# 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) .. " நூற்றாண்டு"
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 = {"-ஆம்", "-ஆம்", "-ஆம்"}, 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 .. "-ஆம்"
end
end  
function trim(s)
return s:match "^%s*(.-)%s*$"
end  
function p.findydcportal
-- Expects one parameter
-- } = a 3- or 4-digit year or deacde
-- e.g. 1916
-- 1504
-- 1630s
-- 920s
local arg1 = .args[1]
if arg1 == nil then
return ""
end
arg1 = trim(arg1) -- strip leading and trailing spaces
if (mw.ustring.match(arg1, "^%d%d%d%d?$")) 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