-- Load dependencies.
local getArgs = require('Module:Arguments').getArgs
local numToRoman = require( 'Module:Roman' ).main
local getOlympiad = require( 'Module:Ancient Olympiads' )._main
local getDynasty = require( 'Module:Ancient Egypt era' )._main
local getPharaoh = require( 'Module:Ancient Egypt kings' )._main
local numToArmenian = require( 'Module:Armenian' ).main
local getRegnal = require( 'Module:British regnal year' ).main
local japaneseEra = require( 'Module:Japanese calendar' ).era()

-- Define constants.
local lang = mw.language.getContentLanguage()
local currentYear = tonumber( lang:formatDate( 'Y' ) )

--------------------------------------------------------------------
-- Helper functions
--------------------------------------------------------------------

local function isInteger( num )
	-- Checks if a value is an integer. If so, returns the value converted to a number.
	-- If not, returns false.
	num = tonumber( num )
	if num and math.floor( num ) == num and num ~= math.huge then
		return num
	else
		return false
	end
end

local function BCToNum( s )
	-- Converts strings of the format "n BC" to their corresponding
	-- numerical values.
	if type( s ) ~= 'string' then
		return nil
	end
	s = mw.ustring.match( mw.ustring.upper( s ), '^([1-9]%d*)%s*TCN$' )
	if not s then
		return nil
	end
	local num = tonumber( s )
	num = ( num - 1 ) * -1
	return num
end

local function numToBC( num )
	-- For BC years, returns a string with the year name appended with " BC".
	-- Otherwise returns nil.
	num = isInteger( num )
	if not num then return end
	if num <= 0 then
		return string.format( '%d TCN', 1 - num )
	end
end

local function ADToNum( s )
	-- Converts strings of the format "AD n"
	-- to their corresponding numerical values.
	if type( s ) ~= 'string' then
		return nil
	end
	s = mw.ustring.match( mw.ustring.upper( s ), '^%s*([1-9]%d*)$' )
	if not s then
		return nil
	end
	local num = tonumber( s )
	return num
end

local function numToAD( num )
	-- For AD years up to 100, returns a string with the year name prepended with "AD ".
	-- Otherwise returns nil.
	num = isInteger( num )
	if not num then return end
	if (num <= 100) then
		return string.format( '%d', num )
	end
end

local function formatNegative(s)
	-- Replaces hyphens in a string with minus signs if the hyphen comes before a number.
	s = mw.ustring.gsub( s, '%-(%d)', '−%1' )
	return s
end

--------------------------------------------------------------------
-- Calendar box class definition
--------------------------------------------------------------------

local calendarBox = {}
calendarBox.__index = calendarBox

function calendarBox:new( init )
	init = type( init ) == 'table' and init or {}
	local obj = {}
	local pagename = mw.title.getCurrentTitle().text

	-- Set the year. If the year is specified as an argument, use that.
	-- Otherwise, use the page name if it is valid. If the pagename isn't
	-- valid, use the current year.
	local yearNum = isInteger( init.year )
	local yearBC = BCToNum( init.year )
	local yearAD = ADToNum( init.year )
	local pageNum = isInteger( pagename )
	local pageBC = BCToNum( pagename )
	local pageAD = ADToNum( pagename )
	if yearNum then -- First, see if the year parameter is a number.
		self.year = yearNum
	elseif yearBC then -- Second, see if the year parameter is a "yyyy BC" string.
		self.year = yearBC
	elseif yearAD then -- Third, see if the year parameter is an AD/CE/year string.
		self.year = yearAD
	elseif pageNum then -- Fourth, see if the pagename is an integer.
		self.year = pageNum
	elseif pageBC then -- Fifth, see if the pagename is a "yyyy BC" string.
		self.year = pageBC
	elseif pageAD then -- Sixth, see if the pagename is an AD/CE/year string.
		self.year = pageAD
	else
		self.year = currentYear -- If none of the above apply, use the current year.
	end

