mrp_bot/vk_api/audio_url_decoder.py

# -*- coding: utf-8 -*-
from .exceptions import VkAudioUrlDecodeError

VK_STR = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMN0PQRSTUVWXYZO123456789+/="


def splice(l, a, b, c):
    """ JS's Array.prototype.splice

    var x = [1, 2, 3],
        y = x.splice(0, 2, 1337);

    eq

    x = [1, 2, 3]
    x, y = splice(x, 0, 2, 1337)
    """

    return l[:a] + [c] + l[a + b:], l[a:a + b]


def decode_audio_url(string, user_id):
    vals = string.split("?extra=", 1)[1].split("#")

    tstr = vk_o(vals[0])
    ops_list = vk_o(vals[1]).split('\x09')[::-1]

    for op_data in ops_list:

        split_op_data = op_data.split('\x0b')
        cmd = split_op_data[0]
        if len(split_op_data) > 1:
            arg = split_op_data[1]
        else:
            arg = None

        if cmd == 'v':
            tstr = tstr[::-1]

        elif cmd == 'r':
            tstr = vk_r(tstr, arg)

        elif cmd == 'x':
            tstr = vk_xor(tstr, arg)
        elif cmd == 's':
            tstr = vk_s(tstr, arg)
        elif cmd == 'i':
            tstr = vk_i(tstr, arg, user_id)
        else:
            raise VkAudioUrlDecodeError(
                'Unknown decode cmd: "{}"; Please send bugreport'.format(cmd)
            )

    return tstr


def vk_o(string):
    result = []
    index2 = 0

    for s in string:
        sym_index = VK_STR.find(s)

        if sym_index != -1:
            if index2 % 4 != 0:
                i = (i << 6) + sym_index
            else:
                i = sym_index

            if index2 % 4 != 0:
                index2 += 1
                shift = -2 * index2 & 6
                result += [chr(0xFF & (i >> shift))]
            else:
                index2 += 1

    return ''.join(result)


def vk_r(string, i):
    vk_str2 = VK_STR + VK_STR
    vk_str2_len = len(vk_str2)

    result = []

    for s in string:
        index = vk_str2.find(s)

        if index != -1:
            offset = index - int(i)

            if offset < 0:
                offset += vk_str2_len

            result += [vk_str2[offset]]
        else:
            result += [s]

    return ''.join(result)


def vk_xor(string, i):
    xor_val = ord(i[0])

    return ''.join(chr(ord(s) ^ xor_val) for s in string)


def vk_s_child(t, e):
    i = len(t)

    if not i:
        return []

    o = []
    e = int(e)

    for a in range(i - 1, -1, -1):
        e = (i * (a + 1) ^ e + a) % i
        o.append(e)

    return o[::-1]


def vk_s(t, e):
    i = len(t)

    if not i:
        return t

    o = vk_s_child(t, e)
    t = list(t)

    for a in range(1, i):
        t, y = splice(t, o[i - 1 - a], 1, t[a])
        t[a] = y[0]

    return ''.join(t)


def vk_i(t, e, user_id):
    return vk_s(t, int(e) ^ user_id)