// Copyright 2016 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 main

import (
	"context"
	"fmt"
	"math/rand"
	"sync"
	"sync/atomic"
	"time"

	"github.com/coreos/etcd/etcdserver/api/v3rpc/rpctypes"
	pb "github.com/coreos/etcd/etcdserver/etcdserverpb"

	"golang.org/x/time/rate"
	"google.golang.org/grpc"
)

const (
	// time to live for lease
	TTL      = 120
	TTLShort = 2
)

type leaseStresser struct {
	endpoint string
	cancel   func()
	conn     *grpc.ClientConn
	kvc      pb.KVClient
	lc       pb.LeaseClient
	ctx      context.Context

	rateLimiter *rate.Limiter
	// atomicModifiedKey records the number of keys created and deleted during a test case
	atomicModifiedKey int64
	numLeases         int
	keysPerLease      int

	aliveLeases      *atomicLeases
	revokedLeases    *atomicLeases
	shortLivedLeases *atomicLeases

	runWg   sync.WaitGroup
	aliveWg sync.WaitGroup
}

type atomicLeases struct {
	// rwLock is used to protect read/write access of leases map
	// which are accessed and modified by different go routines.
	rwLock sync.RWMutex
	leases map[int64]time.Time
}

func (al *atomicLeases) add(leaseID int64, t time.Time) {
	al.rwLock.Lock()
	al.leases[leaseID] = t
	al.rwLock.Unlock()
}

func (al *atomicLeases) update(leaseID int64, t time.Time) {
	al.rwLock.Lock()
	_, ok := al.leases[leaseID]
	if ok {
		al.leases[leaseID] = t
	}
	al.rwLock.Unlock()
}

func (al *atomicLeases) read(leaseID int64) (rv time.Time, ok bool) {
	al.rwLock.RLock()
	rv, ok = al.leases[leaseID]
	al.rwLock.RUnlock()
	return rv, ok
}

func (al *atomicLeases) remove(leaseID int64) {
	al.rwLock.Lock()
	delete(al.leases, leaseID)
	al.rwLock.Unlock()
}

func (al *atomicLeases) getLeasesMap() map[int64]time.Time {
	leasesCopy := make(map[int64]time.Time)
	al.rwLock.RLock()
	for k, v := range al.leases {
		leasesCopy[k] = v
	}
	al.rwLock.RUnlock()
	return leasesCopy
}

func (ls *leaseStresser) setupOnce() error {
	if ls.aliveLeases != nil {
		return nil
	}
	if ls.numLeases == 0 {
		panic("expect numLeases to be set")
	}
	if ls.keysPerLease == 0 {
		panic("expect keysPerLease to be set")
	}

	ls.aliveLeases = &atomicLeases{leases: make(map[int64]time.Time)}

	return nil
}

func (ls *leaseStresser) Stress() error {
	plog.Infof("lease Stresser %v starting ...", ls.endpoint)
	if err := ls.setupOnce(); err != nil {
		return err
	}

	conn, err := grpc.Dial(ls.endpoint, grpc.WithInsecure(), grpc.WithBackoffMaxDelay(1*time.Second))
	if err != nil {
		return fmt.Errorf("%v (%s)", err, ls.endpoint)
	}
	ls.conn = conn
	ls.kvc = pb.NewKVClient(conn)
	ls.lc = pb.NewLeaseClient(conn)
	ls.revokedLeases = &atomicLeases{leases: make(map[int64]time.Time)}
	ls.shortLivedLeases = &atomicLeases{leases: make(map[int64]time.Time)}

	ctx, cancel := context.WithCancel(context.Background())
	ls.cancel = cancel
	ls.ctx = ctx

	ls.runWg.Add(1)
	go ls.run()
	return nil
}

func (ls *leaseStresser) run() {
	defer ls.runWg.Done()
	ls.restartKeepAlives()
	for {
		// the number of keys created and deleted is roughly 2x the number of created keys for an iteration.
		// the rateLimiter therefore consumes 2x ls.numLeases*ls.keysPerLease tokens where each token represents a create/delete operation for key.
		err := ls.rateLimiter.WaitN(ls.ctx, 2*ls.numLeases*ls.keysPerLease)
		if err == context.Canceled {
			return
		}
		plog.Debugf("creating lease on %v", ls.endpoint)
		ls.createLeases()
		plog.Debugf("done creating lease on %v", ls.endpoint)
		plog.Debugf("dropping lease on %v", ls.endpoint)
		ls.randomlyDropLeases()
		plog.Debugf("done dropping lease on %v", ls.endpoint)
	}
}

