implab/implabjs-djx Commit - r142:894b8239b953

code review, minor refactoring

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r142:894b8239b953 v1.9.0-rc5 default

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r142:894b8239b953

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djx/src/main/ts/observable.ts +32 -24

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

djx/src/main/ts/operators/subject.ts +18 -8

              import { Observable, Sink, Subscribable, observe } from "../observable";
              const noop = () => { };
-             /** Joins multiple subscribers to the single one. The resulting subscriber
+             /** Connects multiple subscribers to the single producer. The producer
               * will be created when the first client subscribes and will be released
               * with the the last client unsubscribed.
               *
               * Use this wrapper to prevent spawning multiple producers.
               *
+              * The emitted values are not cached therefore the new subscriber will not receive
+              * the values emitted before it has been subscribed.
+              *
               * @param source The source observable
-              * @returns The wrapped producer
+              * @returns The new observable
               */
              export const subject = <T>(source: Subscribable<T>): Observable<T> => {
-                 let subscribers: Sink<T>[] = [];
+                 let subscribers: Sink<T>[] = []; // the list of active subscribers
-                 let subscription = { unsubscribe: noop };
+                 let subscription = { unsubscribe: noop }; // current subscription
                  // cleanup method to release resources held by this subscription
                  const cleanup = (cb: (item: Sink<T>) => void) => {
                      const _subscribers = subscribers;
-                     subscribers = [];
+                     subscribers = []; // this will prevent a client cleanup login to run
                      _subscribers.forEach(cb);
-                     subscription.unsubscribe();
+                     // we don't need subscription.unsubscribe(), because cleanup is called
+                     // from complete or error methods.
                  };
                  const sink: Sink<T> = {
                      isClosed: () => false,
                      complete: () => cleanup(s => s.complete()),
                      error: e => cleanup(s => s.error(e)),
                      next: v => subscribers.forEach(s => s.next(v))
                  };
                  return observe(client => {
                      const _subscribers = subscribers;
                      subscribers.push(client);
-                     if (subscribers.length === 1)
-                         subscription = source.subscribe(sink);
+                     if (subscribers.length === 1) // this is the first client
+                         subscription = source.subscribe(sink); // activate the producer
                      return () => {
+                         // this is a cleanup logic for an individual client
                          if (_subscribers === subscribers) {
+                             // is the current subscription to the producer is active
+                             // find this client in the list of subscribers
                              const pos = subscribers.indexOf(client);
                              if (pos >= 0)
                                  subscribers.splice(pos, 1);
+                             // is this is the last subscriber we need to release the producer
                              if (!subscribers.length)
                                  subscription.unsubscribe();
                          }
                      };
                  });
              };

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