Module:Unsubst

local p = {}

local specialParams = {
	['$N'] = 'template name',
	['$B'] = 'template content',
}

p[''] = function ( frame )
	if not frame:getParent() then
		error( '{{#invoke:Unsubst|unsubst}} makes no sense without a parent frame' )
	end
	for k, v in pairs( specialParams ) do
		if not frame.args[k] then
			error( '{{#invoke:Unsubst|unsubst}} requires parameter ' .. k .. ' (' .. v .. ')' )
		end
	end
	
	if mw.isSubsting() then
		---- substing
		-- Combine passed args with passed defaults
		local args = {}
		for k, v in pairs( frame.args ) do
			if not specialParams[k] then
				if v == '__DATE__' then
					v = mw.getContentLanguage():formatDate( 'F Y' )
				end
				args[k] = v
			end
		end
		for k, v in pairs( frame:getParent().args ) do
			args[k] = v
		end

		-- Now, build an equivalent template invocation
		-- First numbered args, then named
		local ret = '{{' .. frame.args['$N']
		for k, v in ipairs( args ) do
			if string.find( v, '=', 1, true ) then
				-- likely something like 1=foo=bar, we need to do it as a named arg
				break
			end
			ret = ret .. '|' .. v
			args[k] = nil
		end
		for k, v in pairs( args ) do
			ret = ret .. '|' .. k .. '=' .. v
		end
		
		return ret .. '}}'
	else
		---- Not substing
		-- Just return the "body"
		return frame.args['$B']
	end
end

return p