func (ls *leaseStresser) restartKeepAlives() {
	for leaseID := range ls.aliveLeases.getLeasesMap() {
		ls.aliveWg.Add(1)
		go func(id int64) {
			ls.keepLeaseAlive(id)
		}(leaseID)
	}
}

func (ls *leaseStresser) createLeases() {
	ls.createAliveLeases()
	ls.createShortLivedLeases()
}

func (ls *leaseStresser) createAliveLeases() {
	neededLeases := ls.numLeases - len(ls.aliveLeases.getLeasesMap())
	var wg sync.WaitGroup
	for i := 0; i < neededLeases; i++ {
		wg.Add(1)
		go func() {
			defer wg.Done()
			leaseID, err := ls.createLeaseWithKeys(TTL)
			if err != nil {
				plog.Debugf("lease creation error: (%v)", err)
				return
			}
			ls.aliveLeases.add(leaseID, time.Now())
			// keep track of all the keep lease alive go routines
			ls.aliveWg.Add(1)
			go ls.keepLeaseAlive(leaseID)
		}()
	}
	wg.Wait()
}

func (ls *leaseStresser) createShortLivedLeases() {
	// one round of createLeases() might not create all the short lived leases we want due to falures.
	// thus, we want to create remaining short lived leases in the future round.
	neededLeases := ls.numLeases - len(ls.shortLivedLeases.getLeasesMap())
	var wg sync.WaitGroup
	for i := 0; i < neededLeases; i++ {
		wg.Add(1)
		go func() {
			defer wg.Done()
			leaseID, err := ls.createLeaseWithKeys(TTLShort)
			if err != nil {
				return
			}
			ls.shortLivedLeases.add(leaseID, time.Now())
		}()
	}
	wg.Wait()
}

func (ls *leaseStresser) createLeaseWithKeys(ttl int64) (int64, error) {
	leaseID, err := ls.createLease(ttl)
	if err != nil {
		plog.Debugf("lease creation error: (%v)", err)
		return -1, err
	}
	plog.Debugf("lease %v created ", leaseID)
	if err := ls.attachKeysWithLease(leaseID); err != nil {
		return -1, err
	}
	return leaseID, nil
}

func (ls *leaseStresser) randomlyDropLeases() {
	var wg sync.WaitGroup
	for l := range ls.aliveLeases.getLeasesMap() {
		wg.Add(1)
		go func(leaseID int64) {
			defer wg.Done()
			dropped, err := ls.randomlyDropLease(leaseID)
			// if randomlyDropLease encountered an error such as context is cancelled, remove the lease from aliveLeases
			// because we can't tell whether the lease is dropped or not.
			if err != nil {
				plog.Debugf("drop lease %v has failed error (%v)", leaseID, err)
				ls.aliveLeases.remove(leaseID)
				return
			}
			if !dropped {
				return
			}
			plog.Debugf("lease %v dropped", leaseID)
			ls.revokedLeases.add(leaseID, time.Now())
			ls.aliveLeases.remove(leaseID)
		}(l)
	}
	wg.Wait()
}

func (ls *leaseStresser) createLease(ttl int64) (int64, error) {
	resp, err := ls.lc.LeaseGrant(ls.ctx, &pb.LeaseGrantRequest{TTL: ttl})
	if err != nil {
		return -1, err
	}
	return resp.ID, nil
}

func (ls *leaseStresser) keepLeaseAlive(leaseID int64) {
	defer ls.aliveWg.Done()
	ctx, cancel := context.WithCancel(ls.ctx)
	stream, err := ls.lc.LeaseKeepAlive(ctx)
	defer func() { cancel() }()
	for {
		select {
		case <-time.After(500 * time.Millisecond):
		case <-ls.ctx.Done():
			plog.Debugf("keepLeaseAlive lease %v context canceled ", leaseID)
			// it is  possible that lease expires at invariant checking phase but not at keepLeaseAlive() phase.
			// this scenerio is possible when alive lease is just about to expire when keepLeaseAlive() exists and expires at invariant checking phase.
			// to circumvent that scenerio, we check each lease before keepalive loop exist to see if it has been renewed in last TTL/2 duration.
			// if it is renewed, this means that invariant checking have at least ttl/2 time before lease exipres which is long enough for the checking to finish.
			// if it is not renewed, we remove the lease from the alive map so that the lease doesn't exipre during invariant checking
			renewTime, ok := ls.aliveLeases.read(leaseID)
			if ok && renewTime.Add(TTL/2*time.Second).Before(time.Now()) {
				ls.aliveLeases.remove(leaseID)
				plog.Debugf("keepLeaseAlive lease %v has not been renewed. drop it.", leaseID)
			}
			return
		}

