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import { id as mid} from "module";
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import { Cancellation } from "@implab/core-amd/Cancellation";
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import { ICancellation } from "@implab/core-amd/interfaces";
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import { TraceSource } from "@implab/core-amd/log/TraceSource";
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import { isPromise } from "@implab/core-amd/safe";
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const trace = TraceSource.get(mid);
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/**
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* The interface for the consumer of an observable sequence
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*/
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export interface Observer<T> {
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/**
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* Called for the next element in the sequence
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*/
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next?(value: T): void;
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/**
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* Called once when the error occurs in the sequence.
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*/
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error?(e: unknown): void;
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/**
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* Called once at the end of the sequence.
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*/
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complete?(): void;
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}
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/**
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* The group of functions to feed an observable. These methods are provided to
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* the producer to generate a stream of events.
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*/
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export type Sink<T> = {
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/**
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* Call to send the next element in the sequence
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*/
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next: (value: T) => void;
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/**
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* Call to notify about the error occurred in the sequence.
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*/
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error: (e: unknown) => void;
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/**
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* Call to signal the end of the sequence.
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*/
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complete: () => void;
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/**
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* Checks whether the sink is accepting new elements. It's safe to
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* send elements to the closed sink.
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*/
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isClosed: () => boolean;
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};
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export type Producer<T> = (sink: Sink<T>) => (void | (() => void));
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type FusedSink<T> = Omit<Sink<T>, "isClosed">;
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type FusedProducer<T> = (sink: FusedSink<T>) => (void | (() => void));
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export interface Unsubscribable {
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unsubscribe(): void;
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}
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export const isUnsubscribable = (v: unknown): v is Unsubscribable =>
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v !== null && v !== undefined && typeof (v as Unsubscribable).unsubscribe === "function";
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export const isSubscribable = <T = unknown>(v: unknown): v is Subscribable<T> =>
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v !== null && v !== undefined && typeof (v as Subscribable<unknown>).subscribe === "function";
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export interface Subscribable<T> {
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/** Subscribes a consumer to events. If a consumer isn't specified
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* this method activates the producer to achieve side affects if any.
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*/
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subscribe(consumer?: Observer<T>): Unsubscribable;
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}
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export type AccumulatorFn<T, A> = (acc: A, value: T) => A;
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export type OperatorFn<T, U> = (source: Observable<T>) => Observable<U>;
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/** The observable source of items. */
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export interface Observable<T> extends Subscribable<T> {
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/** Transforms elements of the sequence with the specified mapper
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*
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* @param mapper The mapper used to transform the values
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*/
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map<T2>(mapper: (value: T) => T2): Observable<T2>;
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/** Injects the specified observer into the each producer to consumer chain.
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* The method is used to add side effect to the events processing.
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*
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* @param observer The consumer for the events
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*/
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tap(observer: Observer<T>): Observable<T>;
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/** Filters elements of the sequence. The resulting sequence will
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* contain only elements which match the specified predicate.
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*
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* @param predicate The filter predicate.
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*/
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filter(predicate: (value: T) => boolean): Observable<T>;
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/** Completes the sequence once the condition is met.
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* @param predicate The condition which should be met to complete the sequence
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*/
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until(predicate: (value: T) => boolean): Observable<T>;
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/** Keeps the sequence running while elements satisfy the condition.
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*
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* @param predicate The condition which should be met to continue.
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*/
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while(predicate: (value: T) => boolean): Observable<T>;
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/** Applies accumulator to each value in the sequence and
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* emits the accumulated value for each source element
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*
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* @param accumulator
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* @param initial
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*/
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scan<A>(accumulator: AccumulatorFn<T, A>, initial: A): Observable<A>;
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scan(accumulator: AccumulatorFn<T, T>): Observable<T>;
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/** Applies accumulator to each value in the sequence and
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* emits the accumulated value at the end of the sequence
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*
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* @param accumulator
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* @param initial
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*/
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reduce<A>(accumulator: AccumulatorFn<T, A>, initial: A): Observable<A>;
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reduce(accumulator: AccumulatorFn<T, T>): Observable<T>;
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/** Concatenates the specified sequences with this observable
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*
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* @param seq sequences to concatenate with the current observable
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*
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* The concatenation doesn't accumulate values from the specified sequences,
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* The result of the concatenation is the new observable which will switch
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* to the next observable after the previous one completes. Values emitted
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* before the next observable being active are lost.
