# base85.py: pure python base85 codec

#

# Copyright (C) 2009 Brendan Cully <brendan@kublai.com>

#

# This software may be used and distributed according to the terms of the

# GNU General Public License version 2 or any later version.

from __future__ import absolute_import

import struct

_b85chars2 = [(a + b) for a in _b85chars for b in _b85chars]

_b85dec = {}

def _mkb85dec():

    for i, c in enumerate(_b85chars):

        _b85dec[c] = i

def b85encode(text, pad=False):

    """encode text in base85 format"""

    l = len(text)

    r = l % 4

    if r:

        text += '\0' * (4 - r)

    longs = len(text) >> 2

    words = struct.unpack('>%dL' % (longs), text)

    out = ''.join(_b85chars[(word // 52200625) % 85] +

                  _b85chars2[(word // 7225) % 7225] +

                  _b85chars2[word % 7225]

                  for word in words)

    if pad:

        return out

    # Trim padding

    olen = l % 4

    if olen:

        olen += 1

    olen += l // 4 * 5

    return out[:olen]

def b85decode(text):

    """decode base85-encoded text"""

    if not _b85dec:

        _mkb85dec()

    l = len(text)

    out = []

    for i in range(0, len(text), 5):

        chunk = text[i:i + 5]

        acc = 0

        for j, c in enumerate(chunk):

            try:

                acc = acc * 85 + _b85dec[c]

            except KeyError:

                raise ValueError('bad base85 character at position %d'

                                 % (i + j))

        if acc > 4294967295:

            raise ValueError('Base85 overflow in hunk starting at byte %d' % i)

        out.append(acc)

    # Pad final chunk if necessary

    cl = l % 5

    if cl:

        acc *= 85 ** (5 - cl)

        if cl > 1:

            acc += 0xffffff >> (cl - 2) * 8

        out[-1] = acc

    out = struct.pack('>%dL' % (len(out)), *out)

    if cl:

        out = out[:-(5 - cl)]

    return out