// Copyright 2015 The Vanadium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

package vsync

// Veyron Sync hook to the Store Watch API.  When applications update objects
// in the local Veyron Store, Sync learns about these via the Watch API stream
// of object mutations.  In turn, this Sync watcher thread updates the DAG and
// ILog records to track the object change histories.

import (
	"time"

	"v.io/v23/context"
	"v.io/x/lib/vlog"
)

var (
	// watchRetryDelay is how long the watcher waits before calling the Watch() RPC again
	// after the previous call fails.
	watchRetryDelay = 2 * time.Second
	// streamRetryDelay is how long the watcher waits before creating a new Watch stream
	// after the previous stream ends.
	streamRetryDelay = 1 * time.Second
)

// syncWatcher contains the metadata for the Sync Watcher thread.
type syncWatcher struct {
	// syncd is a pointer to the Syncd instance owning this Watcher.
	syncd *syncd
}

// newWatcher creates a new Sync Watcher instance attached to the given Syncd instance.
func newWatcher(syncd *syncd) *syncWatcher {
	return &syncWatcher{syncd: syncd}
}

func (w *syncWatcher) watchStreamCanceler(cancel context.CancelFunc, done <-chan struct{}) {
	select {
	case <-w.syncd.closed:
		vlog.VI(1).Info("watchStreamCanceler: Syncd channel closed, cancel stream and exit")
		cancel()
	case <-done:
		vlog.VI(1).Info("watchStreamCanceler: done, exit")
	}
}

// watchStore consumes change records obtained by watching the store
// for updates and applies them to the sync DBs.
func (w *syncWatcher) watchStore() {
	defer w.syncd.pending.Done()

	// 	// If no Veyron store is configured, there is nothing to watch.
	// 	if w.syncd.store == nil {
	// 		vlog.VI(1).Info("watchStore: Veyron store not configured; skipping the watcher")
	// 		return
	// 	}

	// 	// Get a Watch stream, process it, repeat till end-of-life.
	// 	for {
	// 		ctx, _ := vtrace.SetNewTrace(w.syncd.ctx)
	// 		ctx, cancel := context.WithCancel(ctx)
	// 		stream := w.getWatchStream(ctx)
	// 		if stream == nil {
	// 			return // Syncd is exiting.
	// 		}

	// 		// Spawn a goroutine to detect the Syncd "closed" channel and cancel the RPC stream
	// 		// to unblock the watcher.  The "done" channel lets the watcher terminate the goroutine.
	// 		go w.watchStreamCanceler(cancel, ctx.Done())

	// 		// Process the stream of Watch updates until it closes (similar to "tail -f").
	// 		w.processWatchStream(stream)

	// 		if w.syncd.isSyncClosing() {
	// 			return // Syncd is exiting.
	// 		}

	// 		stream.Finish()
	// 		cancel()

	// 		// TODO(rdaoud): we need a rate-limiter here in case the stream closes too quickly.
	// 		// If the stream stays up long enough, no need to sleep before getting a new one.
	// 		time.Sleep(streamRetryDelay)
	// 	}
}

// // getWatchStream() returns a Watch API stream and handles retries if the Watch() call fails.
// // If the stream is nil, it means Syncd is exiting cleanly and the caller should terminate.
// func (w *syncWatcher) getWatchStream(ctx *context.T) watch.GlobWatcherWatchGlobCall {
// 	for {
// 		w.syncd.lock.RLock()
// 		resmark := w.syncd.devtab.head.Resmark
// 		w.syncd.lock.RUnlock()

// 		req := raw.Request{}
// 		if resmark != nil {
// 			req.ResumeMarker = resmark
// 		}

// 		stream, err := w.syncd.store.Watch(ctx, req)
// 		if err == nil {
// 			return stream
// 		}

// 		if w.syncd.isSyncClosing() {
// 			vlog.VI(1).Info("getWatchStream: exiting, Syncd closed its channel: ", err)
// 			return nil
// 		}

// 		vlog.VI(1).Info("getWatchStream: call to Watch() failed, retrying a bit later: ", err)
// 		time.Sleep(watchRetryDelay)
// 	}
// }

// // processWatchStream reads the stream of Watch updates and applies the object mutations.
// // Ideally this call does not return as the stream should be un-ending (like "tail -f").
// // If the stream is closed, distinguish between the cases of end-of-stream vs Syncd canceling
// // the stream to trigger a clean exit.
// func (w *syncWatcher) processWatchStream(call watch.GlobWatcherWatchGlobCall) {
// 	var txChanges []*types.Change = nil
// 	var syncTime int64

// 	stream := call.RecvStream()
// 	for stream.Advance() {
// 		change := stream.Value()

// 		// Timestamp of the start of a batch of changes arriving at the Sync server.
// 		if txChanges == nil {
// 			syncTime = time.Now().UnixNano()
// 		}
// 		txChanges = append(txChanges, &change)

