local checkType = require('libraryUtil').checkType

local p = {}

local BODY_PARAM = '$B'

local specialParams = {
	['$params'] = 'parameter list',
	['$aliases'] = 'parameter aliases',
	['$flags'] = 'flags',
	['$format'] = 'date format',
	['$B'] = 'template content'
}

function p.main(frame, body)
	-- If we are substing, this function returns a template invocation, and if
	-- not, it returns the template body. The template body can be specified in
	-- the body parameter, or in the template parameter defined in the
	-- BODY_PARAM variable. This function can be called from Lua or from
	-- #invoke.

	-- Return the template body if we aren't substing.
	if not mw.isSubsting() then
		if body ~= nil then
			return body
		elseif frame.args[BODY_PARAM] ~= nil then
			return frame.args[BODY_PARAM]
		else
			error(string.format(
				"no template content specified (use parameter '%s' from #invoke)",
				BODY_PARAM
			), 2)
		end
	end

	-- Sanity check for the frame object.
	if type(frame) ~= 'table'
		or type(frame.getParent) ~= 'function'
		or not frame:getParent()
	then
		error(
			"argument #1 to 'main' must be a frame object with a parent " ..
			"frame available",
			2
		)
	end

	-- Find the invocation name.
	local mTemplateInvocation = require('Module:Template invocation')
	local name = mTemplateInvocation.name(frame:getParent():getTitle())

	-- Combine passed args with passed defaults
	local args = {}
	local format = frame.args['$format'] or 'j xg Y'
	if string.find( ','..(frame.args['$flags'] or '')..',', ',%s*override%s*,' ) then
		for k, v in pairs( frame:getParent().args ) do
			args[k] = v
		end
		for k, v in pairs( frame.args ) do
			if not specialParams[k] then
				if v == '__DATE__' then
					v = mw.getContentLanguage():formatDate( format )
				end
				args[k] = v
			end
		end
	else
		for k, v in pairs( frame.args ) do
			if not specialParams[k] then
				if v == '__DATE__' then
					v = mw.getContentLanguage():formatDate( format )
				end
				args[k] = v
			end
		end
		for k, v in pairs( frame:getParent().args ) do
			args[k] = v
		end
	end

	-- Trim parameters, if not specified otherwise
	if not string.find( ','..(frame.args['$flags'] or '')..',', ',%s*keep%-whitespace%s*,' ) then
		for k, v in pairs( args ) do args[k] = mw.ustring.match(v, '^%s*(.*)%s*$') or '' end
	end

	-- Pull information from parameter aliases
	local aliases = {}
	if frame.args['$aliases'] then
		local list = mw.text.split( frame.args['$aliases'], '%s*,%s*' )
		for k, v in ipairs( list ) do
			local tmp = mw.text.split( v, '%s*>%s*' )
			aliases[tonumber(mw.ustring.match(tmp[1], '^[1-9][0-9]*$')) or tmp[1]] = ((tonumber(mw.ustring.match(tmp[2], '^[1-9][0-9]*$'))) or tmp[2])
		end
	end
	for k, v in pairs( aliases ) do
		if args[k] and ( not args[v] or args[v] == '' ) then
			args[v] = args[k]
		end
		args[k] = nil
	end

	-- Remove empty parameters, if specified
	if string.find( ','..(frame.args['$flags'] or '')..',', ',%s*remove%-empty%s*,' ) then
		local tmp = 0
		for k, v in ipairs( args ) do
			if v ~= '' or ( args[k+1] and args[k+1] ~= '' ) or ( args[k+2] and args[k+2] ~= '' ) then
				tmp = k
			else
				break
			end
		end
		for k, v in pairs( args ) do
			if v == '' then
				if not (type(k) == 'number' and k < tmp) then args[k] = nil end
			end
		end
	end

	-- Order parameters
	if frame.args['$params'] then
		local params, tmp = mw.text.split( frame.args['$params'], '%s*,%s*' ), {}
		for k, v in ipairs(params) do
			v = tonumber(mw.ustring.match(v, '^[1-9][0-9]*$')) or v
			if args[v] then tmp[v], args[v] = args[v], nil end
		end
		for k, v in pairs(args) do tmp[k], args[k] = args[k], nil end
		args = tmp
	end

	return mTemplateInvocation.invocation(name, args)
end

p[''] = p.main -- For backwards compatibility

return p