ix/src/asynciterable/operators/except.ts

The Interactive Extensions for JavaScript

import { AsyncIterableX } from '../asynciterablex.js';
import { arrayIndexOfAsync } from '../../util/arrayindexof.js';
import { comparerAsync } from '../../util/comparer.js';
import { MonoTypeOperatorAsyncFunction } from '../../interfaces.js';
import { wrapWithAbort } from './withabort.js';
import { throwIfAborted } from '../../aborterror.js';

/** @ignore */
export class ExceptAsyncIterable<TSource> extends AsyncIterableX<TSource> {
  private _first: AsyncIterable<TSource>;
  private _second: AsyncIterable<TSource>;
  private _comparer: (x: TSource, y: TSource) => boolean | Promise<boolean>;

  constructor(
    first: AsyncIterable<TSource>,
    second: AsyncIterable<TSource>,
    comparer: (x: TSource, y: TSource) => boolean | Promise<boolean>
  ) {
    super();
    this._first = first;
    this._second = second;
    this._comparer = comparer;
  }

  async *[Symbol.asyncIterator](signal?: AbortSignal) {
    throwIfAborted(signal);
    const map = [] as TSource[];
    for await (const secondItem of wrapWithAbort(this._second, signal)) {
      map.push(secondItem);
    }

    for await (const firstItem of wrapWithAbort(this._first, signal)) {
      if ((await arrayIndexOfAsync(map, firstItem, this._comparer)) === -1) {
        map.push(firstItem);
        yield firstItem;
      }
    }
  }
}

/**
 *  Produces the set difference of two async-iterable sequences by using the specified equality comparer to compare values.
 *
 * @template TSource The type of the elements of the input sequences.
 * @param {AsyncIterable<TSource>} second An async-iterable sequence whose elements that also occur in the
 * operator sequence will cause those elements to be removed from the returned sequence.
 * @param {((x: TSource, y: TSource) => boolean | Promise<boolean>)} [comparer=comparerAsync] An equality comparer to compare values
 * @returns {MonoTypeOperatorAsyncFunction<TSource>} An operator that returns a sequence that contains the set
 * difference of the elements of two sequences.
 */
export function except<TSource>(
  second: AsyncIterable<TSource>,
  comparer: (x: TSource, y: TSource) => boolean | Promise<boolean> = comparerAsync
): MonoTypeOperatorAsyncFunction<TSource> {
  return function exceptOperatorFunction(first: AsyncIterable<TSource>): AsyncIterableX<TSource> {
    return new ExceptAsyncIterable<TSource>(first, second, comparer);
  };
}