const isValidDate = (date: string | Date) => !isNaN(Date.parse('' + date))

const createIsoParser = (regex: RegExp) =>
  (dateStr: string) => {
    const match = typeof dateStr === 'string' && dateStr.match(regex)
    return match ?
      // tslint:disable-next-line
      new Date(Date.UTC(+match[1], +match[2] - 1, +match[3] || 0, +match[4] + parseInt(match[8], 10) || 0, +match[5] || 0, +match[6] || 0, parseInt(match[7], 10) || 0))
    : null
  }

// tslint:disable-next-line
const regexIso8601 = /^(\d{4}|\+\d{6})(?:-?(\d{2})(?:-?(\d{2})(?:T(\d{2})(?::?(\d{2})(?::?(\d{2})(?:(?:\.|,)(\d{1,}))?)?)?(Z|([\-+])(\d{2})(?::?(\d{2}))?)?)?)?)?$/
export const parseDateIso8601 = createIsoParser(regexIso8601)

export const naiveParser = (dateStr: string) => {
  const date = new Date(dateStr)
  return isValidDate(date) ? date : null
}

export const parseDate = (dateStr: Date | string) =>
  // list of date-parsers we need
  (typeof dateStr === 'string' && (
       naiveParser(dateStr)
    || parseDateIso8601(dateStr)
  )) || dateStr // final fallback to the string / date