from Crypto.Cipher import DES
from secrets import token_bytes
import sys
import datetime

def encrypt(message):
    cipher = DES.new(key, DES.MODE_EAX)
    nonce = cipher.nonce
    ciphertext, tag = cipher.encrypt_and_digest(message.encode('ascii'))
    return nonce, ciphertext, tag

def decrypt(nonce, ciphertext, tag):
    cipher = DES.new(key, DES.MODE_EAX, nonce=nonce)
    plaintext = cipher.decrypt(ciphertext)
    try:
        cipher.verify(tag)
        return plaintext.decoce('ascii')
    except:
        return False


key=token_bytes(8)

print('Zahajuji čtení souboru.')
start_time = datetime.datetime.now()
filename = str(sys.argv[1])
file = open(filename)
lines = file.readlines()
file.close()
text = ''
for line in lines:
    text += str(line)
filereaddelta = datetime.datetime.now() - start_time
print('Čtení souboru úspěšné.')

n = 5000000
chunks = [text[i:i+n] for i in range(0, len(text), n)]
ciphertext = bytes(''.encode('ascii'))
encryptdelta = int(filereaddelta.total_seconds() * 1000)
decryptdelta = 0
filename = filename.replace(".", "_encrypted.")
filewrite = open(filename, 'w')
fileread = open(filename, 'r')

for chunk in chunks:
    start_time = datetime.datetime.now()
    nonce, ciphertext, tag = encrypt(chunk)
    filewrite.write(str(ciphertext))
    delta = datetime.datetime.now() - start_time
    encryptdelta += int(delta.total_seconds() * 1000)
    start_time = datetime.datetime.now()
    text = fileread.readlines()
    plaintext = decrypt(nonce, ciphertext, tag)
    delta = datetime.datetime.now() - start_time
    decryptdelta += int(delta.total_seconds() * 1000)


filewrite.close()
fileread.close()
print('Šifrování trvalo: %s ms' % encryptdelta)
print('Rozšifrování trvalo: %s ms' % decryptdelta)