import { curryN } from "@unboxing/function";
import { OrdFunc, Ord } from '@unboxing/core'

interface StableSortBy {
  <T, R extends Ord>(fn: OrdFunc<T, R>, list: ArrayLike<T>): T[];
  <T, R extends Ord>(fn: OrdFunc<T, R>): (list: ArrayLike<T>) => T[];
}

/**
 * Sorts the array according to the supplied function and keeping the order of elements.
 */
export const stableSortBy = curryN(2, <T, R extends Ord>(fn: OrdFunc<T, R>, arr: ArrayLike<T> = []) => {
  const len = arr.length;
  const indexes = new Array(len);

  for (let i = 0; i < len; i++) {
      indexes[i] = i;
  }

  indexes.sort((a, b) => {
      const valueA = arr[a];
      const valueB = arr[b];
      const x = fn(valueA);
      const y = fn(valueB);

      if (x < y) {
          return -1;
      } else if (x > y) {
          return 1;
      }

      return a - b;
  });

  const result = new Array(len);

  for (let i = 0; i < len; i++) {
      result[i] = arr[indexes[i]];
  }

  return result;
}) as StableSortBy;