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import { OperatorFunction, ObservableInput, ObservedValueOf, SubjectLike } from '../types';
import { Observable } from '../Observable';
import { Subject } from '../Subject';
import { innerFrom } from '../observable/innerFrom';
import { operate } from '../util/lift';
import { fromSubscribable } from '../observable/fromSubscribable';
/**
* An object used to configure {@link connect} operator.
*/
export interface ConnectConfig<T> {
/**
* A factory function used to create the Subject through which the source
* is multicast. By default, this creates a {@link Subject}.
*/
connector: () => SubjectLike<T>;
}
/**
* The default configuration for `connect`.
*/
const DEFAULT_CONFIG: ConnectConfig<unknown> = {
connector: () => new Subject<unknown>(),
};
/**
* Creates an observable by multicasting the source within a function that
* allows the developer to define the usage of the multicast prior to connection.
*
* This is particularly useful if the observable source you wish to multicast could
* be synchronous or asynchronous. This sets it apart from {@link share}, which, in the
* case of totally synchronous sources will fail to share a single subscription with
* multiple consumers, as by the time the subscription to the result of {@link share}
* has returned, if the source is synchronous its internal reference count will jump from
* 0 to 1 back to 0 and reset.
*
* To use `connect`, you provide a `selector` function that will give you
* a multicast observable that is not yet connected. You then use that multicast observable
* to create a resulting observable that, when subscribed, will set up your multicast. This is
* generally, but not always, accomplished with {@link merge}.
*
* Note that using a {@link takeUntil} inside of `connect`'s `selector` _might_ mean you were looking
* to use the {@link takeWhile} operator instead.
*
* When you subscribe to the result of `connect`, the `selector` function will be called. After
* the `selector` function returns, the observable it returns will be subscribed to, _then_ the
* multicast will be connected to the source.
*
* ## Example
*
* Sharing a totally synchronous observable
*
* ```ts
* import { of, tap, connect, merge, map, filter } from 'rxjs';
*
* const source$ = of(1, 2, 3, 4, 5).pipe(
* tap({
* subscribe: () => console.log('subscription started'),
* next: n => console.log(`source emitted ${ n }`)
* })
* );
*
* source$.pipe(
* // Notice in here we're merging 3 subscriptions to `shared$`.
* connect(shared$ => merge(
* shared$.pipe(map(n => `all ${ n }`)),
* shared$.pipe(filter(n => n % 2 === 0), map(n => `even ${ n }`)),
* shared$.pipe(filter(n => n % 2 === 1), map(n => `odd ${ n }`))
* ))
* )
* .subscribe(console.log);
*
* // Expected output: (notice only one subscription)
* 'subscription started'
* 'source emitted 1'
* 'all 1'
* 'odd 1'
* 'source emitted 2'
* 'all 2'
* 'even 2'
* 'source emitted 3'
* 'all 3'
* 'odd 3'
* 'source emitted 4'
* 'all 4'
* 'even 4'
* 'source emitted 5'
* 'all 5'
* 'odd 5'
* ```
*
* @param selector A function used to set up the multicast. Gives you a multicast observable
* that is not yet connected. With that, you're expected to create and return
* and Observable, that when subscribed to, will utilize the multicast observable.
* After this function is executed -- and its return value subscribed to -- the
* operator will subscribe to the source, and the connection will be made.
* @param config The configuration object for `connect`.
*/
export function connect<T, O extends ObservableInput<unknown>>(
selector: (shared: Observable<T>) => O,
config: ConnectConfig<T> = DEFAULT_CONFIG
): OperatorFunction<T, ObservedValueOf<O>> {
const { connector } = config;
return operate((source, subscriber) => {
const subject = connector();
innerFrom(selector(fromSubscribable(subject))).subscribe(subscriber);
subscriber.add(source.subscribe(subject));
});
}