1import { Operator } from '../Operator';
2import { Observable } from '../Observable';
3import { Subscriber } from '../Subscriber';
4import { Subscription } from '../Subscription';
5
6import { MonoTypeOperatorFunction, SubscribableOrPromise, TeardownLogic } from '../types';
7import { SimpleOuterSubscriber, innerSubscribe, SimpleInnerSubscriber } from '../innerSubscribe';
8
9export interface ThrottleConfig {
10  leading?: boolean;
11  trailing?: boolean;
12}
13
14export const defaultThrottleConfig: ThrottleConfig = {
15  leading: true,
16  trailing: false
17};
18
19/**
20 * Emits a value from the source Observable, then ignores subsequent source
21 * values for a duration determined by another Observable, then repeats this
22 * process.
23 *
24 * <span class="informal">It's like {@link throttleTime}, but the silencing
25 * duration is determined by a second Observable.</span>
26 *
27 * ![](throttle.png)
28 *
29 * `throttle` emits the source Observable values on the output Observable
30 * when its internal timer is disabled, and ignores source values when the timer
31 * is enabled. Initially, the timer is disabled. As soon as the first source
32 * value arrives, it is forwarded to the output Observable, and then the timer
33 * is enabled by calling the `durationSelector` function with the source value,
34 * which returns the "duration" Observable. When the duration Observable emits a
35 * value or completes, the timer is disabled, and this process repeats for the
36 * next source value.
37 *
38 * ## Example
39 * Emit clicks at a rate of at most one click per second
40 * ```ts
41 * import { fromEvent } from 'rxjs';
42 * import { throttle } from 'rxjs/operators';
43 *
44 * const clicks = fromEvent(document, 'click');
45 * const result = clicks.pipe(throttle(ev => interval(1000)));
46 * result.subscribe(x => console.log(x));
47 * ```
48 *
49 * @see {@link audit}
50 * @see {@link debounce}
51 * @see {@link delayWhen}
52 * @see {@link sample}
53 * @see {@link throttleTime}
54 *
55 * @param {function(value: T): SubscribableOrPromise} durationSelector A function
56 * that receives a value from the source Observable, for computing the silencing
57 * duration for each source value, returned as an Observable or a Promise.
58 * @param {Object} config a configuration object to define `leading` and `trailing` behavior. Defaults
59 * to `{ leading: true, trailing: false }`.
60 * @return {Observable<T>} An Observable that performs the throttle operation to
61 * limit the rate of emissions from the source.
62 * @method throttle
63 * @owner Observable
64 */
65export function throttle<T>(durationSelector: (value: T) => SubscribableOrPromise<any>,
66                            config: ThrottleConfig = defaultThrottleConfig): MonoTypeOperatorFunction<T> {
67  return (source: Observable<T>) => source.lift(new ThrottleOperator(durationSelector, !!config.leading, !!config.trailing));
68}
69
70class ThrottleOperator<T> implements Operator<T, T> {
71  constructor(private durationSelector: (value: T) => SubscribableOrPromise<any>,
72              private leading: boolean,
73              private trailing: boolean) {
74  }
75
76  call(subscriber: Subscriber<T>, source: any): TeardownLogic {
77    return source.subscribe(
78      new ThrottleSubscriber(subscriber, this.durationSelector, this.leading, this.trailing)
79    );
80  }
81}
82
83/**
84 * We need this JSDoc comment for affecting ESDoc
85 * @ignore
86 * @extends {Ignored}
87 */
88class ThrottleSubscriber<T, R> extends SimpleOuterSubscriber<T, R> {
89  private _throttled?: Subscription;
90  private _sendValue?: T;
91  private _hasValue = false;
92
93  constructor(protected destination: Subscriber<T>,
94              private durationSelector: (value: T) => SubscribableOrPromise<number>,
95              private _leading: boolean,
96              private _trailing: boolean) {
97    super(destination);
98  }
99
100  protected _next(value: T): void {
101    this._hasValue = true;
102    this._sendValue = value;
103
104    if (!this._throttled) {
105      if (this._leading) {
106        this.send();
107      } else {
108        this.throttle(value);
109      }
110    }
111  }
112
113  private send() {
114    const { _hasValue, _sendValue } = this;
115    if (_hasValue) {
116      this.destination.next(_sendValue);
117      this.throttle(_sendValue!);
118    }
119    this._hasValue = false;
120    this._sendValue = undefined;
121  }
122
123  private throttle(value: T): void {
124    const duration = this.tryDurationSelector(value);
125    if (!!duration) {
126      this.add(this._throttled = innerSubscribe(duration, new SimpleInnerSubscriber(this)));
127    }
128  }
129
130  private tryDurationSelector(value: T): SubscribableOrPromise<any> | null {
131    try {
132      return this.durationSelector(value);
133    } catch (err) {
134      this.destination.error(err);
135      return null;
136    }
137  }
138
139  private throttlingDone() {
140    const { _throttled, _trailing } = this;
141    if (_throttled) {
142      _throttled.unsubscribe();
143    }
144    this._throttled = undefined;
145
146    if (_trailing) {
147      this.send();
148    }
149  }
150
151  notifyNext(): void {
152    this.throttlingDone();
153  }
154
155  notifyComplete(): void {
156    this.throttlingDone();
157  }
158}
159