Utf16 = {}

-- 支持这种写法：local str = L"测试的Utf16字符串"
function L(utf8String)
	return Utf16:create(utf8String)
end

-- 从Utf8字符串构造一个Utf16字符串
function Utf16:create(value)
	local instance = {}
	if type(value) == "string" then
		instance.s = utf8.utf8_to_utf16(value);
	elseif type(value) == "number" then
		instance.s = utf8.utf16_char(value);
	else
		instance.s = "";
	end
	setmetatable(instance , Utf16);
	return instance;
end

-- 返回utf8字符串
function Utf16:str()
	return utf8.utf16_to_utf8(self.s);
end

-- 获得长度
function Utf16:__len()
	return self:len();
end

-- 获得长度
function Utf16:len()
	return string.len(self.s) / 2;
end

-- 等于符号
function Utf16:__eq(target)
	return self.s == target.s;
end

-- 连接字符串
function Utf16:__concat(target)
	local sourceLength = string.len(self.s);
	if sourceLength > 0 then
		self.s = string.sub(self.s , 0 , string.len(self.s)) .. target
	else
		self.s = target;
	end
	return self;
end

-- 获取一个子字符串
function Utf16:sub(startIndex , endIndex)
	if endIndex == -1 or endIndex == nil then
		endIndex = startIndex;
	end
	local str = Utf16:create();
	str.s = string.sub(self.s , startIndex * 2 - 1 , endIndex * 2);
	return str;
end

-- 通过str[1] = 123的形式赋值
function Utf16:__newindex(index , value)
	error("不允许对Utf16进行[]=赋值")
--	local up = math.floor(value / 256);
--	
--	local startIndex = index * 2 - 1;
--	self.s[startIndex] = value - up * 256;
--	self.s[startIndex + 1] = up;
end

-- 通过str[1]的形式获取第几个字符，返回Utf16字符数值
function Utf16:__index(index)
	if type(index) == "number" then
		local startIndex = index * 2 - 1;
		local ch1 , ch2 = string.byte(self.s , startIndex , startIndex + 1);
		return ch2 * 256 + ch1;
	else
		return Utf16[index]
	end
end