# All files / core sync_engine.ts

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     /**
     * Copyright 2017 Google Inc.
     *
     * 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.
     */

    import { User } from '../auth/user';
    import { EagerGarbageCollector } from '../local/eager_garbage_collector';
    import { LocalStore } from '../local/local_store';
    import { LocalViewChanges } from '../local/local_view_changes';
    import { QueryData, QueryPurpose } from '../local/query_data';
    import { ReferenceSet } from '../local/reference_set';
    import { MaybeDocumentMap } from '../model/collections';
    import { MaybeDocument, NoDocument } from '../model/document';
    import { DocumentKey } from '../model/document_key';
    import { Mutation } from '../model/mutation';
    import { MutationBatchResult } from '../model/mutation_batch';
    import { CurrentStatusUpdate, RemoteEvent } from '../remote/remote_event';
    import { RemoteStore } from '../remote/remote_store';
    import { RemoteSyncer } from '../remote/remote_syncer';
    import { assert, fail } from '../util/assert';
    import { FirestoreError } from '../util/error';
    import * as log from '../util/log';
    import { AnyJs, primitiveComparator } from '../util/misc';
    import * as objUtils from '../util/obj';
    import { ObjectMap } from '../util/obj_map';
    import { Deferred } from '../util/promise';
    import { SortedMap } from '../util/sorted_map';
    import { isNullOrUndefined } from '../util/types';

    import { Query } from './query';
    import { SnapshotVersion } from './snapshot_version';
    import { TargetIdGenerator } from './target_id_generator';
    import { Transaction } from './transaction';
    import { BatchId, OnlineState, ProtoByteString, TargetId } from './types';
    import {
      AddedLimboDocument,
      LimboDocumentChange,
      RemovedLimboDocument,
      View,
      ViewDocumentChanges
    } from './view';
    import { ViewSnapshot } from './view_snapshot';

    const LOG_TAG = 'SyncEngine';

    export type ViewHandler = (viewSnaps: ViewSnapshot[]) => void;
    export type ErrorHandler = (query: Query, error: Error) => void;

    /**
     * QueryView contains all of the data that SyncEngine needs to keep track of for
     * a particular query.
     */
    class QueryView {
      constructor(
        /**
         * The query itself.
         */
        public query: Query,
        /**
         * The target number created by the client that is used in the watch
         * stream to identify this query.
         */
        public targetId: TargetId,
        /**
         * An identifier from the datastore backend that indicates the last state
         * of the results that was received. This can be used to indicate where
         * to continue receiving new doc changes for the query.
         */
        public resumeToken: ProtoByteString,
        /**
         * The view is responsible for computing the final merged truth of what
         * docs are in the query. It gets notified of local and remote changes,
         * and applies the query filters and limits to determine the most correct
         * possible results.
         */
        public view: View
      ) {}
    }

    /**
     * SyncEngine is the central controller in the client SDK architecture. It is
     * the glue code between the EventManager, LocalStore, and RemoteStore. Some of
     * SyncEngine's responsibilities include:
     * 1. Coordinating client requests and remote events between the EventManager
     *    and the local and remote data stores.
     * 2. Managing a View object for each query, providing the unified view between
     *    the local and remote data stores.
     * 3. Notifying the RemoteStore when the LocalStore has new mutations in its
     *    queue that need sending to the backend.
     *
     * The SyncEngine’s methods should only ever be called by methods running in the
     * global async queue.
     */
    export class SyncEngine implements RemoteSyncer {
      private viewHandler: ViewHandler | null = null;
      private errorHandler: ErrorHandler | null = null;

      private queryViewsByQuery = new ObjectMap<Query, QueryView>(q =>
        q.canonicalId()
      );
      private queryViewsByTarget: { [targetId: number]: QueryView } = {};
      private limboTargetsByKey = new SortedMap<DocumentKey, TargetId>(
        DocumentKey.comparator
      );
      private limboKeysByTarget: { [targetId: number]: DocumentKey } = {};
      private limboDocumentRefs = new ReferenceSet();
      private limboCollector = new EagerGarbageCollector();
      /** Stores user completion handlers, indexed by User and BatchId. */
      private mutationUserCallbacks = {} as {
        [uidKey: string]: SortedMap<BatchId, Deferred<void>>;
      };
      private targetIdGenerator = TargetIdGenerator.forSyncEngine();

      constructor(
        private localStore: LocalStore,
        private remoteStore: RemoteStore,
        private currentUser: User
      ) {}

