import six
import struct


def _make_packer(format_string):
    try:
        packer = struct.Struct(format_string)  # new in Python 2.5
    except AttributeError:
        pack = lambda x: struct.pack(format_string, x)
        unpack = lambda s: struct.unpack(format_string, s)
    else:
        pack = packer.pack
        unpack = lambda s: packer.unpack(s)[0]
    return pack, unpack

int64_pack, int64_unpack = _make_packer('>q')
int32_pack, int32_unpack = _make_packer('>i')
int16_pack, int16_unpack = _make_packer('>h')
int8_pack, int8_unpack = _make_packer('>b')
uint64_pack, uint64_unpack = _make_packer('>Q')
uint32_pack, uint32_unpack = _make_packer('>I')
uint16_pack, uint16_unpack = _make_packer('>H')
uint8_pack, uint8_unpack = _make_packer('>B')
float_pack, float_unpack = _make_packer('>f')
double_pack, double_unpack = _make_packer('>d')

# Special case for cassandra header
header_struct = struct.Struct('>BBBB')
header_pack = header_struct.pack
header_unpack = header_struct.unpack


if six.PY3:
    def varint_unpack(term):
        val = int(''.join("%02x" % i for i in term), 16)
        if (term[0] & 128) != 0:
            val -= 1 << (len(term) * 8)
        return val
else:
    def varint_unpack(term):
        val = int(term.encode('hex'), 16)
        if (ord(term[0]) & 128) != 0:
            val = val - (1 << (len(term) * 8))
        return val


def bitlength(n):
    bitlen = 0
    while n > 0:
        n >>= 1
        bitlen += 1
    return bitlen


def varint_pack(big):
    pos = True
    if big == 0:
        return b'\x00'
    if big < 0:
        bytelength = bitlength(abs(big) - 1) // 8 + 1
        big = (1 << bytelength * 8) + big
        pos = False
    revbytes = bytearray()
    while big > 0:
        revbytes.append(big & 0xff)
        big >>= 8
    if pos and revbytes[-1] & 0x80:
        revbytes.append(0)
    revbytes.reverse()
    return six.binary_type(revbytes)