contract Foo is IEntropyConsumer {
    // Entropy Address on Optimism
    IEntropy private entropy = IEntropy(0xdF21D137Aadc95588205586636710ca2890538d5);
    address private entropyProvider = 0x52DeaA1c84233F7bb8C8A45baeDE41091c616506;

    function requestRandomNumber(bytes32 userRandomNumber) external payable {
        uint256 fee = entropy.getFee(entropyProvider);

        uint64 sequenceNumber = entropy.requestWithCallback{value: fee}(
            entropyProvider,
            userRandomNumber
        );
    }

    function entropyCallback(
        uint64 sequenceNumber,
        address,
        bytes32 entropyRandomNumber
    ) internal override {
        // Consume entropyRandomNumber as needed
    }
}