// Licensed to Elasticsearch B.V. under one or more contributor
// license agreements. See the NOTICE file distributed with
// this work for additional information regarding copyright
// ownership. Elasticsearch B.V. licenses this file to you 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 logstash

import (
	"math"
	"sync/atomic"
)

type window struct {
	windowSize      int32
	maxOkWindowSize int // max window size sending was successful for
	maxWindowSize   int
}

func newWindower(start, max int) *window {
	w := &window{}
	w.init(start, max)
	return w
}

func (w *window) init(start, max int) {
	*w = window{
		windowSize:    int32(start),
		maxWindowSize: max,
	}
}

func (w *window) get() int {
	return int(atomic.LoadInt32(&w.windowSize))
}

// Increase window size by factor 1.5 until max window size
// (window size grows exponentially)
// TODO: use duration until ACK to estimate an ok max window size value
func (w *window) tryGrowWindow(batchSize int) {
	windowSize := w.get()

	if windowSize <= batchSize {
		if w.maxOkWindowSize < windowSize {
			w.maxOkWindowSize = windowSize

			newWindowSize := int(math.Ceil(1.5 * float64(windowSize)))

			if windowSize <= batchSize && batchSize < newWindowSize {
				newWindowSize = batchSize
			}
			if newWindowSize > w.maxWindowSize {
				newWindowSize = int(w.maxWindowSize)
			}

			windowSize = newWindowSize
		} else if windowSize < w.maxOkWindowSize {
			windowSize = int(math.Ceil(1.5 * float64(windowSize)))
			if windowSize > w.maxOkWindowSize {
				windowSize = w.maxOkWindowSize
			}
		}

		atomic.StoreInt32(&w.windowSize, int32(windowSize))
	}
}

func (w *window) shrinkWindow() {
	windowSize := w.get()
	orig := windowSize

	windowSize = windowSize / 2
	if windowSize < minWindowSize {
		windowSize = minWindowSize
		if windowSize == orig {
			return
		}
	}

	atomic.StoreInt32(&w.windowSize, int32(windowSize))
}