import { Observable } from '../Observable';
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import { async } from '../scheduler/async';
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import { SchedulerAction, SchedulerLike } from '../types';
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import { isNumeric } from '../util/isNumeric';
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import { Subscriber } from '../Subscriber';
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/**
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* Creates an Observable that emits sequential numbers every specified
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* interval of time, on a specified {@link SchedulerLike}.
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*
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* <span class="informal">Emits incremental numbers periodically in time.
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* </span>
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*
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* 
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*
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* `interval` returns an Observable that emits an infinite sequence of
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* ascending integers, with a constant interval of time of your choosing
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* between those emissions. The first emission is not sent immediately, but
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* only after the first period has passed. By default, this operator uses the
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* `async` {@link SchedulerLike} to provide a notion of time, but you may pass any
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* {@link SchedulerLike} to it.
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*
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* ## Example
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* Emits ascending numbers, one every second (1000ms) up to the number 3
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* ```ts
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* import { interval } from 'rxjs';
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* import { take } from 'rxjs/operators';
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*
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* const numbers = interval(1000);
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*
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* const takeFourNumbers = numbers.pipe(take(4));
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*
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* takeFourNumbers.subscribe(x => console.log('Next: ', x));
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*
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* // Logs:
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* // Next: 0
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* // Next: 1
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* // Next: 2
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* // Next: 3
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* ```
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*
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* @see {@link timer}
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* @see {@link delay}
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*
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* @param {number} [period=0] The interval size in milliseconds (by default)
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* or the time unit determined by the scheduler's clock.
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* @param {SchedulerLike} [scheduler=async] The {@link SchedulerLike} to use for scheduling
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* the emission of values, and providing a notion of "time".
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* @return {Observable} An Observable that emits a sequential number each time
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* interval.
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* @static true
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* @name interval
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* @owner Observable
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*/
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export function interval(period = 0,
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scheduler: SchedulerLike = async): Observable<number> {
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if (!isNumeric(period) || period < 0) {
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period = 0;
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}
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if (!scheduler || typeof scheduler.schedule !== 'function') {
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scheduler = async;
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}
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return new Observable<number>(subscriber => {
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subscriber.add(
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scheduler.schedule(dispatch, period, { subscriber, counter: 0, period })
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);
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return subscriber;
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});
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}
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function dispatch(this: SchedulerAction<IntervalState>, state: IntervalState) {
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const { subscriber, counter, period } = state;
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subscriber.next(counter);
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this.schedule({ subscriber, counter: counter + 1, period }, period);
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}
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interface IntervalState {
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subscriber: Subscriber<number>;
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counter: number;
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period: number;
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}
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