Calculate the entropy of a passphrase that would be generated.

def generated_passphrase_entropy(self) -> float:
        """Calculate the entropy of a passphrase that would be generated."""
        if (
                self.amount_w is None
                or self.amount_n is None
                or not self.wordlist
        ):
            raise ValueError("Can't calculate the passphrase entropy: "
                             "wordlist is empty or amount_n or "
                             "amount_w isn't set")

        if self.amount_n == 0 and self.amount_w == 0:
            return 0.0

        entropy_n = self.entropy_bits((self.randnum_min, self.randnum_max))

        # The entropy for EFF Large Wordlist is ~12.9, no need to calculate
        entropy_w = self._wordlist_entropy_bits \
            if self._wordlist_entropy_bits \
            else self.entropy_bits(self.wordlist)

        return calc_passphrase_entropy(
            self.amount_w,
            entropy_w,
            entropy_n,
            self.amount_n
        )