Module:FindYDCportal

--  For a given 3- or 4-digit year or decade, find the most specific portal   which actually exists.   Takes one parameter, which must be either a year (e.g. "1879", "1123")   or a decade (e.g. "1940s", "790s").   If a portal is found, return its name without the namespace prefix   (e.g. for "Portal:1980s" return "1980s"); otherwise return an empty string.   If the parameter is missing, empty, or does not fit the required format,   an empty string is returned"

local p = {}

-- This table of existing decade portals is the first check of whether a portal -- exists for a given decade. -- If the decade is listed in this table, then a system call is made to verify its existence -- This approach has two advantages: -- 1/ It reduces server load by reducing the number of expensive system calls -- 2/ It avoids creating backlinks to non-existing portals, because a each .exists check --   generates a backlink local existingDecadePortals = { ["1920s"] = true, ["1950s"] = true, ["1960s"] = true, ["1980s"] = true, ["1990s"] = true }

-- check for the existence of a portal with the given name -- if it exists, returns the name -- otherwise returns nil function doesPortalExist(portalName) local portalPage = mw.title.new( portalName, "Portal" ) if (portalPage.exists) then return portalName end return nil end

-- check for the existence of a portal with the name of that year -- if it exists, returns the year -- otherwise calls decadeCheck, and returns that result -- otherwise returns nil function checkYear(yearParam) -- the year portals have all been deleted, so comment out this section	if doesPortalExist(yearParam) then		return yearParam	end -- -- myDecade = the year, with the last digit stripped --           e.g. "1694" → "1690" --           Note that a decade is written as usul=ally written "YYY0s" local myDecade = mw.ustring.gsub(yearParam, "%d$", "") return checkDecade(myDecade) end

-- check for the existence of a portal with the name of that decade -- if it exists, returns the year -- otherwise calls decadeCheck, and returns that result -- otherwise returns nil function checkDecade(decadeParam) local mydecade = decadeParam .. "0s" if (existingDecadePortals[mydecade] == true) then if doesPortalExist(mydecade) then return mydecade end end -- We don't have a portal for the decade, so now try the century. --[[ the century portals have all been deleted, so comment out this section

local myCenturyString = mw.ustring.gsub(decadeParam, "%d$", "") local myCenturyNum = tonumber(myCenturyString) local myCenturyNum = tonumber(myCenturyString) -- increment by one, because we have now conveted e.g. "1870s" to "18" -- but that's the 19th century myCenturyNum = myCenturyNum + 1 -- the century portals have all been deleted, so disable the centeury checking -- return checkCentury(tostring(myCenturyNum)) ]]--	return "" end

-- check for the existence of a portal with the name of that century -- if it exists, returns the century -- otherwise returns an empty string function checkCentury(centuryParam) local myCenturyString = ordinal_numbers(centuryParam) .. " century" if doesPortalExist(myCenturyString) then return myCenturyString end return "" end

-- converts a string number to an string ordinal -- e.g. 21 → 21st --     17 → 17th -- code copied from https://stackoverflow.com/questions/20694133/how-to-to-add-th-or-rd-to-the-date (license:CC BY-SA 3.0 ) function ordinal_numbers(n) local ordinal, digit = {"st", "nd", "rd"}, string.sub(n, -1) if tonumber(digit) > 0 and tonumber(digit) <= 3 and string.sub(n,-2) ~= 11 and string.sub(n,-2) ~= 12 and string.sub(n,-2) ~= 13 then return n .. ordinal[tonumber(digit)] else return n .. "th" end end

function trim(s) return s:match "^%s*(.-)%s*$" end

function p.findydcportal(frame) -- Expects one parameter -- = a 3- or 4-digit year or deacde --   e.g. 1916 --        1504	--         1630s --        920s local arg1 = frame.args[1] if arg1 == nil then return "" end arg1 = trim(arg1) -- strip leading and trailing spaces if (mw.ustring.match(arg1, "^%d%d%d%d?$")) then -- it's a 3- or 4-digit-year return checkYear(arg1) elseif (mw.ustring.match(arg1, "^%d%d%d?0s$")) then -- it's a 3- or 4-digit decade -- so strip the trailing "0s" local decadeArg = mw.ustring.gsub(arg1, "0s$", "") return checkDecade(decadeArg) end -- If we get here, then arg1 was neither a year nor a decade -- This is going to be a helper template, and diagnostics woud be intrusive -- So just return an empty string return "" end

return p