	-- Set year text values.
	self.BCYearName = numToBC( self.year )
	self.ADYearName = numToAD( self.year )
	if self.BCYearName then
		self.yearText = self.BCYearName
	elseif self.ADYearName then
		self.yearText = self.ADYearName
	else
		self.yearText = tostring( self.year )
	end

	-- Set other fields.
	self.caption = self.yearText
	self.footnotes = init.footnotes

	return setmetatable( obj, {
			__index = self
		})
end

function calendarBox:setCaption( s )
	-- Sets the calendar box caption.
	if type( s ) ~= 'string' or s == '' then return end
	self.caption = s
end

function calendarBox:addCalendar( obj )
	-- Adds a calendar or a calendar group.
	if type( obj ) ~= 'table' and type( obj.new ) ~= 'function' then return end -- Exit if the object is invalid.
	self.calendars = self.calendars or {}
	table.insert( self.calendars, obj )
end

-- Add an alias for adding calendar groups. The function is the same, but it might be confusing for users
-- to have to use the name "addCalendar" for a calendar group.
calendarBox.addCalendarGroup = calendarBox.addCalendar

function calendarBox:export()
	-- Outputs the calendar box wikitext.
	local root = mw.html.create( 'table' )
	-- Export the calendar box headers.
	root
	:addClass( 'infobox vevent' )
	:css( 'width', '22em' )
	:tag( 'caption' )
	:css( 'font-size', '125%' )
	:tag( 'span' )
	:addClass( 'summary dtstart' )
	:wikitext( self.caption )

	-- Export the calendars and calendar groups. "calendar:export()" works for both kinds
	-- of objects. Some export functions can return nil, so we need to check for that.
	if type( self.calendars ) == 'table' then
		for _, calendar in ipairs( self.calendars ) do
			local calendarText = calendar:export()
			if type( calendarText ) == 'string' then
				root:wikitext( calendarText )
			end
		end
	end

	-- Add footnotes.
	if type( self.footnotes ) == 'string' and self.footnotes ~= '' then
		root
		:tag( 'tr' )
		:tag( 'td' )
		:attr( 'colspan', '2' )
		:wikitext( string.format( '<small>%s</small>', self.footnotes ) )
	end

	return tostring( root )
end

--------------------------------------------------------------------
-- Calendar group class definition
--------------------------------------------------------------------

--  Calendar groups are used to group different calendars together. 
--  Previously, the template did this by including a table row with
--  no year value. By using objects we can do the same thing more
--  semantically.

local calendarGroup = {}
calendarGroup.__index = calendarGroup

function calendarGroup:new( init )
	init = type( init ) == 'table' and init or {}
	local obj = {}

	-- Get the heading and throw an error if it is invalid.
	obj.heading = init.heading
	if type( obj.heading ) ~= 'string' then
		error( 'calendarGroup: no heading detected' )
	end

	-- Set the metatable and return the object.
	self.__index = self
	return setmetatable( obj, {
			__index = self
		})
end

function calendarGroup:addCalendar( calendar )
	-- Adds a calendar object to the calendar group.
	self.calendars = self.calendars or {}
	if type( calendar ) == 'table' and type( calendar.getLink ) == 'function' then
		table.insert( self.calendars, calendar )
	end
end

function calendarGroup:export()
	-- Exports the calendar group's wikitext.
	-- Indent and italicise each calendar's link if it exists.
	for i, calendar in ipairs( self.calendars ) do
		local link = calendar:getLink()
		if type( link ) == 'string' then
			self.calendars[ i ]:setRawLink( string.format( "&nbsp;- ''%s''", link ) )
		end
	end
	-- Create the heading row html and export the calendar objects.
	local ret = mw.html.create()
	ret
	:tag( 'tr' )
	:tag( 'td' )
	:wikitext( self.heading )
	:done()
	:tag( 'td' ) -- Use a blank tag to make the html look nice.
	:allDone()
	for _, calendar in ipairs( self.calendars ) do
		ret:wikitext( calendar:export() )
	end
	return tostring( ret )
end

