import { createHash } from 'node:crypto'
import { getClientIp } from './request-ip'

const ANALYTICS_WINDOW_MS = 60 * 1000
const ANALYTICS_PAGEVIEW_LIMIT = 120
const ANALYTICS_HEARTBEAT_LIMIT = 240
const ANALYTICS_BUCKET_LIMIT = 20000
const analyticsBuckets = new Map()
let lastCleanupAt = 0

/**
 * 통계 제한 키에 사용할 IP 해시를 생성한다.
 * @param {import('h3').H3Event} event - 요청 이벤트
 * @param {'pageview'|'heartbeat'} kind - 통계 요청 종류
 * @returns {string} 제한 버킷 키
 */
const createAnalyticsLimitKey = (event, kind) => createHash('sha256')
  .update(`${kind}:${getClientIp(event)}`)
  .digest('hex')

/**
 * 만료된 통계 제한 버킷을 정리한다.
 * @param {number} now - 현재 시각
 * @returns {void}
 */
const cleanupAnalyticsBuckets = (now) => {
  if (now - lastCleanupAt < ANALYTICS_WINDOW_MS && analyticsBuckets.size < ANALYTICS_BUCKET_LIMIT) {
    return
  }

  lastCleanupAt = now
  for (const [key, bucket] of analyticsBuckets) {
    if (bucket.expiresAt <= now) {
      analyticsBuckets.delete(key)
    }
  }

  while (analyticsBuckets.size >= ANALYTICS_BUCKET_LIMIT) {
    const oldestKey = analyticsBuckets.keys().next().value
    if (!oldestKey) {
      break
    }
    analyticsBuckets.delete(oldestKey)
  }
}

/**
 * 현재 IP의 통계 쓰기 요청을 허용할지 확인한다.
 * @param {import('h3').H3Event} event - 요청 이벤트
 * @param {'pageview'|'heartbeat'} kind - 통계 요청 종류
 * @returns {boolean} 허용 여부
 */
export const shouldAcceptAnalyticsRequest = (event, kind) => {
  const now = Date.now()
  const limit = kind === 'heartbeat' ? ANALYTICS_HEARTBEAT_LIMIT : ANALYTICS_PAGEVIEW_LIMIT
  const key = createAnalyticsLimitKey(event, kind)

  cleanupAnalyticsBuckets(now)

  const current = analyticsBuckets.get(key)
  if (!current || current.expiresAt <= now) {
    analyticsBuckets.set(key, {
      count: 1,
      expiresAt: now + ANALYTICS_WINDOW_MS
    })
    return true
  }

  current.count += 1
  return current.count <= limit
}