# (c) Copyright 2018 by Coinkite Inc. This file is covered by license found in COPYING-CC.
#
# descriptor.py - Bitcoin Core's descriptors and their specialized checksums.
#
# Based on: https://github.com/bitcoin/bitcoin/blob/master/src/script/descriptor.cpp
#

def polymod(c, val):
    c0 = c >> 35
    c = ((c & 0x7ffffffff) << 5) ^ val
    if (c0 & 1):
        c ^= 0xf5dee51989
    if (c0 & 2):
        c ^= 0xa9fdca3312
    if (c0 & 4):
        c ^= 0x1bab10e32d
    if (c0 & 8):
        c ^= 0x3706b1677a
    if (c0 & 16):
        c ^= 0x644d626ffd

    return c

def descriptor_checksum(desc):
    INPUT_CHARSET = "0123456789()[],'/*abcdefgh@:$%{}IJKLMNOPQRSTUVWXYZ&+-.;<=>?!^_|~ijklmnopqrstuvwxyzABCDEFGH`#\"\\ "
    CHECKSUM_CHARSET = "qpzry9x8gf2tvdw0s3jn54khce6mua7l"

    c = 1
    cls = 0
    clscount = 0
    for ch in desc:
        pos = INPUT_CHARSET.find(ch)
        if pos == -1:
            raise ValueError(ch)

        c = polymod(c, pos & 31)
        cls = cls * 3 + (pos >> 5)
        clscount += 1
        if clscount == 3:
            c = polymod(c, cls)
            cls = 0
            clscount = 0

    if clscount > 0:
        c = polymod(c, cls)
    for j in range(0, 8):
        c = polymod(c, 0)
    c ^= 1

    rv = ''
    for j in range(0, 8):
        rv += CHECKSUM_CHARSET[(c >> (5 * (7 - j))) & 31]

    return rv

def append_checksum(desc):
    return desc + "#" + descriptor_checksum(desc)

# EOF