--------------------------------------------------------------------
-- Calendar class definition
--------------------------------------------------------------------

local calendar = {}
calendar.__index = calendar
calendar.type = 'calendar'

function calendar:new()
	local obj = {}
	return setmetatable( obj, {
			__index = self
		})
end

function calendar:setLink( link, display )
	-- Sets the calendar's wikilink, with optional display text and italics.
	if type( link ) ~= 'string' or link == '' then return end
	display = type( display ) == 'string' and display ~= '' and display
	if display then
		self.link = string.format( '[[%s|%s]]', link, display )
	else
		self.link = string.format( '[[%s]]', link )
	end
end

function calendar:setRawLink( s )
	-- Sets the calendar's wikilink as raw wikitext.
	if type( s ) ~= 'string' or s == '' then return end
	self.link = s
end

function calendar:getLink()
	-- Returns the calendar's link value.
	return self.link
end

function calendar:setYear( year )
	-- Sets a single year. Can be passed either a string or a number.
	-- If passed as a number, it is formatted with minus signs instead of hyphens.
	-- If passed as a string, no minus-sign formatting occurs; this should be done in the individual calendar definitions.
	if type( year ) == 'number' then
		year = tostring( year )
		self.year = formatNegative( year )
	elseif type( year ) == 'string' then
		self.year = year
	end
end

function calendar:setYearRange( year1, year2 )
	-- Sets a year range. Must be passed two numbers.
	if type( year1 ) == 'number' and type( year2 ) == 'number' then
		local year
		if year1 < 0 or year2 < 0 then -- Leave a gap for negative years to avoid having a minus sign and a dash right next to each other.
			year = string.format( '%d – %d', year1, year2 )
			year = formatNegative( year )
		else
			year = string.format( '%d–%d', year1, year2 )
		end
		self.year = year
	end
end

function calendar:setYearCouple( year1, year2 )
	-- Same as setYearRange, only with a slash (/) in the middle. Must be passed two numbers. 
	-- Additional text possible, must be defined as follows: addtext = string.format( 'additional text or link')
	-- See example in Seleucid era calendar
	if type( year1 ) == 'number' and type( year2 ) == 'number' then
		local year
		if year1 < 0 or year2 < 0 then -- Leave no gap for negative years.
			year = string.format( '%d/%d %s', year1, year2, addtext )
			year = formatNegative( year )
		else
			year = string.format( '%d/%d %s', year1, year2, addtext )
		end
		self.year = year
	end
end

function calendar:export()
	-- Outputs the calendar wikitext.
	-- Exit if no link has been specified.
	local link = self.link
	if type( link ) ~= 'string' or link == '' then return end

	-- If no year has been specified, set the year value to N/A.
	local year = self.year
	if type( year ) ~= 'string' or year == '' then
		year = "''N/A''"
	end

	-- Build the table row.
	local ret = mw.html.create()
	ret
	:tag( 'tr' )
	:tag( 'td' )
	:wikitext( link )
	:done()
	:tag( 'td' )
	:wikitext( year )
	:allDone()
	return tostring( ret )
end

--------------------------------------------------------------------
-- Build the box
--------------------------------------------------------------------

local function makeCalendarBox( args )
	-- Initiate the box and get the year values.
	local init = args
	local box = calendarBox:new( init )
	local year = box.year
	local yearText = box.yearText

    -- Set the caption.
    box:setCaption( box.caption .. ' trong lịch khác' )

    ----------------------------------------------------------------------
    -- Gregorian calendar
    ----------------------------------------------------------------------

    local gregorian = calendar:new()
    gregorian:setLink( 'Lịch Gregory' )
    -- Get the year link.
    local gregcal = args.gregcal
    if type( gregcal ) == 'string' and gregcal ~= '' then
        gregorian.yearLink = mw.ustring.format( '[[%s|%s]]', gregcal, yearText )
    else
        gregorian.yearLink = yearText
    end
	-- Set the year.
	gregorian.romanYear = numToRoman{ math.abs(year) } .. (year < 0 and ' TCN' or '')
	if gregorian.romanYear then
		gregorian:setYear( string.format(
				[[%s<br /><span style="font-family: serif;">''%s''</span>]],
				gregorian.yearLink, gregorian.romanYear
				) )
	else
		gregorian:setYear( gregorian.yearLink )
	end
	box:addCalendar( gregorian ) 

