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import { Observable } from '../Observable';
import { Operator } from '../Operator';
import { Subscriber } from '../Subscriber';
import { Notification } from '../Notification';
import { MonoTypeOperatorFunction, PartialObserver, SchedulerAction, SchedulerLike, TeardownLogic } from '../types';
/**
*
* Re-emits all notifications from source Observable with specified scheduler.
*
* <span class="informal">Ensure a specific scheduler is used, from outside of an Observable.</span>
*
* `observeOn` is an operator that accepts a scheduler as a first parameter, which will be used to reschedule
* notifications emitted by the source Observable. It might be useful, if you do not have control over
* internal scheduler of a given Observable, but want to control when its values are emitted nevertheless.
*
* Returned Observable emits the same notifications (nexted values, complete and error events) as the source Observable,
* but rescheduled with provided scheduler. Note that this doesn't mean that source Observables internal
* scheduler will be replaced in any way. Original scheduler still will be used, but when the source Observable emits
* notification, it will be immediately scheduled again - this time with scheduler passed to `observeOn`.
* An anti-pattern would be calling `observeOn` on Observable that emits lots of values synchronously, to split
* that emissions into asynchronous chunks. For this to happen, scheduler would have to be passed into the source
* Observable directly (usually into the operator that creates it). `observeOn` simply delays notifications a
* little bit more, to ensure that they are emitted at expected moments.
*
* As a matter of fact, `observeOn` accepts second parameter, which specifies in milliseconds with what delay notifications
* will be emitted. The main difference between {@link delay} operator and `observeOn` is that `observeOn`
* will delay all notifications - including error notifications - while `delay` will pass through error
* from source Observable immediately when it is emitted. In general it is highly recommended to use `delay` operator
* for any kind of delaying of values in the stream, while using `observeOn` to specify which scheduler should be used
* for notification emissions in general.
*
* ## Example
* Ensure values in subscribe are called just before browser repaint.
* ```javascript
* const intervals = interval(10); // Intervals are scheduled
* // with async scheduler by default...
* intervals.pipe(
* observeOn(animationFrameScheduler), // ...but we will observe on animationFrame
* ) // scheduler to ensure smooth animation.
* .subscribe(val => {
* someDiv.style.height = val + 'px';
* });
* ```
*
* @see {@link delay}
*
* @param {SchedulerLike} scheduler Scheduler that will be used to reschedule notifications from source Observable.
* @param {number} [delay] Number of milliseconds that states with what delay every notification should be rescheduled.
* @return {Observable<T>} Observable that emits the same notifications as the source Observable,
* but with provided scheduler.
*
* @method observeOn
* @owner Observable
*/
export function observeOn<T>(scheduler: SchedulerLike, delay: number = 0): MonoTypeOperatorFunction<T> {
return function observeOnOperatorFunction(source: Observable<T>): Observable<T> {
return source.lift(new ObserveOnOperator(scheduler, delay));
};
}
export class ObserveOnOperator<T> implements Operator<T, T> {
constructor(private scheduler: SchedulerLike, private delay: number = 0) {
}
call(subscriber: Subscriber<T>, source: any): TeardownLogic {
return source.subscribe(new ObserveOnSubscriber(subscriber, this.scheduler, this.delay));
}
}
/**
* We need this JSDoc comment for affecting ESDoc.
* @ignore
* @extends {Ignored}
*/
export class ObserveOnSubscriber<T> extends Subscriber<T> {
/** @nocollapse */
static dispatch(this: SchedulerAction<ObserveOnMessage>, arg: ObserveOnMessage) {
const { notification, destination } = arg;
notification.observe(destination);
this.unsubscribe();
}
constructor(destination: Subscriber<T>,
private scheduler: SchedulerLike,
private delay: number = 0) {
super(destination);
}
private scheduleMessage(notification: Notification<any>): void {
this.add(this.scheduler.schedule(
ObserveOnSubscriber.dispatch,
this.delay,
new ObserveOnMessage(notification, this.destination)
));
}
protected _next(value: T): void {
this.scheduleMessage(Notification.createNext(value));
}
protected _error(err: any): void {
this.scheduleMessage(Notification.createError(err));
}
protected _complete(): void {
this.scheduleMessage(Notification.createComplete());
}
}
export class ObserveOnMessage {
constructor(public notification: Notification<any>,
public destination: PartialObserver<any>) {
}
}
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