// waitDeletes efficiently waits until all keys matched by Get(key, opts...) are deleted
func waitDeletes(ctx context.Context, client *v3.Client, key string, opts ...v3.OpOption) error {
	getOpts := []v3.OpOption{v3.WithSort(v3.SortByCreatedRev, v3.SortAscend)}
	getOpts = append(getOpts, opts...)
	resp, err := client.Get(ctx, key, getOpts...)
	maxRev := int64(math.MaxInt64)
	getOpts = append(getOpts, v3.WithRev(0))
	for err == nil {
		for len(resp.Kvs) > 0 {
			i := len(resp.Kvs) - 1
			if resp.Kvs[i].CreateRevision <= maxRev {
				break
			}
			resp.Kvs = resp.Kvs[:i]
		}
		if len(resp.Kvs) == 0 {
			break
		}
		lastKV := resp.Kvs[len(resp.Kvs)-1]
		maxRev = lastKV.CreateRevision
		err = waitDelete(ctx, client, string(lastKV.Key), maxRev)
		if err != nil || len(resp.Kvs) == 1 {
			break
		}
		getOpts = append(getOpts, v3.WithLimit(int64(len(resp.Kvs)-1)))
		resp, err = client.Get(ctx, key, getOpts...)
	}
	return err
}

func (s *syncer) SyncBase(ctx context.Context) (<-chan clientv3.GetResponse, chan error) {
	respchan := make(chan clientv3.GetResponse, 1024)
	errchan := make(chan error, 1)

	kapi := clientv3.NewKV(s.c)
	// if rev is not specified, we will choose the most recent revision.
	if s.rev == 0 {
		resp, err := kapi.Get(ctx, "foo")
		if err != nil {
			errchan <- err
			close(respchan)
			close(errchan)
			return respchan, errchan
		}
		s.rev = resp.Header.Revision
	}

	go func() {
		defer close(respchan)
		defer close(errchan)

		var key string

		opts := []clientv3.OpOption{clientv3.WithLimit(batchLimit), clientv3.WithRev(s.rev)}

		if len(s.prefix) == 0 {
			// If len(s.prefix) == 0, we will sync the entire key-value space.
			// We then range from the smallest key (0x00) to the end.
			opts = append(opts, clientv3.WithFromKey())
			key = "\x00"
		} else {
			// If len(s.prefix) != 0, we will sync key-value space with given prefix.
			// We then range from the prefix to the next prefix if exists. Or we will
			// range from the prefix to the end if the next prefix does not exists.
			opts = append(opts, clientv3.WithPrefix())
			key = s.prefix
		}

		for {
			resp, err := kapi.Get(ctx, key, opts...)
			if err != nil {
				errchan <- err
				return
			}

			respchan <- (clientv3.GetResponse)(*resp)

			if !resp.More {
				return
			}
			// move to next key
			key = string(append(resp.Kvs[len(resp.Kvs)-1].Key, 0))
		}
	}()

	return respchan, errchan
}

func getGetOp(cmd *cobra.Command, args []string) (string, []clientv3.OpOption) {
	if len(args) == 0 {
		ExitWithError(ExitBadArgs, fmt.Errorf("range command needs arguments."))
	}

	opts := []clientv3.OpOption{}
	key := args[0]
	if len(args) > 1 {
		opts = append(opts, clientv3.WithRange(args[1]))
	}
	opts = append(opts, clientv3.WithLimit(getLimit))

	sortByOrder := clientv3.SortNone
	sortOrder := strings.ToUpper(getSortOrder)
	switch {
	case sortOrder == "ASCEND":
		sortByOrder = clientv3.SortAscend
	case sortOrder == "DESCEND":
		sortByOrder = clientv3.SortDescend
	case sortOrder == "":
		// nothing
	default:
		ExitWithError(ExitBadFeature, fmt.Errorf("bad sort order %v", getSortOrder))
	}