    ----------------------------------------------------------------------
    -- Ab urbe condita
    ----------------------------------------------------------------------
    
    local abUrbe = calendar:new()
    abUrbe:setLink( 'Ab urbe condita' )
    abUrbe:setYear( year + 753 )
    box:addCalendar( abUrbe )

    ----------------------------------------------------------------------
    -- Regnal year
    ----------------------------------------------------------------------

    local regnal = calendar:new()
    regnal:setLink( 'Niên hiệu Anh', 'Năm niên hiệu Anh' )
    regnal:setYear( getRegnal( year ) )
    box:addCalendar( regnal )

    ----------------------------------------------------------------------
    -- Armenian calendar
    ----------------------------------------------------------------------
    
    local armenian = calendar:new()
    armenian:setLink( 'Lịch Armenia' )
    if year > 551 then
        local armenianYear = year - 551
        armenian:setYear( mw.ustring.format( '%s<br />ԹՎ %s', armenianYear, numToArmenian( armenianYear ) ) )
    end
    box:addCalendar( armenian )

    ----------------------------------------------------------------------
    -- Assyrian calendar
    ----------------------------------------------------------------------

    local assyrian = calendar:new()
    assyrian:setLink( 'Lịch Assyria' )
    assyrian:setYear( year + 4750 )
    box:addCalendar( assyrian )
    
    ----------------------------------------------------------------------
    -- Hindu calendars
    ----------------------------------------------------------------------

    local hindu = calendarGroup:new{ heading = '[[Lịch Ấn Độ giáo]]' }

    -- Vikram Samvat

    local vikramSamvat = calendar:new()
    vikramSamvat:setLink( 'Vikram Samvat' )
    vikramSamvat:setYearRange( year + 56, year + 57 )
    hindu:addCalendar( vikramSamvat )

    -- Shaka Samvat

    local shakaSamvat = calendar:new()
    shakaSamvat:setLink( 'Quốc lịch Ấn Độ', 'Shaka Samvat' )
    if year - 76 > 0 then
        shakaSamvat:setYearRange( year - 78, year - 77 )
    end
    hindu:addCalendar( shakaSamvat )

    -- Kali Yuga
    
    local kaliYuga = calendar:new()
    kaliYuga:setLink( 'Kali Yuga' ) -- use italics
    kaliYuga:setYearRange( year + 3101, year + 3102 )
    hindu:addCalendar( kaliYuga )

    box:addCalendarGroup( hindu )

    ----------------------------------------------------------------------
    -- Bahá'í calendar
    ----------------------------------------------------------------------
    
    local bahai = calendar:new()
    bahai:setLink( "Lịch Bahá'í", 'Lịch Bahá’í' )
    bahai:setYearRange( year - 1844, year - 1843 )
    box:addCalendar( bahai )

    ----------------------------------------------------------------------
    -- Bengali calendar
    ----------------------------------------------------------------------

    local bengali = calendar:new()
    bengali:setLink( 'Lịch Bengal' )
    bengali:setYear( year - 593 )
    box:addCalendar( bengali )

    ----------------------------------------------------------------------
    -- Berber calendar
    ----------------------------------------------------------------------
    
    local berber = calendar:new()
    berber:setLink( 'Lịch Berber' )
    berber:setYear( year + 950 )
    box:addCalendar( berber )

    ----------------------------------------------------------------------
    -- Chinese calendar
    ----------------------------------------------------------------------
    
    local chinese = calendar:new()
    chinese:setLink( 'Can Chi' )

    -- Define the information for the "heavenly stems" and "earthly branches" year cycles.
    -- See [[Can Chi]] for information.

