// Copyright 2017 The etcd Authors
//
// 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 v3compactor

import (
	"context"
	"errors"
	"sync"
	"time"

	"github.com/jonboulle/clockwork"
	"go.uber.org/zap"

	pb "go.etcd.io/etcd/api/v3/etcdserverpb"
	"go.etcd.io/etcd/server/v3/storage/mvcc"
)

// Periodic compacts the log by purging revisions older than
// the configured retention time.
type Periodic struct {
	lg     *zap.Logger
	clock  clockwork.Clock
	period time.Duration

	rg RevGetter
	c  Compactable

	revs   []int64
	ctx    context.Context
	cancel context.CancelFunc

	// mu protects paused
	mu     sync.RWMutex
	paused bool
}

// newPeriodic creates a new instance of Periodic compactor that purges
// the log older than h Duration.
func newPeriodic(lg *zap.Logger, clock clockwork.Clock, h time.Duration, rg RevGetter, c Compactable) *Periodic {
	pc := &Periodic{
		lg:     lg,
		clock:  clock,
		period: h,
		rg:     rg,
		c:      c,
	}
	// revs won't be longer than the retentions.
	pc.revs = make([]int64, 0, pc.getRetentions())
	pc.ctx, pc.cancel = context.WithCancel(context.Background())
	return pc
}

/*
Compaction period 1-hour:
  1. compute compaction period, which is 1-hour
  2. record revisions for every 1/10 of 1-hour (6-minute)
  3. keep recording revisions with no compaction for first 1-hour
  4. do compact with revs[0]
	- success? continue on for-loop and move sliding window; revs = revs[1:]
	- failure? update revs, and retry after 1/10 of 1-hour (6-minute)

Compaction period 24-hour:
  1. compute compaction period, which is 24-hour
  2. record revisions for every 1/10 of 24-hour (144-minute)
  3. keep recording revisions with no compaction for first 24-hour
  4. do compact with revs[0]
	- success? continue on for-loop and move sliding window; revs = revs[1:]
	- failure? update revs, and retry after 1/10 of 24-hour (144-minute)

Compaction period 59-min:
  1. compute compaction period, which is 59-min
  2. record revisions for every 1/10 of 59-min (5.9-min)
  3. keep recording revisions with no compaction for first 59-min
  4. do compact with revs[0]
	- success? continue on for-loop and move sliding window; revs = revs[1:]
	- failure? update revs, and retry after 1/10 of 59-min (5.9-min)

Compaction period 5-sec:
  1. compute compaction period, which is 5-sec
  2. record revisions for every 1/10 of 5-sec (0.5-sec)
  3. keep recording revisions with no compaction for first 5-sec
  4. do compact with revs[0]
	- success? continue on for-loop and move sliding window; revs = revs[1:]
	- failure? update revs, and retry after 1/10 of 5-sec (0.5-sec)
*/

// Run runs periodic compactor.
func (pc *Periodic) Run() {
	compactInterval := pc.getCompactInterval()
	retryInterval := pc.getRetryInterval()
	retentions := pc.getRetentions()

	go func() {
		lastRevision := int64(0)
		lastSuccess := pc.clock.Now()
		baseInterval := pc.period
		for {
			pc.revs = append(pc.revs, pc.rg.Rev())
			if len(pc.revs) > retentions {
				pc.revs = pc.revs[1:] // pc.revs[0] is always the rev at pc.period ago
			}

			select {
			case <-pc.ctx.Done():
				return
			case <-pc.clock.After(retryInterval):
				pc.mu.RLock()
				p := pc.paused
				pc.mu.RUnlock()
				if p {
					continue
				}
			}
			rev := pc.revs[0]
			if pc.clock.Now().Sub(lastSuccess) < baseInterval || rev == lastRevision {
				continue
			}

			// wait up to initial given period
			if baseInterval == pc.period {
				baseInterval = compactInterval
			}

			pc.lg.Info(
				"starting auto periodic compaction",
				zap.Int64("revision", rev),
				zap.Duration("compact-period", pc.period),
			)
			startTime := pc.clock.Now()
			_, err := pc.c.Compact(pc.ctx, &pb.CompactionRequest{Revision: rev})
			if err == nil || errors.Is(err, mvcc.ErrCompacted) {
				pc.lg.Info(
					"completed auto periodic compaction",
					zap.Int64("revision", rev),
					zap.Duration("compact-period", pc.period),
					zap.Duration("took", pc.clock.Now().Sub(startTime)),
				)
				lastRevision = rev
				lastSuccess = pc.clock.Now()
			} else {
				pc.lg.Warn(
					"failed auto periodic compaction",
					zap.Int64("revision", rev),
					zap.Duration("compact-period", pc.period),
					zap.Duration("retry-interval", retryInterval),
					zap.Error(err),
				)
			}
		}
	}()
}

// if given compaction period x is <1-hour, compact every x duration.
// (e.g. --auto-compaction-mode 'periodic' --auto-compaction-retention='10m', then compact every 10-minute)
// if given compaction period x is >1-hour, compact every hour.
// (e.g. --auto-compaction-mode 'periodic' --auto-compaction-retention='2h', then compact every 1-hour)
func (pc *Periodic) getCompactInterval() time.Duration {
	itv := pc.period
	if itv > time.Hour {
		itv = time.Hour
	}
	return itv
}

func (pc *Periodic) getRetentions() int {
	return int(pc.period/pc.getRetryInterval()) + 1
}

const retryDivisor = 10

func (pc *Periodic) getRetryInterval() time.Duration {
	itv := pc.period
	if itv > time.Hour {
		itv = time.Hour
	}
	return itv / retryDivisor
}

// Stop stops periodic compactor.
func (pc *Periodic) Stop() {
	pc.cancel()
}

// Pause pauses periodic compactor.
func (pc *Periodic) Pause() {
	pc.mu.Lock()
	pc.paused = true
	pc.mu.Unlock()
}

// Resume resumes periodic compactor.
func (pc *Periodic) Resume() {
	pc.mu.Lock()
	pc.paused = false
	pc.mu.Unlock()
}