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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. This 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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[k in keyof Observer<T>]: (this: void, ...args: Parameters<Observer<T>[k]>) => void;
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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 = (v: unknown): v is Subscribable<unknown> =>
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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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}
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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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}
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};
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const fuse = <T>({ next, error, complete }: Sink<T>) => {
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let done = false;
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return {
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next: (value: T) => { !done && next(value) },
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error: (e: unknown) => { !done && (done = true, error(e)) },
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complete: () => { !done && (done = true, complete()) }
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}
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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, error, complete }) =>
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producer({
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next: next !== noop ? (v: T) => next(mapper(v)) : noop,
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error,
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complete
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})
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),
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filter: (predicate) => _observe(({ next, error, complete }) =>
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producer({
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next: next !== noop ?
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(v: T) => predicate(v) ? next(v) : void(0) : noop,
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error,
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complete
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})
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),
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scan: (accumulator, initial) => _observe(({ next, error, complete }) => {
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let _acc = initial;
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return producer({
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next: next !== noop ?
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(v: T) => next(_acc = accumulator(_acc, v)) : noop,
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error,
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complete
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});
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})
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});
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export const observe = <T>(producer: Producer<T>): Observable<T> => ({
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subscribe: (consumer: Partial<Observer<T>>) => ({
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unsubscribe: producer(fuse(sink(consumer))) ?? noop
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}),
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map: (mapper) => _observe(({ next, error, complete }) =>
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producer(fuse({
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next: next !== noop ?
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(v: T) => next(mapper(v)) : noop,
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error,
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complete
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}))
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),
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filter: (predicate) => _observe(({ next, error, complete }) =>
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producer(fuse({
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next: next !== noop ?
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(v: T) => predicate(v) ? next(v) : void (0) : noop,
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error,
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complete
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}))
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),
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scan: (accumulator, initial?) => observe(({ next, error, complete }) => {
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let _acc = initial;
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return producer(fuse({
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next: next !== noop ? (v: T) => next(_acc = accumulator(_acc, v)) : noop,
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error,
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complete
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}));
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})
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});
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