--- I18n library for message storage in Lua datastores.
--  The module is designed to enable message separation from modules &
--  templates. It has support for handling language fallbacks. This
--  module is a Lua port of [[wikia:dev:I18n-js]] and i18n modules that can be loaded
--  by it are editable through [[wikia:dev:I18nEdit]].
--  
--  On Wikimedia projects, i18n messages are editable 
--  through [[c:Special:PrefixIndex/Data:i18n/|Data:i18n/]] subpages on
--  Wikimedia Commons.
--  
--  @module		 i18n
--  @version		1.4.0
--  @require		Module:Entrypoint
--  @require		Module:Fallbacklist
--  @author		 [[wikia:dev:User:KockaAdmiralac|KockaAdmiralac]] (original Fandom implementation)
--  @author		 [[wikia:dev:User:Speedit|Speedit]] (original Fandom implementation)
--  @author			[[User:Awesome Aasim|Awesome Aasim]] (Wikimedia port)
--  @attribution	[[wikia:dev:User:Cqm|Cqm]]
--  @release		beta
--  @see			[[wikia:dev:I18n|I18n guide]]
--  @see			[[wikia:dev:I18n-js]]
--  @see			[[wikia:dev:I18nEdit]]
--  <nowiki>
local i18n, _i18n = {}, {}

--  Module variables & dependencies.
local title = mw.title.getCurrentTitle()
local fallbacks = require('Module:Fallbacklist')
local entrypoint = require('Module:Entrypoint')
local uselang

--- Argument substitution as $n where n > 0.
--  @function		   _i18n.handleArgs
--  @param			  {string} msg Message to substitute arguments into.
--  @param			  {table} args Arguments table to substitute.
--  @return			 {string} Resulting message.
--  @local
function _i18n.handleArgs(msg, args)
	for i, a in ipairs(args) do
		msg = (string.gsub(msg, '%$' .. tostring(i), tostring(a)))
	end
	return msg
end

--- Checks whether a language code is valid.
--  @function		   _i18n.isValidCode
--  @param			  {string} code Language code to check.
--  @return			 {boolean} Whether the language code is valid.
--  @local
function _i18n.isValidCode(code)
	return type(code) == 'string' and #mw.language.fetchLanguageName(code) ~= 0
end

--- Checks whether a message contains unprocessed wikitext.
--  Used to optimise message getter by not preprocessing pure text.
--  @function		   _i18n.isWikitext
--  @param			  {string} msg Message to check.
--  @return			 {boolean} Whether the message contains wikitext.
function _i18n.isWikitext(msg)
	return
		type(msg) == 'string' and
		(
			msg:find('%-%-%-%-') or
			msg:find('%f[^\n%z][;:*#] ') or
			msg:find('%f[^\n%z]==* *[^\n|]+ =*=%f[\n]') or
			msg:find('%b<>') or msg:find('\'\'') or
			msg:find('%[%b[]%]') or msg:find('{%b{}}')
		)
end

--- I18n datastore class.
--  This is used to control language translation and access to individual
--  messages. The datastore instance provides language and message
--  getter-setter methods, which can be used to internationalize Lua modules.
--  The language methods (any ending in `Lang`) are all **chainable**.
--  @type			Data
local Data = {}
Data.__index = Data