	sortByTarget := clientv3.SortByKey
	sortTarget := strings.ToUpper(getSortTarget)
	switch {
	case sortTarget == "CREATE":
		sortByTarget = clientv3.SortByCreatedRev
	case sortTarget == "KEY":
		sortByTarget = clientv3.SortByKey
	case sortTarget == "MODIFY":
		sortByTarget = clientv3.SortByModifiedRev
	case sortTarget == "VALUE":
		sortByTarget = clientv3.SortByValue
	case sortTarget == "VERSION":
		sortByTarget = clientv3.SortByVersion
	case sortTarget == "":
		// nothing
	default:
		ExitWithError(ExitBadFeature, fmt.Errorf("bad sort target %v", getSortTarget))
	}

	opts = append(opts, clientv3.WithSort(sortByTarget, sortByOrder))
	return key, opts
}

func RangeRequestToOp(r *pb.RangeRequest) clientv3.Op {
	opts := []clientv3.OpOption{}
	if len(r.RangeEnd) != 0 {
		opts = append(opts, clientv3.WithRange(string(r.RangeEnd)))
	}
	opts = append(opts, clientv3.WithRev(r.Revision))
	opts = append(opts, clientv3.WithLimit(r.Limit))
	opts = append(opts, clientv3.WithSort(
		clientv3.SortTarget(r.SortTarget),
		clientv3.SortOrder(r.SortOrder)),
	)

	if r.Serializable {
		opts = append(opts, clientv3.WithSerializable())
	}

	return clientv3.OpGet(string(r.Key), opts...)
}

func getGetOp(cmd *cobra.Command, args []string) (string, []clientv3.OpOption) {
	if len(args) == 0 {
		ExitWithError(ExitBadArgs, fmt.Errorf("range command needs arguments."))
	}

	if getPrefix && getFromKey {
		ExitWithError(ExitBadArgs, fmt.Errorf("`--prefix` and `--from-key` cannot be set at the same time, choose one."))
	}

	opts := []clientv3.OpOption{}
	switch getConsistency {
	case "s":
		opts = append(opts, clientv3.WithSerializable())
	case "l":
	default:
		ExitWithError(ExitBadFeature, fmt.Errorf("unknown consistency flag %q", getConsistency))
	}

	key := args[0]
	if len(args) > 1 {
		if getPrefix || getFromKey {
			ExitWithError(ExitBadArgs, fmt.Errorf("too many arguments, only accept one arguement when `--prefix` or `--from-key` is set."))
		}
		opts = append(opts, clientv3.WithRange(args[1]))
	}

	opts = append(opts, clientv3.WithLimit(getLimit))
	if getRev > 0 {
		opts = append(opts, clientv3.WithRev(getRev))
	}

	sortByOrder := clientv3.SortNone
	sortOrder := strings.ToUpper(getSortOrder)
	switch {
	case sortOrder == "ASCEND":
		sortByOrder = clientv3.SortAscend
	case sortOrder == "DESCEND":
		sortByOrder = clientv3.SortDescend
	case sortOrder == "":
		// nothing
	default:
		ExitWithError(ExitBadFeature, fmt.Errorf("bad sort order %v", getSortOrder))
	}

	sortByTarget := clientv3.SortByKey
	sortTarget := strings.ToUpper(getSortTarget)
	switch {
	case sortTarget == "CREATE":
		sortByTarget = clientv3.SortByCreateRevision
	case sortTarget == "KEY":
		sortByTarget = clientv3.SortByKey
	case sortTarget == "MODIFY":
		sortByTarget = clientv3.SortByModRevision
	case sortTarget == "VALUE":
		sortByTarget = clientv3.SortByValue
	case sortTarget == "VERSION":
		sortByTarget = clientv3.SortByVersion
	case sortTarget == "":
		// nothing
	default:
		ExitWithError(ExitBadFeature, fmt.Errorf("bad sort target %v", getSortTarget))
	}

	opts = append(opts, clientv3.WithSort(sortByTarget, sortByOrder))

	if getPrefix {
		opts = append(opts, clientv3.WithPrefix())
	}

	if getFromKey {
		opts = append(opts, clientv3.WithFromKey())
	}

	return key, opts
}