# Pyrogram - Telegram MTProto API Client Library for Python
# Copyright (C) 2017-2019 Dan Tès <https://github.com/delivrance>
#
# This file is part of Pyrogram.
#
# Pyrogram is free software: you can redistribute it and/or modify
# it under the terms of the GNU Lesser General Public License as published
# by the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
#
# Pyrogram is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU Lesser General Public License for more details.
#
# You should have received a copy of the GNU Lesser General Public License
# along with Pyrogram.  If not, see <http://www.gnu.org/licenses/>.

import hashlib
import os

from pyrogram.api import types


def btoi(b: bytes) -> int:
    return int.from_bytes(b, "big")


def itob(i: int) -> bytes:
    return i.to_bytes(256, "big")


def sha256(data: bytes) -> bytes:
    return hashlib.sha256(data).digest()


def xor(a: bytes, b: bytes) -> bytes:
    return bytes(i ^ j for i, j in zip(a, b))


def compute_hash(algo: types.PasswordKdfAlgoSHA256SHA256PBKDF2HMACSHA512iter100000SHA256ModPow, password: str) -> bytes:
    hash1 = sha256(algo.salt1 + password.encode() + algo.salt1)
    hash2 = sha256(algo.salt2 + hash1 + algo.salt2)
    hash3 = hashlib.pbkdf2_hmac("sha512", hash2, algo.salt1, 100000)

    return sha256(algo.salt2 + hash3 + algo.salt2)


# noinspection PyPep8Naming
def compute_check(r: types.account.Password, password: str) -> types.InputCheckPasswordSRP:
    algo = r.current_algo

    p_bytes = algo.p
    p = btoi(algo.p)

    g_bytes = itob(algo.g)
    g = algo.g

    B_bytes = r.srp_B
    B = btoi(B_bytes)

    srp_id = r.srp_id

    x_bytes = compute_hash(algo, password)
    x = btoi(x_bytes)

    g_x = pow(g, x, p)

    k_bytes = sha256(p_bytes + g_bytes)
    k = btoi(k_bytes)

    kg_x = (k * g_x) % p

    while True:
        a_bytes = os.urandom(256)
        a = btoi(a_bytes)

        A = pow(g, a, p)
        A_bytes = itob(A)

        u = btoi(sha256(A_bytes + B_bytes))

        if u > 0:
            break

    g_b = (B - kg_x) % p

    ux = u * x
    a_ux = a + ux
    S = pow(g_b, a_ux, p)
    S_bytes = itob(S)

    K_bytes = sha256(S_bytes)

    M1_bytes = sha256(
        xor(sha256(p_bytes), sha256(g_bytes))
        + sha256(algo.salt1)
        + sha256(algo.salt2)
        + A_bytes
        + B_bytes
        + K_bytes
    )

    return types.InputCheckPasswordSRP(srp_id, A_bytes, M1_bytes)