--- Datastore message getter utility.
--  This method returns localized messages from the datastore corresponding
--  to a `key`. These messages may have `$n` parameters, which can be
--  replaced by optional argument strings supplied by the `msg` call.
--  
--  This function supports [[mw:Extension:Scribunto/Lua reference manual#named_arguments|named
--  arguments]]. The named argument syntax is more versatile despite its
--  verbosity; it can be used to select message language & source(s).
--  @function		   Data:msg
--  @usage
--  
--	  ds:msg{
--		  key = 'message-name',
--		  lang = '',
--		  args = {...},
--		  sources = {}
--	  }
--  
--  @usage
--  
--	  ds:msg('message-name', ...)
--  
--  @param			  {string|table} opts Message configuration or key.
--  @param[opt]		 {string} opts.key Message key to return from the
--					  datastore.
--  @param[opt]		 {table} opts.args Arguments to substitute into the
--					  message (`$n`).
--  @param[opt]		 {table} opts.sources Source names to limit to (see
--					  `Data:fromSources`).
--  @param[opt]		 {table} opts.lang Temporary language to use (see
--					  `Data:inLang`).
--  @param[opt]		 {string} ... Arguments to substitute into the message
--					  (`$n`).
--  @error[115]		 {string} 'missing arguments in Data:msg'
--  @return			 {string} Localised datastore message or `'<key>'`.
function Data:msg(opts, ...)
	local frame = mw.getCurrentFrame()
	-- Argument normalization.
	if not self or not opts then
		error('missing arguments in Data:msg')
	end
	local key = type(opts) == 'table' and opts.key or opts
	local args = opts.args or {...}
	-- Configuration parameters.
	if opts.sources then
		self:fromSources(unpack(opts.sources))
	end
	if opts.lang then
		self:inLang(opts.lang)
	end
	-- Source handling.
	local source_n = self.tempSources or self._sources
	local source_i = {}
	for n, i in pairs(source_n) do
		source_i[i] = n
	end
	self.tempSources = nil
	-- Language handling.
	local lang = self.tempLang or self.defaultLang
	self.tempLang = nil
	-- Message fetching.
	local msg
	for i, messages in ipairs(self._messages) do
		-- Message data.
		local msg = (messages[lang] or {})[key]
		-- Fallback support (experimental).
		for _, l in ipairs((fallbacks[lang] or {})) do
			if msg == nil then
				msg = (messages[l] or {})[key]
			end
		end
		-- Internal fallback to 'en'.
		msg = msg ~= nil and msg or messages.en[key]
		-- Handling argument substitution from Lua.
		if msg and source_i[i] and #args > 0 then
			msg = _i18n.handleArgs(msg, args)
		end
		if msg and source_i[i] and lang ~= 'qqx' then
			return frame and _i18n.isWikitext(msg)
				and frame:preprocess(mw.text.trim(msg))
				or  mw.text.trim(msg)
		end
	end
	return '&#x29FC;' .. mw.text.nowiki(key) .. '&#x29FD;'
end

--- Datastore template parameter getter utility.
--  This method, given a table of arguments, tries to find a parameter's
--  localized name in the datastore and returns its value, or nil if
--  not present.
--
--  This method always uses the wiki's content language.
--  @function		   Data:parameter
--  @param			  {string} parameter Parameter's key in the datastore
--  @param			  {table} args Arguments to find the parameter in
--  @error[176]		 {string} 'missing arguments in Data:parameter'
--  @return			 {string|nil} Parameter's value or nil if not present
function Data:parameter(key, args)
	-- Argument normalization.
	if not self or not key or not args then
		error('missing arguments in Data:parameter')
	end
	local contentLang = mw.language.getContentLanguage():getCode()
	-- Message fetching.
	for i, messages in ipairs(self._messages) do
		local msg = (messages[contentLang] or {})[key]
		if msg ~= nil and args[msg] ~= nil then
			return args[msg]
		end
		for _, l in ipairs((fallbacks[contentLang] or {})) do
			if msg == nil or args[msg] == nil then
				-- Check next fallback.
				msg = (messages[l] or {})[key]
			else
				-- A localized message was found.
				return args[msg]
			end
		end
		-- Fallback to English.
		msg = messages.en[key]
		if msg ~= nil and args[msg] ~= nil then
			return args[msg]
		end
	end
end

--- Datastore temporary source setter to a specificed subset of datastores.
--  By default, messages are fetched from the datastore in the same
--  order of priority as `i18n.loadMessages`.
--  @function		   Data:fromSource
--  @param			  {string} ... Source name(s) to use.
--  @return			 {Data} Datastore instance.
function Data:fromSource(...)
	local c = select('#', ...)
	if c ~= 0 then
		self.tempSources = {}
		for i = 1, c do
			local n = select(i, ...)
			if type(n) == 'string' and type(self._sources[n]) == 'number' then
				self.tempSources[n] = self._sources[n]
			end
		end
	end
	return self
end

--- Datastore default language getter.
--  @function		   Data:getLang
--  @return			 {string} Default language to serve datastore messages in.
function Data:getLang()
	return self.defaultLang
end

--- Datastore language setter to `wgUserLanguage`.
--  @function		   Data:useUserLang
--  @return			 {Data} Datastore instance.
--  @note			   Scribunto only registers `wgUserLanguage` when an
--					  invocation is at the top of the call stack.
function Data:useUserLang()
	self.defaultLang = i18n.getLang() or self.defaultLang
	return self
end

