import struct

class Struct(object):
	__slots__ = ('__attrs__', '__baked__', '__defs__', '__endian__', '__next__', '__sizes__', '__values__')
	int8 = ('b', 1)
	uint8 = ('B', 1)
	
	int16 = ('h', 2)
	uint16 = ('H', 2)
	
	int32 = ('l', 4)
	uint32 = ('L', 4)
	
	float = ('f', 4)
	
	@classmethod
	def string(cls, len):
		return ('s', len)
	
	LE = '<'
	BE = '>'
	__endian__ = '<'
	
	def __init__(self):
		self.__defs__ = []
		self.__sizes__ = []
		self.__attrs__ = []
		self.__values__ = {}
		self.__next__ = True
		self.__baked__ = False
		
		self.__format__()
		
		self.__baked__ = True
	
	def __setattr__(self, name, value):
		if name in self.__slots__:
			return object.__setattr__(self, name, value)
		
		if self.__baked__ == False:
			type, size = value
			
			if type == 's':
				self.__defs__.append(Struct.string)
				self.__sizes__.append(size)
				self.__attrs__.append(name)
				self.__values__[name] = ''
				self.__next__ = True
			else:
				if self.__next__:
					self.__defs__.append('')
					self.__sizes__.append(0)
					self.__attrs__.append([])
					self.__next__ = False
				
				self.__defs__[-1] += type
				self.__sizes__[-1] += size
				self.__attrs__[-1].append(name)
				self.__values__[name] = 0
		else:
			self.__values__[name] = value
	
	def __getattr__(self, name):
		if self.__baked__ == False:
			return name
		else:
			try:
				return self.__values__[name]
			except KeyError:
				raise AttributeError(name)
	
	def unpack(self, data):
		pos = 0
		for i in range(len(self.__defs__)):
			sdef, size, attrs = self.__defs__[i], self.__sizes__[i], self.__attrs__[i]
			
			if sdef == Struct.string:
				if isinstance(size, str):
					size = self.__values__[size]
				self.__values__[attrs] = data[pos:pos+size]
				pos += size
			else:
				values = struct.unpack(self.__endian__+sdef, data[pos:pos+size])
				pos += size
				j = 0
				for name in attrs:
					self.__values__[name] = values[j]
					j += 1
		
		return self
	
	def pack(self):
		ret = ''
		for i in range(len(self.__defs__)):
			sdef, size, attrs = self.__defs__[i], self.__sizes__[i], self.__attrs__[i]
			
			if sdef == Struct.string:
				if isinstance(size, str):
					size = self.__values__[size]
				temp = self.__values__[attrs][:size]
				ret += temp + ('\0' * (size - len(temp)))
			else:
				values = [self.__values__[name] for name in attrs]
				ret += struct.pack(self.__endian__+sdef, *values)
		return ret

if __name__=='__main__':
	class TestStruct(Struct):
		__endian__ = Struct.LE
		def __format__(self):
			self.foo, self.bar = Struct.uint32, Struct.float
			self.baz = Struct.string(8)
			
			self.omg = Struct.uint32
			self.wtf = Struct.string(self.omg)
	
	test = TestStruct()
	test.unpack('\xEF\xBE\xAD\xDE\x00\x00\x80\x3Fdeadbeef\x04\x00\x00\x00test')
	print test.bar
	assert test.foo == 0xDEADBEEF
	assert test.bar == 1.0
	assert test.baz == 'deadbeef'
	assert test.omg == 4
	assert test.wtf == 'test'
	
	test.foo = 0xCAFEBABE
	test.bar = 0.0
	assert test.pack() == '\xBE\xBA\xFE\xCA\0\0\0\0deadbeef\x04\x00\x00\x00test'