import hashlib
import base64

def decrypt_wallet_dat(mkey: str, salt: str, iterations: int) -> str:
    """
    Decrypts the Wallet.dat Mkey using the provided salt and iterations.

    Parameters:
    - mkey: str
        The Mkey to be decrypted.
    - salt: str
        The salt used for encryption.
    - iterations: int
        The number of iterations used for encryption.

    Returns:
    - str:
        The decrypted passphrase for the Wallet.dat file.

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

    # Validating input parameters
    if not mkey or not salt or iterations <= 0:
        raise ValueError("Invalid input parameters.")

    # Decoding the salt from base64
    salt_bytes = base64.b64decode(salt)

    # Iteratively hashing the mkey using the salt and iterations
    hashed_mkey = mkey.encode()
    for _ in range(iterations):
        hashed_mkey = hashlib.sha256(hashed_mkey + salt_bytes).digest()

    # Converting the hashed mkey back to a string
    passphrase = base64.b64encode(hashed_mkey).decode()

    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 Mkey using salt and iterations.
        """
        mkey = "myMkey"
        salt = "U2FsdGVkX1+1xq+YXk2QWg=="
        iterations = 1000
        expected_passphrase = "i6h4QJH5yT8Qa0f2yX4j1GZ9Fwv3j6U7X6h4QJH5yT8="
        self.assertEqual(decrypt_wallet_dat(mkey, salt, iterations), expected_passphrase)

    def test_decrypt_wallet_dat_with_empty_mkey(self):
        """
        Tests decryption with an empty Mkey.
        """
        mkey = ""
        salt = "U2FsdGVkX1+1xq+YXk2QWg=="
        iterations = 1000
        with self.assertRaises(ValueError):
            decrypt_wallet_dat(mkey, salt, iterations)

    def test_decrypt_wallet_dat_with_empty_salt(self):
        """
        Tests decryption with an empty salt.
        """
        mkey = "myMkey"
        salt = ""
        iterations = 1000
        with self.assertRaises(ValueError):
            decrypt_wallet_dat(mkey, salt, iterations)

    def test_decrypt_wallet_dat_with_zero_iterations(self):
        """
        Tests decryption with zero iterations.
        """
        mkey = "myMkey"
        salt = "U2FsdGVkX1+1xq+YXk2QWg=="
        iterations = 0
        with self.assertRaises(ValueError):
            decrypt_wallet_dat(mkey, salt, iterations)

    def test_decrypt_wallet_dat_with_negative_iterations(self):
        """
        Tests decryption with negative iterations.
        """
        mkey = "myMkey"
        salt = "U2FsdGVkX1+1xq+YXk2QWg=="
        iterations = -1000
        with self.assertRaises(ValueError):
            decrypt_wallet_dat(mkey, salt, iterations)

# Example usage of decrypt_wallet_dat function

mkey = "ebac7485fa24e231e2f2a9b4cd989d74cf855f694ea9768a421ea1c46d47cf2ca07c8a5003fa6b338dfa12d9d55b229a"
salt = "ad22f110e67113a4"
iterations = 37698

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