local getArgs = require('Module:Arguments').getArgs
local dateUtils = {}

local year = {
											--1  2   3   4   5   6   7   8   9  10  11  12  13
	--[2460351] = { name = "甲辰", months = { 29, 30, 29, 29, 30, 29, 30, 30, 29, 30, 30, 29 }, intercalary = 0 },
	[2460705] = { name = "乙巳", months = { 30, 29, 30, 29, 29, 30, 29, 30, 29, 30, 30, 30, 29 }, intercalary = 6 },
	[2461089] = { name = "丙午", months = { 30, 29, 30, 29, 29, 30, 29, 29, 30, 30, 30, 29 }, intercalary = 0 },
}

local sb60 = {
    "甲子", "乙丑", "丙寅", "丁卯", "戊辰", "己巳", "庚午", "辛未", "壬申", "癸酉",
    "甲戌", "乙亥", "丙子", "丁丑", "戊寅", "己卯", "庚辰", "辛巳", "壬午", "癸未",
    "甲申", "乙酉", "丙戌", "丁亥", "戊子", "己丑", "庚寅", "辛卯", "壬辰", "癸巳",
    "甲午", "乙未", "丙申", "丁酉", "戊戌", "己亥", "庚子", "辛丑", "壬寅", "癸卯",
    "甲辰", "乙巳", "丙午", "丁未", "戊申", "己酉", "庚戌", "辛亥", "壬子", "癸丑",
    "甲寅", "乙卯", "丙辰", "丁巳", "戊午", "己未", "庚申", "辛酉", "壬戌", "癸亥"
}

local m12 = {
    "一", "二", "三", "四", "五", "六", "七", "八", "九", "十", "十一", "十二"
}

local d30 = {
	"初一", "初二", "初三", "初四", "初五", "初六", "初七", "初八", "初九", "初十",
	"十一", "十二", "十三", "十四", "十五", "十六", "十七", "十八", "十九", "二十", 
	"廿一", "廿二", "廿三", "廿四", "廿五", "廿六", "廿七", "廿八", "廿九", "三十", "卅一"
}

local makeNow = function()
	local d = os.date("*t", os.time())
	return os.time {year = d.year, month = d.month, day = d.day} -- + 8 * 60 * 60 -- data based on UTC+8
end

local makeTime = function(Y, M, D)
	return os.time {year = Y, month = M, day = D}
end

local makeAjd = function(t)
	return math.floor((t / 86400) + 2440587.5)
end

dateUtils.cdate = function(frame)
	local Y = tonumber(frame.args.y) or 2025
	local M = tonumber(frame.args.m) or 3
	local D = tonumber(frame.args.d) or 1
	local today = frame.args.today
	local t
	if today then
		t = makeNow()
	else
		t = makeTime(Y, M, D)
	end
	local ajd_int = makeAjd(t)
	local year_name = ''
	local month_name = ''
	local day_name = ''
	local day_sb_name = ''
	
	for i, year_data in pairs(year) do
		local days = 0
		for i,v in pairs(year_data.months) do
			days = days + v
		end
		local year_start = i
		local year_end = year_start + days
		if ajd_int >= year_start and year_start < year_end then
			local month_start = year_start
			local month_end = 0
			local month = 0
			--local yy = (os.date("*t", os.date((year_start - 2440587.5 ) * 86400)).year - 4) % 60 + 1

			for i, v in pairs(year_data.months) do
				month = i
				
				month_end = month_start + v
				if ajd_int >= month_start and ajd_int < month_end then
					year_name = year_data.name .. '年'
					if month == year_data.intercalary + 1 then
						month_name = "閏" .. m12[month - 1]
					else
						if month > year_data.intercalary + 1 then
							month_name = m12[month - 1]
						else
							month_name = m12[month]
						end
					end
					month_name = month_name .. '月'
					local day = ajd_int - month_start + 1
					day_name = d30[day]
					local day_sb = ( ajd_int - 11) % 60 + 1
					day_sb_name = sb60[day_sb]

					break
				else
					month_start = month_start + v
				end
			end
			break
		else
		end
	end
	local d = os.date("%Y-%m-%d ", t)
	-- local d = os.date("%Y-%m-%d %H:%M:%S", t)
	return d .. year_name  .. month_name  .. day_name .. day_sb_name
end

dateUtils.d60 = function(text)
	local jd = tonumber(text.args[1])
	local ajd = jd - 0.5
	local ajd_int = math.floor(ajd)
	local sb = ( ajd_int - 9 ) % 60
	local sb60_x = sb60[sb]
	return sb60_x
end

