/**
 * 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.storm.messaging.netty;

import java.io.IOException;
import java.security.Principal;
import java.security.PrivilegedActionException;
import java.security.PrivilegedExceptionAction;
import java.util.Map;
import java.util.TreeMap;
import javax.security.auth.Subject;
import javax.security.auth.callback.Callback;
import javax.security.auth.callback.CallbackHandler;
import javax.security.auth.callback.UnsupportedCallbackException;
import javax.security.auth.kerberos.KerberosTicket;
import javax.security.auth.login.Configuration;
import javax.security.auth.login.LoginException;
import javax.security.sasl.Sasl;
import javax.security.sasl.SaslClient;
import javax.security.sasl.SaslException;
import org.apache.storm.security.auth.ClientAuthUtils;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
 * Implements SASL logic for storm worker client processes.
 */
public class KerberosSaslNettyClient {

    private static final Logger LOG = LoggerFactory
        .getLogger(KerberosSaslNettyClient.class);

    /**
     * Used to respond to server's counterpart, SaslServer with SASL tokens represented as byte arrays.
     */
    private SaslClient saslClient;
    private Subject subject;
    private String jaasSection;

    /**
     * Create a KerberosSaslNettyClient for authentication with servers.
     */
    public KerberosSaslNettyClient(Map<String, Object> topoConf, String jaasSection, String host) {
        LOG.debug("KerberosSaslNettyClient: Creating SASL {} client to authenticate to server ",
                  SaslUtils.KERBEROS);

        LOG.info("Creating Kerberos Client.");

        Configuration loginConf;
        try {
            loginConf = ClientAuthUtils.getConfiguration(topoConf);
        } catch (Throwable t) {
            LOG.error("Failed to get loginConf: ", t);
            throw t;
        }
        LOG.debug("KerberosSaslNettyClient: authmethod {}", SaslUtils.KERBEROS);

        SaslClientCallbackHandler ch = new SaslClientCallbackHandler();

        subject = null;
        try {
            LOG.debug("Setting Configuration to login_config: {}", loginConf);
            //specify a configuration object to be used
            Configuration.setConfiguration(loginConf);
            //now login
            LOG.debug("Trying to login.");
            Login login = new Login(jaasSection, ch);
            subject = login.getSubject();
            LOG.debug("Got Subject: {}", subject.toString());
        } catch (LoginException ex) {
            LOG.error("Client failed to login in principal:" + ex, ex);
            throw new RuntimeException(ex);
        }

        //check the credential of our principal
        if (subject.getPrivateCredentials(KerberosTicket.class).isEmpty()) {
            LOG.error("Failed to verify user principal.");
            throw new RuntimeException("Fail to verify user principal with section \""
                    + jaasSection
                    + "\" in login configuration file "
                    + loginConf);
        }

        String serviceName = null;
        try {
            serviceName = ClientAuthUtils.get(loginConf, jaasSection, "serviceName");
        } catch (IOException e) {
            LOG.error("Failed to get service name.", e);
            throw new RuntimeException(e);
        }

        try {
            Principal principal = (Principal) subject.getPrincipals().toArray()[0];
            final String fPrincipalName = principal.getName();
            final String fHost = host;
            final String fServiceName = serviceName;
            final CallbackHandler fch = ch;
            LOG.debug("Kerberos Client with principal: {}, host: {}", fPrincipalName, fHost);
            saslClient = Subject.doAs(subject, new PrivilegedExceptionAction<SaslClient>() {
                @Override
                public SaslClient run() {
                    try {
                        Map<String, String> props = new TreeMap<String, String>();
                        props.put(Sasl.QOP, "auth");
                        props.put(Sasl.SERVER_AUTH, "false");
                        return Sasl.createSaslClient(
                            new String[]{ SaslUtils.KERBEROS },
                            fPrincipalName,
                            fServiceName,
                            fHost,
                            props, fch);
                    } catch (Exception e) {
                        LOG.error("Subject failed to create sasl client.", e);
                        return null;
                    }
                }
            });
            LOG.info("Got Client: {}", saslClient);

        } catch (PrivilegedActionException e) {
            LOG.error("KerberosSaslNettyClient: Could not create Sasl Netty Client.");
            throw new RuntimeException(e);
        }
    }

    public boolean isComplete() {
        return saslClient.isComplete();
    }

    /**
     * Respond to server's SASL token.
     *
     * @param saslTokenMessage contains server's SASL token
     * @return client's response SASL token
     */
    public byte[] saslResponse(SaslMessageToken saslTokenMessage) {
        try {
            final SaslMessageToken fSaslTokenMessage = saslTokenMessage;
            byte[] retval = Subject.doAs(subject, new PrivilegedExceptionAction<byte[]>() {
                @Override
                public byte[] run() {
                    try {
                        byte[] retval = saslClient.evaluateChallenge(fSaslTokenMessage
                                                                         .getSaslToken());
                        return retval;
                    } catch (SaslException e) {
                        LOG.error("saslResponse: Failed to respond to SASL server's token:",
                                  e);
                        throw new RuntimeException(e);
                    }
                }
            });
            return retval;
        } catch (PrivilegedActionException e) {
            LOG.error("Failed to generate response for token: ", e);
            throw new RuntimeException(e);
        }
    }

    /**
     * Implementation of javax.security.auth.callback.CallbackHandler that works with Storm topology tokens.
     */
    private static class SaslClientCallbackHandler implements CallbackHandler {

        /**
         * Implementation used to respond to SASL tokens from server.
         *
         * @param callbacks objects that indicate what credential information the server's SaslServer requires from the client.
         */
        @Override
        public void handle(Callback[] callbacks) throws UnsupportedCallbackException {
            for (Callback callback : callbacks) {
                LOG.info("Kerberos Client Callback Handler got callback: {}", callback.getClass());
            }
        }
    }

}