/**
 * 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：bit 16=闰月大小(1 大月 / 0 小月)，bit 15-4=12 个月大小(1大/0小)，bit 3-0=闰月位置(0 无闰)
// 数据源：github.com/jjonline/calendar.js（权威，经过修订）
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, 0x16a95, 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, 0x06b58, 0x05ac0, 0x0ab60, 0x096d5, 0x092e0, // 1990-1999
  0x0c960, 0x0d954, 0x0d4a0, 0x0da50, 0x07552, 0x056a0, 0x0abb7, 0x025d0, 0x092d0, 0x0cab5, // 2000-2009
  0x0a950, 0x0b4a0, 0x0baa4, 0x0ad50, 0x055d9, 0x04ba0, 0x0a5b0, 0x15176, 0x052b0, 0x0a930, // 2010-2019
  0x07954, 0x06aa0, 0x0ad50, 0x05b52, 0x04b60, 0x0a6e6, 0x0a4e0, 0x0d260, 0x0ea65, 0x0d530, // 2020-2029
  0x05aa0, 0x076a3, 0x096d0, 0x04afb, 0x04ad0, 0x0a4d0, 0x1d0b6, 0x0d250, 0x0d520, 0x0dd45, // 2030-2039
  0x0b5a0, 0x056d0, 0x055b2, 0x049b0, 0x0a577, 0x0a4b0, 0x0aa50, 0x1b255, 0x06d20, 0x0ada0, // 2040-2049
  0x14b63, 0x09370, 0x049f8, 0x04970, 0x064b0, 0x168a6, 0x0ea50, 0x06b20, 0x1a6c4, 0x0aae0, // 2050-2059
  0x092e0, 0x0d2e3, 0x0c960, 0x0d557, 0x0d4a0, 0x0da50, 0x05d55, 0x056a0, 0x0a6d0, 0x055d4, // 2060-2069
  0x052d0, 0x0a9b8, 0x0a950, 0x0b4a0, 0x0b6a6, 0x0ad50, 0x055a0, 0x0aba4, 0x0a5b0, 0x052b0, // 2070-2079
  0x0b273, 0x06930, 0x07337, 0x06aa0, 0x0ad50, 0x14b55, 0x04b60, 0x0a570, 0x054e4, 0x0d160, // 2080-2089
  0x0e968, 0x0d520, 0x0daa0, 0x16aa6, 0x056d0, 0x04ae0, 0x0a9d4, 0x0a2d0, 0x0d150, 0x0f252, // 2090-2099
  0x0d520                                                                                  // 2100
]

// 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
 * 算法移植自 github.com/jjonline/calendar.js（权威），与本地原版的差异在月循环退出时
 * 必须保留 temp 保存最后一次月份天数，否则闰月非初一的日期会被错误地归到下一个普通月份。
 * @param {Date} solarDate
 * @returns {{ year, month, day, isLeap, lunarText }}
 */
function solarToLunar(solarDate) {
  const y = solarDate.getFullYear()
  const m = solarDate.getMonth() + 1
  const d = solarDate.getDate()

  let offset = (Date.UTC(y, m - 1, d) - Date.UTC(1900, 0, 31)) / 86400000
  let i, leap = 0, temp = 0

  for (i = 1900; i < 2101 && offset > 0; i++) {
    temp = _lunarYearDays(i)
    offset -= temp
  }
  if (offset < 0) {
    offset += temp
    i--
  }

  const year = i
  leap = _leapMonth(i)
  let isLeap = false

  for (i = 1; i < 13 && offset > 0; i++) {
    if (leap > 0 && i === (leap + 1) && isLeap === false) {
      --i
      isLeap = true
      temp = _leapDays(year)
    } else {
      temp = _monthDays(year, i)
    }
    if (isLeap === true && i === (leap + 1)) {
      isLeap = false
    }
    offset -= temp
  }

  // 闰月下标重叠导致 offset 恰好为 0 时的取反
  if (offset === 0 && leap > 0 && i === leap + 1) {
    if (isLeap) {
      isLeap = false
    } else {
      isLeap = true
      --i
    }
  }
  if (offset < 0) {
    offset += temp
    --i
  }

  const month = i
  const day = offset + 1

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

/**
 * 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
}