/**
 * 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 backtype.storm.security.auth.digest;

import java.io.IOException;
import java.util.HashMap;
import java.util.Map;

import backtype.storm.security.auth.ReqContext;
import backtype.storm.security.auth.SaslTransportPlugin;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import javax.security.auth.Subject;
import javax.security.auth.callback.Callback;
import javax.security.auth.callback.CallbackHandler;
import javax.security.auth.callback.NameCallback;
import javax.security.auth.callback.PasswordCallback;
import javax.security.auth.callback.UnsupportedCallbackException;
import javax.security.auth.login.AppConfigurationEntry;
import javax.security.auth.login.Configuration;
import javax.security.sasl.AuthorizeCallback;
import javax.security.sasl.RealmCallback;

import backtype.storm.security.auth.AuthUtils;

/**
 * SASL server side collback handler
 */
public class ServerCallbackHandler implements CallbackHandler {
    private static final String USER_PREFIX = "user_";
    private static final Logger LOG = LoggerFactory.getLogger(ServerCallbackHandler.class);
    private static final String SYSPROP_SUPER_PASSWORD = "storm.SASLAuthenticationProvider.superPassword";

    private String userName;
    private final Map<String, String> credentials = new HashMap<String, String>();

    public ServerCallbackHandler(Configuration configuration) throws IOException {
        if (configuration == null)
            return;

        AppConfigurationEntry configurationEntries[] = configuration.getAppConfigurationEntry(AuthUtils.LOGIN_CONTEXT_SERVER);
        if (configurationEntries == null) {
            String errorMessage = "Could not find a '" + AuthUtils.LOGIN_CONTEXT_SERVER + "' entry in this configuration: Server cannot start.";
            throw new IOException(errorMessage);
        }
        credentials.clear();
        for (AppConfigurationEntry entry : configurationEntries) {
            Map<String, ?> options = entry.getOptions();
            // Populate DIGEST-MD5 user -> password map with JAAS configuration entries from the "Server" section.
            // Usernames are distinguished from other options by prefixing the username with a "user_" prefix.
            for (Map.Entry<String, ?> pair : options.entrySet()) {
                String key = pair.getKey();
                if (key.startsWith(USER_PREFIX)) {
                    String userName = key.substring(USER_PREFIX.length());
                    credentials.put(userName, (String) pair.getValue());
                }
            }
        }
    }

    public void handle(Callback[] callbacks) throws UnsupportedCallbackException {
        for (Callback callback : callbacks) {
            if (callback instanceof NameCallback) {
                handleNameCallback((NameCallback) callback);
            } else if (callback instanceof PasswordCallback) {
                handlePasswordCallback((PasswordCallback) callback);
            } else if (callback instanceof RealmCallback) {
                handleRealmCallback((RealmCallback) callback);
            } else if (callback instanceof AuthorizeCallback) {
                handleAuthorizeCallback((AuthorizeCallback) callback);
            }
        }
    }

    private void handleNameCallback(NameCallback nc) {
        LOG.debug("handleNameCallback");
        userName = nc.getDefaultName();
        nc.setName(nc.getDefaultName());
    }

    private void handlePasswordCallback(PasswordCallback pc) {
        LOG.debug("handlePasswordCallback");
        if ("super".equals(this.userName) && System.getProperty(SYSPROP_SUPER_PASSWORD) != null) {
            // superuser: use Java system property for password, if available.
            pc.setPassword(System.getProperty(SYSPROP_SUPER_PASSWORD).toCharArray());
        } else if (credentials.containsKey(userName)) {
            pc.setPassword(credentials.get(userName).toCharArray());
        } else {
            LOG.warn("No password found for user: " + userName);
        }
    }

    private void handleRealmCallback(RealmCallback rc) {
        LOG.debug("handleRealmCallback: " + rc.getDefaultText());
        rc.setText(rc.getDefaultText());
    }

    private void handleAuthorizeCallback(AuthorizeCallback ac) {
        String authenticationID = ac.getAuthenticationID();
        LOG.info("Successfully authenticated client: authenticationID = " + authenticationID + " authorizationID = " + ac.getAuthorizationID());

        // if authorizationId is not set, set it to authenticationId.
        if (ac.getAuthorizationID() == null) {
            ac.setAuthorizedID(authenticationID);
        }

        // When authNid and authZid are not equal , authNId is attempting to impersonate authZid, We
        // add the authNid as the real user in reqContext's subject which will be used during authorization.
        if (!authenticationID.equals(ac.getAuthorizationID())) {
            LOG.info("Impersonation attempt  authenticationID = " + ac.getAuthenticationID() + " authorizationID = " + ac.getAuthorizationID());
            ReqContext.context().setRealPrincipal(new SaslTransportPlugin.User(ac.getAuthenticationID()));
        }

        ac.setAuthorized(true);
    }
}