"""
    Cryptography related stuff - mostly
    encrypting and decrypting user data.
"""

from cryptography.hazmat.backends import default_backend
from cryptography.hazmat.primitives import hashes
from cryptography.hazmat.primitives.kdf.pbkdf2 import PBKDF2HMAC
from cryptography.fernet import Fernet
import base64
import os

def get_key(password: str) -> bytes:
    """
        Derives a bytes key
        from a given password.

        Useful when you want
        to generate the same
        key over and over again.
        E.g. to encrypt/decrypt
        locally stored user data.
    """

    password = password.encode()

    salt = b'?\x0f\xa1\x97otT\xe48\xc9O\xb4\x1f\xef\xf5\xea'

    kdf = PBKDF2HMAC(
        algorithm=hashes.SHA256,
        length=32,
        salt=salt,
        iterations=100000,
        backend=default_backend()
    )

    key = base64.urlsafe_b64encode(kdf.derive(password))
    return key

def encrypt_and_write_to_file(password: str, strdata: str, file_path: str) -> bool:
    """
        Encrypts the given string data
        and stores them in a file.
    """

    try:
        key = get_key(password)
    
        f = Fernet(key)

        encrypted = f.encrypt(strdata.encode())
        if os.path.exists(file_path):        
            with open(file_path, "wb") as ef:
                ef.write(encrypted)
        else:
            os.system(f"touch {file_path}")
            with open(file_path, "wb") as ef:
                ef.write(encrypted)

        return 0
    except:
        return 1

def read_from_file_and_decrypt(password: str, file_path: str) -> str:
    """
        Reads contents of an encrypted file
        and decrypts them.
    """

    try:
        key = get_key(password)

        f = Fernet(key)

        if os.path.exists(file_path):
            with open(file_path, "rb") as ef:
                decrypted = f.decrypt(ef.read())
        else:
            os.system(f"touch {file_path}")
            with open(file_path, "rb") as ef:
                decrypted = f.decrypt(ef.read())
       
        return decrypted.decode()
    except:
        return ""