import toDate from '../toDate/index'
import requiredArgs from '../_lib/requiredArgs/index'

/**
 * @name startOfMonth
 * @category Month Helpers
 * @summary Return the start of a month for the given date.
 *
 * @description
 * Return the start of a month for the given date.
 * The result will be in the local timezone.
 *
 * @param {Date|Number} date - the original date
 * @returns {Date} the start of a month
 * @throws {TypeError} 1 argument required
 *
 * @example
 * // The start of a month for 2 September 2014 11:55:00:
 * const result = startOfMonth(new Date(2014, 8, 2, 11, 55, 0))
 * //=> Mon Sep 01 2014 00:00:00
 */
export default function startOfMonth(dirtyDate: Date | number): Date {
  requiredArgs(1, arguments)

  const date = toDate(dirtyDate)
  date.setDate(1)
  date.setHours(0, 0, 0, 0)
  return date
}