from Crypto.Hash import SHA256

K = [
    0x428a2f98, 0x71374491, 0xb5c0fbcf, 0xe9b5dba5, 0x3956c25b, 0x59f111f1, 0x923f82a4, 0xab1c5ed5,
    0xd807aa98, 0x12835b01, 0x243185be, 0x550c7dc3, 0x72be5d74, 0x80deb1fe, 0x9bdc06a7, 0xc19bf174,
    0xe49b69c1, 0xefbe4786, 0x0fc19dc6, 0x240ca1cc, 0x2de92c6f, 0x4a7484aa, 0x5cb0a9dc, 0x76f988da,
    0x983e5152, 0xa831c66d, 0xb00327c8, 0xbf597fc7, 0xc6e00bf3, 0xd5a79147, 0x06ca6351, 0x14292967,
    0x27b70a85, 0x2e1b2138, 0x4d2c6dfc, 0x53380d13, 0x650a7354, 0x766a0abb, 0x81c2c92e, 0x92722c85,
    0xa2bfe8a1, 0xa81a664b, 0xc24b8b70, 0xc76c51a3, 0xd192e819, 0xd6990624, 0xf40e3585, 0x106aa070,
    0x19a4c116, 0x1e376c08, 0x2748774c, 0x34b0bcb5, 0x391c0cb3, 0x4ed8aa4a, 0x5b9cca4f, 0x682e6ff3,
    0x748f82ee, 0x78a5636f, 0x84c87814, 0x8cc70208, 0x90befffa, 0xa4506ceb, 0xbef9a3f7, 0xc67178f2
]

H = [0x6a09e667, 0xbb67ae85, 0x3c6ef372, 0xa54ff53a, 0x510e527f, 0x9b05688c, 0x1f83d9ab, 0x5be0cd19]


def addition(*args, mod=32):
    res = 0
    for i in args:
        res += i % 2 ** mod
    return res % 2 ** mod


def padding(message):
    tmp = len(message) * 8
    k = (448 - tmp - 1) % 512
    add = b'1' + b'0' * k + bin(tmp)[2:].rjust(64, '0').encode()
    return message + bytes.fromhex(hex(int(add, 2))[2:])


def split(chunk):
    w = []
    for i in range(16):
        cur = chunk[4 * i: 4 * i + 4]
        w.append(int(cur.hex(), 16))
    w += [0] * 48
    return w


def rrot(x, n):
    return (x >> n) | (x << 32 - n)


def SHA(message):
    global H
    message = message.encode()
    pad = padding(message)
    chunk_num = len(pad) // 512

    chunks = [pad[512 * i: 512 * i + 512] for i in range(chunk_num)]

    for tmp in chunks:
        w = split(tmp)
        for i in range(16, 64):
            s0 = rrot(w[i - 15], 7) ^ rrot(w[i - 15], 18) ^ (w[i - 15] >> 3)
            s1 = rrot(w[i - 2], 17) ^ rrot(w[i - 2], 19) ^ (w[i - 2] >> 10)
            w[i] = addition(w[i - 16], s0, w[i - 7], s1)

        a, b, c, d, e, f, g, h = H[0], H[1], H[2], H[3], H[4], H[5], H[6], H[7]

        for i in range(64):
            s1 = rrot(e, 6) ^ rrot(e, 11) ^ rrot(e, 25)
            ch = (e & f) ^ (~ e & g)
            sch1 = addition(h, s1, ch, K[i], w[i])
            s0 = rrot(a, 2) ^ rrot(a, 13) ^ rrot(a, 22)
            maj = (a & b) ^ (a & c) ^ (b & c)
            sch2 = addition(s0, maj)

            h, g, f, e, d, c, b, a = g, f, e, addition(d + sch1), c, b, a, addition(sch1, sch2)

        H = [addition(*i) for i in zip(H, [a, b, c, d, e, f, g, h])]

    return b''.join(list(map(lambda x: bytes.fromhex(hex(x)[2:]), H))).hex()


if __name__ == '__main__':

    test = "London is the capital of Great Britain"
    print(SHA(test))
    print(SHA(test) == SHA256.SHA256Hash(test).hexdigest())
