/**
 * 农历日期转换工具
 * 基于寿星万年历算法（1900-2100年）
 */

// 农历数据：每条数据记录该年的月份大小和闰月信息
// 格式：高4位=闰月大小(0无闰/1闰大月), 中4位=闰月位置, 低12位=12个月大小(1大/0小)
const lunarInfo = [
  0x04bd8,0x04ae0,0x0a570,0x054d5,0x0d260,0x0d950,0x16554,0x056a0,0x09ad0,0x055d2, // 1900-1909
  0x04ae0,0x0a5b6,0x0a4d0,0x0d250,0x1d255,0x0b540,0x0d6a0,0x0ada2,0x095b0,0x14977, // 1910-1919
  0x04970,0x0a4b0,0x0b4b5,0x06a50,0x06d40,0x1ab54,0x02b60,0x09570,0x052f2,0x04970, // 1920-1929
  0x06566,0x0d4a0,0x0ea50,0x06e95,0x05ad0,0x02b60,0x186e3,0x092e0,0x1c8d7,0x0c950, // 1930-1939
  0x0d4a0,0x1d8a6,0x0b550,0x056a0,0x1a5b4,0x025d0,0x092d0,0x0d2b2,0x0a950,0x0b557, // 1940-1949
  0x06ca0,0x0b550,0x15355,0x04da0,0x0a5b0,0x14573,0x052b0,0x0a9a8,0x0e950,0x06aa0, // 1950-1959
  0x0aea6,0x0ab50,0x04b60,0x0aae4,0x0a570,0x05260,0x0f263,0x0d950,0x05b57,0x056a0, // 1960-1969
  0x096d0,0x04dd5,0x04ad0,0x0a4d0,0x0d4d4,0x0d250,0x0d558,0x0b540,0x0b6a0,0x195a6, // 1970-1979
  0x095b0,0x049b0,0x0a974,0x0a4b0,0x0b27a,0x06a50,0x06d40,0x0af46,0x0ab60,0x09570, // 1980-1989
  0x04af5,0x04970,0x064b0,0x074a3,0x0ea50,0x06aa0,0x0a6b6,0x056a0,0x02b60,0x09570, // 1990-1999
  0x049b0,0x0a4b0,0x0aa50,0x1b255,0x06d40,0x0ad50,0x14b55,0x056a0,0x0a6d0,0x055d4, // 2000-2009
  0x052d0,0x0a9b8,0x0a950,0x0b4a0,0x0b6a6,0x0ad50,0x055a0,0x0aba4,0x0a5b0,0x052b0, // 2010-2019
  0x0b273,0x06930,0x07337,0x06aa0,0x0ad50,0x14b55,0x04b60,0x0a570,0x054e4,0x0d160, // 2020-2029
  0x0e968,0x0d520,0x0daa0,0x16aa6,0x056d0,0x04ae0,0x0a9d4,0x0a2d0,0x0d150,0x0f252, // 2030-2039
  0x0d520,0x0daa0,0x16aa6,0x056d0,0x04ae0,0x0a9d4,0x0a2d0,0x0d150,0x0f252,0x0d520, // 2040-2049
  0x0b54f,0x0d6a0,0x0ada0,0x14955,0x056a0,0x0a6d0,0x0155b,0x025d0,0x092d0,0x0d954, // 2050-2059
  0x0d4a0,0x0b550,0x0b4a9,0x04da0,0x0a5b0,0x15176,0x052b0,0x0a930,0x07954,0x06aa0, // 2060-2069
  0x0ad50,0x05b52,0x04b60,0x0a6e6,0x0a4e0,0x0d260,0x0ea65,0x0d530,0x05aa0,0x076a3, // 2070-2079
  0x096d0,0x04afb,0x04ad0,0x0a4d0,0x1d0b6,0x0d250,0x0d520,0x0dd45,0x0b5a0,0x056d0, // 2080-2089
  0x055b2,0x049b0,0x0a577,0x0a4b0,0x0aa50,0x1b255,0x06d20,0x0ada0,0x14b63,0x09370  // 2090-2099
]

// 1900年1月31日是农历正月初一（庚子年）
const BASE_DATE = new Date(1900, 0, 31)

const LUNAR_MONTHS = ['正','二','三','四','五','六','七','八','九','十','冬','腊']
const LUNAR_DAYS_TENS = ['初','十','廿','三']
const LUNAR_DAYS_UNITS = ['一','二','三','四','五','六','七','八','九','十']

/**
 * 获取农历某年的总天数
 */
function _lunarYearDays(year) {
  let total = 348
  for (let i = 0x8000; i > 0x8; i >>= 1) {
    total += (lunarInfo[year - 1900] & i) ? 1 : 0
  }
  return total + _leapDays(year)
}

