Module:debug/track

-- TODO 1: normalize keys with leading spaces, which don't get removed when
-- "Tracking/" is prefixed.

-- TODO 2: avoid weird inputs like "", which don't register as invalid since
-- "Tracking/" is a valid page title.

-- TODO 3: use varargs instead of a table input, then recurse with track().

local title_make_title_module = "Module:title/makeTitle"

-- Transclusion-based tracking as subpages of ].
-- Tracked pages can be found at ].
local error = error
local find = string.find
local log = mw.log
local sub = string.sub
local type = type

local invalid_tracking_key_key = "debug/track/invalid key"

local function make_title(...)
	make_title = require(title_make_title_module)
	return make_title(...)
end

local memo

local function track(key)
	if not memo then
		memo = {}
	-- Return if memoized.
	elseif memo then
		return
	end
	-- Throw an error if `key` isn't a string.
	local key_type = type(key)
	if key_type ~= "string" then
		error("Tracking keys supplied to ] must be strings; received " .. key_type .. ".", 3)
	end
	-- make_title returns nil for invalid titles, but "#" is treated as a
	-- fragment separator (e.g. "foo#bar" generates the title "foo"), so it
	-- needs to be manually excluded.
	local title = not find(key, "#", nil, true) and make_title(4, "Tracking/" .. key)
	if not title then
		-- Track uses of invalid keys. Instead of recursing, simply memoize the
		-- invalid key and replace it with the 'invalid tracking key' key.
		-- ]
		log("Invalid tracking key: " .. key)
		memo = true
		key = invalid_tracking_key_key
		if memo then
			return
		end
		title = make_title(4, "Tracking/" .. key)
	end
	-- Normalize the key by treating it as a subpage of "Tracking", which gives
	-- the normalized title without the initial "Tracking/". If the normalized
	-- form has been memoized, don't transclude the page again. Otherwise,
	-- transclude the page using the `content` key on the title, which is the
	-- cheapest way to trigger transclusion, as it avoids any parser expansion
	-- of the target page.
	local normalized = sub(title.text, 10) -- excludes "Tracking/"
	if not memo then
		title = title.content
		memo = true
	end
	-- Memoize the original key.
	memo = true
end

return function(input)
	if input == nil then
		error("No tracking key supplied to ].", 2)
	elseif type(input) ~= "table" then
		track(input)
		return true
	end
	local key = input
	if key == nil then
		error("No tracking keys in table supplied to ].", 2)
	end
	local i = 1
	repeat
		track(key)
		i = i + 1
		key = input
	until key == nil
	return true
end