import { Operator } from '../Operator';
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import { Subscriber } from '../Subscriber';
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import { ArgumentOutOfRangeError } from '../util/ArgumentOutOfRangeError';
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import { Observable } from '../Observable';
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import { MonoTypeOperatorFunction, TeardownLogic } from '../types';
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/**
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* Skip the last `count` values emitted by the source Observable.
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*
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* 
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*
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* `skipLast` returns an Observable that accumulates a queue with a length
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* enough to store the first `count` values. As more values are received,
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* values are taken from the front of the queue and produced on the result
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* sequence. This causes values to be delayed.
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*
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* ## Example
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* Skip the last 2 values of an Observable with many values
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* ```ts
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* import { range } from 'rxjs';
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* import { skipLast } from 'rxjs/operators';
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*
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* const many = range(1, 5);
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* const skipLastTwo = many.pipe(skipLast(2));
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* skipLastTwo.subscribe(x => console.log(x));
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*
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* // Results in:
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* // 1 2 3
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* ```
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*
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* @see {@link skip}
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* @see {@link skipUntil}
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* @see {@link skipWhile}
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* @see {@link take}
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*
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* @throws {ArgumentOutOfRangeError} When using `skipLast(i)`, it throws
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* ArgumentOutOrRangeError if `i < 0`.
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*
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* @param {number} count Number of elements to skip from the end of the source Observable.
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* @returns {Observable<T>} An Observable that skips the last count values
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* emitted by the source Observable.
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* @method skipLast
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* @owner Observable
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*/
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export function skipLast<T>(count: number): MonoTypeOperatorFunction<T> {
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return (source: Observable<T>) => source.lift(new SkipLastOperator(count));
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}
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class SkipLastOperator<T> implements Operator<T, T> {
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constructor(private _skipCount: number) {
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if (this._skipCount < 0) {
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throw new ArgumentOutOfRangeError;
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}
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}
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call(subscriber: Subscriber<T>, source: any): TeardownLogic {
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if (this._skipCount === 0) {
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// If we don't want to skip any values then just subscribe
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// to Subscriber without any further logic.
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return source.subscribe(new Subscriber(subscriber));
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} else {
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return source.subscribe(new SkipLastSubscriber(subscriber, this._skipCount));
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}
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}
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}
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/**
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* We need this JSDoc comment for affecting ESDoc.
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* @ignore
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* @extends {Ignored}
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*/
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class SkipLastSubscriber<T> extends Subscriber<T> {
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private _ring: T[];
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private _count: number = 0;
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constructor(destination: Subscriber<T>, private _skipCount: number) {
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super(destination);
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this._ring = new Array<T>(_skipCount);
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}
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protected _next(value: T): void {
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const skipCount = this._skipCount;
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const count = this._count++;
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if (count < skipCount) {
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this._ring[count] = value;
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} else {
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const currentIndex = count % skipCount;
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const ring = this._ring;
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const oldValue = ring[currentIndex];
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ring[currentIndex] = value;
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this.destination.next(oldValue);
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}
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}
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}
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