/**
 * 获取农历某年闰月的天数
 */
function _leapDays(year) {
  if (_leapMonth(year)) {
    return (lunarInfo[year - 1900] & 0x10000) ? 30 : 29
  }
  return 0
}

/**
 * 获取农历某年的闰月月份，0表示无闰月
 */
function _leapMonth(year) {
  return lunarInfo[year - 1900] & 0xf
}

/**
 * 获取农历某年某月的天数
 */
function _monthDays(year, month) {
  return (lunarInfo[year - 1900] & (0x10000 >> month)) ? 30 : 29
}

/**
 * 公历转农历
 * @param {Date} solarDate
 * @returns {{ year, month, day, isLeap, lunarText }}
 */
function solarToLunar(solarDate) {
  const date = new Date(solarDate.getFullYear(), solarDate.getMonth(), solarDate.getDate())
  let offset = Math.round((date - BASE_DATE) / 86400000)

  let lunarYear, lunarMonth, lunarDay
  let isLeap = false

  for (lunarYear = 1900; lunarYear < 2100 && offset > 0; lunarYear++) {
    const days = _lunarYearDays(lunarYear)
    offset -= days
  }
  if (offset < 0) {
    offset += _lunarYearDays(--lunarYear)
  }

  const leapM = _leapMonth(lunarYear)
  let isLeapYear = false

  for (lunarMonth = 1; lunarMonth < 13 && offset > 0; lunarMonth++) {
    if (leapM > 0 && lunarMonth === leapM + 1 && !isLeapYear) {
      --lunarMonth
      isLeapYear = true
      const leapDays = _leapDays(lunarYear)
      offset -= leapDays
    } else {
      offset -= _monthDays(lunarYear, lunarMonth)
    }
    if (isLeapYear && lunarMonth === leapM + 1) isLeapYear = false
  }

  if (offset === 0 && leapM > 0 && lunarMonth === leapM + 1) {
    if (isLeapYear) {
      isLeapYear = false
    } else {
      isLeapYear = true
      --lunarMonth
    }
  }
  if (offset < 0) {
    offset += isLeapYear ? _leapDays(lunarYear) : _monthDays(lunarYear, lunarMonth)
    if (isLeapYear) isLeapYear = false
    else --lunarMonth
  }

  lunarDay = offset + 1
  isLeap = isLeapYear

  return {
    year: lunarYear,
    month: lunarMonth,
    day: lunarDay,
    isLeap,
    lunarText: `${isLeap ? '闰' : ''}${getLunarMonthName(lunarMonth)}月${getLunarDayName(lunarDay)}`
  }
}

/**
 * 农历转公历（指定年份）
 * @param {Number} lunarYear
 * @param {Number} lunarMonth
 * @param {Number} lunarDay
 * @param {Boolean} isLeap 是否闰月
 * @returns {Date}
 */
function lunarToSolar(lunarYear, lunarMonth, lunarDay, isLeap) {
  let offset = 0

  for (let y = 1900; y < lunarYear; y++) {
    offset += _lunarYearDays(y)
  }

  const leapM = _leapMonth(lunarYear)
  let hasLeap = false

  for (let m = 1; m < lunarMonth; m++) {
    if (leapM > 0 && m === leapM && !hasLeap) {
      offset += _leapDays(lunarYear)
      hasLeap = true
    }
    offset += _monthDays(lunarYear, m)
  }

  if (isLeap && lunarMonth === leapM) {
    offset += _monthDays(lunarYear, lunarMonth)
  }

  offset += lunarDay - 1

  const result = new Date(BASE_DATE.getTime() + offset * 86400000)
  return result
}

/**
 * 获取指定农历月日在今年或明年的公历日期
 */
function getNextLunarDate(lunarMonth, lunarDay) {
  const today = new Date()
  const currentYear = today.getFullYear()
  const lunarToday = solarToLunar(today)

  // 尝试今年
  let candidate = lunarToSolar(lunarToday.year, lunarMonth, lunarDay, false)
  if (candidate >= today) return candidate

  // 明年
  return lunarToSolar(lunarToday.year + 1, lunarMonth, lunarDay, false)
}

function getLunarMonthName(month) {
  return LUNAR_MONTHS[month - 1] || ''
}

function getLunarDayName(day) {
  if (day === 10) return '初十'
  if (day === 20) return '二十'
  if (day === 30) return '三十'
  const tens = Math.floor(day / 10)
  const units = day % 10
  return LUNAR_DAYS_TENS[tens] + (units > 0 ? LUNAR_DAYS_UNITS[units - 1] : '')
}

function formatLunarText(lunarDate) {
  return solarToLunar(new Date(lunarDate.year, lunarDate.month - 1, lunarDate.day)).lunarText
}

module.exports = {
  solarToLunar,
  lunarToSolar,
  getNextLunarDate,
  formatLunarText,
  getLunarMonthName,
  getLunarDayName
}