package limiter

import (
 "fmt"
 "testing"
 "time"

 "golang.org/x/time/rate"
)

func TestLimter(t *testing.T) {
 limiter := rate.NewLimiter(rate.Every(time.Millisecond*31), 2)
 //time.Sleep(time.Second)
 for i := 0; i < 10; i++ {
  var ok bool
  if limiter.Allow() {
   ok = true
  }
  time.Sleep(time.Millisecond * 20)
  fmt.Println(ok, limiter.Burst())
 }
}

func NewLimiter(r Limit, b int) *Limiter {
 return &Limiter{
  limit: r,
  burst: b,
 }
}

// The methods AllowN, ReserveN, and WaitN consume n tokens.
type Limiter struct {
 mu     sync.Mutex
 limit  Limit
 burst  int
 tokens float64
 // last is the last time the limiter's tokens field was updated
 last time.Time
 // lastEvent is the latest time of a rate-limited event (past or future)
 lastEvent time.Time
}

type Reservation struct {
  ok        bool  // 是否滿足條件分配到了tokens
  lim       *Limiter // 發(fā)送令牌的限流器
  tokens    int   // tokens 的數(shù)量
  timeToAct time.Time  //  滿足令牌發(fā)放的時間
  limit Limit  // 令牌發(fā)放速度
}

// Allow is shorthand for AllowN(time.Now(), 1).
func (lim *Limiter) Allow() bool {
 return lim.AllowN(time.Now(), 1)
}

// AllowN reports whether n events may happen at time now.
// Use this method if you intend to drop / skip events that exceed the rate limit.
// Otherwise use Reserve or Wait.
func (lim *Limiter) AllowN(now time.Time, n int) bool {
 return lim.reserveN(now, n, 0).ok
}

// maxFutureReserve specifies the maximum reservation wait duration allowed.
// reserveN returns Reservation, not *Reservation, to avoid allocation in AllowN and WaitN.
func (lim *Limiter) reserveN(now time.Time, n int, maxFutureReserve time.Duration) Reservation {
 lim.mu.Lock()
 // 首先判斷是否放入頻次是否為無窮大，如果為無窮大，說明暫時不限流
 if lim.limit == Inf {
  lim.mu.Unlock()
  return Reservation{
   ok:        true,
   lim:       lim,
   tokens:    n,
   timeToAct: now,
  }
 }
   // 拿到截止 now 時間時，可以獲取的令牌 tokens 數(shù)量，上一次拿走令牌的時間是last
 now, last, tokens := lim.advance(now)

 // Calculate the remaining number of tokens resulting from the request.
 //  更新 tokens數(shù)量，把需要拿走的去掉
 tokens -= float64(n)

 // Calculate the wait duration
 // 如果 tokens 數(shù)量為負(fù)數(shù)，說明需要等待，計算等待時間 WaitDuration
 var waitDuration time.Duration
 if tokens < 0 {
  waitDuration = lim.limit.durationFromTokens(-tokens)
 }

 // Decide result
 // 計算是否滿足分配要求
 // 1. 需要分配的大小不超過桶容量
 // 2. 等待時間不超過設(shè)定的等待時長
 ok := n <= lim.burst && waitDuration <= maxFutureReserve

 // Prepare reservation
 // 最后構(gòu)造一個 Resvervation 對象
 r := Reservation{
  ok:    ok,
  lim:   lim,
  limit: lim.limit,
 }
 if ok {
  r.tokens = n
  r.timeToAct = now.Add(waitDuration)
 }

 // Update state
   // 需要更新當(dāng)前 limit 的值 
 if ok {
  lim.last = now
  lim.tokens = tokens
  lim.lastEvent = r.timeToAct
 } else {
  lim.last = last
 }

 lim.mu.Unlock()
 return r
}