      /** Subscribes view and error handler. Can be called only once. */
      subscribe(viewHandler: ViewHandler, errorHandler: ErrorHandler): void {
        assert(
          viewHandler !== null && errorHandler !== null,
          'View and error handlers cannot be null'
        );
        assert(
          this.viewHandler === null && this.errorHandler === null,
          'SyncEngine already has a subscriber.'
        );
        this.viewHandler = viewHandler;
        this.errorHandler = errorHandler;
        this.limboCollector.addGarbageSource(this.limboDocumentRefs);
      }

      /**
       * Initiates the new listen, resolves promise when listen enqueued to the
       * server. All the subsequent view snapshots or errors are sent to the
       * subscribed handlers. Returns the targetId of the query.
       */
      listen(query: Query): Promise<TargetId> {
        this.assertSubscribed('listen()');
        assert(
          !this.queryViewsByQuery.has(query),
          'We already listen to the query: ' + query
        );

        return this.localStore.allocateQuery(query).then(queryData => {
          return this.localStore
            .executeQuery(query)
            .then(docs => {
              return this.localStore
                .remoteDocumentKeys(queryData.targetId)
                .then(remoteKeys => {
                  const view = new View(query, remoteKeys);
                  const viewDocChanges = view.computeDocChanges(docs);
                  const viewChange = view.applyChanges(viewDocChanges);
                  assert(
                    viewChange.limboChanges.length === 0,
                    'View returned limbo docs before target ack from the server.'
                  );
                  assert(
                    !!viewChange.snapshot,
                    'applyChanges for new view should always return a snapshot'
                  );

                  const data = new QueryView(
                    query,
                    queryData.targetId,
                    queryData.resumeToken,
                    view
                  );
                  this.queryViewsByQuery.set(query, data);
                  this.queryViewsByTarget[queryData.targetId] = data;
                  this.viewHandler!([viewChange.snapshot!]);
                  this.remoteStore.listen(queryData);
                });
            })
            .then(() => {
              return queryData.targetId;
            });
        });
      }

      /** Stops listening to the query. */
      unlisten(query: Query): Promise<void> {
        this.assertSubscribed('unlisten()');

        const queryView = this.queryViewsByQuery.get(query)!;
        assert(!!queryView, 'Trying to unlisten on query not found:' + query);

        return this.localStore.releaseQuery(query).then(() => {
          this.remoteStore.unlisten(queryView.targetId);
          return this.removeAndCleanupQuery(queryView).then(() => {
            return this.localStore.collectGarbage();
          });
        });
      }

      /**
       * Initiates the write of local mutation batch which involves adding the
       * writes to the mutation queue, notifying the remote store about new
       * mutations and raising events for any changes this write caused.
       *
       * The promise returned by this call is resolved when the above steps
       * have completed, *not* when the write was acked by the backend. The
       * userCallback is resolved once the write was acked/rejected by the
       * backend (or failed locally for any other reason).
       */
      write(batch: Mutation[], userCallback: Deferred<void>): Promise<void> {
        this.assertSubscribed('write()');
        return this.localStore
          .localWrite(batch)
          .then(result => {
            this.addMutationCallback(result.batchId, userCallback);
            return this.emitNewSnapsAndNotifyLocalStore(result.changes);
          })
          .then(() => {
            return this.remoteStore.fillWritePipeline();
          });
      }

      // TODO(klimt): Wrap the given error in a standard Firestore error object.
      private wrapUpdateFunctionError(error: AnyJs): AnyJs {
        return error;
      }

