import each from './each';
import isArray from './is-array';
import isFunction from './is-function';

/**
 * @param {Array} arr The array to iterate over.
 * @param {Function} [fn] The iteratee invoked per element.
 * @return {*} Returns the minimum value.
 * @example
 *
 * var objects = [{ 'n': 1 }, { 'n': 2 }];
 *
 * minBy(objects, function(o) { return o.n; });
 * // => { 'n': 1 }
 *
 * minBy(objects, 'n');
 * // => { 'n': 1 }
 */
export default <T>(arr: T[], fn: ((v: T) => number) | string): T | undefined => {
  if (!isArray(arr)) {
    return undefined;
  }

  let minItem;
  let min = Infinity;

  for (let i = 0; i < arr.length; i++) {
    const item = arr[i];
    const v = isFunction(fn) ? fn(item) : item[fn];

    if (v < min) {
      minItem = item;
      min = v;
    }
  }

  return minItem;
};