    local heavenlyStems = {
        { '甲', 'Giáp' },   -- 1
        { '乙', 'Ất' },     -- 2
        { '丙', 'Bính' },   -- 3
        { '丁', 'Đinh' },   -- 4
        { '戊', 'Mậu' },    -- 5
        { '己', 'Kỷ' },     -- 6
        { '庚', 'Canh' },   -- 7
        { '辛', 'Tân' },    -- 8
        { '壬', 'Nhâm' },   -- 9
        { '癸', 'Quý' }     -- 10
    }

    local earthlyBranches = {
        { '子', 'Tý' },     -- 1
        { '丑', 'Sửu' },    -- 2
        { '寅', 'Dần' },    -- 3
        { '卯', 'Mão' },    -- 4
        { '辰', 'Thìn' },   -- 5
        { '巳', 'Tỵ' },     -- 6
        { '午', 'Ngọ' },    -- 7
        { '未', 'Mùi' },    -- 8
        { '申', 'Thân' },   -- 9
        { '酉', 'Dậu' },    -- 10
        { '戌', 'Tuất' },   -- 11
        { '亥', 'Hợi' }     -- 12
    }

    -- Calculate the cycle numbers from the year. The first sexagenary year corresponds to the ''previous'' year's entry
    -- in [[:en:Chinese calendar correspondence table]], as the Chinese New Year doesn't happen until Jan/Feb in
    -- Gregorian years.
    local sexagenaryYear1 = ( year - 4 ) % 60
    local sexagenaryYear2 = ( year - 3 ) % 60
    local heavenlyNum1 = sexagenaryYear1 % 10
    local heavenlyNum2 = sexagenaryYear2 % 10
    local earthlyNum1 = sexagenaryYear1 % 12
    local earthlyNum2 = sexagenaryYear2 % 12

    -- If the value is 0 increase it by one cycle so that we can use it with Lua arrays.
    if heavenlyNum1 == 0 then
        heavenlyNum1 = 10
    end
    if heavenlyNum2 == 0 then
        heavenlyNum2 = 10
    end
    if earthlyNum1 == 0 then
        earthlyNum1 = 12
    end
    if earthlyNum2 == 0 then
        earthlyNum2 = 12
    end

    -- Get the data tables for each permutation.
    local heavenlyTable1 = heavenlyStems[ heavenlyNum1 ]
    local heavenlyTable2 = heavenlyStems[ heavenlyNum2 ]
    local earthlyTable1 = earthlyBranches[ earthlyNum1 ]
    local earthlyTable2 = earthlyBranches[ earthlyNum2 ]

    -- Work out the continously-numbered year. (See [[:en:Chinese calendar#Continuously numbered years]].)
    local year1 = year + 2696
    local year2 = year + 2697
    local year1Alt = year1 - 60
    local year2Alt = year2 - 60

    -- Return all of that data in a (hopefully) reader-friendly format.
    chinese:setYear( mw.ustring.format(
        [=[[[%s&nbsp;%s]] (%s%s年)<br />%d hoặc %d<br />&nbsp;&nbsp;&nbsp;&nbsp;''—&nbsp;đến&nbsp;—''<br />[[%s&nbsp;%s]] (%s%s年)<br />%d hoặc %d]=],
        heavenlyTable1[ 2 ],
        earthlyTable1[ 2 ],
        heavenlyTable1[ 1 ],
        earthlyTable1[ 1 ],
        year1,
        year1Alt,
        heavenlyTable2[ 2 ],
        earthlyTable2[ 2 ],
        heavenlyTable2[ 1 ],
        earthlyTable2[ 1 ],
        year2,
        year2Alt
    ) )

    box:addCalendar( chinese )
    
    ----------------------------------------------------------------------
    -- Juche calendar
    ----------------------------------------------------------------------

    local juche = calendar:new()
    juche:setLink( 'Lịch Bắc Triều Tiên', 'Lịch Chủ thể' )
    if year > 1911 then
        juche:setYear( year - 1911 )
    end
    box:addCalendar( juche )
    
    ----------------------------------------------------------------------
    -- Coptic calendar
    ----------------------------------------------------------------------

    local coptic = calendar:new()
    coptic:setLink( 'Lịch Copt' )
    coptic:setYearRange( year - 284, year - 283 )
    box:addCalendar( coptic )

