// Licensed to the LF AI & Data foundation under one
// or more contributor license agreements. See the NOTICE file
// distributed with this work for additional information
// regarding copyright ownership. The ASF 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 gc

import (
	"math"
	"os"
	"runtime"
	"strconv"
	"sync"
	"time"

	"go.uber.org/zap"

	"github.com/milvus-io/milvus/pkg/log"
	"github.com/milvus-io/milvus/pkg/util/hardware"
)

var (
	f    *finalizer
	once sync.Once

	defaultGOGC     int
	previousGOGC    uint32
	minGOGC         uint32
	maxGOGC         uint32
	memoryThreshold uint64

	action func(uint32)
)

type finalizer struct {
	ref *finalizerRef
}

type finalizerRef struct {
	parent *finalizer
}

// just a finializer to handle go gc
func finalizerHandler(f *finalizerRef) {
	optimizeGOGC()
	runtime.SetFinalizer(f, finalizerHandler)
}

func optimizeGOGC() {
	var m runtime.MemStats
	// This will trigger a STW so be careful
	runtime.ReadMemStats(&m)

	heapuse := m.HeapInuse

	totaluse := hardware.GetUsedMemoryCount()

	var newGoGC uint32
	if totaluse > memoryThreshold {
		newGoGC = minGOGC
	} else {
		heapTarget := memoryThreshold - (totaluse - heapuse)
		newGoGC = uint32(math.Floor(float64(heapTarget-heapuse) / float64(heapuse) * 100))
		if newGoGC < minGOGC {
			newGoGC = minGOGC
		} else if newGoGC > maxGOGC {
			newGoGC = maxGOGC
		}
	}

	action(newGoGC)

	toMB := func(mem uint64) uint64 {
		return mem / 1024 / 1024
	}

	// currently we assume 20 ms as long gc pause
	if (m.PauseNs[(m.NumGC+255)%256] / uint64(time.Millisecond)) < 20 {
		log.Debug("GC Tune done", zap.Uint32("previous GOGC", previousGOGC),
			zap.Uint64("heapuse ", toMB(heapuse)),
			zap.Uint64("total memory", toMB(totaluse)),
			zap.Uint64("next GC", toMB(m.NextGC)),
			zap.Uint32("new GOGC", newGoGC),
			zap.Duration("gc-pause", time.Duration(m.PauseNs[(m.NumGC+255)%256])),
			zap.Uint64("gc-pause-end", m.PauseEnd[(m.NumGC+255)%256]),
		)
	} else {
		log.Warn("GC Tune done, and the gc is slow", zap.Uint32("previous GOGC", previousGOGC),
			zap.Uint64("heapuse ", toMB(heapuse)),
			zap.Uint64("total memory", toMB(totaluse)),
			zap.Uint64("next GC", toMB(m.NextGC)),
			zap.Uint32("new GOGC", newGoGC),
			zap.Duration("gc-pause", time.Duration(m.PauseNs[(m.NumGC+255)%256])),
			zap.Uint64("gc-pause-end", m.PauseEnd[(m.NumGC+255)%256]),
		)
	}
	previousGOGC = newGoGC
}

func NewTuner(targetPercent float64, minimumGOGCConfig uint32, maximumGOGCConfig uint32, fn func(uint322 uint32)) *finalizer {
	once.Do(func() {
		// initiate GOGC parameter
		if envGOGC := os.Getenv("GOGC"); envGOGC != "" {
			n, err := strconv.Atoi(envGOGC)
			if err == nil {
				defaultGOGC = n
			}
		} else {
			// the default value of GOGC is 100 for now
			defaultGOGC = 100
		}
		action = fn
		minGOGC = minimumGOGCConfig
		maxGOGC = maximumGOGCConfig

		previousGOGC = uint32(defaultGOGC)

		totalMemory := hardware.GetMemoryCount()
		if totalMemory == 0 {
			log.Warn("Failed to get memory count, disable gc auto tune", zap.Int("Initial GoGC", defaultGOGC))
			// noop
			action = func(uint32) {}
			return
		}
		memoryThreshold = uint64(float64(totalMemory) * targetPercent)
		log.Info("GC Helper initialized.", zap.Uint32("Initial GoGC", previousGOGC),
			zap.Uint32("minimumGOGC", minGOGC),
			zap.Uint32("maximumGOGC", maxGOGC),
			zap.Uint64("memoryThreshold", memoryThreshold))
		f := &finalizer{}

		f.ref = &finalizerRef{parent: f}
		runtime.SetFinalizer(f.ref, finalizerHandler)
		f.ref = nil
	})
	return f
}