-- date_utils.lua
--[[
    Lua Date & Calendar Utilities Module
    ------------------------------------
    Provides:
      - getJD(yyyy, mm, dd)            → Julian Day at midnight UT
      - NdaysGregJul(y)                → Number of days in year (Julian/Gregorian)
      - get_Western_calendar_name(y)   → Calendar name by year
      - langConstant(lang)             → Language constants (0=English, 1=Traditional, 2=Simplified Chinese)

    Usage:
        local dateUtils = require("date_utils")

        local jd = dateUtils.getJD(2025, 8, 16)
        local days = dateUtils.NdaysGregJul(2024)
        local calName = dateUtils.get_Western_calendar_name(2025)
        local langData = dateUtils.langConstant(1) -- Traditional Chinese
--]]

--local dateUtils = {}

-------------------------------------------------
-- Julian Day Number Calculation
-------------------------------------------------
function dateUtils.getJD(yyyy, mm, dd)
    local yy, m = yyyy, mm
    if m <= 2 then
        m = m + 12
        yy = yy - 1
    end

    local ymd = 10000 * yy + 100 * m + dd
    local B
    if ymd <= 15821004 then
        B = -2 + math.floor((yy + 4716) / 4) - 1179
    else
        B = math.floor(yy / 400) - math.floor(yy / 100) + math.floor(yy / 4)
    end

    return 365 * yy - 679004 + B + math.floor(30.6001 * (m + 1)) + dd + 2400000.5
end

-------------------------------------------------
-- Number of days in a Gregorian/Julian year
-------------------------------------------------
function dateUtils.NdaysGregJul(y)
    local ndays = (y == 1582) and 355 or 365

    if y % 4 == 0 then
        ndays = ndays + 1
    end
    if y > 1582 then
        if y % 100 == 0 then ndays = ndays - 1 end
        if y % 400 == 0 then ndays = ndays + 1 end
    end

    return ndays
end

-------------------------------------------------
-- Calendar name by year
-------------------------------------------------
function dateUtils.get_Western_calendar_name(y)
    if y > 1582 then
        return {"額曆"}
    elseif y == 1582 then
        return {"儒曆額曆"}
    elseif y > 7 then
        return {"儒曆"}
    else
        return {"逆推儒曆"}
    end
end

-------------------------------------------------
-- Language constants for calendar rendering
-------------------------------------------------
function dateUtils.langConstant(lang)
    -- Chinese data
    local gMonthChi = {"壹月","貳月","叄月","肆月","伍月","陸月","柒月","捌月","久月","拾月","拾壹月","拾貳月"}
    local weeksChi = {"日曜日","月曜日","火曜日","水曜日","木曜日","金曜日","土曜日"}
    local heavenChi = {"甲","乙","丙","丁","戊","己","庚","辛","壬","癸"}
    local earthChi  = {"子","丑","寅","卯","辰","巳","午","未","申","酉","戌","亥"}
    local animalChi = {"鼠","牛","虎","兔","龍","蛇","馬","羊","猴","雞","狗","豬"}
    local animalSim = {"鼠","牛","虎","兔","龙","蛇","马","羊","猴","鸡","狗","猪"}
    local month_numChi = {"正","二","三","四","五","六","七","八","九","十","十一","十二"}

