from Crypto.Cipher import AES
import json
import base64
import struct
import binascii
import random


def aes_cbc_encrypt(data, key):
    aes_cipher = AES.new(key, AES.MODE_CBC, '\0' * 16)
    return aes_cipher.encrypt(data)


def aes_cbc_decrypt(data, key):
    aes_cipher = AES.new(key, AES.MODE_CBC, '\0' * 16)
    return aes_cipher.decrypt(data)


def aes_cbc_encrypt_a32(data, key):
    return str_to_a32(aes_cbc_encrypt(a32_to_str(data), a32_to_str(key)))


def aes_cbc_decrypt_a32(data, key):
    return str_to_a32(aes_cbc_decrypt(a32_to_str(data), a32_to_str(key)))


def stringhash(str, aeskey):
    s32 = str_to_a32(str)
    h32 = [0, 0, 0, 0]
    for i in range(len(s32)):
        h32[i % 4] ^= s32[i]
    for r in range(0x4000):
        h32 = aes_cbc_encrypt_a32(h32, aeskey)
    return a32_to_base64((h32[0], h32[2]))


def prepare_key(arr):
    pkey = [0x93C467E3, 0x7DB0C7A4, 0xD1BE3F81, 0x0152CB56]
    for r in range(0x10000):
        for j in range(0, len(arr), 4):
            key = [0, 0, 0, 0]
            for i in range(4):
                if i + j < len(arr):
                    key[i] = arr[i + j]
            pkey = aes_cbc_encrypt_a32(pkey, key)
    return pkey


def encrypt_key(a, key):
    return sum(
        (aes_cbc_encrypt_a32(a[i:i + 4], key)
            for i in range(0, len(a), 4)), ())


def decrypt_key(a, key):
    return sum(
        (aes_cbc_decrypt_a32(a[i:i + 4], key)
            for i in range(0, len(a), 4)), ())


def encrypt_attr(attr, key):
    attr = 'MEGA' + json.dumps(attr)
    if len(attr) % 16:
        attr += '\0' * (16 - len(attr) % 16)
    return aes_cbc_encrypt(attr, a32_to_str(key))


def decrypt_attr(attr, key):
    attr = aes_cbc_decrypt(attr, a32_to_str(key)).rstrip('\0')
    return json.loads(attr[4:]) if attr[:6] == 'MEGA{"' else False


def a32_to_str(a):
    return struct.pack('>%dI' % len(a), *a)


def str_to_a32(b):
    if len(b) % 4:
        # pad to multiple of 4
        b += '\0' * (4 - len(b) % 4)
    return struct.unpack('>%dI' % (len(b) / 4), b)


def mpi_to_int(s):
    return int(binascii.hexlify(s[2:]), 16)


def base64_url_decode(data):
    data += '=='[(2 - len(data) * 3) % 4:]
    for search, replace in (('-', '+'), ('_', '/'), (',', '')):
        data = data.replace(search, replace)
    return base64.b64decode(data)


def base64_to_a32(s):
    return str_to_a32(base64_url_decode(s))


def base64_url_encode(data):
    data = base64.b64encode(data)
    for search, replace in (('+', '-'), ('/', '_'), ('=', '')):
        data = data.replace(search, replace)
    return data


def a32_to_base64(a):
    return base64_url_encode(a32_to_str(a))


def get_chunks(size):
    chunks = {}
    p = pp = 0
    i = 1

    while i <= 8 and p < size - i * 0x20000:
        chunks[p] = i * 0x20000
        pp = p
        p += chunks[p]
        i += 1

    while p < size:
        chunks[p] = 0x100000
        pp = p
        p += chunks[p]

    chunks[pp] = size - pp
    if not chunks[pp]:
        del chunks[pp]

    return chunks

# more general functions
def make_id(length):
    text = ''
    possible = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789"
    for i in range(length):
        text += random.choice(possible)
    return text