// Copyright 2018 gf Author(https://github.com/gogf/gf). All Rights Reserved.
//
// This Source Code Form is subject to the terms of the MIT License.
// If a copy of the MIT was not distributed with this file,
// You can obtain one at https://github.com/gogf/gf.

// Package gpool provides object-reusable concurrent-safe pool.
package gpool

import (
	"errors"
	"time"

	"github.com/gogf/gf/g/container/glist"
	"github.com/gogf/gf/g/container/gtype"
	"github.com/gogf/gf/g/os/gtime"
	"github.com/gogf/gf/g/os/gtimer"
)

// Object-Reusable Pool.
type Pool struct {
	list       *glist.List                 // Available/idle list.
	closed     *gtype.Bool                 // Whether the pool is closed.
	Expire     int64                       // Max idle time(ms), after which it is recycled.
	NewFunc    func() (interface{}, error) // Callback function to create item.
	ExpireFunc func(interface{})           // Expired destruction function for objects.
	// This function needs to be defined when the pool object
	// needs to perform additional destruction operations.
	// Eg: net.Conn, os.File, etc.
}

// Pool item.
type poolItem struct {
	expire int64       // Expire time(millisecond).
	value  interface{} // Value.
}

// Creation function for object.
type NewFunc func() (interface{}, error)

// Destruction function for object.
type ExpireFunc func(interface{})

// New returns a new object pool.
// To ensure execution efficiency, the expiration time cannot be modified once it is set.
//
// Expiration logistics:
// expire = 0 : not expired;
// expire < 0 : immediate expired after use;
// expire > 0 : timeout expired;
// Note that the expiration time unit is ** milliseconds **.
func New(expire int, newFunc NewFunc, expireFunc ...ExpireFunc) *Pool {
	r := &Pool{
		list:    glist.New(),
		closed:  gtype.NewBool(),
		Expire:  int64(expire),
		NewFunc: newFunc,
	}
	if len(expireFunc) > 0 {
		r.ExpireFunc = expireFunc[0]
	}
	gtimer.AddSingleton(time.Second, r.checkExpire)
	return r
}

// Put puts an item to pool.
func (p *Pool) Put(value interface{}) {
	item := &poolItem{
		value: value,
	}
	if p.Expire == 0 {
		item.expire = 0
	} else {
		item.expire = gtime.Millisecond() + p.Expire
	}
	p.list.PushBack(item)
}

// Clear clears pool, which means it will remove all items from pool.
func (p *Pool) Clear() {
	p.list.RemoveAll()
}

// Get picks an item from pool.
func (p *Pool) Get() (interface{}, error) {
	for !p.closed.Val() {
		if r := p.list.PopFront(); r != nil {
			f := r.(*poolItem)
			if f.expire == 0 || f.expire > gtime.Millisecond() {
				return f.value, nil
			}
		} else {
			break
		}
	}
	if p.NewFunc != nil {
		return p.NewFunc()
	}
	return nil, errors.New("pool is empty")
}

// Size returns the count of available items of pool.
func (p *Pool) Size() int {
	return p.list.Len()
}

// Close closes the pool. If <p> has ExpireFunc,
// then it automatically closes all items using this function before it's closed.
func (p *Pool) Close() {
	p.closed.Set(true)
}

// checkExpire removes expired items from pool every second.
func (p *Pool) checkExpire() {
	if p.closed.Val() {
		// If p has ExpireFunc,
		// then it must close all items using this function.
		if p.ExpireFunc != nil {
			for {
				if r := p.list.PopFront(); r != nil {
					p.ExpireFunc(r.(*poolItem).value)
				} else {
					break
				}
			}
		}
		gtimer.Exit()
	}
	for {
		// TODO Do not use Pop and Push mechanism, which is not graceful.
		if r := p.list.PopFront(); r != nil {
			item := r.(*poolItem)
			if item.expire == 0 || item.expire > gtime.Millisecond() {
				p.list.PushFront(item)
				break
			}
			if p.ExpireFunc != nil {
				p.ExpireFunc(item.value)
			}
		} else {
			break
		}
	}
}