package limit

import (
	"gd_auth_check/common.in/cache"
	"strconv"
	"sync"
	"sync/atomic"
	"time"

	"github.com/go-redis/redis"
)

const (
	script = `local capacity = tonumber(ARGV[1])
	local requested = tonumber(ARGV[2])
	local used = tonumber(redis.call("hget", KEYS[1], "used"))
	if used == nil then
		used = 0
	end

	local allowed = capacity - used - requested >= 0

	if allowed then
		redis.call("hincrby", KEYS[1], "used", requested)
	end

	redis.call("hset", KEYS[1], "capacity", capacity)

	return allowed`

	resetScript = `local keys =  redis.call('keys', table.concat({'` + redisUsedTokenKey + `', KEYS[1] ,'*'}))
	if next(keys) ~= nil then
		redis.call('del', unpack(redis.call('keys', table.concat({'` + redisUsedTokenKey + `', KEYS[1] ,'*'})))) 
	end
	return redis.call("hmset", KEYS[2], "capacity", ARGV[1], "used", 0)`

	pingInterval        = time.Millisecond * 100
	redisRouterKeyPre   = "rate_limit:router:"
	redisMerchantKeyPre = "rate_limit:merchant:"

	fromMem     = "0"
	fromRedis   = "1"
	pingSuccess = "ping.success"
)

type TokenLimiter struct {
	// 通容量
	burst int
	// redis key
	tokenKey string
	// redi key prefix
	prefix string
	// 储存容器
	store *cache.RedisCache
	// lock
	rescueLock sync.Mutex
	// redis 健康标识
	redisAlive uint32
	// redis故障时采用进程内 令牌桶限流器。容量 = 总容量 / 2
	rescueLimter *Limiter
	// redis监控探测任务标识
	monitorStarted bool
	// 是否更新，用已重载的时候做更新判断
	update bool
}

// 初始化令牌桶
func NewTokenLimiter(burst int, prefix, tokenKey string, update bool, store *cache.RedisCache) *TokenLimiter {
	rescueBurst := burst / 2
	if rescueBurst == 0 {
		rescueBurst = 1
	}
	return &TokenLimiter{
		burst:        burst,
		prefix:       prefix,
		tokenKey:     tokenKey,
		store:        store,
		redisAlive:   1,
		rescueLimter: NewLimiter(rescueBurst),
		update:       update,
	}
}

// 获取令牌, 一次获取一个令牌
func (lim *TokenLimiter) Allow() (bool, string) {
	ok, tokenArr := lim.reserveN(1)
	if ok {
		return ok, tokenArr[0]
	}

	return ok, ""
}

func (lim *TokenLimiter) reserveN(n int) (bool, []string) {
	if atomic.LoadUint32(&lim.redisAlive) == 0 {
		return lim.rescueLimter.AllowN(n)
	}

	resp, err := lim.store.Eval(script, []string{
		lim.prefix + lim.tokenKey,
	}, []string{
		strconv.Itoa(lim.burst),
		strconv.Itoa(n),
	})

	// redis allowed == false
	// Lua boolean false -> r Nil bulk reply
	if err == redis.Nil {
		return false, nil
	} else if err != nil {
		// 执行异常，开启redis健康探测任务
		// 同时采用进程内限流器作为兜底
		lim.startMonitor()
		return lim.rescueLimter.AllowN(n)
	}

	code, ok := resp.(int64)
	if !ok {
		// redis 限流执行失败，使用内存限流
		// 执行异常，开启redis健康探测任务
		// 同时采用进程内限流器作为兜底
		lim.startMonitor()
		return lim.rescueLimter.AllowN(n)
	}

	if code == 1 {
		tokenArr := make([]string, 0, n)
		for i := 0; i < n; i++ {
			// 生成令牌
			token := getToken(fromRedis)
			tokenArr = append(tokenArr, token)

			// 存储令牌
			storeToken(lim.store, lim.prefix, lim.tokenKey, token)
		}

		return true, tokenArr
	}

	return false, nil
}

func (lim *TokenLimiter) startMonitor() {
	lim.rescueLock.Lock()
	defer lim.rescueLock.Unlock()

	if lim.monitorStarted {
		return
	}

	lim.monitorStarted = true
	atomic.StoreUint32(&lim.redisAlive, 0)

	go lim.waitForRedis()
}

func (lim *TokenLimiter) waitForRedis() {
	ticker := time.NewTicker(pingInterval)
	defer func() {
		ticker.Stop()
		lim.rescueLock.Lock()
		lim.monitorStarted = false
		lim.rescueLock.Unlock()
	}()

	for range ticker.C {
		if lim.store.Ping() {
			atomic.StoreUint32(&lim.redisAlive, 1)
			// 重置当前桶
			// 在redis不可用的时候，某些令牌可能得不到释放，所以redis一旦恢复可用直接重置全部桶
			reload(pingSuccess)
			return
		}
	}
}

func (lim *TokenLimiter) Reload() {
	lim.rescueLock.Lock()

	_, err := lim.store.Eval(resetScript, []string{
		lim.tokenKey,
		lim.prefix + lim.tokenKey,
	}, []string{
		strconv.Itoa(lim.burst),
	})

	if err == redis.Nil {
		lim.rescueLock.Unlock()
		// 重载失败
		lim.startMonitor()
		return
	}

	lim.update = false

	lim.rescueLock.Unlock()
	return
}

func (lim *TokenLimiter) release(token string) {
	from := getTokenfrom(token)

	switch from {
	case fromRedis:
		if !releaseToken(lim.store, lim.prefix, lim.tokenKey, token) {
			// redis 限流执行失败
			// 执行异常，开启redis健康探测任务
			lim.startMonitor()
		}
		break
	case fromMem:
		lim.rescueLimter.releaseToken(token)
	}
}