import { MonoTypeOperatorFunction, ObservableInput } from '../types';
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import { operate } from '../util/lift';
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import { createOperatorSubscriber } from './OperatorSubscriber';
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import { noop } from '../util/noop';
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import { innerFrom } from '../observable/innerFrom';
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/**
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* Returns an Observable that emits all items emitted by the source Observable that are distinct by comparison from previous items.
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*
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* If a `keySelector` function is provided, then it will project each value from the source observable into a new value that it will
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* check for equality with previously projected values. If the `keySelector` function is not provided, it will use each value from the
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* source observable directly with an equality check against previous values.
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*
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* In JavaScript runtimes that support `Set`, this operator will use a `Set` to improve performance of the distinct value checking.
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*
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* In other runtimes, this operator will use a minimal implementation of `Set` that relies on an `Array` and `indexOf` under the
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* hood, so performance will degrade as more values are checked for distinction. Even in newer browsers, a long-running `distinct`
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* use might result in memory leaks. To help alleviate this in some scenarios, an optional `flushes` parameter is also provided so
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* that the internal `Set` can be "flushed", basically clearing it of values.
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*
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* ## Examples
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*
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* A simple example with numbers
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*
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* ```ts
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* import { of, distinct } from 'rxjs';
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*
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* of(1, 1, 2, 2, 2, 1, 2, 3, 4, 3, 2, 1)
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* .pipe(distinct())
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* .subscribe(x => console.log(x));
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*
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* // Outputs
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* // 1
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* // 2
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* // 3
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* // 4
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* ```
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*
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* An example using the `keySelector` function
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*
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* ```ts
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* import { of, distinct } from 'rxjs';
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*
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* of(
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* { age: 4, name: 'Foo'},
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* { age: 7, name: 'Bar'},
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* { age: 5, name: 'Foo'}
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* )
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* .pipe(distinct(({ name }) => name))
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* .subscribe(x => console.log(x));
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*
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* // Outputs
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* // { age: 4, name: 'Foo' }
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* // { age: 7, name: 'Bar' }
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* ```
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* @see {@link distinctUntilChanged}
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* @see {@link distinctUntilKeyChanged}
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*
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* @param keySelector Optional `function` to select which value you want to check as distinct.
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* @param flushes Optional `ObservableInput` for flushing the internal HashSet of the operator.
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* @return A function that returns an Observable that emits items from the
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* source Observable with distinct values.
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*/
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export function distinct<T, K>(keySelector?: (value: T) => K, flushes?: ObservableInput<any>): MonoTypeOperatorFunction<T> {
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return operate((source, subscriber) => {
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const distinctKeys = new Set();
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source.subscribe(
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createOperatorSubscriber(subscriber, (value) => {
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const key = keySelector ? keySelector(value) : value;
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if (!distinctKeys.has(key)) {
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distinctKeys.add(key);
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subscriber.next(value);
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}
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})
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);
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flushes && innerFrom(flushes).subscribe(createOperatorSubscriber(subscriber, () => distinctKeys.clear(), noop));
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});
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}
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