package filer

import (
	"context"
	"fmt"
	"io"
	"sync"
	"time"

	"github.com/golang/protobuf/proto"
	"google.golang.org/grpc"

	"github.com/chrislusf/seaweedfs/weed/glog"
	"github.com/chrislusf/seaweedfs/weed/pb"
	"github.com/chrislusf/seaweedfs/weed/pb/filer_pb"
	"github.com/chrislusf/seaweedfs/weed/util/log_buffer"
)

type MetaAggregator struct {
	filers         []string
	grpcDialOption grpc.DialOption
	MetaLogBuffer  *log_buffer.LogBuffer
	// notifying clients
	ListenersLock sync.Mutex
	ListenersCond *sync.Cond
}

// MetaAggregator only aggregates data "on the fly". The logs are not re-persisted to disk.
// The old data comes from what each LocalMetadata persisted on disk.
func NewMetaAggregator(filers []string, grpcDialOption grpc.DialOption) *MetaAggregator {
	t := &MetaAggregator{
		filers:         filers,
		grpcDialOption: grpcDialOption,
	}
	t.ListenersCond = sync.NewCond(&t.ListenersLock)
	t.MetaLogBuffer = log_buffer.NewLogBuffer(LogFlushInterval, nil, func() {
		t.ListenersCond.Broadcast()
	})
	return t
}

func (ma *MetaAggregator) StartLoopSubscribe(f *Filer, self string) {
	for _, filer := range ma.filers {
		go ma.subscribeToOneFiler(f, self, filer)
	}
}

func (ma *MetaAggregator) subscribeToOneFiler(f *Filer, self string, filer string) {

	var maybeReplicateMetadataChange func(*filer_pb.SubscribeMetadataResponse)
	lastPersistTime := time.Now()
	changesSinceLastPersist := 0
	lastTsNs := time.Now().Add(-LogFlushInterval).UnixNano()

	MaxChangeLimit := 100

	if localStore, ok := f.Store.ActualStore.(FilerLocalStore); ok {
		if self != filer {

			if prevTsNs, err := localStore.ReadOffset(filer); err == nil {
				lastTsNs = prevTsNs
			}

			glog.V(0).Infof("follow filer: %v, last %v (%d)", filer, time.Unix(0, lastTsNs), lastTsNs)
			maybeReplicateMetadataChange = func(event *filer_pb.SubscribeMetadataResponse) {
				if err := Replay(f.Store.ActualStore, event); err != nil {
					glog.Errorf("failed to reply metadata change from %v: %v", filer, err)
					return
				}
				changesSinceLastPersist++
				if changesSinceLastPersist >= MaxChangeLimit || lastPersistTime.Add(time.Minute).Before(time.Now()) {
					if err := localStore.UpdateOffset(filer, event.TsNs); err == nil {
						lastPersistTime = time.Now()
						changesSinceLastPersist = 0
					} else {
						glog.V(0).Infof("failed to update offset for %v: %v", filer, err)
					}
				}
			}
		} else {
			glog.V(0).Infof("skipping following self: %v", self)
		}
	}

	processEventFn := func(event *filer_pb.SubscribeMetadataResponse) error {
		data, err := proto.Marshal(event)
		if err != nil {
			glog.Errorf("failed to marshal subscribed filer_pb.SubscribeMetadataResponse %+v: %v", event, err)
			return err
		}
		dir := event.Directory
		// println("received meta change", dir, "size", len(data))
		ma.MetaLogBuffer.AddToBuffer([]byte(dir), data, event.TsNs)
		if maybeReplicateMetadataChange != nil {
			maybeReplicateMetadataChange(event)
		}
		return nil
	}

	for {
		err := pb.WithFilerClient(filer, ma.grpcDialOption, func(client filer_pb.SeaweedFilerClient) error {
			stream, err := client.SubscribeLocalMetadata(context.Background(), &filer_pb.SubscribeMetadataRequest{
				ClientName: "filer:" + self,
				PathPrefix: "/",
				SinceNs:    lastTsNs,
			})
			if err != nil {
				return fmt.Errorf("subscribe: %v", err)
			}

			for {
				resp, listenErr := stream.Recv()
				if listenErr == io.EOF {
					return nil
				}
				if listenErr != nil {
					return listenErr
				}

				if err := processEventFn(resp); err != nil {
					return fmt.Errorf("process %v: %v", resp, err)
				}
				lastTsNs = resp.TsNs
			}
		})
		if err != nil {
			glog.V(0).Infof("subscribing remote %s meta change: %v", filer, err)
			time.Sleep(1733 * time.Millisecond)
		}
	}
}