/*
Copyright 2014 CoreOS Inc.

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

 http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/

package etcdserver

import (
	"bytes"
	"fmt"
	"log"
	"net/http"
	"sync"
	"sync/atomic"
	"time"
)

const (
	maxInflight = 4
)

const (
	participantPeer = iota
	idlePeer
	stoppedPeer
)

type peer struct {
	url           string
	queue         chan []byte
	status        int
	inflight      atomicInt
	c             *http.Client
	followerStats *raftFollowerStats
	mu            sync.RWMutex
	wg            sync.WaitGroup
}

func newPeer(url string, c *http.Client, followerStats *raftFollowerStats) *peer {
	return &peer{
		url:           url,
		status:        idlePeer,
		c:             c,
		followerStats: followerStats,
	}
}

func (p *peer) participate() {
	p.mu.Lock()
	defer p.mu.Unlock()
	p.queue = make(chan []byte)
	p.status = participantPeer
	for i := 0; i < maxInflight; i++ {
		p.wg.Add(1)
		go p.handle(p.queue)
	}
}

func (p *peer) idle() {
	p.mu.Lock()
	defer p.mu.Unlock()
	if p.status == participantPeer {
		close(p.queue)
	}
	p.status = idlePeer
}

func (p *peer) stop() {
	p.mu.Lock()
	if p.status == participantPeer {
		close(p.queue)
	}
	p.status = stoppedPeer
	p.mu.Unlock()
	p.wg.Wait()
}

func (p *peer) handle(queue chan []byte) {
	defer p.wg.Done()
	for d := range queue {
		p.post(d)
	}
}

func (p *peer) send(d []byte) error {
	p.mu.Lock()
	defer p.mu.Unlock()

	switch p.status {
	case participantPeer:
		select {
		case p.queue <- d:
		default:
			return fmt.Errorf("reach max serving")
		}
	case idlePeer:
		if p.inflight.Get() > maxInflight {
			return fmt.Errorf("reach max idle")
		}
		p.wg.Add(1)
		go func() {
			p.post(d)
			p.wg.Done()
		}()
	case stoppedPeer:
		return fmt.Errorf("sender stopped")
	}
	return nil
}

func (p *peer) post(d []byte) {
	p.inflight.Add(1)
	defer p.inflight.Add(-1)
	buf := bytes.NewBuffer(d)
	start := time.Now()
	resp, err := p.c.Post(p.url, "application/octet-stream", buf)
	end := time.Now()
	// TODO: Have no way to detect RPC success or failure now
	p.followerStats.Succ(end.Sub(start))
	if err != nil {
		log.Printf("peer.post url=%s err=\"%v\"", p.url, err)
		return
	}
	resp.Body.Close()
}

// An AtomicInt is an int64 to be accessed atomically.
type atomicInt int64

func (i *atomicInt) Add(d int64) {
	atomic.AddInt64((*int64)(i), d)
}

func (i *atomicInt) Get() int64 {
	return atomic.LoadInt64((*int64)(i))
}

func (i *atomicInt) Set(n int64) {
	atomic.StoreInt64((*int64)(i), n)
}