import { Subject } from './Subject';
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import { TimestampProvider } from './types';
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import { Subscriber } from './Subscriber';
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import { Subscription } from './Subscription';
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import { dateTimestampProvider } from './scheduler/dateTimestampProvider';
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/**
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* A variant of {@link Subject} that "replays" old values to new subscribers by emitting them when they first subscribe.
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*
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* `ReplaySubject` has an internal buffer that will store a specified number of values that it has observed. Like `Subject`,
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* `ReplaySubject` "observes" values by having them passed to its `next` method. When it observes a value, it will store that
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* value for a time determined by the configuration of the `ReplaySubject`, as passed to its constructor.
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*
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* When a new subscriber subscribes to the `ReplaySubject` instance, it will synchronously emit all values in its buffer in
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* a First-In-First-Out (FIFO) manner. The `ReplaySubject` will also complete, if it has observed completion; and it will
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* error if it has observed an error.
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*
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* There are two main configuration items to be concerned with:
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*
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* 1. `bufferSize` - This will determine how many items are stored in the buffer, defaults to infinite.
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* 2. `windowTime` - The amount of time to hold a value in the buffer before removing it from the buffer.
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*
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* Both configurations may exist simultaneously. So if you would like to buffer a maximum of 3 values, as long as the values
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* are less than 2 seconds old, you could do so with a `new ReplaySubject(3, 2000)`.
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*
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* ### Differences with BehaviorSubject
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*
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* `BehaviorSubject` is similar to `new ReplaySubject(1)`, with a couple of exceptions:
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*
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* 1. `BehaviorSubject` comes "primed" with a single value upon construction.
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* 2. `ReplaySubject` will replay values, even after observing an error, where `BehaviorSubject` will not.
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*
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* @see {@link Subject}
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* @see {@link BehaviorSubject}
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* @see {@link shareReplay}
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*/
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export class ReplaySubject<T> extends Subject<T> {
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private _buffer: (T | number)[] = [];
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private _infiniteTimeWindow = true;
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/**
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* @param bufferSize The size of the buffer to replay on subscription
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* @param windowTime The amount of time the buffered items will stay buffered
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* @param timestampProvider An object with a `now()` method that provides the current timestamp. This is used to
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* calculate the amount of time something has been buffered.
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*/
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constructor(
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private _bufferSize = Infinity,
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private _windowTime = Infinity,
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private _timestampProvider: TimestampProvider = dateTimestampProvider
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) {
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super();
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this._infiniteTimeWindow = _windowTime === Infinity;
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this._bufferSize = Math.max(1, _bufferSize);
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this._windowTime = Math.max(1, _windowTime);
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}
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next(value: T): void {
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const { isStopped, _buffer, _infiniteTimeWindow, _timestampProvider, _windowTime } = this;
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if (!isStopped) {
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_buffer.push(value);
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!_infiniteTimeWindow && _buffer.push(_timestampProvider.now() + _windowTime);
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}
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this._trimBuffer();
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super.next(value);
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}
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/** @internal */
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protected _subscribe(subscriber: Subscriber<T>): Subscription {
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this._throwIfClosed();
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this._trimBuffer();
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const subscription = this._innerSubscribe(subscriber);
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const { _infiniteTimeWindow, _buffer } = this;
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// We use a copy here, so reentrant code does not mutate our array while we're
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// emitting it to a new subscriber.
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const copy = _buffer.slice();
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for (let i = 0; i < copy.length && !subscriber.closed; i += _infiniteTimeWindow ? 1 : 2) {
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subscriber.next(copy[i] as T);
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}
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this._checkFinalizedStatuses(subscriber);
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return subscription;
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}
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private _trimBuffer() {
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const { _bufferSize, _timestampProvider, _buffer, _infiniteTimeWindow } = this;
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// If we don't have an infinite buffer size, and we're over the length,
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// use splice to truncate the old buffer values off. Note that we have to
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// double the size for instances where we're not using an infinite time window
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// because we're storing the values and the timestamps in the same array.
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const adjustedBufferSize = (_infiniteTimeWindow ? 1 : 2) * _bufferSize;
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_bufferSize < Infinity && adjustedBufferSize < _buffer.length && _buffer.splice(0, _buffer.length - adjustedBufferSize);
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// Now, if we're not in an infinite time window, remove all values where the time is
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// older than what is allowed.
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if (!_infiniteTimeWindow) {
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const now = _timestampProvider.now();
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let last = 0;
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// Search the array for the first timestamp that isn't expired and
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// truncate the buffer up to that point.
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for (let i = 1; i < _buffer.length && (_buffer[i] as number) <= now; i += 2) {
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last = i;
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}
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last && _buffer.splice(0, last + 1);
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}
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}
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}
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