decoder

import sys, numpy as np

def cipher_encryption():
    msg = input('Enter message: ').upper()
    msg = msg.replace(' ', '')
    len_chk = 0
    if len(msg) % 2 != 0:
        msg += '0'
        len_chk = 1
    row = 2
    col = int(len(msg) / 2)
    msg2d = np.zeros((row, col), dtype=int)
    itr1 = 0
    itr2 = 0
    for i in range(len(msg)):
        if i % 2 == 0:
            msg2d[0][itr1] = int(ord(msg[i]) - 65)
            itr1 += 1
        else:
            msg2d[1][itr2] = int(ord(msg[i]) - 65)
            itr2 += 1
    else:
        key = input('Enter 4 letter Key String: ').upper()
        key = key.replace(' ', '')
        key2d = np.zeros((2, 2), dtype=int)
        itr3 = 0
        for i in range(2):
            for j in range(2):
                key2d[i][j] = ord(key[itr3]) - 65
                itr3 += 1

        else:
            deter = key2d[0][0] * key2d[1][1] - key2d[0][1] * key2d[1][0]
            deter = deter % 26
            mul_inv = -1
            for i in range(26):
                temp_inv = deter * i
                if temp_inv % 26 == 1:
                    mul_inv = i
                    break
                    continue
                    continue
            else:
                if mul_inv == -1:
                    print('Invalid key')
                    sys.exit()
                encryp_text = ''
                itr_count = int(len(msg) / 2)

    if len_chk == 0:
        for i in range(itr_count):
            temp1 = msg2d[0][i] * key2d[0][0] + msg2d[1][i] * key2d[0][1]
            encryp_text += chr(temp1 % 26 + 65)
            temp2 = msg2d[0][i] * key2d[1][0] + msg2d[1][i] * key2d[1][1]
            encryp_text += chr(temp2 % 26 + 65)

    else:
        for i in range(itr_count - 1):
            temp1 = msg2d[0][i] * key2d[0][0] + msg2d[1][i] * key2d[0][1]
            encryp_text += chr(temp1 % 26 + 65)
            temp2 = msg2d[0][i] * key2d[1][0] + msg2d[1][i] * key2d[1][1]
            encryp_text += chr(temp2 % 26 + 65)
        else:
            print('Encrypted Text: {}'.format(encryp_text))


def cipher_decryption():
    msg = input('Enter message: ').upper()
    msg = msg.replace(' ', '')
    len_chk = 0
    if len(msg) % 2 != 0:
        msg += '0'
        len_chk = 1
    row = 2
    col = int(len(msg) / 2)
    msg2d = np.zeros((row, col), dtype=int)
    itr1 = 0
    itr2 = 0
    for i in range(len(msg)):
        if i % 2 == 0:
            msg2d[0][itr1] = int(ord(msg[i]) - 65)
            itr1 += 1
        else:
            msg2d[1][itr2] = int(ord(msg[i]) - 65)
            itr2 += 1
    else:
        key = input('Enter 4 letter Key String: ').upper()
        key = key.replace(' ', '')
        key2d = np.zeros((2, 2), dtype=int)
        itr3 = 0
        for i in range(2):
            for j in range(2):
                key2d[i][j] = ord(key[itr3]) - 65
                itr3 += 1
            else:
                deter = key2d[0][0] * key2d[1][1] - key2d[0][1] * key2d[1][0]
                deter = deter % 26
                mul_inv = -1
                for i in range(26):
                    temp_inv = deter * i
                    if temp_inv % 26 == 1:
                        mul_inv = i
                        break
                        continue
                        continue
                    key2d[0][0], key2d[1][1] = key2d[1][1], key2d[0][0]
                    key2d[0][1] *= -1
                    key2d[1][0] *= -1
                    key2d[0][1] = key2d[0][1] % 26
                    key2d[1][0] = key2d[1][0] % 26
                    for i in range(2):
                        for j in range(2):
                            key2d[i][j] *= mul_inv
                        else:
                            for i in range(2):
                                for j in range(2):
                                    key2d[i][j] = key2d[i][j] % 26
                                else:
                                    decryp_text = ''
                                    itr_count = int(len(msg) / 2)

    if len_chk == 0:
        for i in range(itr_count):
            temp1 = msg2d[0][i] * key2d[0][0] + msg2d[1][i] * key2d[0][1]
            decryp_text += chr(temp1 % 26 + 65)
            temp2 = msg2d[0][i] * key2d[1][0] + msg2d[1][i] * key2d[1][1]
            decryp_text += chr(temp2 % 26 + 65)

    else:
        for i in range(itr_count - 1):
            temp1 = msg2d[0][i] * key2d[0][0] + msg2d[1][i] * key2d[0][1]
            decryp_text += chr(temp1 % 26 + 65)
            temp2 = msg2d[0][i] * key2d[1][0] + msg2d[1][i] * key2d[1][1]
            decryp_text += chr(temp2 % 26 + 65)
        else:
            print('Decrypted Text: {}'.format(decryp_text))


def main():
    choice = int(input('1. Encryption\n2. Decryption\nChoose(1, 2): '))
    if choice == 1:
        print('---Encryption---')
        cipher_encryption()
    else:
        if choice == 2:
            print('---Decryption---')
            cipher_decryption()
        else:
            print('Invalid Choice')


if __name__ == '__main__':
    main()