sortHelper.ts

type SortableType = number | string | boolean;

type SortFn<T> = (el: T) => SortableType;

interface SortHelperApi<T> {
  sortBy(fn: SortFn<T>, decrescent?: boolean): SortHelperApi<T>;
  execute(): T[];
}

/**
 * helps sorting arrays
 * accepts multiple calls to sortBy (1st takes precedence to 2nd, etc.)
 * 2nd argument on sortBy is whether the sorting is in decreasing order
 * one must call execute to get back the sorted array (without side-effects on original array)
 */
export function sortHelper<T>(arr: T[]): SortHelperApi<T> {
  const sortFns: SortFn<T>[] = [];
  const sortDecs: boolean[] = [];

  const api: SortHelperApi<T> = {
    sortBy(fn: SortFn<T>, decrescent = false) {
      sortFns.unshift(fn);
      sortDecs.unshift(decrescent);
      return api;
    },
    execute(): T[] {
      let finalArr = arr.slice();
      let i = 0;
      for (const fn of sortFns) {
        const dec: boolean = sortDecs[i++];
        const arr2: [T, SortableType][] = finalArr.map((el: T) => [el, fn(el)]);
        arr2.sort((a_, b_) => {
          const a = a_[1];
          const b = b_[1];
          if (dec) return a > b ? -1 : a < b ? 1 : 0;
          return a > b ? 1 : a < b ? -1 : 0;
        });
        finalArr = arr2.map((el) => el[0]);
      }
      return finalArr;
    },
  };

  return api;
}

/*
// EXAMPLE USAGE FOLLOWS:
const people = [
  { name: 'john', age: 12, gender: 'm' },
  { name: 'mary', age: 6, gender: 'f' },
  { name: 'mary', age: 21, gender: 'f' },
  { name: 'josh', age: 33, gender: 'm' },
];

const people2 = sortHelper(people)
  .sortBy((p) => p.gender)
  .sortBy((p) => p.age, true)
  .execute();

console.log('people', people);
console.log('people2', people2);
*/