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import sys

import base64

import os

from cryptography.hazmat.primitives.kdf.pbkdf2 import PBKDF2HMAC

from cryptography.hazmat.primitives.hashes import SHA256

from cryptography.hazmat.primitives.ciphers import Cipher, algorithms, modes

from cryptography.hazmat.backends import default_backend

from cryptography.exceptions import InvalidKey

usage_msg = "Usage: " + sys.argv[0] + " (-e/-d) [file] [password]"

help_msg = usage_msg + "\n" + \

           "Examples:\n" + \

           "  To encrypt a file named 'data.txt' with password 'mypassword', do:\n" + \

           "'$ python " + sys.argv[0] + " -e data.txt mypassword'\n" + \

           "  To decrypt the same file, do:\n" + \

           "'$ python " + sys.argv[0] + " -d data.txt.en mypassword'\n"

def derive_key(password, salt):

    """Derive a key from the password and salt using PBKDF2."""

    kdf = PBKDF2HMAC(

        algorithm=SHA256(),

        length=32,

        salt=salt,

        iterations=100000,

        backend=default_backend()

    )

    return kdf.derive(password.encode())

def encrypt_file(file_path, password):

    """Encrypt the file at file_path using the provided password."""

    salt = os.urandom(16)

    key = derive_key(password, salt)

    iv = os.urandom(16)

    cipher = Cipher(algorithms.AES(key), modes.CFB(iv), backend=default_backend())

    encryptor = cipher.encryptor()

    with open(file_path, 'rb') as f:

        data = f.read()

   

    encrypted_data = encryptor.update(data) + encryptor.finalize()

    with open(file_path + '.en', 'wb') as f:

        f.write(salt + iv + encrypted_data)

def decrypt_file(file_path, password):

    """Decrypt the file at file_path using the provided password."""

    with open(file_path, 'rb') as f:

        salt = f.read(16)

        iv = f.read(16)

        encrypted_data = f.read()

   

    key = derive_key(password, salt)

    cipher = Cipher(algorithms.AES(key), modes.CFB(iv), backend=default_backend())

    decryptor = cipher.decryptor()

    try:

        decrypted_data = decryptor.update(encrypted_data) + decryptor.finalize()

    except InvalidKey:

        print("Invalid password or corrupted file.")

        sys.exit(1)

    original_file_path = file_path.replace('.en', '')

    with open(original_file_path, 'wb') as f:

        f.write(decrypted_data)

if len(sys.argv) != 4:

    print(usage_msg)

    sys.exit(1)

mode = sys.argv[1]

file_path = sys.argv[2]

password = sys.argv[3]

if mode == "-e":

    encrypt_file(file_path, password)

    print(f"File '{file_path}' encrypted to '{file_path}.en'")

elif mode == "-d":

    decrypt_file(file_path, password)

    print(f"File '{file_path}' decrypted.")

elif mode == "-h" or mode == "--help":

    print(help_msg)

else:

    print("Unrecognized first argument: " + mode)

    print("Please use '-e', '-d', or '-h'.")

"""The most important point of this code is the derivation of a cryptographic key from the provided password

and salt using PBKDF2, which is then used for secure AES encryption and decryption of the file."""