class BitStream(object):
    def __init__(self, io):
        self.io = io
        self.bits = 0
        self.byte = 0


    def seek(self, offset, whence=0):
        self.io.seek(offset, whence)
        self.byte = 0
        self.bits = 0


    def tell(self):
        return self.io.tell()


    def tell2(self):
        return self.io.tell(), self.bits


    def read_bit(self):
        if not self.bits:
            self.byte = ord(self.io.read(1))
            self.bits = 8
        self.bits -= 1
        return (self.byte >> self.bits) & 0x01


    def read(self, nb_bits):
        value = 0
        for i in range(nb_bits - 1, -1, -1):
            value |= self.read_bit() << i
        return value


    def write_bit(self, bit):
        if self.bits == 8:
            self.io.write(chr(self.byte))
            self.bits = 0
            self.byte = 0
        self.byte &= ~(1 << (7 - self.bits))
        self.byte |= bit << (7 - self.bits)
        self.bits += 1


    def write(self, bits, nb_bits):
        for i in range(nb_bits):
            self.write_bit(bits >> (nb_bits - 1 - i) & 0x01)


    def flush(self):
        self.io.write(chr(self.byte))
        self.bits = 0
        self.byte = 0
        self.io.flush()