/**
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.apache.camel.component.crypto.processor;

import java.security.PublicKey;
import java.security.Signature;
import java.security.SignatureException;
import java.security.cert.Certificate;

import org.apache.camel.Exchange;
import org.apache.camel.component.crypto.DigitalSignatureConfiguration;
import org.apache.camel.util.ExchangeHelper;
import org.apache.commons.codec.binary.Base64;

import static org.apache.camel.component.crypto.DigitalSignatureConstants.SIGNATURE_PUBLIC_KEY_OR_CERT;

/**
 * <code>VerifyingProcessor</code>
 */
public class VerifyingProcessor extends DigitalSignatureProcessor {

    public VerifyingProcessor(DigitalSignatureConfiguration configuration) {
        super(configuration);
    }

    public void process(Exchange exchange) throws Exception {
        Signature signer = createSignatureService();
        Certificate cert = getCertificate(exchange);
        if (cert == null) {
            PublicKey pk = getPublicKeyOrCertificateFromHeader(exchange, PublicKey.class, config.getPublicKey());
            if (pk == null) {
                throw new IllegalStateException(String.format("Cannot verify signature as no Public Key or Certificate has been supplied."
                        + " Either supply one in the route definition or via the message header '%s'", SIGNATURE_PUBLIC_KEY_OR_CERT));
            }
            signer.initVerify(pk);
        } else {
            signer.initVerify(cert);
        }

        calculateSignature(exchange, signer);

        byte[] signature = getSignatureFromExchange(exchange);
        if (!signer.verify(signature)) {
            throw new SignatureException("Cannot verify signature of exchange");
        }
        clearMessageHeaders(exchange.getIn());
    }

    private byte[] getSignatureFromExchange(Exchange exchange) throws Exception {
        String encodedSignature = ExchangeHelper.getMandatoryHeader(exchange, config.getSignatureHeader(), String.class);
        if (encodedSignature == null) {
            throw new IllegalStateException("Cannot verify exchange as no " + config.getSignatureHeader() + " header is present.");
        }
        return new Base64().decode(encodedSignature);
    }

    private Certificate getCertificate(Exchange exchange) throws Exception {
        Certificate cert = config.getCertificate(getAlias(exchange));
        return getPublicKeyOrCertificateFromHeader(exchange, Certificate.class, cert);
    }

    private <T> T getPublicKeyOrCertificateFromHeader(Exchange exchange, Class<? extends T> verificationType, T defaultsTo) {
        T pkOrCert = exchange.getIn().getHeader(SIGNATURE_PUBLIC_KEY_OR_CERT, verificationType);
        if (pkOrCert == null) {
            pkOrCert = defaultsTo;
        }
        return pkOrCert;
    }

}
