[RxJS] Scheduler

class Observable {
  constructor(subscribe) {
    this._subscribe = subscribe;
  }

  subscribe(observer) {
    return this._subscribe(observer);
  }

  static of(value) {
    return new Observable((observer) => {
      observer.next(value);
      observer.complete();

      return {
        unsubscribe() {}
      };
    });
  }

  static concnat(...observables) {
    return new Observable((observer) => {
      const copy = observables.slice();
      let currentSubscription = null;
      // using recurisve call to implement concat effect
      // for each call, there we update currentSubscription
      // when calling unsubscribe on currentSubscription
      // complete() won't be triggered, therefore whole
      // observables stops as well
      const processObservable = () => {
        if (!copy.length) {
          observer.complete();
        } else {
          const observable = copy.shift();
          currentSubscription = observable.subscribe({
            next(data) {
              observer.next(data);
            },
            error(err) {
              observer.error(err);
              currentSubscription.unsubscribe();
            },
            complete() {
              processObservable();
            }
          });
        }
      };
      processObservable();

      return {
        unsubscribe: () => {
          currentSubscription.unsubscribe();
        }
      };
    });
  }

  static timeout(time) {
    return new Observable((observer) => {
      console.log("CALL TIMEOUT");
      const handle = setTimeout(() => {
        observer.next();
        observer.complete();
      }, time);

      return {
        unsubscribe: () => {
          clearTimeout(handle);
        }
      };
    });
  }

  static fromEvent(dom, eventName) {
    return new Observable((observer) => {
      const handle = (e) => {
        observer.next(e);
      };
      dom.addEventListener(eventName, handle);

      return {
        unsubscribe: () => {
          dom.removeEventListener(eventName, handle);
        }
      };
    });
  }

  retry(num) {
    return new Observable((observer) => {
      let currentSub;
      const retry = (currentAmttemptNumber) => {
        currentSub = this.subscribe({
          next(data) {
            observer.next(data);
          },
          error(err) {
            if (currentAmttemptNumber === 0) {
              observer.error(err);
            } else {
              retry(currentAmttemptNumber - 1);
            }
          },
          complete() {
            observer.complete();
          }
        });
      };
      retry(num);

      return {
        unsubscribe() {
          if (currentSub) {
            currentSub.unsubscribe();
          }
        }
      };
    });
  }

  // map is a operator, you need to subscribe it
  map(transfomer) {
    return new Observable((observer) => {
      const subscription = this.subscribe({
        next(data) {
          let value;
          try {
            value = transfomer(data);
            observer.next(value);
          } catch (err) {
            observer.error(err);
            subscription.unsubscribe();
          }
        },
        error(e) {
          observer.error(e);
        },
        complete() {
          observer.complete();
        }
      });

      return subscription;
    });
  }

  filter(predition) {
    return new Observable((observer) => {
      const subscription = this.subscribe({
        next(data) {
          try {
            if (predition(data)) {
              observer.next(data);
            }
          } catch (err) {
            observer.error(err);
            subscription.unsubscribe();
          }
        },
        error(e) {
          observer.error(e);
        },
        complete() {
          observer.complete();
        }
      });

      return subscription;
    });
  }

  share() {
    const subject = new Subject();
    this.subscribe(subject);
    return subject;
  }

  observeOn(scheduler) {
    return new Observable((observer) => {
      return this.subscribe({
        next(v) {
          scheduler(() => observer.next(v));
        },
        error(e) {
          scheduler(() => observer.error(e));
        },
        complete() {
          scheduler(() => observer.complete());
        }
      });
    });
  }

  subscribeOn(scheduler) {
    return new Observable((observer) => {
      scheduler(() =>
        this.subscribe({
          next(v) {
            observer.next(v);
          },
          error(e) {
            observer.error(e);
          },
          complete() {
            observer.complete();
          }
        })
      );
    });
  }
}

class Subject extends Observable {
  constructor() {
    super((observer) => {
      this.observers.add(observer);

      return {
        unsubscribe() {
          this.observers.delete(observer);
        }
      };
    });
    this.observers = new Set();
  }

  next(v) {
    for (let observer of [...this.observers]) {
      observer.next(v);
    }
  }

  error(e) {
    for (let observer of [...this.observers]) {
      observer.next(e);
    }
  }

  complete() {
    for (let observer of [...this.observers]) {
      observer.complete();
    }
  }
}

Observable.of(5)
  .observeOn((action) => {
    setTimeout(action, 1000);
  })
  .subscribe({
    next(v) {
      console.log(v);
    },
    complete() {
      console.log("done");
    }
  });

Observable.of(6)
  .subscribeOn((action) => {
    setTimeout(action, 1000);
  })
  .subscribe({
    next(v) {
      console.log(v);
    },
    complete() {
      console.log("done");
    }
  });