    -- Generate Chinese lunar dates 初一..三十
    local date_numChi = {"初一"}
    for i=2,10 do table.insert(date_numChi,"初"..month_numChi[i]) end
    table.insert(date_numChi,"十一")
    for i=12,19 do table.insert(date_numChi,"十"..month_numChi[i-11]) end
    table.insert(date_numChi,"二十")
    table.insert(date_numChi,"廿一")
    for i=22,29 do table.insert(date_numChi,"廿"..month_numChi[i-21]) end
    table.insert(date_numChi,"三十")

    local monthLChi = {"小","大"}
    local QnamesChi = {"朔","上弦","望","下弦"}
    local soltermNamesChi = {"小寒","大寒","立春","雨水","驚蟄","春分",
                             "清明","穀雨","立夏","小滿","芒種","夏至",
                             "小暑","大暑","立秋","處暑","白露","秋分",
                             "寒露","霜降","立冬","小雪","大雪","冬至","小寒"}

    local note_earlyChi = "朔的時刻接近午夜零時，初一或會提早一天。"
    local note_lateChi  = "朔的時刻接近午夜零時，初一或會推遲一天。"
    local note1929Chi   = "注意。一九二九年以前朔日以北京時計算，遲東經百二度遲十四分鐘，因此列出朔時過了初二零時。"
    local note1914Chi   = "注意。一九一四年前朔計算方法不準確，且一九二九年前用北京時，遲東經百二度遲約十四分鐘。"

    return {
        gMonth = gMonthChi, weeks = weeksChi, lang = lang,
        heaven = heavenChi, earth = earthChi, animal = animalChi,
        region = "default", cmonth = month_numChi, monthL = monthLChi,
        Qnames = QnamesChi, soltermNames = soltermNamesChi,
        julian = false, li_ancient = nil,
        date_numChi = date_numChi,
        note_early = note_earlyChi, note_late = note_lateChi,
        note1929 = note1929Chi, note1914 = note1914Chi
    }
end

--------------------------------------------------
-- Convert kin number to month number & year offset
--------------------------------------------------
function dateUtils.kinToMonthYearoffset(kinIn, y, region)
    local kin = math.abs(kinIn)
    local yearOffset, monNum = 0, kin

    -- Hon dynasty
    if y < -103 and kin > 9 then
        yearOffset = 1
    end

    -- Sun dynasty
    if y == 8 and kin == 12 then
        monNum, yearOffset = 1, 1
    elseif y > 8 and y < 23 then
        monNum = (kin == 12) and 1 or (kin + 1)
        if kin == 12 then yearOffset = 1 end
    elseif y == 23 and kin < 12 then
        monNum = kin + 1
    end

    -- Ngai dynasty
    if ((y == 237 and kin > 2) or (y == 238) or (y == 239 and kin < 12)) and region == "default" then
        monNum = (kin == 12) and 1 or (kin + 1)
        if kin == 12 then yearOffset = 1 end
    end

    -- Tang dynasty
    if y > 688 and y < 700 then
        if kin > 10 then yearOffset = 1 end
    elseif y == 761 and kin > 10 then
        monNum, yearOffset = kin - 10, 1
    elseif y == 762 and kin < 4 then
        monNum = kin + 2
    end

    if kinIn < 0 then
        monNum = -monNum
    end

    return { monNum = monNum, yearOffset = yearOffset }
end

-- ===========================================================================
-- Determine first month number for a year
-- ===========================================================================
function dateUtils.firstMonthNum(y)
    local firstMonth = 1
    if y < -102 then
        firstMonth = 10
    elseif y > 689 and y < 701 then
        firstMonth = 11
    end
    return firstMonth
end

-- ===========================================================================
-- Decompress time values encoded with compression algorithm
-- Compression: t = floor(x) * 1441 + m
-- Inverse: x ≈ floor(t/1441) + (t - floor(t/1441)*1441)/1440
-- ===========================================================================
function dateUtils.decompress_time(t)
    local x = {}
    for i = 1, #t do
        local y = math.floor(t[i] / 1441)
        local m = t[i] - 1441 * y
        if m > 1439.5 then
            m = 1439.9
        end
        table.insert(x, y + m / 1440.0)
    end
    return x
end

-- Returns offsets for solar and lunar calculations
function dateUtils.offset_sunMoon()
    return {solar = 5, lunar = 5}
end

return dateUtils