// 		// Process the transaction when its last change record is received.
// 		if !change.Continued {
// 			if err := w.processTransaction(txChanges, syncTime); err != nil {
// 				// TODO(rdaoud): don't crash, instead add retry policies to attempt some degree of
// 				// self-healing from a data corruption where feasible, otherwise quarantine this device
// 				// from the cluster and stop Syncd to avoid propagating data corruptions.
// 				vlog.Fatal("processWatchStream:", err)
// 			}
// 			txChanges = nil
// 		}
// 	}

// 	err := stream.Err()
// 	if err == nil {
// 		err = io.EOF
// 	}

// 	if w.syncd.isSyncClosing() {
// 		vlog.VI(1).Info("processWatchStream: exiting, Syncd closed its channel: ", err)
// 	} else {
// 		vlog.VI(1).Info("processWatchStream: RPC stream error, re-issue Watch(): ", err)
// 	}
// }

// // matchSyncRoot returns the SyncRoot (SyncGroup root ObjId) that matches the given object path.
// // It traverses the object path looking if any of the IDs along the way are SyncRoots.
// // If no match is found, it returns the invalid ID (zero).
// // Note: the path IDs given by Watch are ordered: object, parent, grand-parent, etc.., root.
// // As a result, this function returns the narrowest matching SyncGroup root ObjId.
// func matchSyncRoot(objPathIDs []ObjId, sgObjIds map[ObjId]struct{}) ObjId {
// 	for _, oid := range objPathIDs {
// 		if _, ok := sgObjIds[oid]; ok {
// 			return oid
// 		}
// 	}
// 	return ObjId{}
// }

// // processTransaction applies a batch of changes (object mutations) that form a single transaction
// // received from the Watch API.  The function grabs the write-lock to access the Log and DAG DBs.
// func (w *syncWatcher) processTransaction(txBatch []*types.Change, syncTime int64) error {
// 	w.syncd.lock.Lock()
// 	defer w.syncd.lock.Unlock()

// 	count := uint32(len(txBatch))
// 	if count == 0 {
// 		return nil
// 	}

// 	// Get the current set of SyncGroup Root ObjIds and use it to determine for each object
// 	// the SyncGroup it belongs to, if any.
// 	sgRootObjIds, err := w.syncd.sgtab.getAllSyncRoots()
// 	if err != nil {
// 		return err
// 	}

// 	// If the batch has more than one mutation, start a DAG transaction for it.
// 	txID := NoTxId
// 	if count > 1 {
// 		txID = w.syncd.dag.addNodeTxStart(txID)
// 		if txID == NoTxId {
// 			return fmt.Errorf("failed to generate transaction ID")
// 		}
// 	}

// 	vlog.VI(1).Infof("processTransaction: ready to process a batch of %d changes for transaction %v", count, txID)

// 	for _, ch := range txBatch {
// 		rc, ok := ch.Value.(*raw.RawChange)
// 		if !ok {
// 			return fmt.Errorf("invalid change value, not a raw change: %#v", ch)
// 		}

// 		mu := &rc.Mutation
// 		isDeleted := ch.State == types.DoesNotExist

// 		// Determine the SyncGroup root ObjId that matches this object, if any.
// 		rootObjId := matchSyncRoot(rc.PathIDs, sgRootObjIds)

// 		if rootObjId.IsValid() {
// 			// The object matches a SyncGroup: process its watch record to track it in the Sync logs.
// 			// All LogValues belonging to the same transaction get the same timestamp.
// 			val := &LogValue{
// 				Mutation: *mu,
// 				SyncTime: syncTime,
// 				Delete:   isDeleted,
// 				TxId:     txID,
// 				TxCount:  count,
// 			}
// 			vlog.VI(2).Infof("processTransaction: processing record %v, Tx %v", val, txID)

// 			err = w.syncd.log.processWatchRecord(mu.Id, mu.Version, mu.PriorVersion, val, rootObjId)
// 		} else {
// 			// The object does not match any SyncGroup: stash it in the "private" table to save its info
// 			// in case it becomes shared in the future, at which time it would be added to the Sync logs.
// 			if isDeleted {
// 				err = w.syncd.dag.delPrivNode(mu.Id)
// 			} else {
// 				priv := &privNode{Mutation: mu, PathIDs: rc.PathIDs, SyncTime: syncTime, TxId: txID, TxCount: count}
// 				err = w.syncd.dag.setPrivNode(mu.Id, priv)
// 			}
// 		}

// 		if err != nil {
// 			return fmt.Errorf("cannot process mutation: %#v, mu %#v: %s", ch, mu, err)
// 		}
// 	}

// 	// End the DAG transaction if any.
// 	if txID != NoTxId {
// 		// Note: if there are no shared objects in the transaction, the addNodeTxEnd() call
// 		// does not persist the Tx state, it only cleans up the in-memory scaffolding.
// 		// This is the desired behavior, Sync only needs to track the state of transactions
// 		// that have at least one shared object.
// 		if err := w.syncd.dag.addNodeTxEnd(txID, count); err != nil {
// 			return err
// 		}
// 	}

// 	// Update the device table with the new resume marker of the last record.
// 	w.syncd.devtab.head.Resmark = txBatch[count-1].ResumeMarker
// 	return nil
// }