package discovery

import (
	"context"
	"errors"
	"github.com/google/uuid"
	clientv3 "go.etcd.io/etcd/client/v3"
	"log"
	"time"
)

// 服务注册的通用接口
type Registrar interface {
	// 注册服务
	Register(service Service) error

	// 注销服务
	DeRegister() error
}

// 基于Etcd的服务发现中间件，实现Registrar
type RegistrarEtcd struct {
	// 客户端信息
	cli *clientv3.Client
	// 租约信息，基于租约来做健康监测
	leaseID  clientv3.LeaseID
	leaseTTL int64
	// 续约响应channel
	leaseKeepAliveRespCh <-chan *clientv3.LeaseKeepAliveResponse
}

const leaseTTL = 5

// 初始化方法
// 实例化一个初始化了必要字段的数据
func NewRegistrarEtcd(endpoints []string) (*RegistrarEtcd, error) {
	// 一，没有etcd的地址，直接返回
	if len(endpoints) == 0 {
		return nil, errors.New("endpoints is empty")
	}

	// 二，连接etcd
	cli, err := clientv3.New(clientv3.Config{
		Endpoints:   endpoints,
		DialTimeout: 3 * time.Second,
	})
	if err != nil {
		return nil, err
	}

	// 三，初始化RegistrarEtcd
	// 设置必要的属性
	re := &RegistrarEtcd{
		cli:      cli,
		leaseTTL: leaseTTL,
	}

	// 返回对象
	return re, nil
}

// 实现接口方法
func (re *RegistrarEtcd) Register(service Service) error {
	//一，租约的申请 lease grant
	grantResp, err := re.cli.Grant(context.Background(), re.leaseTTL)
	if err != nil {
		return err
	}
	//grantResp.ID 就是租约ID
	re.leaseID = grantResp.ID

	//二，将服务标识:服务地址 put到etcd中，同时绑定租约
	key := service.Name() + "-" + uuid.New().String()
	_, err = re.cli.Put(context.Background(), key, service.Addr(), clientv3.WithLease(re.leaseID))
	if err != nil {
		return err
	}

	//三，租约续约
	re.leaseKeepAliveRespCh, err = re.cli.KeepAlive(context.Background(), re.leaseID)
	if err != nil {
		return err
	}
	// 并发的接收续约的响应
	go re.HandleKeepAliveResp()
	// log
	log.Printf("service %s(%s) was registed \n", service.Name(), service.Addr())
	return nil
}
func (re *RegistrarEtcd) HandleKeepAliveResp() {
	// 从ch中接收内容即可
	for resp := range re.leaseKeepAliveRespCh {
		log.Printf("service was Keepalive with %x\n", resp.ID)
	}
}

// 注销
// 撤销租约
func (re *RegistrarEtcd) DeRegister() error {
	// lease revoke
	if _, err := re.cli.Revoke(context.Background(), re.leaseID); err != nil {
		return err
	}

	// close etcd client
	if err := re.cli.Close(); err != nil {
		return err
	}

	return nil
}