class WalletProtobufSerializer {

    public Protos.Wallet walletToProto(Wallet wallet) {
        Protos.Wallet.Builder walletBuilder = Protos.Wallet.newBuilder();
        walletBuilder.setNetworkIdentifier(wallet.getNetworkParameters().getId());
        if (wallet.getDescription() != null) {
            walletBuilder.setDescription(wallet.getDescription());
        }

        for (WalletTransaction wtx : wallet.getWalletTransactions()) {
            Protos.Transaction txProto = makeTxProto(wtx);
            walletBuilder.addTransaction(txProto);
        }

        for (ECKey key : wallet.getKeys()) {
            Protos.Key.Builder keyBuilder = Protos.Key.newBuilder().setCreationTimestamp(key.getCreationTimeSeconds() * 1000)
                                                         // .setLabel() TODO
                                                            .setType(Protos.Key.Type.ORIGINAL);
            if (key.getPrivKeyBytes() != null)
                keyBuilder.setPrivateKey(ByteString.copyFrom(key.getPrivKeyBytes()));

            EncryptedPrivateKey encryptedPrivateKey = key.getEncryptedPrivateKey();
            if (encryptedPrivateKey != null) {
                // Key is encrypted.
                Protos.EncryptedPrivateKey.Builder encryptedKeyBuilder = Protos.EncryptedPrivateKey.newBuilder()
                    .setEncryptedPrivateKey(ByteString.copyFrom(encryptedPrivateKey.getEncryptedBytes()))
                    .setInitialisationVector(ByteString.copyFrom(encryptedPrivateKey.getInitialisationVector()));

                if (key.getKeyCrypter() == null) {
                    throw new IllegalStateException("The encrypted key " + key.toString() + " has no KeyCrypter.");
                } else {
                    // If it is a Scrypt + AES encrypted key, set the persisted key type.
                    if (key.getKeyCrypter().getUnderstoodEncryptionType() == Protos.Wallet.EncryptionType.ENCRYPTED_SCRYPT_AES) {
                        keyBuilder.setType(Protos.Key.Type.ENCRYPTED_SCRYPT_AES);
                    } else {
                        throw new IllegalArgumentException("The key " + key.toString() + " is encrypted with a KeyCrypter of type " + key.getKeyCrypter().getUnderstoodEncryptionType() +
                                ". This WalletProtobufSerialiser does not understand that type of encryption.");
                    }
                }
                keyBuilder.setEncryptedPrivateKey(encryptedKeyBuilder);
            }

            // We serialize the public key even if the private key is present for speed reasons: we don't want to do
            // lots of slow EC math to load the wallet, we prefer to store the redundant data instead. It matters more
            // on mobile platforms.
            keyBuilder.setPublicKey(ByteString.copyFrom(key.getPubKey()));
            walletBuilder.addKey(keyBuilder);
        }

        for (Script script : wallet.getWatchedScripts()) {
            Protos.Script protoScript =
                    Protos.Script.newBuilder()
                            .setProgram(ByteString.copyFrom(script.getProgram()))
                            .setCreationTimestamp(script.getCreationTimeSeconds() * 1000)
                            .build();

            walletBuilder.addWatchedScript(protoScript);
        }

        // Populate the lastSeenBlockHash field.
        Sha256Hash lastSeenBlockHash = wallet.getLastBlockSeenHash();
        if (lastSeenBlockHash != null) {
            walletBuilder.setLastSeenBlockHash(hashToByteString(lastSeenBlockHash));
            walletBuilder.setLastSeenBlockHeight(wallet.getLastBlockSeenHeight());
        }
        if (wallet.getLastBlockSeenTimeSecs() > 0)
            walletBuilder.setLastSeenBlockTimeSecs(wallet.getLastBlockSeenTimeSecs());

        // Populate the scrypt parameters.
        KeyCrypter keyCrypter = wallet.getKeyCrypter();
        if (keyCrypter == null) {
            // The wallet is unencrypted.
            walletBuilder.setEncryptionType(EncryptionType.UNENCRYPTED);
        } else {
            // The wallet is encrypted.
            walletBuilder.setEncryptionType(keyCrypter.getUnderstoodEncryptionType());
            if (keyCrypter instanceof KeyCrypterScrypt) {
                KeyCrypterScrypt keyCrypterScrypt = (KeyCrypterScrypt) keyCrypter;
                walletBuilder.setEncryptionParameters(keyCrypterScrypt.getScryptParameters());
            } else {
                // Some other form of encryption has been specified that we do not know how to persist.
                throw new RuntimeException("The wallet has encryption of type '" + keyCrypter.getUnderstoodEncryptionType() + "' but this WalletProtobufSerializer does not know how to persist this.");
            }
        }

        if (wallet.getKeyRotationTime() != null) {
            long timeSecs = wallet.getKeyRotationTime().getTime() / 1000;
            walletBuilder.setKeyRotationTime(timeSecs);
        }

        populateExtensions(wallet, walletBuilder);

        // Populate the wallet version.
        walletBuilder.setVersion(wallet.getVersion());

        return walletBuilder.build();
    }

    public  WalletProtobufSerializer();

}