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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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/**
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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 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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subscribe(consumer: Partial<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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/** 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: 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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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 which consumes this observable and produces a new one
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*/
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pipe<U>(op: (source: Observable<T>) => Producer<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 to
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*/
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next(ct?: ICancellation): Promise<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: <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, ...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) => {
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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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...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) => {
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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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...rest
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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 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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pipe: <U>(op: (source: Observable<T>) => Producer<U>) => observe(op(_observe(producer))),
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next: (ct?: ICancellation) => {
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const _ct = ct ?? Cancellation.none;
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return new Promise<T>((resolve, reject) => {
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// wrap the producer to handle only single event
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const once = fuse<T>(({ next, complete, error, isClosed }) => {
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const h = _ct.register(error);
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// is the _ct fires it will call error() and isClosed() will return true
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const cleanup = !isClosed() ?
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producer({
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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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isClosed
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}) ?? 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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once({
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next: resolve,
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error: reject,
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complete: noop,
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isClosed: () => false
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});
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});
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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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export const streamArray = <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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export const streamPromise = <T>(promise: PromiseLike<T>) => observe<T>(
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({next, error, complete}) => void promise.then(v => (next(v), complete()), error)
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);
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export const of = <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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export const empty = _observe<never>(({ complete }) => complete());
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