    ----------------------------------------------------------------------
    -- Minguo calendar
    ----------------------------------------------------------------------

    local minguo = calendar:new()
    minguo:setLink( 'Lịch Dân Quốc' )
    if year > 1911 then
        local minguoYear = year - 1911
        minguo:setYear( mw.ustring.format( '[[Trung Hoa Dân Quốc|Dân Quốc]] %d<br /><small>民國%d年</small>', minguoYear, minguoYear ) )
    else
        local minguoYear = 1911 - year + 1
        minguo:setYear( mw.ustring.format( '%d trước [[Trung Hoa Dân Quốc|Dân Quốc]]<br /><small>民前%d年</small>', minguoYear, minguoYear ) )
    end
    box:addCalendar( minguo )
    
    ----------------------------------------------------------------------
    -- Hebrew calendar
    ----------------------------------------------------------------------

    local hebrew = calendar:new()
    hebrew:setLink( 'Lịch Do Thái' )
    hebrew:setYearRange( year + 3760, year + 3761 )
    box:addCalendar( hebrew )

    ----------------------------------------------------------------------
    -- Byzantine calendar
    ----------------------------------------------------------------------

    local byzantine = calendar:new()
    byzantine:setLink( 'Lịch Đông La Mã' )
    byzantine:setYearRange( year + 5508, year + 5509 )
    box:addCalendar( byzantine )

    ----------------------------------------------------------------------
    -- Ethiopian calendar
    ----------------------------------------------------------------------

    local ethiopian = calendar:new()
    ethiopian:setLink( 'Lịch Ethiopia' )
    ethiopian:setYearRange( year - 8, year - 7 )
    box:addCalendar( ethiopian )

    ----------------------------------------------------------------------
    -- Holocene calendar
    ----------------------------------------------------------------------

    local holocene = calendar:new()
    holocene:setLink( 'Thời kỳ con người', 'Lịch Holocen' )
    holocene:setYear( year + 10000 )
    box:addCalendar( holocene )

    ----------------------------------------------------------------------
    -- Islamic calendar
    ----------------------------------------------------------------------

    local islamic = calendar:new()
    islamic:setLink( 'Lịch Hồi giáo' )
    local islamicMult = 1.030684 -- the factor to multiply by
    local islamicSub = 621.5643 -- the factor to subtract by
    if year - 621 > 0 then
        local year1 = math.floor( islamicMult * ( year - islamicSub ) )
        local year2 = math.floor( islamicMult * ( year - islamicSub + 1 ) )
        islamic:setYearRange( year1, year2 )
    else
        local year1 = math.ceil( -islamicMult * ( year - islamicSub ) )
        local year2 = math.ceil( -islamicMult * ( year - islamicSub + 1 ) )
        islamic:setYear( mw.ustring.format( '%d BH&nbsp;– %d BH', year1, year2 ) )
    end
    box:addCalendar( islamic )

    ----------------------------------------------------------------------
    -- Igbo calendar
    ----------------------------------------------------------------------
    
    -- In the old template this was a calendar group with just one calendar; intentionally adding this as a single
    -- calendar here, as the previous behaviour looked like a mistake.
    local igbo = calendar:new()
    igbo:setLink( 'Lịch Igbo' )
    igbo:setYearRange( year - 1000, year - 999 )
    box:addCalendar( igbo )

    ----------------------------------------------------------------------
    -- Iranian calendar
    ----------------------------------------------------------------------

    local iranian = calendar:new()
    iranian:setLink( 'Lịch Iran' )
    if year - 621 > 0 then
        iranian:setYearRange( year - 622, year - 621 )
    else
        iranian:setYear( mw.ustring.format( '%d BP&nbsp;– %d BP', 622 - year, 621 - year ) )
    end
    box:addCalendar( iranian )

