-- This module renders the calendar seen on [[Portal:Current events]].

--[[
	Incoming expected variables:
		frame.args.year = Integer value for year
		frame.args.month = Integer value for month, 1 based.
--]]

local p = {}

local function makeWikilink(link, display)
	if display then
		return string.format('[[%s|%s]]', link, display)
	else
		return string.format('[[%s]]', link)
	end
end

local function getDateStuff(argsDate)
--[[
	Note: This function takes advantage of the formatDate's second argument to
	create data for the archival calendars. If the second arg (argsDate) is nil,
	then formatDate assumes the current date/time.
--]]

	local lang = mw.language.getContentLanguage()
	local firstOfMonth = lang:formatDate('01-m-Y', argsDate)
	return {
		argsDate = argsDate,
		year = tonumber(lang:formatDate('Y', argsDate)),
		month = lang:formatDate('F', argsDate),
		monthAndYear = lang:formatDate('F Y', argsDate),
		previousMonthAndYear = lang:formatDate('F Y', firstOfMonth .. ' -1 month'),
		nextMonthAndYear = lang:formatDate('F Y', firstOfMonth .. ' +1 month'),
		day = tonumber(lang:formatDate('j', argsDate)),
		daysInMonth = tonumber(lang:formatDate('j', firstOfMonth .. ' +1 month -1 day')),
		-- Weekday of the first day of the month
		-- Make compatible with Lua tables so we add 1. Sunday = 1, Saturday = 7.
		firstWeekday = tonumber(lang:formatDate('w', firstOfMonth)) + 1
	}
end

local function isLinkworthy(day, currentDay)
	-- Returns true if the calendar day should be linked, and false if not. Days
	-- should be linked if they are the current day or if they are within the six
	-- preceding days, as that is the number of items on the current events page.
	return currentDay - 6 <= day and day <= currentDay
end

local function makeDayStrings(dateStuff)
	local calStrings = {}
	local currentDay = dateStuff.day
	local currentMonth = dateStuff.month
	local currentYear = dateStuff.year
	for day = 1, dateStuff.daysInMonth do
		if dateStuff.argsDate or isLinkworthy(day, currentDay) then
			table.insert(calStrings, string.format(
				"[[#%d %s %d|%d]]",
				currentYear,
				currentMonth,
				day,
				day
			))
		else
			table.insert(calStrings, tostring(day))
		end
	end
	return calStrings
end

local function export(dayStrings, dateStuff)
	-- Generates the calendar HTML.
	local monthAndYear = dateStuff.monthAndYear
	local root = mw.html.create('table')
	root
		:addClass('current-events-calendar')
		-- Make the table-layout-based Archive pages look good. When the Archives
		-- have been converted to a grid-based layout, this logic can be removed,
		-- and the corressponding CSS margin attribute can be simplified.
		:addClass(dateStuff.argsDate and 'current-events-calendar-archive')
		-- Headings
		:tag('caption')
			:tag('span')
				:addClass('noprint')
				:wikitext(makeWikilink(
					'Portal:Current events/' .. dateStuff.previousMonthAndYear,
					'◀'
				))
				:done()
			:tag('span')
				:wikitext(makeWikilink(
					'Portal:Current events/' .. monthAndYear,
					monthAndYear
				))
				:done()
			:tag('span')
				:addClass('noprint')
				:wikitext(makeWikilink(
					'Portal:Current events/' .. dateStuff.nextMonthAndYear,
					'▶'
				))

	-- Day of week headings
	local dayHeadingRow = root:tag('tr')
	local weekdays = {'S', 'M', 'T', 'W', 'T', 'F', 'S'}
	for _, weekday in ipairs(weekdays) do
		dayHeadingRow:tag('th'):wikitext(weekday)
	end

	-- Days
	-- Tracks the number of day cells. Negative values used for initial blank cells.
	local cellCount = 1 - dateStuff.firstWeekday
	while cellCount < #dayStrings do -- Weekly rows
		local weeklyRow = root:tag('tr')
		for i = 1, 7 do -- Always make 7 cells.
			cellCount = cellCount + 1
			-- Use a blank cell if there is no corresponding dateString
			local dayString = dayStrings[cellCount] or ''
			weeklyRow:tag('td'):wikitext(dayString)
		end
	end

	-- Footer
	if not dateStuff.argsDate then -- No footer necessary on Archive pages.
		root:tag('tr')
			:addClass('current-events-calendar-footer')
		    :addClass('noprint')
			:tag('td')
				:attr('colspan', '7')
				:wikitext(makeWikilink(
					'Portal:Current events/' .. monthAndYear,
					'More ' .. monthAndYear .. ' events...&nbsp;&nbsp;&nbsp;'
				))
	end
	
	return tostring(root)
end

function p.main(frame)
	local argsDate = nil
	if frame and frame.args and frame.args.year and frame.args.month then
		-- If a date is passed in, assume that the display page is an Archive page.
		-- If no date passed in, assume that the display page is the current Current Events page
		-- Construct a date, YYY-M-DD format.
		argsDate = frame.args.year .. "-" .. frame.args.month .. "-01"
	end
	local dateStuff = getDateStuff(argsDate)
	return frame:extensionTag{
		name = 'templatestyles',
		args = { src = 'Module:Current events calendar/styles.css' }
	} .. export(makeDayStrings(dateStuff), dateStuff)
end

return p