		if err != nil {
			plog.Debugf("keepLeaseAlive lease %v creates stream error: (%v)", leaseID, err)
			cancel()
			ctx, cancel = context.WithCancel(ls.ctx)
			stream, err = ls.lc.LeaseKeepAlive(ctx)
			cancel()
			continue
		}
		err = stream.Send(&pb.LeaseKeepAliveRequest{ID: leaseID})
		plog.Debugf("keepLeaseAlive stream sends lease %v keepalive request", leaseID)
		if err != nil {
			plog.Debugf("keepLeaseAlive stream sends lease %v error (%v)", leaseID, err)
			continue
		}
		leaseRenewTime := time.Now()
		plog.Debugf("keepLeaseAlive stream sends lease %v keepalive request succeed", leaseID)
		respRC, err := stream.Recv()
		if err != nil {
			plog.Debugf("keepLeaseAlive stream receives lease %v stream error (%v)", leaseID, err)
			continue
		}
		// lease expires after TTL become 0
		// don't send keepalive if the lease has expired
		if respRC.TTL <= 0 {
			plog.Debugf("keepLeaseAlive stream receives lease %v has TTL <= 0", leaseID)
			ls.aliveLeases.remove(leaseID)
			return
		}
		// renew lease timestamp only if lease is present
		plog.Debugf("keepLeaseAlive renew lease %v", leaseID)
		ls.aliveLeases.update(leaseID, leaseRenewTime)
	}
}

// attachKeysWithLease function attaches keys to the lease.
// the format of key is the concat of leaseID + '_' + '<order of key creation>'
// e.g 5186835655248304152_0 for first created key and 5186835655248304152_1 for second created key
func (ls *leaseStresser) attachKeysWithLease(leaseID int64) error {
	var txnPuts []*pb.RequestOp
	for j := 0; j < ls.keysPerLease; j++ {
		txnput := &pb.RequestOp{Request: &pb.RequestOp_RequestPut{RequestPut: &pb.PutRequest{Key: []byte(fmt.Sprintf("%d%s%d", leaseID, "_", j)),
			Value: []byte(fmt.Sprintf("bar")), Lease: leaseID}}}
		txnPuts = append(txnPuts, txnput)
	}
	// keep retrying until lease is not found or ctx is being canceled
	for ls.ctx.Err() == nil {
		txn := &pb.TxnRequest{Success: txnPuts}
		_, err := ls.kvc.Txn(ls.ctx, txn)
		if err == nil {
			// since all created keys will be deleted too, the number of operations on keys will be roughly 2x the number of created keys
			atomic.AddInt64(&ls.atomicModifiedKey, 2*int64(ls.keysPerLease))
			return nil
		}
		if rpctypes.Error(err) == rpctypes.ErrLeaseNotFound {
			return err
		}
	}
	return ls.ctx.Err()
}

// randomlyDropLease drops the lease only when the rand.Int(2) returns 1.
// This creates a 50/50 percents chance of dropping a lease
func (ls *leaseStresser) randomlyDropLease(leaseID int64) (bool, error) {
	if rand.Intn(2) != 0 {
		return false, nil
	}
	// keep retrying until a lease is dropped or ctx is being canceled
	for ls.ctx.Err() == nil {
		_, err := ls.lc.LeaseRevoke(ls.ctx, &pb.LeaseRevokeRequest{ID: leaseID})
		if err == nil || rpctypes.Error(err) == rpctypes.ErrLeaseNotFound {
			return true, nil
		}
	}
	plog.Debugf("randomlyDropLease error: (%v)", ls.ctx.Err())
	return false, ls.ctx.Err()
}

func (ls *leaseStresser) Pause() {
	ls.Close()
}

func (ls *leaseStresser) Close() {
	plog.Debugf("lease stresser %q is closing...", ls.endpoint)
	ls.cancel()
	ls.runWg.Wait()
	ls.aliveWg.Wait()
	ls.conn.Close()
	plog.Infof("lease stresser %q is closed", ls.endpoint)
}

func (ls *leaseStresser) ModifiedKeys() int64 {
	return atomic.LoadInt64(&ls.atomicModifiedKey)
}

func (ls *leaseStresser) Checker() Checker { return &leaseChecker{endpoint: ls.endpoint, ls: ls} }