      /**
       * Takes an updateFunction in which a set of reads and writes can be performed
       * atomically. In the updateFunction, the client can read and write values
       * using the supplied transaction object. After the updateFunction, all
       * changes will be committed. If some other client has changed any of the data
       * referenced, then the updateFunction will be called again. If the
       * updateFunction still fails after the given number of retries, then the
       * transaction will be rejection.
       *
       * The transaction object passed to the updateFunction contains methods for
       * accessing documents and collections. Unlike other datastore access, data
       * accessed with the transaction will not reflect local changes that have not
       * been committed. For this reason, it is required that all reads are
       * performed before any writes. Transactions must be performed while online.
       *
       * The promise returned is resolved when the transaction is fully committed.
       */
      runTransaction<T>(
        updateFunction: (transaction: Transaction) => Promise<T>,
        retries = 5
      ): Promise<T> {
        assert(retries >= 0, 'Got negative number of retries for transaction.');
        const transaction = this.remoteStore.createTransaction();
        const wrappedUpdateFunction = () => {
          try {
            const userPromise = updateFunction(transaction);
            if (
              isNullOrUndefined(userPromise) ||
              !userPromise.catch ||
              !userPromise.then
            ) {
              return Promise.reject<T>(
                Error('Transaction callback must return a Promise')
              );
            }
            return userPromise.catch(e => {
              return Promise.reject<T>(this.wrapUpdateFunctionError(e));
            });
          } catch (e) {
            return Promise.reject<T>(this.wrapUpdateFunctionError(e));
          }
        };
        return wrappedUpdateFunction().then(result => {
          return transaction
            .commit()
            .then(() => {
              return result;
            })
            .catch(error => {
              if (retries === 0) {
                return Promise.reject<T>(error);
              }
              // TODO(klimt): Put in a retry delay?
              return this.runTransaction(updateFunction, retries - 1);
            });
        });
      }

      applyRemoteEvent(remoteEvent: RemoteEvent): Promise<void> {
        this.assertSubscribed('applyRemoteEvent()');

        // Make sure limbo documents are deleted if there were no results
        objUtils.forEachNumber(
          remoteEvent.targetChanges,
          (targetId, targetChange) => {
            const limboKey = this.limboKeysByTarget[targetId];
            if (
              limboKey &&
              targetChange.currentStatusUpdate ===
                CurrentStatusUpdate.MarkCurrent &&
              !remoteEvent.documentUpdates.get(limboKey)
            ) {
              // When listening to a query the server responds with a snapshot
              // containing documents matching the query and a current marker
              // telling us we're now in sync. It's possible for these to arrive
              // as separate remote events or as a single remote event.
              // For a document query, there will be no documents sent in the
              // response if the document doesn't exist.
              //
              // If the snapshot arrives separately from the current marker,
              // we handle it normally and updateTrackedLimbos will resolve the
              // limbo status of the document, removing it from limboDocumentRefs.
              // This works because clients only initiate limbo resolution when
              // a target is current and because all current targets are
              // always at a consistent snapshot.
              //
              // However, if the document doesn't exist and the current marker
              // arrives, the document is not present in the snapshot and our
              // normal view handling would consider the document to remain in
              // limbo indefinitely because there are no updates to the document.
              // To avoid this, we specially handle this just this case here:
              // synthesizing a delete.
              //
              // TODO(dimond): Ideally we would have an explicit lookup query
              // instead resulting in an explicit delete message and we could
              // remove this special logic.
              remoteEvent.addDocumentUpdate(
                new NoDocument(limboKey, remoteEvent.snapshotVersion)
              );
            }
          }
        );

        return this.localStore.applyRemoteEvent(remoteEvent).then(changes => {
          return this.emitNewSnapsAndNotifyLocalStore(changes, remoteEvent);
        });
      }

      /**
       * Applies an OnlineState change to the sync engine and notifies any views of
       * the change.
       */
      applyOnlineStateChange(onlineState: OnlineState) {
        const newViewSnapshots = [] as ViewSnapshot[];
        this.queryViewsByQuery.forEach((query, queryView) => {
          const viewChange = queryView.view.applyOnlineStateChange(onlineState);
          assert(
            viewChange.limboChanges.length === 0,
            'OnlineState should not affect limbo documents.'
          );
          if (viewChange.snapshot) {
            newViewSnapshots.push(viewChange.snapshot);
          }
        });
        this.viewHandler(newViewSnapshots);
      }

      rejectListen(targetId: TargetId, err: FirestoreError): Promise<void> {
        this.assertSubscribed('rejectListens()');
        const limboKey = this.limboKeysByTarget[targetId];
        if (limboKey) {
          // Since this query failed, we won't want to manually unlisten to it.
          // So go ahead and remove it from bookkeeping.
          this.limboTargetsByKey = this.limboTargetsByKey.remove(limboKey);
          delete this.limboKeysByTarget[targetId];

          // TODO(klimt): We really only should do the following on permission
          // denied errors, but we don't have the cause code here.