    ----------------------------------------------------------------------
    -- Julian calendar
    ----------------------------------------------------------------------

    local julian = calendar:new()
    julian:setLink( 'Lịch Julius' )

    julian.yearVals = {
        { 1901, 'theo lịch Gregory trừ 13 ngày' },
        { 1900, 'theo lịch Gregory trừ 12 hay 13 ngày'},
        { 1801, 'theo lịch Gregory trừ 12 ngày' },
        { 1800, 'theo lịch Gregory trừ 11 hay 12 ngày' },
        { 1701, 'theo lịch Gregory trừ 11 ngày' },
        { 1700, 'theo lịch Gregory trừ 10 hay 11 ngày' },
        { 1582, 'theo lịch Gregory trừ 10 ngày' },
        { -45, gregorian.year }
    }

    for i, t in ipairs( julian.yearVals ) do
        if year >= t[ 1 ] then
            julian:setYear( t[ 2 ] )
            break
        end
    end

    box:addCalendar( julian )
    
    ----------------------------------------------------------------------
    -- Burmese calendar
    ----------------------------------------------------------------------

    local burmese = calendar:new()
    burmese:setLink( 'Lịch Myanma truyền thống', 'Lịch Myanma' )
    burmese:setYear( year - 638 )
    box:addCalendar( burmese )

    ----------------------------------------------------------------------
    -- Japanese calendar
    ----------------------------------------------------------------------

    local japanese = calendar:new()
    japanese:setLink( 'Lịch Nhật Bản' )

    japanese.thisEra = japaneseEra:new{ year = year }
    if japanese.thisEra then
        local japaneseYearText = {}
        japanese.oldEra = japanese.thisEra:getOldEra()
        if japanese.oldEra and japanese.oldEra.eraYear and japanese.thisEra.article ~= japanese.oldEra.article then
            japanese.oldText = mw.ustring.format( '%s %d', japanese.oldEra.link, japanese.oldEra.eraYear )
            table.insert( japaneseYearText, japanese.oldText )
            table.insert( japaneseYearText, ' / ' )
        end
        if japanese.thisEra.eraYear then
            table.insert( japaneseYearText, mw.ustring.format( '%s %d', japanese.thisEra.link, japanese.thisEra.eraYear ) )
        end
        table.insert( japaneseYearText, mw.ustring.format( '<br /><small>(%s%s年)</small>', japanese.thisEra.kanji, japanese.thisEra.eraYearKanji ) )
        japanese:setYear( table.concat( japaneseYearText ) )
    end

    box:addCalendar( japanese )

    ----------------------------------------------------------------------
    -- Buddhist calendar
    ----------------------------------------------------------------------

    local buddhist = calendar:new()
    buddhist:setLink( 'Phật lịch' )
    buddhist:setYear( year + 544 )
    box:addCalendar( buddhist )

    ----------------------------------------------------------------------
    -- Thai solar calendar
    ----------------------------------------------------------------------

    local thai = calendar:new()
    thai:setLink( 'Dương lịch Thái' )
    thai:setYear( year + 543 )
    box:addCalendar( thai )
    
    ----------------------------------------------------------------------
    -- Korean calendar
    ----------------------------------------------------------------------

    local korean = calendar:new()
    korean:setLink( 'Lịch Triều Tiên' )
    korean:setYear( year + 2333 )
    box:addCalendar( korean )
    
    ----------------------------------------------------------------------
    -- Unix time
    ----------------------------------------------------------------------
    
    local unix = calendar:new()

    local function getUnixTime( year )
        if year < 1970 then return end
        local noError, unixTime = pcall( lang.formatDate, lang, 'U', '1 Jan ' .. tostring( year ) )
        if not noError or noError and not unixTime then return end
        unixTime = tonumber( unixTime )
        if unixTime and unixTime >= 0 then
            return unixTime
        end
    end

    unix.thisYear = getUnixTime( year )
    unix.nextYear = getUnixTime( year + 1 )
    if unix.thisYear and unix.nextYear then
        unix:setLink( 'Thời gian Unix' )
        unix:setYearRange( unix.thisYear, unix.nextYear - 1 )
    end

    box:addCalendar( unix )

    return box:export()
end

--------------------------------------------------------------------
-- Process arguments from #gọi
--------------------------------------------------------------------

local p = {}

function p.main( frame )
	-- Process the arguments and pass them to the box-building function.
	local args = getArgs( frame )
	-- Pass year argument with 'year' parameter or without any name but first argument
	args.year = args.year or args[1]
	return makeCalendarBox( args )
end

return p