/**
 * 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.pulsar.broker.authentication;

import java.io.IOException;
import java.security.Principal;
import java.security.PrivilegedActionException;
import java.security.PrivilegedExceptionAction;
import java.util.regex.Pattern;

import javax.naming.AuthenticationException;
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.login.LoginException;
import javax.security.sasl.AuthorizeCallback;
import javax.security.sasl.Sasl;
import javax.security.sasl.SaslException;
import javax.security.sasl.SaslServer;

import lombok.extern.slf4j.Slf4j;
import org.apache.pulsar.common.api.AuthData;
import org.apache.pulsar.common.sasl.KerberosName;
import org.apache.pulsar.common.sasl.SaslConstants;


/**
 * Server side Sasl implementation.
 */
@Slf4j
public class PulsarSaslServer {

    private final SaslServer saslServer;
    private final Pattern allowedIdsPattern;
    private final Subject serverSubject;
    private static final String GSSAPI = "GSSAPI";

    public PulsarSaslServer(Subject subject, Pattern allowedIdsPattern)
        throws IOException, LoginException {
        this.serverSubject = subject;
        this.allowedIdsPattern = allowedIdsPattern;
        saslServer = createSaslServer(serverSubject);
    }

    private SaslServer createSaslServer(final Subject subject)
        throws IOException {
        SaslServerCallbackHandler callbackHandler = new SaslServerCallbackHandler(allowedIdsPattern);
        if (subject.getPrincipals().size() > 0) {
            try {
                final Object[] principals = subject.getPrincipals().toArray();
                final Principal servicePrincipal = (Principal) principals[0];
                if (log.isDebugEnabled()) {
                    log.debug("Authentication will use SASL/JAAS/Kerberos, servicePrincipal is {}", servicePrincipal);
                }

                // e.g. servicePrincipalNameAndHostname := "broker/myhost.foo.com@EXAMPLE.COM"
                final String servicePrincipalNameAndHostname = servicePrincipal.getName();
                int indexOf = servicePrincipalNameAndHostname.indexOf("/");

                // e.g. serviceHostnameAndKerbDomain := "myhost.foo.com@EXAMPLE.COM"
                final String serviceHostnameAndKerbDomain = servicePrincipalNameAndHostname.substring(indexOf + 1
                );
                int indexOfAt = serviceHostnameAndKerbDomain.indexOf("@");

                // Handle Kerberos Service as well as User Principal Names
                final String servicePrincipalName, serviceHostname;
                if (indexOf > 0) {
                    // e.g. servicePrincipalName := "pulsar"
                    servicePrincipalName = servicePrincipalNameAndHostname.substring(0, indexOf);
                    // e.g. serviceHostname := "myhost.foo.com"
                    serviceHostname = serviceHostnameAndKerbDomain.substring(0, indexOfAt);
                } else {
                    servicePrincipalName = servicePrincipalNameAndHostname.substring(0, indexOfAt);
                    serviceHostname = null;
                }

                if (log.isDebugEnabled()) {
                    log.debug("serviceHostname is '{}', servicePrincipalName is '{}', SASL mechanism(mech) is '{}'.",
                        serviceHostname, servicePrincipalName, GSSAPI);
                }

                try {
                    return Subject.doAs(subject, new PrivilegedExceptionAction<SaslServer>() {
                            @Override
                            public SaslServer run() {
                                try {
                                    SaslServer saslServer;
                                    saslServer = Sasl.createSaslServer(GSSAPI, servicePrincipalName, serviceHostname,
                                        null, callbackHandler);
                                    return saslServer;
                                } catch (SaslException e) {
                                    throw new RuntimeException(e);
                                }
                            }
                        }
                    );
                } catch (PrivilegedActionException e) {
                    throw new SaslException("error on GSSAPI boot", e.getCause());
                }
            } catch (IndexOutOfBoundsException e) {
                throw new SaslException("error on GSSAPI boot", e);
            }
        } else {
            String errorMessage = "Authentication use SASL/JAAS/GSSAPI but server not have Principals";
            log.error(errorMessage);
            throw new SaslException(errorMessage);
        }
    }

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

    /**
     * Reports the authorization ID in effect for the client of this
     * session.
     * This method can only be called if isComplete() returns true.
     * @return The authorization ID of the client.
     * @exception IllegalStateException if this authentication session has not completed
     */
    public String getAuthorizationID() throws IllegalStateException {
        return saslServer.getAuthorizationID();
    }

    public AuthData response(AuthData token) throws AuthenticationException {
        try {
            return AuthData.of(saslServer.evaluateResponse(token.getBytes()));
        } catch (SaslException e) {
            log.error("response: Failed to evaluate client token:", e);
            throw new AuthenticationException(e.getMessage());
        }
    }

    static class SaslServerCallbackHandler implements CallbackHandler {
        Pattern allowedIdsPattern;

        public SaslServerCallbackHandler(Pattern pattern) {
            this.allowedIdsPattern = pattern;
        }

        @Override
        public void handle(Callback[] callbacks) throws UnsupportedCallbackException {
            for (Callback callback : callbacks) {
                if (callback instanceof AuthorizeCallback) {
                    handleAuthorizeCallback((AuthorizeCallback) callback);
                } else {
                    throw new UnsupportedCallbackException(callback, "Unrecognized SASL GSSAPI Server Callback.");
                }
            }
        }

        private void handleAuthorizeCallback(AuthorizeCallback ac) {
            String authenticationID = ac.getAuthenticationID();
            String authorizationID = ac.getAuthorizationID();
            if (!authenticationID.equals(authorizationID)) {
                ac.setAuthorized(false);
                log.info("Forbidden access to client: authenticationID: {} is different from authorizationID: {}",
                    authenticationID, authorizationID);
                return;
            }
            if (!allowedIdsPattern.matcher(authenticationID).matches()) {
                ac.setAuthorized(false);
                log.info("Forbidden access to client: authenticationID {}, is not allowed (see {} property).",
                    authenticationID, SaslConstants.JAAS_CLIENT_ALLOWED_IDS);
                return;
            }

            ac.setAuthorized(true);
            log.info("Successfully authenticated client: authenticationID: {};  authorizationID: {}.",
                authenticationID, authorizationID);
        }
    }
}
