import { OperatorFunction } from '../types';
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import { operate } from '../util/lift';
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import { createOperatorSubscriber } from './OperatorSubscriber';
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import { arrRemove } from '../util/arrRemove';
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/**
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* Buffers the source Observable values until the size hits the maximum
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* `bufferSize` given.
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*
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* <span class="informal">Collects values from the past as an array, and emits
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* that array only when its size reaches `bufferSize`.</span>
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*
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* 
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*
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* Buffers a number of values from the source Observable by `bufferSize` then
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* emits the buffer and clears it, and starts a new buffer each
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* `startBufferEvery` values. If `startBufferEvery` is not provided or is
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* `null`, then new buffers are started immediately at the start of the source
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* and when each buffer closes and is emitted.
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*
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* ## Examples
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*
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* Emit the last two click events as an array
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*
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* ```ts
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* import { fromEvent, bufferCount } from 'rxjs';
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*
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* const clicks = fromEvent(document, 'click');
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* const buffered = clicks.pipe(bufferCount(2));
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* buffered.subscribe(x => console.log(x));
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* ```
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*
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* On every click, emit the last two click events as an array
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*
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* ```ts
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* import { fromEvent, bufferCount } from 'rxjs';
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*
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* const clicks = fromEvent(document, 'click');
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* const buffered = clicks.pipe(bufferCount(2, 1));
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* buffered.subscribe(x => console.log(x));
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* ```
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*
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* @see {@link buffer}
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* @see {@link bufferTime}
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* @see {@link bufferToggle}
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* @see {@link bufferWhen}
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* @see {@link pairwise}
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* @see {@link windowCount}
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*
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* @param {number} bufferSize The maximum size of the buffer emitted.
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* @param {number} [startBufferEvery] Interval at which to start a new buffer.
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* For example if `startBufferEvery` is `2`, then a new buffer will be started
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* on every other value from the source. A new buffer is started at the
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* beginning of the source by default.
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* @return A function that returns an Observable of arrays of buffered values.
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*/
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export function bufferCount<T>(bufferSize: number, startBufferEvery: number | null = null): OperatorFunction<T, T[]> {
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// If no `startBufferEvery` value was supplied, then we're
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// opening and closing on the bufferSize itself.
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startBufferEvery = startBufferEvery ?? bufferSize;
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return operate((source, subscriber) => {
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let buffers: T[][] = [];
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let count = 0;
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source.subscribe(
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createOperatorSubscriber(
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subscriber,
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(value) => {
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let toEmit: T[][] | null = null;
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// Check to see if we need to start a buffer.
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// This will start one at the first value, and then
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// a new one every N after that.
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if (count++ % startBufferEvery! === 0) {
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buffers.push([]);
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}
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// Push our value into our active buffers.
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for (const buffer of buffers) {
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buffer.push(value);
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// Check to see if we're over the bufferSize
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// if we are, record it so we can emit it later.
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// If we emitted it now and removed it, it would
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// mutate the `buffers` array while we're looping
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// over it.
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if (bufferSize <= buffer.length) {
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toEmit = toEmit ?? [];
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toEmit.push(buffer);
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}
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}
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if (toEmit) {
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// We have found some buffers that are over the
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// `bufferSize`. Emit them, and remove them from our
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// buffers list.
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for (const buffer of toEmit) {
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arrRemove(buffers, buffer);
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subscriber.next(buffer);
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}
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}
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},
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() => {
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// When the source completes, emit all of our
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// active buffers.
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for (const buffer of buffers) {
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subscriber.next(buffer);
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}
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subscriber.complete();
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},
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// Pass all errors through to consumer.
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undefined,
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() => {
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// Clean up our memory when we finalize
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buffers = null!;
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}
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)
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);
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});
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}
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