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import { PromiseOrValue } from "@implab/core-amd/interfaces";
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import { isPromise } from "@implab/core-amd/safe";
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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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export interface Unsubscribable {
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unsubscribe(): void;
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}
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export const isUnsubsribable = (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 isSubsribable = <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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subscribe(consumer: Partial<Observer<T>>): Unsubscribable;
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}
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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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/** 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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/** 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: (acc: A, value: T) => A, initial: A): Observable<A>;
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cat(...seq: Subscribable<T>[]): Observable<T>;
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}
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const noop = () => { };
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const sink = <T>(consumer: Partial<Observer<T>>) => {
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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) : noop,
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complete: complete ? complete.bind(consumer) : noop,
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isClosed: () => false
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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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* @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 }: Sink<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 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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cleanup = producer(safeSink) ?? noop;
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return done ?
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(cleanup(), noop) :
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_fin(noop);
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};
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const _observe = <T>(producer: Producer<T>): Observable<T> => ({
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subscribe: (consumer: Partial<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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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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scan: (accumulator, initial) => _observe(({ next, ...rest }) => {
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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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cat: (...seq) => _observe(({ next, complete: final, ...rest }) => {
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let cleanup: () => void;
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const complete = () => {
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const continuation = seq.shift();
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if (continuation) {
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// if we have a next sequence, subscribe to it
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const subscription = continuation.subscribe({ next, complete, ...rest });
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cleanup = subscription.unsubscribe.bind(subscription);
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} else {
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// otherwise notify the consumer about completion
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final();
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}
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};
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cleanup = producer({ next, complete, ...rest }) ?? noop;
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return () => cleanup();
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})
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});
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export interface OrderUpdate<T> {
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/** The item is being updated */
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item: T;
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/** The previous index of the item, -1 in case it is inserted */
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prevIndex: number;
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/** The new index of the item, -1 in case it is deleted */
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newIndex: number;
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}
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interface ObservableResults<T> {
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/**
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* Allows observation of results
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*/
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observe(listener: (object: T, previousIndex: number, newIndex: number) => void, includeUpdates?: boolean): {
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remove(): void;
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};
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}
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interface Queryable<T, A extends unknown[]> {
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query(...args: A): PromiseOrValue<T[]>;
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}
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export const isObservableResults = <T>(v: object): v is ObservableResults<T> =>
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v && (typeof (v as { observe?: unknown; }).observe === "function");
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export const observe = <T>(producer: Producer<T>) => _observe(fuse(producer));
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export const empty = observe<never>(({ complete }) => complete());
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export const query = <T, A extends unknown[]>(store: Queryable<T, A>) =>
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(...args: A) => {
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return observe<OrderUpdate<T>>(({ next, complete, error }) => {
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try {
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const results = store.query(...args);
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if (isPromise(results)) {
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results.then(items => items.forEach((item, newIndex) => next({ item, newIndex, prevIndex: -1 })))
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.then(undefined, error);
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} else {
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results.forEach((item, newIndex) => next({ item, newIndex, prevIndex: -1 }));
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}
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if (isObservableResults<T>(results)) {
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const h = results.observe((item, prevIndex, newIndex) => next({ item, prevIndex, newIndex }));
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return () => h.remove();
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} else {
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complete();
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}
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} catch (err) {
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error(err);
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}
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});
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};
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