abstract_context_manager.py

from abc import ABC, abstractmethod
from contextlib import contextmanager
from cryptography.fernet import Fernet

class CryptoFileManager(ABC):
    @abstractmethod
    @contextmanager
    def secure_file_handler(self, path, mode, key):
        """A context manager for encrypting or decrypting files."""
        pass

class FileEncryptor(CryptoFileManager):
    @contextmanager
    def secure_file_handler(self, path, mode, key):
        """Encrypts file content on write."""
        try:
            cipher = Fernet(key)
            with open(path, mode) as file:
                data = file.read()
                encrypted_data = cipher.encrypt(data.encode())
                file.seek(0)
                file.write(encrypted_data.decode())
                yield file
        except Exception as e:
            print(f"Failed to encrypt file: {e}")
        finally:
            print(f"File encryption completed and file {path} has been closed.")

class FileDecryptor(CryptoFileManager):
    @contextmanager
    def secure_file_handler(self, path, mode, key):
        """Decrypts file content on read."""
        file = None
        try:
            cipher = Fernet(key)
            file = open(path, mode)
            encrypted_data = file.read()
            decrypted_data = cipher.decrypt(encrypted_data.encode())
            file.seek(0)
            file.write(decrypted_data.decode())
            file.seek(0)
            yield file
        except Exception as e:
            print(f"Failed to decrypt file: {e}")
        finally:
            if file:
                file.close()
                print(f"File decryption completed and file {path} has been closed.")

# Example usage
key = Fernet.generate_key()  # Normally you would store and retrieve this securely
if __name__ == "__main__":
    encryptor = FileEncryptor()
    decryptor = FileDecryptor()
    # Encrypt data
    with encryptor.secure_file_handler('testfile.txt', 'w+', key) as file:
        file.write("Sensitive data that needs encryption.")
    # Decrypt data
    with decryptor.secure_file_handler('testfile.txt', 'r+', key) as file:
        print("Decrypted content:", file.read())