--- Datastore language setter to `wgContentLanguage`.
--  @function		   Data:useContentLang
--  @return			 {Data} Datastore instance.
function Data:useContentLang()
	self.defaultLang = mw.language.getContentLanguage():getCode()
	return self
end

--- Datastore language setter to specificed language.
--  @function		   Data:useLang
--  @param			  {string} code Language code to use.
--  @return			 {Data} Datastore instance.
function Data:useLang(code)
	self.defaultLang = _i18n.isValidCode(code)
		and code
		or  self.defaultLang
	return self
end

--- Temporary datastore language setter to `wgUserLanguage`.
--  The datastore language reverts to the default language in the next
--  @{Data:msg} call.
--  @function		   Data:inUserLang
--  @return			 {Data} Datastore instance.
function Data:inUserLang()
	self.tempLang = i18n.getLang() or self.tempLang
	return self
end

--- Temporary datastore language setter to `wgContentLanguage`.
--  Only affects the next @{Data:msg} call.
--  @function		   Data:inContentLang
--  @return			 {Data} Datastore instance.
function Data:inContentLang()
	self.tempLang = mw.language.getContentLanguage():getCode()
	return self
end

--- Temporary datastore language setter to a specificed language.
--  Only affects the next @{Data:msg} call.
--  @function		   Data:inLang
--  @param			  {string} code Language code to use.
--  @return			 {Data} Datastore instance.
function Data:inLang(code)
	self.tempLang = _i18n.isValidCode(code)
		and code
		or  self.tempLang
	return self
end

--  Package functions.

--- Localized message getter by key.
--  Can be used to fetch messages in a specific language code through `uselang`
--  parameter. Extra numbered parameters can be supplied for substitution into
--  the datastore message.
--  @function		   i18n.getMsg
--  @param			  {table} frame Frame table from invocation.
--  @param			  {table} frame.args Metatable containing arguments.
--  @param			  {string} frame.args[1] ROOTPAGENAME of i18n submodule.
--  @param			  {string} frame.args[2] Key of i18n message.
--  @param[opt]		 {string} frame.args.lang Default language of message.
--  @error[271]		 {string} 'missing arguments in i18n.getMsg'
--  @return			 {string} I18n message in localised language.
function i18n.getMsg(frame)
	if
		not frame or
		not frame.args or
		not frame.args[1] or
		not frame.args[2]
	then
		error('missing arguments in i18n.getMsg')
	end
	local source = frame.args[1]
	local key = frame.args[2]
	-- Pass through extra arguments.
	local repl = {}
	for i, a in ipairs(frame.args) do
		if i >= 3 then
			repl[i-2] = a
		end
	end
	-- Load message data.
	local ds = i18n.loadMessages(source)
	-- Pass through language argument.
	ds:inLang(frame.args.uselang)
	-- Return message.
	return ds:msg { key = key, args = repl }
end
 
--- I18n message datastore loader.
--  @function		   i18n.loadMessages
--  @param			  {string} ... ROOTPAGENAME/path for target i18n
--					  submodules.
--  @error[322]		 {string} 'no source supplied to i18n.loadMessages'
--  @return			 {table} I18n datastore instance.
--  @usage			  require('Module:I18n').loadMessages('1', '2')
function i18n.loadMessages(...)
	local ds
	local i = 0
	local s = {}
	for j = 1, select('#', ...) do
		local source = select(j, ...)
		if type(source) == 'string' and source ~= '' then
			i = i + 1
			s[source] = i
			if not ds then
				-- Instantiate datastore.
				ds = {}
				ds._messages = {}
				-- Set default language.
				setmetatable(ds, Data)
				ds:useUserLang()
			end
			source = string.gsub(source, '^.', mw.ustring.upper)
			local success, messages = pcall(mw.loadData, mw.ustring.find(source, ':')
				and source
				or  'Module:' .. source .. '/i18n')
			if success then
				local msgCopy = {}
				local langSecond = nil
				for lang_id, msgtbl in pairs(messages) do
					if langSecond == nil then
						if lang_id == "qqq" or fallbacks[lang_id] ~= nil then
							langSecond = false
						else
							langSecond = true
						end
					end
					for id_lang, msg in pairs(msgtbl) do
						if langSecond then
							msgCopy[id_lang] = msgCopy[id_lang] or {}
							msgCopy[id_lang][lang_id] = msg
						else
							msgCopy[lang_id] = msgCopy[lang_id] or {}
							msgCopy[lang_id][id_lang] = msg
						end
					end
				end
				ds._messages[i] = msgCopy
			end
			local tab = mw.ext.data.get('I18n/' .. source .. '.tab', '_')
			local T = {}
			if not success and not tab then error("i18n for " .. source .. " is missing") end
			for _, row in pairs(tab.data) do -- convert the output into a dictionary table
				local id, t = unpack(row)
				for lang, msg in pairs(t) do
					if not T[lang] then T[lang] = {} end
					T[lang][id] = msg
				end
			end
			if not success then
				ds._messages[i] = T
			else
				for lang, msgTbl in pairs(T) do
					ds._messages[i][lang] = ds._messages[i][lang] or msgTbl
				end
			end
		end
	end
	if not ds then
		error('no source supplied to i18n.loadMessages')
	else
		-- Attach source index map.
		ds._sources = s
		-- Return datastore instance.
		return ds
	end
end

