import struct

class Data:
    def __init__(self, rawdata = b"", off = 0):
        self.data = rawdata
        self.offset = off
    def setData(self, rawdata, off = 0):
        self.data = rawdata
        self.offset = off
    def seek(self, off):
        self.offset = off
    def seekEnd(self, off = 0):
        self.offset = len(self.data) + off
    def seekRel(self, off = 0):
        self.offset += off
    def tell(self):
        return self.offset
    def decode(self, fmt):
        size = struct.calcsize(fmt)
        val = struct.unpack(fmt, self.data[self.offset : self.offset + size])
        self.offset += size
        return val
    def encode(self, fmt, *args):
        data = struct.pack(fmt, *args)
        self.write(data)
    def read(self, length):
        val = self.data[self.offset : self.offset + length]
        self.offset += length
        return val
    def write(self, data):
        #todo: handle
        if self.offset == len(self.data):
            self.data += data
            self.offset = len(self.data)
        elif self.offset > len(self.data):
            self.data += ZERO_BYTE * (self.offset - len(self.data))
            self.data += data
            self.offset = len(self.data)
        elif self.offset + len(data) >= len(self.data):
            self.data = self.data[0 : self.offset] + data
        else:
            self.data = self.data[0 : self.offset] + data + self.data [self.offset + len(data) : ]
    def truncate(self, offset = None):
        if offset is None:
            offset = self.offset
        self.data[0 : offset]
    def __len__(self):
        return len(self.data)
    def __str__(self):
        return str(self.data)
    def __repr__(self):
        return repr(self.data)