const formatTime = (seconds) => {
  const m = Math.floor(seconds / 60)
  const s = seconds % 60
  return `${String(m).padStart(2, '0')}:${String(s).padStart(2, '0')}`
}

const formatDuration = (seconds) => {
  if (seconds < 60) return `${seconds}秒`
  const m = Math.floor(seconds / 60)
  const s = seconds % 60
  return s > 0 ? `${m}分${s}秒` : `${m}分钟`
}

const getDaysInMonth = (year, month) => new Date(year, month, 0).getDate()

const getMonthCalendar = (year, month) => {
  const firstDay = new Date(year, month - 1, 1)
  const daysInMonth = new Date(year, month, 0).getDate()
  const startDayOfWeek = firstDay.getDay()

  const weeks = []
  let week = [null, null, null, null, null, null, null]

  for (let d = 1; d <= daysInMonth; d++) {
    const 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
}

/**
 * Format a Date as `YYYY-MM-DD HH:MM:SS` in local time.
 *
 * Used as the canonical `record.date` string so each record has a
 * precise timestamp (e.g. "2026-06-11 14:30:45"). Use `_dateOnly()`
 * to strip back to YYYY-MM-DD for date-level comparisons (streak,
 * leaderboard day filter, etc.).
 */
const formatDate = (date) => {
  const y = date.getFullYear()
  const mo = String(date.getMonth() + 1).padStart(2, '0')
  const d = String(date.getDate()).padStart(2, '0')
  const h = String(date.getHours()).padStart(2, '0')
  const mi = String(date.getMinutes()).padStart(2, '0')
  const s = String(date.getSeconds()).padStart(2, '0')
  return `${y}-${mo}-${d} ${h}:${mi}:${s}`
}

/** Strip the time portion of a formatDate string → "YYYY-MM-DD". */
const _dateOnly = (s) => (typeof s === 'string' && s.length >= 10) ? s.substring(0, 10) : ''

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