/**
 * 请假按自然日：1 天 = 24 小时；含 0.5 天时用「上午 / 下午」落在当天或最后一天的半日边界。
 * @param {string} startDateStr YYYY-MM-DD
 * @param {number} days 正数，且为 0.5 的倍数
 * @param {'am'|'pm'} dayHalfPeriod 半天取上午或下午（仅在天数含 0.5 时参与计算）
 * @returns {{ leaveStartTime: string, leaveEndTime: string, leaveHour: string }}
 */
export function computeLeaveRangeNaturalDay(startDateStr, days, dayHalfPeriod) {
  const d = Number(days)
  if (!startDateStr || !d || d <= 0) {
    return { leaveStartTime: '', leaveEndTime: '', leaveHour: '' }
  }
  if (d * 2 !== Math.round(d * 2)) {
    return { leaveStartTime: '', leaveEndTime: '', leaveHour: '' }
  }
  const period = dayHalfPeriod === 'pm' ? 'pm' : 'am'
  const halves = Math.round(d * 2)
  const fullDayCount = Math.floor(halves / 2)
  const hasHalf = halves % 2 === 1

  const base = new Date(String(startDateStr).replace(/-/g, '/') + ' 00:00:00')
  if (Number.isNaN(base.getTime())) {
    return { leaveStartTime: '', leaveEndTime: '', leaveHour: '' }
  }

  function formatDate(date) {
    const y = date.getFullYear()
    const m = `${date.getMonth() + 1}`.padStart(2, '0')
    const day = `${date.getDate()}`.padStart(2, '0')
    return `${y}-${m}-${day}`
  }

  function pad2(n) {
    return String(n).padStart(2, '0')
  }

  function addDays(date, n) {
    const x = new Date(date.getTime())
    x.setDate(x.getDate() + n)
    return x
  }

  let start
  let end

  if (fullDayCount === 0 && hasHalf) {
    if (period === 'pm') {
      start = new Date(base)
      start.setHours(12, 0, 0, 0)
      end = new Date(base)
      end.setHours(23, 59, 59, 0)
    } else {
      start = new Date(base)
      start.setHours(0, 0, 0, 0)
      end = new Date(base)
      end.setHours(11, 59, 59, 0)
    }
  } else if (fullDayCount > 0 && hasHalf) {
    start = new Date(base)
    start.setHours(0, 0, 0, 0)
    end = addDays(base, fullDayCount)
    if (period === 'am') {
      end.setHours(11, 59, 59, 0)
    } else {
      end.setHours(23, 59, 59, 0)
    }
  } else {
    start = new Date(base)
    start.setHours(0, 0, 0, 0)
    if (fullDayCount <= 0) {
      return { leaveStartTime: '', leaveEndTime: '', leaveHour: '' }
    }
    end = addDays(base, fullDayCount - 1)
    end.setHours(23, 59, 59, 0)
  }

  const leaveStartTime = `${formatDate(start)} ${pad2(start.getHours())}:${pad2(start.getMinutes())}:${pad2(start.getSeconds())}`
  const leaveEndTime = `${formatDate(end)} ${pad2(end.getHours())}:${pad2(end.getMinutes())}:${pad2(end.getSeconds())}`
  const h = d * 24
  const leaveHour = Number.isInteger(h) ? String(h) : h.toFixed(1)

  return { leaveStartTime, leaveEndTime, leaveHour }
}