-- wengwengweng

local int = {}

local function class(specs)

	local struct = {}
	local types = {}
	local fns = {}

	local super = specs.__super

	if type(super) == "table" then

		local super_types = super.__types
		local super_fns = super.__fns

		if type(super_types) == "table" then
			for k, v in pairs(super_types) do
				types[k] = v
			end
		end

		if type(super_fns) == "table" then
			for k, v in pairs(super_fns) do
				fns[k] = v
			end
		end

	end

	for k, v in pairs(specs) do
		if type(v) == "table" then
			if v == string then
				types[k] = "string"
			elseif v == int then
				types[k] = "number"
			end
		elseif type(v) == "function" then
			fns[k] = v
		else
			error("expected type or function")
		end
	end

	struct.__types = types
	struct.__fns = fns

	setmetatable(struct, {

		__call = function()

			local obj = {}
			local proxy = {}

			for k, v in pairs(fns) do
				obj[k] = function()
					v(obj)
				end
			end

			setmetatable(obj, {

				__index = function(self, k)
					return proxy[k]
				end,

				__newindex = function(self, k, v)

					local expected_type = types[k]
					local actual_type = type(v)

					if not expected_type then
						error("failed to set " .. k)
					else
						if actual_type ~= expected_type then
							error("expected " .. expected_type .. ", found " .. actual_type)
						end
					end

					proxy[k] = v

				end,

			})

			return obj

		end,

	})

	return struct

end

local A = class {
	name = string,
	age = int,
	foo = function(self)
		print("from A", self.name, self.age)
	end
}

local B = class {
	__super = A,
	foo = function(self)
		print("from B", self.name, self.age)
	end
}

local a = A()

a.name = "hanmeimei"
a.age = 17
a:foo()

local b = B()

b.name = "lilei"
b.age = 18
b:foo()

a.name = 20
a.age = "20"
b.foo = "x"