          // It's a limbo doc. Create a synthetic event saying it was deleted.
          // This is kind of a hack. Ideally, we would have a method in the local
          // store to purge a document. However, it would be tricky to keep all of
          // the local store's invariants with another method.
          let docMap = new SortedMap<DocumentKey, MaybeDocument>(
            DocumentKey.comparator
          );
          docMap = docMap.insert(
            limboKey,
            new NoDocument(limboKey, SnapshotVersion.forDeletedDoc())
          );
          const event = new RemoteEvent(SnapshotVersion.MIN, {}, docMap);
          return this.applyRemoteEvent(event);
        } else {
          const queryView = this.queryViewsByTarget[targetId];
          assert(!!queryView, 'Unknown targetId: ' + targetId);
          return this.localStore.releaseQuery(queryView.query).then(() => {
            return this.removeAndCleanupQuery(queryView).then(() => {
              this.errorHandler!(queryView.query, err);
            });
          });
        }
      }

      applySuccessfulWrite(
        mutationBatchResult: MutationBatchResult
      ): Promise<void> {
        this.assertSubscribed('applySuccessfulWrite()');

        // The local store may or may not be able to apply the write result and
        // raise events immediately (depending on whether the watcher is caught
        // up), so we raise user callbacks first so that they consistently happen
        // before listen events.
        this.processUserCallback(
          mutationBatchResult.batch.batchId,
          /*error=*/ null
        );

        return this.localStore
          .acknowledgeBatch(mutationBatchResult)
          .then(changes => {
            return this.emitNewSnapsAndNotifyLocalStore(changes);
          });
      }

      rejectFailedWrite(batchId: BatchId, error: FirestoreError): Promise<void> {
        this.assertSubscribed('rejectFailedWrite()');

        // The local store may or may not be able to apply the write result and
        // raise events immediately (depending on whether the watcher is caught up),
        // so we raise user callbacks first so that they consistently happen before
        // listen events.
        this.processUserCallback(batchId, error);

        return this.localStore.rejectBatch(batchId).then(changes => {
          return this.emitNewSnapsAndNotifyLocalStore(changes);
        });
      }

      private addMutationCallback(
        batchId: BatchId,
        callback: Deferred<void>
      ): void {
        let newCallbacks = this.mutationUserCallbacks[this.currentUser.toKey()];
        if (!newCallbacks) {
          newCallbacks = new SortedMap<BatchId, Deferred<void>>(
            primitiveComparator
          );
        }
        newCallbacks = newCallbacks.insert(batchId, callback);
        this.mutationUserCallbacks[this.currentUser.toKey()] = newCallbacks;
      }

      /**
       * Resolves or rejects the user callback for the given batch and then discards
       * it.
       */
      private processUserCallback(batchId: BatchId, error: Error | null): void {
        let newCallbacks = this.mutationUserCallbacks[this.currentUser.toKey()];

        // NOTE: Mutations restored from persistence won't have callbacks, so it's
        // okay for there to be no callback for this ID.
        if (newCallbacks) {
          const callback = newCallbacks.get(batchId);
          Eif (callback) {
            assert(
              batchId === newCallbacks.minKey(),
              'Mutation callbacks processed out-of-order?'
            );
            if (error) {
              callback.reject(error);
            } else {
              callback.resolve();
            }
            newCallbacks = newCallbacks.remove(batchId);
          }
          this.mutationUserCallbacks[this.currentUser.toKey()] = newCallbacks;
        }
      }

      private removeAndCleanupQuery(queryView: QueryView): Promise<void> {
        this.queryViewsByQuery.delete(queryView.query);
        delete this.queryViewsByTarget[queryView.targetId];

        this.limboDocumentRefs.removeReferencesForId(queryView.targetId);
        return this.gcLimboDocuments();
      }

