import { unionWith as unionWithToolkit } from '../../array/unionWith.ts';

/**
 * Creates a function that returns unique values using a custom equality function.
 *
 * Values from the piped array are considered before values from secondArray. The equality
 * function decides whether two values represent the same item.
 *
 * @template T - The type of elements in the arrays.
 * @param secondArray - Values to include after the piped array.
 * @param areItemsEqual - Returns true when two values are equal.
 * @returns A function that maps a readonly array to its union with secondArray.
 *
 * @example
 * import { pipe, unionWith } from 'es-toolkit/fp';
 *
 * pipe([{ id: 1 }], unionWith([{ id: 1 }, { id: 2 }], (a, b) => a.id === b.id));
 * // => [{ id: 1 }, { id: 2 }]
 */
export function unionWith<T>(
  secondArray: readonly T[],
  areItemsEqual: (item: T, other: T) => boolean
): (array: readonly T[]) => T[] {
  return function (array: readonly T[]): T[] {
    return unionWithToolkit(array, secondArray, areItemsEqual);
  };
}
