/**
 * Finds the element in an array that has the minimum value when applying
 * the `getValue` function to each element.
 *
 * @template T - The type of elements in the array.
 * @param items The nonempty array of elements to search.
 * @param getValue A function that selects a numeric value from each element.
 * @returns The element with the minimum value as determined by the `getValue` function.
 * @example
 * minBy([{ a: 1 }, { a: 2 }, { a: 3 }], x => x.a); // Returns: { a: 1 }
 * minBy([], x => x.a); // Returns: undefined
 * minBy([3, NaN, 1], x => x); // Returns: NaN (NaN propagates, matching Math.min)
 * minBy(
 *   [
 *     { name: 'john', age: 30 },
 *     { name: 'jane', age: 28 },
 *     { name: 'joe', age: 26 },
 *   ],
 *   x => x.age
 * ); // Returns: { name: 'joe', age: 26 }
 */
export function minBy<T>(
  items: readonly [T, ...T[]],
  getValue: (element: T, index: number, array: readonly T[]) => number
): T;
/**
 * Finds the element in an array that has the minimum value when applying
 * the `getValue` function to each element.
 *
 * @template T - The type of elements in the array.
 * @param items The array of elements to search.
 * @param getValue A function that selects a numeric value from each element.
 * @returns The element with the minimum value as determined by the `getValue` function,
 * or `undefined` if the array is empty.
 * @example
 * minBy([{ a: 1 }, { a: 2 }, { a: 3 }], x => x.a); // Returns: { a: 1 }
 * minBy([], x => x.a); // Returns: undefined
 * minBy([3, NaN, 1], x => x); // Returns: NaN (NaN propagates, matching Math.min)
 * minBy(
 *   [
 *     { name: 'john', age: 30 },
 *     { name: 'jane', age: 28 },
 *     { name: 'joe', age: 26 },
 *   ],
 *   x => x.age
 * ); // Returns: { name: 'joe', age: 26 }
 */
export function minBy<T>(
  items: readonly T[],
  getValue: (element: T, index: number, array: readonly T[]) => number
): T | undefined;
/**
 * Finds the element in an array that has the minimum value when applying
 * the `getValue` function to each element.
 *
 * @template T - The type of elements in the array.
 * @param items The array of elements to search.
 * @param getValue A function that selects a numeric value from each element.
 * @returns The element with the minimum value as determined by the `getValue` function,
 * or `undefined` if the array is empty.
 * @example
 * minBy([{ a: 1 }, { a: 2 }, { a: 3 }], x => x.a); // Returns: { a: 1 }
 * minBy([], x => x.a); // Returns: undefined
 * minBy([3, NaN, 1], x => x); // Returns: NaN (NaN propagates, matching Math.min)
 * minBy(
 *   [
 *     { name: 'john', age: 30 },
 *     { name: 'jane', age: 28 },
 *     { name: 'joe', age: 26 },
 *   ],
 *   x => x.age
 * ); // Returns: { name: 'joe', age: 26 }
 */
export function minBy<T>(
  items: readonly T[],
  getValue: (element: T, index: number, array: readonly T[]) => number
): T | undefined {
  if (items.length === 0) {
    return undefined;
  }

  let minElement = items[0];
  let min = Infinity;

  for (let i = 0; i < items.length; i++) {
    const element = items[i];
    const value = getValue(element, i, items);

    if (Number.isNaN(value)) {
      return element;
    }

    if (value < min) {
      min = value;
      minElement = element;
    }
  }

  return minElement;
}