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*/
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cat(...seq: Subscribable<T>[]): Observable<T>;
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/** Pipes the specified operator to produce the new observable
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* @param op The operator consumes this observable and produces a new one
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*
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* The operator is a higher order function which takes a source observable
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* and returns a producer for the new observable.
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*
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* This function can be used to create a complex mapping between source and
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* resulting observables. The operator may have a state (or a side effect)
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* and can be connected to multiple observables.
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*/
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pipe<U>(op: OperatorFn<T, U>): Observable<U>;
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/** Waits for the next event to occur and returns a promise for the next value
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* @param ct Cancellation token
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*/
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next(ct?: ICancellation): Promise<T>;
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/** Collects items of the sequence to the array. */
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collect(ct?: ICancellation): Promise<T[]>;
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}
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const noop = () => { };
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const errorFallback = (e: unknown) => trace.error("Unhandled observable error: {0}", e);
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const sink = <T>(consumer: Observer<T>) => {
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// eslint-disable-next-line @typescript-eslint/unbound-method
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const { next, error, complete } = consumer;
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return {
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next: next ? next.bind(consumer) : noop,
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error: error ? error.bind(consumer) : errorFallback, // report unhandled errors
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complete: complete ? complete.bind(consumer) : noop
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};
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};
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/** Wraps the producer to handle tear down logic and subscription management
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*
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* The resulting producer will invoke cleanup logic on error or complete events
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* and will prevent calling of any method from the sink.
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*
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* @param producer The producer to wrap
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* @returns The wrapper producer
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*/
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const fuse = <T>(producer: Producer<T>) => ({ next, error, complete }: FusedSink<T>) => {
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let done = false;
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let cleanup = noop;
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const _fin = <A extends unknown[]>(fn: (...args: A) => void) =>
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(...args: A) => done ?
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void (0) :
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(done = true, cleanup(), fn(...args));
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const _fin0 = () => done ? void (0) : (done = true, cleanup());
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const safeSink = {
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next: (value: T) => { !done && next(value); },
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error: _fin(error),
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complete: _fin(complete),
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isClosed: () => done
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};
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// call the producer
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cleanup = producer(safeSink) ?? noop;
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// if the producer throws exception bypass it to the caller rather then to
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// the sink. This is a feature.
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// if the producer completed the sequence immediately call the cleanup in place
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return done ? cleanup() : _fin0;
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};
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const _observe = <T>(producer: FusedProducer<T>): Observable<T> => ({
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subscribe: (consumer: Observer<T> = {}) => ({
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unsubscribe: producer(sink(consumer)) ?? noop
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}),
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map: (mapper) => _observe(({ next, ...rest }) =>
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producer({
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next: next !== noop ? (v: T) => next(mapper(v)) : noop,
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...rest
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})
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),
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tap: ({next: tapNext, complete: tapComplete, error: tapError}) => _observe(({next,complete, error}) =>
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producer({
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next: tapNext ? (v => (tapNext(v), next(v))) : next,
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complete: tapComplete ? (() => (tapComplete(), complete())): complete,
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error: tapError ? (e => (tapError(e), error(e))) : error
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})
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),
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filter: (predicate) => _observe(({ next, ...rest }) =>
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producer({
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next: next !== noop ? (v: T) => predicate(v) ? next(v) : void (0) : noop,
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...rest
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})
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),
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until: predicate => _observe(({ next, complete, ...rest }) =>
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producer({
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next: v => predicate(v) ? complete() : next(v),
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complete,
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...rest
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})
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),
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while: predicate => _observe(({ next, complete, ...rest }) =>
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producer({
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next: v => predicate(v) ? next(v) : complete(),
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complete,
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...rest
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})
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),
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scan: <A>(...args: [AccumulatorFn<T, A>, A] | [AccumulatorFn<T, T>]) => _observe<T | A>(({ next, ...rest }) => {
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if (args.length === 1) {
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const [accumulator] = args;
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let _acc: T;
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let index = 0;
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return producer({
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next: next !== noop ? (v: T) => next(index++ === 0 ? _acc = v : _acc = accumulator(_acc, v)) : noop,
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...rest
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});
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} else {
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const [accumulator, initial] = args;
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let _acc = initial;
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return producer({
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next: next !== noop ? (v: T) => next(_acc = accumulator(_acc, v)) : noop,
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...rest
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});
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}
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}),
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reduce: <A>(...args: [AccumulatorFn<T, A>, A] | [AccumulatorFn<T, T>]) => _observe<T | A>(({ next, complete, error }) => {
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if (args.length === 1) {
