# All files / local local_view_changes.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 { Query } from '../core/query';
    import { ChangeType, ViewSnapshot } from '../core/view_snapshot';
    import { documentKeySet, DocumentKeySet } from '../model/collections';

    /**
     * A set of changes to what documents are currently in view and out of view for
     * a given query. These changes are sent to the LocalStore by the View (via
     * the SyncEngine) and are used to pin / unpin documents as appropriate.
     */
    export class LocalViewChanges {
      constructor(
        readonly query: Query,
        readonly addedKeys: DocumentKeySet,
        readonly removedKeys: DocumentKeySet
      ) {}

      static fromSnapshot(viewSnapshot: ViewSnapshot): LocalViewChanges {
        let addedKeys = documentKeySet();
        let removedKeys = documentKeySet();

        for (const docChange of viewSnapshot.docChanges) {
          switch (docChange.type) {
            case ChangeType.Added:
              addedKeys = addedKeys.add(docChange.doc.key);
              break;
            case ChangeType.Removed:
              removedKeys = removedKeys.add(docChange.doc.key);
              break;
            default:
            // do nothing
          }
        }

        return new LocalViewChanges(viewSnapshot.query, addedKeys, removedKeys);
      }
    }