//++++++++++++++++++++++++++++++++++++++++
// 《Go语言设计模式》源码
//++++++++++++++++++++++++++++++++++++++++
// Author:廖显东（ShirDon）
// Blog:https://www.shirdon.com/
// 作者知乎：https://www.zhihu.com/people/shirdonl
// 仓库地址：https://gitee.com/shirdonl/goDesignPattern
// 仓库地址：https://github.com/shirdonl/goDesignPattern
// 交流咨询，请关注公众号"源码大数据"
//++++++++++++++++++++++++++++++++++++++++

package actualCombat

import (
	"errors"
	"log"
	"math/rand"
	"sync"
	"time"
)

const getResMaxTime = 3 * time.Second

var (
	ErrPoolNotExist  = errors.New("pool not exist")
	ErrGetResTimeout = errors.New("get resource time out")
)

//资源类
type Resource struct {
	reusable int
}

//初始化资源对象
//模拟缓慢的资源访问，例如，TCP 连接等
func NewResource(id int) *Resource {
	time.Sleep(500 * time.Millisecond)
	return &Resource{reusable: id}
}

//模拟资源耗时
func (r *Resource) Do(workId int) {
	time.Sleep(time.Duration(rand.Intn(5)) * 100 * time.Millisecond)
	log.Printf("using resource #%d finished work %d finish\n", r.reusable, workId)
}

//对象池
type Pool chan *Resource

//并发创建资源对象，节省资源对象初始化时间
func New(size int) Pool {
	p := make(Pool, size)
	wg := new(sync.WaitGroup)
	wg.Add(size)
	for i := 0; i < size; i++ {
		go func(reusable int) {
			p <- NewResource(reusable)
			wg.Done()
		}(i)
	}
	wg.Wait()
	return p
}

//从获取对象池获取对象
func (p Pool) GetResource() (r *Resource, err error) {
	select {
	case r := <-p:
		return r, nil
	case <-time.After(getResMaxTime):
		return nil, ErrGetResTimeout
	}
}

//将资源返回到资源池
func (p Pool) GiveBackResource(r *Resource) error {
	if p == nil {
		return ErrPoolNotExist
	}
	p <- r
	return nil
}