'spend' ? 'spend' : 'request'} limit)` } });
  }
  return response.status(429).json({ error: { message: `Rate limit exceeded (${result.reason === 'spend' ? 'spend' : 'request'} limit)`, type: 'rate_limit_error' } });
}