/*
Copyright IBM Corp. 2016 All Rights Reserved.

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 gossip

import (
	"fmt"
	"sync"
	"sync/atomic"
	"time"
)

type emitBatchCallback func([]interface{})

//batchingEmitter is used for the gossip push/forwarding phase.
// Messages are added into the batchingEmitter, and they are forwarded periodically T times in batches and then discarded.
// If the batchingEmitter's stored message count reaches a certain capacity, that also triggers a message dispatch
type batchingEmitter interface {
	// Add adds a message to be batched
	Add(interface{})

	// Stop stops the component
	Stop()

	// Size returns the amount of pending messages to be emitted
	Size() int
}

// newBatchingEmitter accepts the following parameters:
// iterations: number of times each message is forwarded
// burstSize: a threshold that triggers a forwarding because of message count
// latency: the maximum delay that each message can be stored without being forwarded
// cb: a callback that is called in order for the forwarding to take place
func newBatchingEmitter(iterations, burstSize int, latency time.Duration, cb emitBatchCallback) batchingEmitter {
	if iterations < 0 {
		panic(fmt.Errorf("Got a negative iterations number"))
	}

	p := &batchingEmitterImpl{
		cb:         cb,
		delay:      latency,
		iterations: iterations,
		burstSize:  burstSize,
		lock:       &sync.Mutex{},
		buff:       make([]*batchedMessage, 0),
		stopFlag:   int32(0),
	}

	if iterations != 0 {
		go p.periodicEmit()
	}

	return p
}

func (p *batchingEmitterImpl) periodicEmit() {
	for !p.toDie() {
		time.Sleep(p.delay)
		p.lock.Lock()
		p.emit()
		p.lock.Unlock()
	}
}

func (p *batchingEmitterImpl) emit() {
	if p.toDie() {
		return
	}
	if len(p.buff) == 0 {
		return
	}
	msgs2beEmitted := make([]interface{}, len(p.buff))
	for i, v := range p.buff {
		msgs2beEmitted[i] = v.data
	}

	p.cb(msgs2beEmitted)
	p.decrementCounters()
}

func (p *batchingEmitterImpl) decrementCounters() {
	n := len(p.buff)
	for i := 0; i < n; i++ {
		msg := p.buff[i]
		msg.iterationsLeft--
		if msg.iterationsLeft == 0 {
			p.buff = append(p.buff[:i], p.buff[i+1:]...)
			n--
			i--
		}
	}
}

func (p *batchingEmitterImpl) toDie() bool {
	return atomic.LoadInt32(&(p.stopFlag)) == int32(1)
}

type batchingEmitterImpl struct {
	iterations int
	burstSize  int
	delay      time.Duration
	cb         emitBatchCallback
	lock       *sync.Mutex
	buff       []*batchedMessage
	stopFlag   int32
}

type batchedMessage struct {
	data           interface{}
	iterationsLeft int
}

func (p *batchingEmitterImpl) Stop() {
	atomic.StoreInt32(&(p.stopFlag), int32(1))
}

func (p *batchingEmitterImpl) Size() int {
	p.lock.Lock()
	defer p.lock.Unlock()
	return len(p.buff)
}

func (p *batchingEmitterImpl) Add(message interface{}) {
	if p.iterations == 0 {
		return
	}
	p.lock.Lock()
	defer p.lock.Unlock()

	p.buff = append(p.buff, &batchedMessage{data: message, iterationsLeft: p.iterations})

	if len(p.buff) >= p.burstSize {
		p.emit()
	}
}