import { IterableX } from '../iterablex.js';
import { arrayIndexOf } from '../../util/arrayindexof.js';
import { comparer as defaultComparer } from '../../util/comparer.js';
import { MonoTypeOperatorFunction } from '../../interfaces.js';

/** @ignore */
export class UnionIterable<TSource> extends IterableX<TSource> {
  private _left: Iterable<TSource>;
  private _right: Iterable<TSource>;
  private _comparer: (x: TSource, y: TSource) => boolean;

  constructor(
    left: Iterable<TSource>,
    right: Iterable<TSource>,
    comparer: (x: TSource, y: TSource) => boolean
  ) {
    super();
    this._left = left;
    this._right = right;
    this._comparer = comparer;
  }

  *[Symbol.iterator]() {
    const map = [] as TSource[];
    for (const lItem of this._left) {
      if (arrayIndexOf(map, lItem, this._comparer) === -1) {
        map.push(lItem);
        yield lItem;
      }
    }

    for (const rItem of this._right) {
      if (arrayIndexOf(map, rItem, this._comparer) === -1) {
        map.push(rItem);
        yield rItem;
      }
    }
  }
}

/**
 * Produces the set union of two sequences by using the given equality comparer.
 *
 * @template TSource The type of the elements of the input sequences.
 * @param {AsyncIterable<TSource>} right An iterable sequence whose distinct elements form the second set for the union.
 * @param {((x: TSource, y: TSource) => boolean)} [comparer=defaultComparer] The equality comparer to compare values.
 * @returns {MonoTypeOperatorFunction<TSource>} An iterable sequence that contains the elements from both input sequences,
 * excluding duplicates.
 */
export function union<TSource>(
  right: Iterable<TSource>,
  comparer: (x: TSource, y: TSource) => boolean = defaultComparer
): MonoTypeOperatorFunction<TSource> {
  return function unionOperatorFunction(left: Iterable<TSource>): IterableX<TSource> {
    return new UnionIterable<TSource>(left, right, comparer);
  };
}