import hashlib
from Crypto.Cipher import AES
from Crypto.Util.Padding import pad, unpad

def decrypt_wallet_dat(mkey: str, salt: str, iterations: int, wallet_dat: bytes) -> str:

    Decrypts the Wallet.dat Mkey using Salt and Iterations to obtain the wallet.dat passphrase.

    Parameters:
    - mkey: str
        The Mkey used for decryption.
    - salt: str
        The salt value used for key derivation.
    - iterations: int
        The number of iterations used for key derivation.
    - wallet_dat: bytes
        The encrypted wallet.dat file.

    Returns:
    - str:
        The decrypted wallet.dat passphrase.

    Raises:
    - ValueError:
        Raises an error if any of the input parameters are empty or invalid.
    """

    # Validating the input parameters
    if not mkey or not salt or not iterations or not wallet_dat:
        raise ValueError("Invalid input parameters.")

    # Deriving the encryption key using PBKDF2 with the provided salt and iterations
    key = hashlib.pbkdf2_hmac('sha256', mkey.encode(), salt.encode(), iterations)

    # Decrypting the wallet.dat using AES CBC mode
    cipher = AES.new(key, AES.MODE_CBC)
    decrypted_data = cipher.decrypt(wallet_dat)

    # Removing the padding from the decrypted data
    unpadded_data = unpad(decrypted_data, AES.block_size)

    # Converting the decrypted data to string (assuming it's in UTF-8 encoding)
    passphrase = unpadded_data.decode('utf-8')

    return passphrase

# Unit tests for decrypt_wallet_dat function

import unittest

class TestDecryptWalletDat(unittest.TestCase):

    def test_decrypt_wallet_dat(self):
        """
        Tests the decryption of wallet.dat using the provided Mkey, salt, iterations, and encrypted data.
        """
        mkey = "myMkey"
        salt = "mySalt"
        iterations = 1000
        wallet_dat = b'\x9c\x8f\x9e\x8f\x9e\x8f\x9e\x8f\x9e\x8f\x9e\x8f\x9e\x8f\x9e\x8f'
        expected_passphrase = "myPassphrase"

        passphrase = decrypt_wallet_dat(mkey, salt, iterations, wallet_dat)
        self.assertEqual(passphrase, expected_passphrase)

    def test_invalid_input_parameters(self):
        """
        Tests if ValueError is raised when any of the input parameters are empty or invalid.
        """
        with self.assertRaises(ValueError):
            decrypt_wallet_dat("", "mySalt", 1000, b'\x9c\x8f\x9e\x8f\x9e\x8f\x9e\x8f\x9e\x8f\x9e\x8f\x9e\x8f\x9e\x8f')
        with self.assertRaises(ValueError):
            decrypt_wallet_dat("myMkey", "", 1000, b'\x9c\x8f\x9e\x8f\x9e\x8f\x9e\x8f\x9e\x8f\x9e\x8f\x9e\x8f\x9e\x8f')
        with self.assertRaises(ValueError):
            decrypt_wallet_dat("myMkey", "mySalt", None, b'\x9c\x8f\x9e\x8f\x9e\x8f\x9e\x8f\x9e\x8f\x9e\x8f\x9e\x8f\x9e\x8f')
        with self.assertRaises(ValueError):
            decrypt_wallet_dat("myMkey", "mySalt", 1000, b'')

# Example usage of decrypt_wallet_dat function

mkey = "myMkey"
salt = "mySalt"
iterations = 1000
wallet_dat = b'\x9c\x8f\x9e\x8f\x9e\x8f\x9e\x8f\x9e\x8f\x9e\x8f\x9e\x8f\x9e\x8f'

try:
    passphrase = decrypt_wallet_dat(mkey, salt, iterations, wallet_dat)
    print(f"The decrypted wallet.dat passphrase is: {passphrase}")
except ValueError as e:
    print(f"Error while decrypting wallet.dat: {e}")