rxjs/src/operators/sequenceEqual.ts

Reactive Extensions for modern JavaScript

import { Operator } from '../Operator';
import { Observer } from '../Observer';
import { Observable } from '../Observable';
import { Subscriber } from '../Subscriber';
import { tryCatch } from '../util/tryCatch';
import { errorObject } from '../util/errorObject';

import { OperatorFunction } from '../interfaces';

/**
 * Compares all values of two observables in sequence using an optional comparor function
 * and returns an observable of a single boolean value representing whether or not the two sequences
 * are equal.
 *
 * <span class="informal">Checks to see of all values emitted by both observables are equal, in order.</span>
 *
 * <img src="./img/sequenceEqual.png" width="100%">
 *
 * `sequenceEqual` subscribes to two observables and buffers incoming values from each observable. Whenever either
 * observable emits a value, the value is buffered and the buffers are shifted and compared from the bottom
 * up; If any value pair doesn't match, the returned observable will emit `false` and complete. If one of the
 * observables completes, the operator will wait for the other observable to complete; If the other
 * observable emits before completing, the returned observable will emit `false` and complete. If one observable never
 * completes or emits after the other complets, the returned observable will never complete.
 *
 * @example <caption>figure out if the Konami code matches</caption>
 * var code = Rx.Observable.from([
 *  "ArrowUp",
 *  "ArrowUp",
 *  "ArrowDown",
 *  "ArrowDown",
 *  "ArrowLeft",
 *  "ArrowRight",
 *  "ArrowLeft",
 *  "ArrowRight",
 *  "KeyB",
 *  "KeyA",
 *  "Enter" // no start key, clearly.
 * ]);
 *
 * var keys = Rx.Observable.fromEvent(document, 'keyup')
 *  .map(e => e.code);
 * var matches = keys.bufferCount(11, 1)
 *  .mergeMap(
 *    last11 =>
 *      Rx.Observable.from(last11)
 *        .sequenceEqual(code)
 *   );
 * matches.subscribe(matched => console.log('Successful cheat at Contra? ', matched));
 *
 * @see {@link combineLatest}
 * @see {@link zip}
 * @see {@link withLatestFrom}
 *
 * @param {Observable} compareTo The observable sequence to compare the source sequence to.
 * @param {function} [comparor] An optional function to compare each value pair
 * @return {Observable} An Observable of a single boolean value representing whether or not
 * the values emitted by both observables were equal in sequence.
 * @method sequenceEqual
 * @owner Observable
 */
export function sequenceEqual<T>(compareTo: Observable<T>,
                                 comparor?: (a: T, b: T) => boolean): OperatorFunction<T, boolean> {
  return (source: Observable<T>) => source.lift(new SequenceEqualOperator(compareTo, comparor));
}

export class SequenceEqualOperator<T> implements Operator<T, boolean> {
  constructor(private compareTo: Observable<T>,
              private comparor: (a: T, b: T) => boolean) {
  }

  call(subscriber: Subscriber<boolean>, source: any): any {
    return source.subscribe(new SequenceEqualSubscriber(subscriber, this.compareTo, this.comparor));
  }
}

/**
 * We need this JSDoc comment for affecting ESDoc.
 * @ignore
 * @extends {Ignored}
 */
export class SequenceEqualSubscriber<T, R> extends Subscriber<T> {
  private _a: T[] = [];
  private _b: T[] = [];
  private _oneComplete = false;

  constructor(destination: Observer<R>,
              private compareTo: Observable<T>,
              private comparor: (a: T, b: T) => boolean) {
    super(destination);
    this.add(compareTo.subscribe(new SequenceEqualCompareToSubscriber(destination, this)));
  }

  protected _next(value: T): void {
    if (this._oneComplete && this._b.length === 0) {
      this.emit(false);
    } else {
      this._a.push(value);
      this.checkValues();
    }
  }

  public _complete(): void {
    if (this._oneComplete) {
      this.emit(this._a.length === 0 && this._b.length === 0);
    } else {
      this._oneComplete = true;
    }
  }

  checkValues() {
    const { _a, _b, comparor } = this;
    while (_a.length > 0 && _b.length > 0) {
      let a = _a.shift();
      let b = _b.shift();
      let areEqual = false;
      if (comparor) {
        areEqual = tryCatch(comparor)(a, b);
        if (areEqual === errorObject) {
          this.destination.error(errorObject.e);
        }
      } else {
        areEqual = a === b;
      }
      if (!areEqual) {
        this.emit(false);
      }
    }
  }

  emit(value: boolean) {
    const { destination } = this;
    destination.next(value);
    destination.complete();
  }

  nextB(value: T) {
    if (this._oneComplete && this._a.length === 0) {
      this.emit(false);
    } else {
      this._b.push(value);
      this.checkValues();
    }
  }
}

class SequenceEqualCompareToSubscriber<T, R> extends Subscriber<T> {
  constructor(destination: Observer<R>, private parent: SequenceEqualSubscriber<T, R>) {
    super(destination);
  }

  protected _next(value: T): void {
    this.parent.nextB(value);
  }

  protected _error(err: any): void {
    this.parent.error(err);
  }

  protected _complete(): void {
    this.parent._complete();
  }
}