Module:Namespace detect

 --[[
 --------------------------------------------------------------------------------
 -- --
 -- NAMESPACE DETECT --
 -- --
 -- This module implements the {{namespace detect}} template in Lua, with a --
 -- few improvements: all namespaces and all namespace aliases are supported, --
 -- and namespace names are detected automatically for the local wiki. The --
 -- module can also use the corresponding subject namespace value if it is --
 -- used on a talk page. Parameter names can be configured for different wikis --
 -- by altering the values in the "cfg" table in --
 -- Module:Namespace detect/config. --
 -- --
 --------------------------------------------------------------------------------
 --]]

 local data = mw.loadData('Module:Namespace detect/data')
 local argKeys = data.argKeys
 local cfg = data.cfg
 local mappings = data.mappings

 local yesno = require('Module:Yesno')
 local mArguments -- Lazily initialise Module:Arguments
 local mTableTools -- Lazily initilalise Module:TableTools
 local ustringLower = mw.ustring.lower

 local p = {}

 local function fetchValue(t1, t2)
	-- Fetches a value from the table t1 for the first key in array t2 where
	-- a non-nil value of t1 exists.
	for i, key in ipairs(t2) do
		local value = t1[key]
		if value ~= nil then
			return value
		end
	end
	return nil
 end

 local function equalsArrayValue(t, value)
	-- Returns true if value equals a value in the array t. Otherwise
	-- returns false.
	for i, arrayValue in ipairs(t) do
		if value == arrayValue then
			return true
		end
	end
	return false
 end

 function p.getPageObject(page)
	-- Get the page object, passing the function through pcall in case of
	-- errors, e.g. being over the expensive function count limit.
	if page then
		local success, pageObject = pcall(mw.title.new, page)
		if success then
			return pageObject
		else
			return nil
		end
	else
		return mw.title.getCurrentTitle()
	end
 end

 -- Provided for backward compatibility with other modules
 function p.getParamMappings()
	return mappings
 end

 local function getNamespace(args)
	-- This function gets the namespace name from the page object.
	local page = fetchValue(args, argKeys.demopage)
	if page == '' then
		page = nil
	end
	local demospace = fetchValue(args, argKeys.demospace)
	if demospace == '' then
		demospace = nil
	end
	local subjectns = fetchValue(args, argKeys.subjectns)
	local ret
	if demospace then
		-- Handle "demospace = main" properly.
		if equalsArrayValue(argKeys.main, ustringLower(demospace)) then
			ret = mw.site.namespaces[0].name
		else
			ret = demospace
		end
	else
		local pageObject = p.getPageObject(page)
		if pageObject then
			if pageObject.isTalkPage then
				-- Get the subject namespace if the option is set,
				-- otherwise use "talk".
				if yesno(subjectns) then
					ret = mw.site.namespaces[pageObject.namespace].subject.name
				else
					ret = 'talk'
				end
			else
				ret = pageObject.nsText
			end
		else
			return nil -- return nil if the page object doesn't exist.
		end
	end
	ret = ret:gsub('_', ' ')
	return ustringLower(ret)
 end

 function p._main(args)
	-- Check the parameters stored in the mappings table for any matches.
	local namespace = getNamespace(args) or 'other' -- "other" avoids nil table keys
	local params = mappings[namespace] or {}
	local ret = fetchValue(args, params)
	--[[
 	-- If there were no matches, return parameters for other namespaces.
 	-- This happens if there was no text specified for the namespace that
 	-- was detected or if the demospace parameter is not a valid
 	-- namespace. Note that the parameter for the detected namespace must be
 	-- completely absent for this to happen, not merely blank.
 	--]]
	if ret == nil then
		ret = fetchValue(args, argKeys.other)
	end
	return ret
 end

 function p.main(frame)
	mArguments = require('Module:Arguments')
	local args = mArguments.getArgs(frame, {removeBlanks = false})
	local ret = p._main(args)
	return ret or ''
 end

 function p.table(frame)
	--[[
 	-- Create a wikitable of all subject namespace parameters, for
 	-- documentation purposes. The talk parameter is optional, in case it
 	-- needs to be excluded in the documentation.
 	--]]
	
	-- Load modules and initialise variables.
	mTableTools = require('Module:TableTools')
	local namespaces = mw.site.namespaces
	local cfg = data.cfg
	local useTalk = type(frame) == 'table' 
		and type(frame.args) == 'table' 
		and yesno(frame.args.talk) -- Whether to use the talk parameter.
	
	-- Get the header names.
	local function checkValue(value, default)
		if type(value) == 'string' then
			return value
		else
			return default
		end
	end
	local nsHeader = checkValue(cfg.wikitableNamespaceHeader, 'Namespace')
	local aliasesHeader = checkValue(cfg.wikitableAliasesHeader, 'Aliases')

	-- Put the namespaces in order.
	local mappingsOrdered = {}
	for nsname, params in pairs(mappings) do
		if useTalk or nsname ~= 'talk' then
			local nsid = namespaces[nsname].id
			-- Add 1, as the array must start with 1; nsid 0 would be lost otherwise.
			nsid = nsid + 1 
			mappingsOrdered[nsid] = params
		end
	end
	mappingsOrdered = mTableTools.compressSparseArray(mappingsOrdered)

	-- Build the table.
	local ret = '{| class="wikitable"'
		.. '\n|-'
		.. '\n! ' .. nsHeader
		.. '\n! ' .. aliasesHeader
	for i, params in ipairs(mappingsOrdered) do
		for j, param in ipairs(params) do
			if j == 1 then
				ret = ret .. '\n|-'
					.. '\n| <code>' .. param .. '</code>'
					.. '\n| '
			elseif j == 2 then
				ret = ret .. '<code>' .. param .. '</code>'
			else
				ret = ret .. ', <code>' .. param .. '</code>'
			end
		end
	end
	ret = ret .. '\n|-'
		.. '\n|}'
	return ret
 end

 return p