import os
import re
import json
import codecs
import random
import base64
import struct
import shutil
import requests
import tempfile

from Crypto.Cipher import AES
from Crypto.Util import Counter

def makebyte(x):
    return codecs.latin_1_encode(x)[0]

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

def get_chunks(size):
    p, s = 0, 0x20000

    while p + s < size:
        yield(p, s)
        p += s

        if s < 0x100000: s += 0x20000

    yield(p, size - p)

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

def decrypt_attr(attr, key):
    attr = codecs.latin_1_decode(aes_cbc_decrypt(attr, a32_to_str(key)))[0].rstrip('\0')
    return json.loads(attr[4:]) if attr[:6] == 'MEGA{"' else False

def _api_request(data):
    sequence_num = random.randint(0, 0xFFFFFFFF)
    params = {'id': sequence_num}
    sequence_num += 1

    if not isinstance(data, list): data = [data]
    json_resp = json.loads(requests.post('{0}://g.api.{1}/cs'.format('https', 'mega.co.nz'), params=params, data=json.dumps(data), timeout=160).text)
    if isinstance(json_resp, int): raise Exception(json_resp)

    return json_resp[0]

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 str_to_a32(b):
    if isinstance(b, str): b = makebyte(b)
    if len(b) % 4: b += b'\0' * (4 - len(b) % 4)
    return struct.unpack('>%dI' % (len(b) / 4), b)

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

def mega_download_file(file_handle, file_key, dest_path=None):
    file_key = base64_to_a32(file_key)
    file_data = _api_request({'a': 'g', 'g': 1, 'p': file_handle})

    k = (file_key[0] ^ file_key[4], file_key[1] ^ file_key[5], file_key[2] ^ file_key[6], file_key[3] ^ file_key[7])
    iv = file_key[4:6] + (0, 0)

    if 'g' not in file_data: raise Exception

    file_size = file_data['s']
    attribs = decrypt_attr(base64_url_decode(file_data['at']), k)
    input_file = requests.get(file_data['g'], stream=True).raw

    temp_output_file = tempfile.NamedTemporaryFile(mode='w+b', prefix='megapy_', delete=False)
    k_str = a32_to_str(k)
    aes = AES.new(k_str, AES.MODE_CTR, counter=Counter.new(128, initial_value=((iv[0] << 32) + iv[1]) << 64))

    mac_str = b'\0' * 16
    mac_encryptor = AES.new(k_str, AES.MODE_CBC, mac_str)
    iv_str = a32_to_str([iv[0], iv[1], iv[0], iv[1]])

    for _, chunk_size in get_chunks(file_size):
        chunk = aes.decrypt(input_file.read(chunk_size))
        temp_output_file.write(chunk)

        encryptor = AES.new(k_str, AES.MODE_CBC, iv_str)

        for i in range(0, len(chunk) - 16, 16):
            block = chunk[i:i + 16]
            encryptor.encrypt(block)

        i = (i + 16) if file_size > 16 else 0
        block = chunk[i:i + 16]
        if len(block) % 16: block += b'\0' * (16 - (len(block) % 16))

        mac_str = mac_encryptor.encrypt(encryptor.encrypt(block))

    file_mac = str_to_a32(mac_str)
    temp_output_file.close()

    if (file_mac[0] ^ file_mac[1], file_mac[2] ^ file_mac[3]) != file_key[6:8]: raise ValueError

    file_path = os.path.join(dest_path, attribs['n'])
    if os.path.exists(file_path): os.remove(file_path)

    shutil.move(temp_output_file.name, file_path)

def mega_download_url(url, dest_path=None):
    if '/file/' in url:
        url = url.replace(' ', '')
        file_id = re.findall(r'\W\w\w\w\w\w\w\w\w\W', url)[0][1:-1]
        path = f'{file_id}!{url[re.search(file_id, url).end() + 1:]}'.split('!')
    elif '!' in url: path = re.findall(r'/#!(.*)', url)[0].split('!')
    else: raise Exception

    return mega_download_file(path[0], path[1], dest_path)