# All files / local eager_garbage_collector.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 { DocumentKeySet, documentKeySet } from '../model/collections';
    import { DocumentKey } from '../model/document_key';

    import { GarbageCollector } from './garbage_collector';
    import { GarbageSource } from './garbage_source';
    import { PersistenceTransaction } from './persistence';
    import { PersistencePromise } from './persistence_promise';

    /**
     * A garbage collector implementation that eagerly collects documents as soon as
     * they're no longer referenced in any of its registered GarbageSources.
     *
     * This implementation keeps track of a set of keys that are potentially garbage
     * without keeping an exact reference count. During collectGarbage, the
     * collector verifies that all potential garbage keys actually have no
     * references by consulting its list of garbage sources.
     */
    export class EagerGarbageCollector implements GarbageCollector {
      readonly isEager = true;

      /**
       * The garbage collectible sources to double-check during garbage collection.
       */
      private sources: GarbageSource[] = [];

      /**
       * A set of potentially garbage keys.
       * PORTING NOTE: This would be a mutable set if Javascript had one.
       */
      private potentialGarbage: DocumentKeySet = documentKeySet();

      addGarbageSource(garbageSource: GarbageSource): void {
        this.sources.push(garbageSource);
        garbageSource.setGarbageCollector(this);
      }

      removeGarbageSource(garbageSource: GarbageSource): void {
        this.sources.splice(this.sources.indexOf(garbageSource), 1);
        garbageSource.setGarbageCollector(null);
      }

      addPotentialGarbageKey(key: DocumentKey): void {
        this.potentialGarbage = this.potentialGarbage.add(key);
      }

      collectGarbage(
        txn: PersistenceTransaction | null
      ): PersistencePromise<DocumentKeySet> {
        const promises: Array<PersistencePromise<void>> = [];
        let garbageKeys = documentKeySet();

        this.potentialGarbage.forEach(key => {
          const hasRefsPromise = this.documentHasAnyReferences(txn, key);
          promises.push(
            hasRefsPromise.next(hasRefs => {
              // If there are no references, get the key.
              if (!hasRefs) {
                garbageKeys = garbageKeys.add(key);
              }
              return PersistencePromise.resolve();
            })
          );
        });

        // Clear locally retained potential keys and returned confirmed garbage.
        this.potentialGarbage = documentKeySet();
        return PersistencePromise.waitFor(promises).next(() => garbageKeys);
      }

      documentHasAnyReferences(
        txn: PersistenceTransaction | null,
        key: DocumentKey
      ): PersistencePromise<boolean> {
        const initial = PersistencePromise.resolve(false);
        return this.sources
          .map(source => () => source.containsKey(txn, key))
          .reduce<PersistencePromise<boolean>>((promise, nextPromise) => {
            return promise.next(result => {
              if (result) {
                return PersistencePromise.resolve(true);
              } else {
                return nextPromise();
              }
            });
          }, initial);
      }
    }