1// Copyright (C) 2019 The Android Open Source Project
2//
3// Licensed under the Apache License, Version 2.0 (the "License");
4// you may not use this file except in compliance with the License.
5// You may obtain a copy of the License at
6//
7//      http://www.apache.org/licenses/LICENSE-2.0
8//
9// Unless required by applicable law or agreed to in writing, software
10// distributed under the License is distributed on an "AS IS" BASIS,
11// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
12// See the License for the specific language governing permissions and
13// limitations under the License.
14
15import {LoadingTracker} from '../common/engine';
16import {globals} from './globals';
17
18// Used to keep track of whether the engine is currently querying.
19export class LoadingManager implements LoadingTracker {
20  private static _instance: LoadingManager;
21  private numQueuedQueries = 0;
22  private numLastUpdate = 0;
23
24  static get getInstance(): LoadingManager {
25    return this._instance || (this._instance = new this());
26  }
27
28  beginLoading() {
29    this.update(1);
30  }
31
32  endLoading() {
33    this.update(-1);
34  }
35
36  private update(change: number) {
37    this.numQueuedQueries += change;
38    if (this.numQueuedQueries === 0 ||
39        Math.abs(this.numLastUpdate - this.numQueuedQueries) > 2) {
40      this.numLastUpdate = this.numQueuedQueries;
41      globals.publish('Loading', this.numQueuedQueries);
42    }
43  }
44}
45