function formatTime(seconds) {
  var m = Math.floor(seconds / 60)
  var s = seconds % 60
  return (m < 10 ? '0' : '') + m + ':' + (s < 10 ? '0' : '') + s
}

function formatDuration(seconds) {
  if (seconds < 60) return seconds + '秒'
  var m = Math.floor(seconds / 60)
  var s = seconds % 60
  return s > 0 ? m + '分' + s + '秒' : m + '分钟'
}

function getDaysInMonth(year, month) {
  return new Date(year, month, 0).getDate()
}

function getMonthCalendar(year, month) {
  var firstDay = new Date(year, month - 1, 1)
  var lastDay = new Date(year, month, 0)
  var daysInMonth = lastDay.getDate()
  var startDayOfWeek = firstDay.getDay()

  var weeks = []
  var week = [null, null, null, null, null, null, null]

  for (var d = 1; d <= daysInMonth; d++) {
    var dow = (startDayOfWeek + d - 1) % 7
    week[dow] = d
    if (dow === 6 || d === daysInMonth) {
      weeks.push(week.slice())
      week = [null, null, null, null, null, null, null]
    }
  }

  return weeks
}

module.exports = {
  formatTime: formatTime,
  formatDuration: formatDuration,
  getDaysInMonth: getDaysInMonth,
  getMonthCalendar: getMonthCalendar
}