      private updateTrackedLimbos(
        targetId: TargetId,
        limboChanges: LimboDocumentChange[]
      ): Promise<void> {
        for (const limboChange of limboChanges) {
          if (limboChange instanceof AddedLimboDocument) {
            this.limboDocumentRefs.addReference(limboChange.key, targetId);
            this.trackLimboChange(limboChange);
          } else Eif (limboChange instanceof RemovedLimboDocument) {
            log.debug(LOG_TAG, 'Document no longer in limbo: ' + limboChange.key);
            this.limboDocumentRefs.removeReference(limboChange.key, targetId);
          } else {
            fail('Unknown limbo change: ' + JSON.stringify(limboChange));
          }
        }
        return this.gcLimboDocuments();
      }

      private trackLimboChange(limboChange: AddedLimboDocument): void {
        const key = limboChange.key;
        Eif (!this.limboTargetsByKey.get(key)) {
          log.debug(LOG_TAG, 'New document in limbo: ' + key);
          const limboTargetId = this.targetIdGenerator.next();
          const query = Query.atPath(key.path);
          this.limboKeysByTarget[limboTargetId] = key;
          this.remoteStore.listen(
            new QueryData(query, limboTargetId, QueryPurpose.Listen)
          );
          this.limboTargetsByKey = this.limboTargetsByKey.insert(
            key,
            limboTargetId
          );
        }
      }

      private gcLimboDocuments(): Promise<void> {
        // HACK: We can use a null transaction here, because we know that the
        // reference set is entirely within memory and doesn't need a store engine.
        return this.limboCollector
          .collectGarbage(null)
          .next(keys => {
            keys.forEach(key => {
              const limboTargetId = this.limboTargetsByKey.get(key);
              if (limboTargetId === null) {
                // This target already got removed, because the query failed.
                return;
              }
              this.remoteStore.unlisten(limboTargetId);
              this.limboTargetsByKey = this.limboTargetsByKey.remove(key);
              delete this.limboKeysByTarget[limboTargetId];
            });
          })
          .toPromise();
      }

      // Visible for testing
      currentLimboDocs(): SortedMap<DocumentKey, TargetId> {
        return this.limboTargetsByKey;
      }

      private emitNewSnapsAndNotifyLocalStore(
        changes: MaybeDocumentMap,
        remoteEvent?: RemoteEvent
      ): Promise<void> {
        const newSnaps: ViewSnapshot[] = [];
        const docChangesInAllViews: LocalViewChanges[] = [];
        const queriesProcessed: Array<Promise<void>> = [];

        this.queryViewsByQuery.forEach((_, queryView) => {
          queriesProcessed.push(
            Promise.resolve()
              .then(() => {
                const viewDocChanges = queryView.view.computeDocChanges(changes);
                if (!viewDocChanges.needsRefill) {
                  return viewDocChanges;
                }
                // The query has a limit and some docs were removed, so we need
                // to re-run the query against the local store to make sure we
                // didn't lose any good docs that had been past the limit.
                return this.localStore.executeQuery(queryView.query).then(docs => {
                  return queryView.view.computeDocChanges(docs, viewDocChanges);
                });
              })
              .then((viewDocChanges: ViewDocumentChanges) => {
                const targetChange =
                  remoteEvent && remoteEvent.targetChanges[queryView.targetId];
                const viewChange = queryView.view.applyChanges(
                  viewDocChanges,
                  targetChange
                );
                return this.updateTrackedLimbos(
                  queryView.targetId,
                  viewChange.limboChanges
                ).then(() => {
                  if (viewChange.snapshot) {
                    newSnaps.push(viewChange.snapshot);
                    const docChanges = LocalViewChanges.fromSnapshot(
                      viewChange.snapshot
                    );
                    docChangesInAllViews.push(docChanges);
                  }
                });
              })
          );
        });

        return Promise.all(queriesProcessed)
          .then(() => {
            this.viewHandler!(newSnaps);
            return this.localStore.notifyLocalViewChanges(docChangesInAllViews);
          })
          .then(() => {
            return this.localStore.collectGarbage();
          });
      }

      private assertSubscribed(fnName: string): void {
        assert(
          this.viewHandler !== null && this.errorHandler !== null,
          'Trying to call ' + fnName + ' before calling subscribe().'
        );
      }

      handleUserChange(user: User): Promise<void> {
        this.currentUser = user;
        return this.localStore
          .handleUserChange(user)
          .then(changes => {
            return this.emitNewSnapsAndNotifyLocalStore(changes);
          })
          .then(() => {
            return this.remoteStore.handleUserChange(user);
          });
      }
    }