Module:Sandbox/trappist the monk/random sort

require('strict');
local content = mw.title.getCurrentTitle():getContent() or '';					-- get the content of the list page

--[[--------------------------< R A N D O M _ S O R T >--------------------------------------------------------

swaps two members of a sequence table.  One member is indexed sequentially (starting at [1]), the other index
is randomly selected.

]]

local function random_sort (frame)
	local source = setmetatable({}, {__index = table})
	local r_idx;

	for article in content:gmatch ('([^\r\n]+)[\r\n]+') do						-- get an article title
		if not (
			article:match ('<!%-%-') or 										-- skip any line that has opening comment
			article:match ('%-%->') or											-- skip any line that has closing comment
			article:match ('{{') or												-- skip the line that holds the {{#invoke:}} for this function
			'' == article) then	-- skip these									-- skip empty lines
				source:insert (article);										-- all others, add to the list
		end
	end

	math.randomseed (os.time());												-- init random number generator with current timestamp

	for i, v in ipairs (source) do
		r_idx = math.random (i, #source)										-- random index between i and length of source{} ([[Fisher–Yates shuffle]] per Anomie at my talk page)

		if i ~= r_idx then														-- if i and r_idx happen to be the same, don't bother swapping this article title with itself
			source[i], source[r_idx] = source[r_idx], source[i];				-- swap article titles source[i] and source[r_idx]
		end
	end

	return table.concat ({'count = ', #source, '<br />',
		frame:callParserFunction ('#tag:syntaxhighlight', source:concat ('\n'))});
end


--[[--------------------------< E X P O R T E D   F U N C T I O N----------------------------------------------
]]

return {
	random_sort = random_sort
	}