--- Language code getter.
--  Can validate a template's language code through `uselang` parameter.
--  @function		   i18n.getLang
--  @return			 {string} Language code.
function i18n.getLang()
	local frame = mw.getCurrentFrame() or {}
	local parentFrame = frame.getParent and frame:getParent() or {}

	local code = mw.language.getContentLanguage():getCode()
	local subPage = title.subpageText

	-- Language argument test.
	local langOverride =
		(frame.args or {}).uselang or
		(parentFrame.args or {}).uselang
	if _i18n.isValidCode(langOverride) then
		code = langOverride

	-- Subpage language test.
	elseif title.isSubpage and _i18n.isValidCode(subPage) then
		code = _i18n.isValidCode(subPage) and subPage or code

	-- User language test.
	elseif parentFrame.preprocess or frame.preprocess then
		uselang = uselang
			or  parentFrame.preprocess
				and parentFrame:preprocess('{{int:lang}}')
				or  frame:preprocess('{{int:lang}}')
		local decodedLang = mw.text.decode(uselang) 
		if decodedLang ~= '<lang>' and decodedLang ~= '⧼lang⧽' then
			code = decodedLang == '(lang)'
				and 'qqx'
				or  uselang
		end
	end

	return code
end

-- Credit to http://stackoverflow.com/a/1283608/2644759
-- cc-by-sa 3.0
local function tableMerge(t1, t2, overwrite)
	for k,v in pairs(t2) do
		if type(v) == "table" and type(t1[k]) == "table" then
			-- since type(t1[k]) == type(v) == "table", so t1[k] and v is true
			tableMerge(t1[k], v, overwrite) -- t2[k] == v
		else
			if overwrite or t1[k] == nil then t1[k] = v end
		end
	end
	return t1
end

--- Given an i18n table instantiates the values (deprecated)
--  @function i18n.loadI18n
--  @param {string} name name of module with i18n
--  @param {table} i18n_arg existing i18n
function i18n.loadI18n(name, i18n_arg)
	local exist, res = pcall(require, name)
	if exist and next(res) ~= nil then
		if i18n_arg then
			tableMerge(i18n_arg, res.i18n, true)
		end
	end
end

--- Loads an i18n for a specific frame (deprecated)
--  @function i18n.loadI18nFrame
--  @param {string} name name of module with i18n
--  @param {table} i18n_arg existing i18n
function i18n.loadI18nFrame(frame, i18n_arg)
	return i18n.loadI18n(frame:getTitle().."/i18n", i18n_arg)
end

--- Wrapper for the module.
--  @function		   i18n.main
--  @param			  {table} frame Frame invocation object.
--  @return			 {string} Module output in template context.
--  @usage			  {{#invoke:i18n|main}}
i18n.main = entrypoint(i18n)

return require("Module:Deprecated")(i18n, 
	{
		["loadI18n"] = {
			deprecated = true,
			replacement = "use <code>i18n.loadMessages</code>"
		},
		["loadI18nFrame"] = {
			deprecated = true,
			replacement = "use <code>i18n.loadMessages</code>"
		}
	}
)
-- </nowiki>