Module:Sort title

local match = require("Module:String")._match

local p = {}

--[[
Local function which is used to return a number without commas.
For example: 4,722 will become 4722.
--]]
local function cleanNumberFromCommas(title)
 return string.gsub(title, "(%d+)(,+)", "%1")
end

--[[
Local function which is used to check if the word is an article.
Returns true if it is, false if it isn't.
--]]
local function isFirstWordAnArticle(word)
 word = string.lower(word)
 if (word == "a" or word == "an" or word == "the") then
  return true
 else
  return false
 end
end

--[[
Local function which is used to return the title without its disambiguation.
--]]
local function getTitleWithoutDisambiguation(title, disambiguation)
 local newTitle = string.gsub(title, "%(".. disambiguation .. "%)", "")
 return mw.text.trim(newTitle)
end

--[[
Local function which is used to return a title without its first word.
--]]
local function getTitleWithoutFirstWord(title)
 return mw.ustring.gsub(title, "^[^%s]*%s*", "")
end

--[[
Local function which is used to return the first word from a title.
--]]
local function getFirstWord(title)
 return match(title, "^[^%s]*", 1, 1, false, "")
end

--[[
Local function which is used to return a sort key for a specific part.
--]]
local function getSortKey(title, firstWord)
 local sortKey = title
 if (isFirstWordAnArticle(firstWord) and firstWord ~= title) then
  title = getTitleWithoutFirstWord(title)
  sortKey = title .. ", " .. firstWord
 end
 
 return sortKey
end

--[[
Local function which is used to return the disambiguation sort key.
--]]
local function getDisambiguationSortKey(disambiguation)
 if (disambiguation == "") then
  return ""
 end
 
 local firstWord = getFirstWord(disambiguation)
 local disambiguationSortKey = getSortKey(disambiguation, firstWord)
 return "(" .. disambiguationSortKey .. ")"
end

--[[
Local function which is used to return the disambiguation from a title.
--]]
local function getDisambiguation(title)
 local disambiguation = match(title, "%s%((.-)%)", 1, -1, false, "")
 if (disambiguation == "") then
  return ""
 else
  return disambiguation
 end
end

--[[
The main function.
--]]
local function _main(title)
 if (not title) then
  title = mw.title.getCurrentTitle().text
 end

 local firstWord = getFirstWord(title)
 local disambiguation = getDisambiguation(title)
 local disambiguationSortKey = getDisambiguationSortKey(disambiguation)
 
 title = getTitleWithoutDisambiguation(title, disambiguation)
 title = cleanNumberFromCommas(title)
 title = getSortKey(title, firstWord)
 
 local sortKey = title .. " " .. disambiguationSortKey
 return mw.text.trim(sortKey)
end

--[[
Public function which allows modules to retrieve a sort key.
--]]
function p._getSortKey()
 return _main(nil)
end

--[[
Public function which allows templates to retrieve a sort key.
--]]
function p.getSortKey(frame)
 return _main(nil) 
end

--[[
Public function which allows templates to retrieve the sort key inside a DEFAULTSORT.
--]]
function p.getDefaultSort(frame)
 local sortKey = _main(nil)
 return frame:preprocess{text = "{{DEFAULTSORT:" .. sortKey .. "}}"} 
end

--[[
Public function which is used for testing various names and not the current page name.
--]]
function p.testcases(frame)
 local getArgs = require('Module:Arguments').getArgs
 local args = getArgs(frame)
 return _main(args[1])
end

return p