class SHA256Custom:
    """
    Custom SHA256 function, its not really custom but rewritten using the pseudocode from wikipedia and
    should mimic the built in function
    """
    def __init__(self,  data=None):
        # Setting up the initial bit values, i wont pretend to understand the math involved but these seem hardcoded
        self.__ks = [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]

        self.__hs = [0x6a09e667, 0xbb67ae85, 0x3c6ef372, 0xa54ff53a, 0x510e527f, 0x9b05688c, 0x1f83d9ab, 0x5be0cd19]

        # Copy the initial bit values for use since they are changed
        self.__h = self.__hs[:]
        self.__k = self.__ks[:]

        # Create variables we will need in the class
        self.__string_byte_len = 0
        self.__buffer = b''
        self.__string_hashed = False
        self.__digested_string = b''

        if data is not None:
            self.update(data)

    # Static methods because pycharm is moaning about them not needing to be inside of the class
    @staticmethod
    def pad_string(string_len: int) -> bytes:
        """Static method to pad the string digest for the hash"""
        # Adding a "1" bit to the end, although it seems to use 63 as the actual value, im guessing its possibly to do
        # with chunk size
        string_di = string_len & 0x3f
        # Get the 64bit big endian length of the post processed hash length
        post_process_length = (string_len << 3).to_bytes(8, "big")
        padded_length = 55
        if string_di < 56:
            padded_length -= string_di
        else:
            padded_length -= 199 - string_di

        return b'\x80' + b'\x00' * padded_length + post_process_length

    @staticmethod
    def rotate_right(a, b):
        """Static method to rotate a and b bits right """
        return ((a >> b) | (a << (32 - b))) & 0xffffffff

    def update(self, string_in: bytes) -> None:
        """Method to update the hash value"""
        if (string_in and len(string_in) > 0) and not self.__string_hashed:
            self.__string_byte_len += len(string_in)
            string_buffer = self.__buffer + string_in

            # Process the string as 512 bit chunks (64 bytes)
            for i in range(0, len(string_buffer) // 64):
                self.calculate_hash(string_buffer[64 * i:64 * (i + 1)])

            # Set the class buffer
            self.__buffer = string_buffer[len(string_buffer) - (len(string_buffer) % 64):]
        else:
            return

    def digest(self) -> bytes:
        """Method to get the bytes digest of our hash value"""
        if not self.__string_hashed:
            self.update(self.pad_string(self.__string_byte_len))
            self.__digested_string = b''.join(val.to_bytes(4, 'big') for val in self.__h[:8])
            self.__string_hashed = True
        return self.__digested_string

    def hexdigest(self) -> str:
        """Method to get the hex digest of our hash value"""
        # Hex characters to use when changing the hex value back into a string
        tab = '0123456789abcdef'
        return "".join(tab[byt >> 4] + tab[byt & 0xf] for byt in self.digest())

    def calculate_hash(self, chunk) -> None:
        """Method to calculate the actual hash value"""
        # Create an array of 32bit words
        words = [0] * 64

        # Converted from the pseudo code, but i believe its filling the word array with first 16 words we add
        words[0:16] = [int.from_bytes(chunk[i:i + 4], "big") for i in range(0, len(chunk), 4)]

        for i in range(16, 64):
            s0 = self.rotate_right(words[i - 15], 7) ^ self.rotate_right(words[i - 15], 18) ^ (words[i - 15] >> 3)
            s1 = self.rotate_right(words[i - 2], 17) ^ self.rotate_right(words[i - 2], 19) ^ (words[i - 2] >> 10)
            words[i] = (words[i - 16] + s0 + words[i - 7] + s1) & 0xffffffff

        # Initialize the values with the default hash value
        a, b, c, d, e, f, g, h = self.__h

        # Calculation main loop
        for i in range(64):
            s0 = self.rotate_right(a, 2) ^ self.rotate_right(a, 13) ^ self.rotate_right(a, 22)
            t2 = s0 + self.maj(a, b, c)
            s1 = self.rotate_right(e, 6) ^ self.rotate_right(e, 11) ^ self.rotate_right(e, 25)
            t1 = h + s1 + self.ch(e, f, g) + self.__k[i] + words[i]

            h = g
            g = f
            f = e
            e = (d + t1) & 0xffffffff
            d = c
            c = b
            b = a
            a = (t1 + t2) & 0xffffffff

        for i, (x, y) in enumerate(zip(self.__h, [a, b, c, d, e, f, g, h])):
            self.__h[i] = (x + y) & 0xffffffff

    @staticmethod
    def maj(a, b, c):
        """Static method for the calculation of the maj variable in the pseudo code"""
        return (a & b) ^ (a & c) ^ (b & c)

    @staticmethod
    def ch(a, b, c):
        """Static method to calculate the ch variable in the pseudo code"""
        return (a & b) ^ ((~a) & c)