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const [accumulator] = args;
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let _acc: T;
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let index = 0;
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return producer({
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next: next !== noop ? (v: T) => {
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_acc = index++ === 0 ? v : accumulator(_acc, v);
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} : noop,
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complete: () => {
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if (index === 0) {
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error(new Error("The sequence can't be empty"));
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} else {
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next(_acc);
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complete();
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}
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},
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error
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});
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} else {
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const [accumulator, initial] = args;
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let _acc = initial;
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return producer({
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next: next !== noop ? (v: T) => {
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_acc = accumulator(_acc, v);
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} : noop,
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complete: () => {
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next(_acc);
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complete();
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},
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error
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});
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}
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}),
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cat: (...seq) => _observe(({ next, complete: final, ...rest }) => {
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let cleanup: () => void;
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const len = seq.length;
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const complete = (i: number) => i < len ?
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() => {
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const subscription = seq[i].subscribe({ next, complete: complete(i + 1), ...rest });
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cleanup = subscription.unsubscribe.bind(subscription);
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} : final;
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cleanup = producer({ next, complete: complete(0), ...rest }) ?? noop;
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return () => cleanup();
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}),
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pipe: <U>(op: OperatorFn<T, U>) => op(_observe(producer)),
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next: collect(
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producer,
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({ next, complete, error }) => ({
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next: v => (next(v), complete()),
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complete: () => error(new Error("The sequence is empty")),
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error
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})
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),
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collect: collect(
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producer,
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({ next, complete, error}) => {
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const data: T[] = [];
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return {
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next: v => data.push(v),
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complete: () => (next(data), complete()),
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error
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};
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}
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)
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});
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const collect = <T, U>(
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producer: FusedProducer<T>,
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collector: (result: FusedSink<U>) => FusedSink<T>
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) => (ct = Cancellation.none) => new Promise<U>((resolve, reject) => {
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const fused = fuse<U>(({ next, complete, error, isClosed }) => {
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const h = ct.register(error);
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const cleanup = !isClosed() ?
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producer(collector({ next, complete, error })) ?? noop :
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noop;
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return () => {
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h.destroy();
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cleanup();
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};
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});
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fused({
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next: resolve,
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error: reject,
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complete: noop
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});
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});
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export const observe = <T>(producer: Producer<T>) => _observe(fuse(producer));
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/** Converts an array to the observable sequence of its elements. */
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export const ofArray = <T>(items: T[]) => _observe<T>(
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({ next, complete }) => (
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items.forEach(next),
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complete()
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)
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);
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/** Converts a subscribable to the observable */
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export const ofSubscribable = <T>(subscribable: Subscribable<T>) =>
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observe<T>(sink => {
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const subscription = subscribable.subscribe(sink);
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return () => subscription.unsubscribe();
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});
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const of1 = <T>(item: T | PromiseLike<T>) => observe<T>(
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({ next, error, complete }) =>
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isPromise(item) ?
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void item.then(
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v => (next(v), complete()),
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error
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) :
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(next(item), complete())
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);
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/** Converts a list of parameter values to the observable sequence. The
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* order of elements in the list will be preserved in the resulting sequence.
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*/
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export const of = <T>(...items: (T | PromiseLike<T>)[]) => items.length === 1 ?
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of1(items[0]) :
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observe<T>(
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({ next, error, complete, isClosed }) => {
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const n = items.length;
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const _next = (start: number) => {
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if (start > 0 && isClosed()) // when resumed
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return;
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for (let i = start; i < n; i++) {
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const r = items[i];
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if (isPromise(r)) {
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r.then(v => (next(v), _next(i + 1)), error);
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return; // suspend
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} else {
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next(r);
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}
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}
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complete();
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};
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_next(0);
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}
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);
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export const empty = _observe<never>(({ complete }) => complete());
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