// Copyright (c) Shenyang Leading Edge Intelligent Technology Co., Ltd. All rights reserved.
package etcd

import (
	"context"
	"fmt"
	clientv3 "go.etcd.io/etcd/client/v3"
	"time"
)

/******************************************************************************
 *
 * @Function Name      :
 *-----------------------------------------------------------------------------
 *
 * @Description        :
 *
 * @Function Parameters:
 *
 * @Return Value       :
 *
 * @Author             : Lou Wenzhi
 *
 * @Date               : 2021/3/25 9:02
 *
 ******************************************************************************/

// 分布式锁(TXN事务)
type JobLock struct {
	// etcd客户端
	Client *clientv3.Client
	Kv clientv3.KV
	Lease clientv3.Lease
	JobName string // 任务名
	CancelFunc context.CancelFunc	// 用于终止自动续租
	LeaseId clientv3.LeaseID // 租约ID
	IsLocked bool // 是否上锁成功
}

var(
	G_jobLock *JobLock
)

//初始化任务锁
func InitJobLock() (err error) {
	var (
		config  clientv3.Config
		client  *clientv3.Client
		kv      clientv3.KV
		lease   clientv3.Lease

	)
	//创建config
	config = clientv3.Config{
		Endpoints:[]string{"127.0.0.1:2379"},
		DialTimeout: 5000 * time.Millisecond,
	}
	//创建client
	if client, err = clientv3.New(config); err != nil {
		fmt.Println(err)
	}
	//创建kv, lease
	kv = clientv3.NewKV(client)
	lease = clientv3.NewLease(client)
	//赋值单例
	G_jobLock = &JobLock{
		Client:client,
		Kv:kv,
		Lease:lease,
	}
	return
}


//尝试上锁
func (jobLock *JobLock) TryLock(jobName string) (err error){

	var(
		ctx context.Context
		cancelFunc context.CancelFunc
		leaseGrantRes *clientv3.LeaseGrantResponse
		leaseId clientv3.LeaseID
		KeepResChan <- chan *clientv3.LeaseKeepAliveResponse
		txn clientv3.Txn
		lockKey string
		txnRes *clientv3.TxnResponse

	)
	//创建上下文
	ctx, cancelFunc = context.WithCancel(context.TODO())
	//创建续租
	leaseGrantRes, err = jobLock.Lease.Grant(ctx, 5)
	//续租id
	leaseId = leaseGrantRes.ID
	//保持续租
	if KeepResChan, err = jobLock.Lease.KeepAlive(ctx, leaseId); err != nil{
		fmt.Println(err)
		goto FAIL
	}
	//每隔1秒续约续租
	go func() {
		var keepRes *clientv3.LeaseKeepAliveResponse
		for{
			select {
			case keepRes = <- KeepResChan:
				//如果续约失败
				if keepRes == nil{
					goto END
				}
			}
			time.Sleep(1*time.Second)
		}
	END:
	}()

	//创建事务txn
	txn = jobLock.Kv.Txn(context.TODO())
	//锁路径
	lockKey = jobName
	//事务枪锁
	txn.If(clientv3.Compare(clientv3.CreateRevision(lockKey), "=", 0)).
		Then(clientv3.OpPut(lockKey, "", clientv3.WithLease(leaseId))).
		Else(clientv3.OpGet(lockKey))

	//提交事务
	if txnRes, err = txn.Commit(); err != nil{
		fmt.Println("提交创建锁失败", err)
		goto FAIL

	}
	//如果抢锁失败
	if !txnRes.Succeeded{
		err = fmt.Errorf("锁被占用")
		goto FAIL
	}

	jobLock.CancelFunc = cancelFunc
	jobLock.LeaseId = leaseId
	jobLock.IsLocked = true

	return

FAIL:
	//释放上下文,取消续约
	cancelFunc()
	jobLock.Lease.Revoke(ctx, leaseId)  //释放租约
	return
}


//释放锁
func (jobLock *JobLock)UnLock()  {
	if jobLock.IsLocked{
		jobLock.CancelFunc() //取消自动续租协程
		jobLock.Lease.Revoke(context.TODO(), jobLock.LeaseId)  // 释放租约
	}
}