/**
 * 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.kafka.common.security.kerberos;

import javax.security.auth.kerberos.KerberosPrincipal;
import javax.security.auth.login.AppConfigurationEntry;
import javax.security.auth.login.Configuration;
import javax.security.auth.login.LoginContext;
import javax.security.auth.login.LoginException;
import javax.security.auth.callback.CallbackHandler;
import javax.security.auth.kerberos.KerberosTicket;
import javax.security.auth.Subject;

import org.apache.kafka.common.security.authenticator.SaslClientAuthenticator.ClientCallbackHandler;
import org.apache.kafka.common.security.JaasUtils;
import org.apache.kafka.common.config.SaslConfigs;
import org.apache.kafka.common.utils.Shell;
import org.apache.kafka.common.utils.Time;
import org.apache.kafka.common.utils.SystemTime;

import org.apache.kafka.common.utils.Utils;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import java.util.Date;
import java.util.Random;
import java.util.Set;
import java.util.Map;

/**
 * This class is responsible for refreshing Kerberos credentials for
 * logins for both Kafka client and server.
 */
public class Login {
    private static final Logger log = LoggerFactory.getLogger(Login.class);

    private static final Random RNG = new Random();

    private final Thread t;
    private final boolean isKrbTicket;
    private final boolean isUsingTicketCache;

    private final String loginContextName;
    private final String principal;
    private final Time time = new SystemTime();
    private final CallbackHandler callbackHandler = new ClientCallbackHandler();

    // LoginThread will sleep until 80% of time from last refresh to
    // ticket's expiry has been reached, at which time it will wake
    // and try to renew the ticket.
    private final double ticketRenewWindowFactor;

    /**
     * Percentage of random jitter added to the renewal time
     */
    private final double ticketRenewJitter;

    // Regardless of ticketRenewWindowFactor setting above and the ticket expiry time,
    // thread will not sleep between refresh attempts any less than 1 minute (60*1000 milliseconds = 1 minute).
    // Change the '1' to e.g. 5, to change this to 5 minutes.
    private final long minTimeBeforeRelogin;

    private final String kinitCmd;

    private volatile Subject subject;

    private LoginContext login;
    private long lastLogin;

    /**
     * Login constructor. The constructor starts the thread used
     * to periodically re-login to the Kerberos Ticket Granting Server.
     * @param loginContextName
     *               name of section in JAAS file that will be use to login.
     *               Passed as first param to javax.security.auth.login.LoginContext().
     * @param configs configure Login with the given key-value pairs.
     * @throws javax.security.auth.login.LoginException
     *               Thrown if authentication fails.
     */
    public Login(final String loginContextName, Map<String, ?> configs) throws LoginException {
        this.loginContextName = loginContextName;
        this.ticketRenewWindowFactor = (Double) configs.get(SaslConfigs.SASL_KERBEROS_TICKET_RENEW_WINDOW_FACTOR);
        this.ticketRenewJitter = (Double) configs.get(SaslConfigs.SASL_KERBEROS_TICKET_RENEW_JITTER);
        this.minTimeBeforeRelogin = (Long) configs.get(SaslConfigs.SASL_KERBEROS_MIN_TIME_BEFORE_RELOGIN);
        this.kinitCmd = (String) configs.get(SaslConfigs.SASL_KERBEROS_KINIT_CMD);

        this.lastLogin = currentElapsedTime();
        login = login(loginContextName);
        subject = login.getSubject();
        isKrbTicket = !subject.getPrivateCredentials(KerberosTicket.class).isEmpty();

        AppConfigurationEntry[] entries = Configuration.getConfiguration().getAppConfigurationEntry(loginContextName);
        if (entries.length == 0) {
            isUsingTicketCache = false;
            principal = null;
        } else {
            // there will only be a single entry
            AppConfigurationEntry entry = entries[0];
            if (entry.getOptions().get("useTicketCache") != null) {
                String val = (String) entry.getOptions().get("useTicketCache");
                isUsingTicketCache = val.equals("true");
            } else
                isUsingTicketCache = false;
            if (entry.getOptions().get("principal") != null)
                principal = (String) entry.getOptions().get("principal");
            else
                principal = null;
        }

        if (!isKrbTicket) {
            log.debug("It is not a Kerberos ticket");
            t = null;
            // if no TGT, do not bother with ticket management.
            return;
        }
        log.debug("It is a Kerberos ticket");

        // Refresh the Ticket Granting Ticket (TGT) periodically. How often to refresh is determined by the
        // TGT's existing expiry date and the configured minTimeBeforeRelogin. For testing and development,
        // you can decrease the interval of expiration of tickets (for example, to 3 minutes) by running:
        //  "modprinc -maxlife 3mins <principal>" in kadmin.
        t = Utils.newThread("kafka-kerberos-refresh-thread", new Runnable() {
            public void run() {
                log.info("TGT refresh thread started.");
                while (true) {  // renewal thread's main loop. if it exits from here, thread will exit.
                    KerberosTicket tgt = getTGT();
                    long now = currentWallTime();
                    long nextRefresh;
                    Date nextRefreshDate;
                    if (tgt == null) {
                        nextRefresh = now + minTimeBeforeRelogin;
                        nextRefreshDate = new Date(nextRefresh);
                        log.warn("No TGT found: will try again at {}", nextRefreshDate);
                    } else {
                        nextRefresh = getRefreshTime(tgt);
                        long expiry = tgt.getEndTime().getTime();
                        Date expiryDate = new Date(expiry);
                        if (isUsingTicketCache && tgt.getRenewTill() != null && tgt.getRenewTill().getTime() < expiry) {
                            log.error("The TGT cannot be renewed beyond the next expiry date: {}." +
                                    "This process will not be able to authenticate new SASL connections after that " +
                                    "time (for example, it will not be able to authenticate a new connection with a Kafka " +
                                    "Broker).  Ask your system administrator to either increase the " +
                                    "'renew until' time by doing : 'modprinc -maxrenewlife {} ' within " +
                                    "kadmin, or instead, to generate a keytab for {}. Because the TGT's " +
                                    "expiry cannot be further extended by refreshing, exiting refresh thread now.",
                                    expiryDate, principal, principal);
                            return;
                        }
                        // determine how long to sleep from looking at ticket's expiry.
                        // We should not allow the ticket to expire, but we should take into consideration
                        // minTimeBeforeRelogin. Will not sleep less than minTimeBeforeRelogin, unless doing so
                        // would cause ticket expiration.
                        if ((nextRefresh > expiry) || (now + minTimeBeforeRelogin > expiry)) {
                            // expiry is before next scheduled refresh).
                            log.info("Refreshing now because expiry is before next scheduled refresh time.");
                            nextRefresh = now;
                        } else {
                            if (nextRefresh < (now + minTimeBeforeRelogin)) {
                                // next scheduled refresh is sooner than (now + MIN_TIME_BEFORE_LOGIN).
                                Date until = new Date(nextRefresh);
                                Date newUntil = new Date(now + minTimeBeforeRelogin);
                                log.warn("TGT refresh thread time adjusted from {} to {} since the former is sooner " +
                                        "than the minimum refresh interval ({} seconds) from now.",
                                        until, newUntil, minTimeBeforeRelogin / 1000);
                            }
                            nextRefresh = Math.max(nextRefresh, now + minTimeBeforeRelogin);
                        }
                        nextRefreshDate = new Date(nextRefresh);
                        if (nextRefresh > expiry) {
                            log.error("Next refresh: {} is later than expiry {}. This may indicate a clock skew problem." +
                                    "Check that this host and the KDC hosts' clocks are in sync. Exiting refresh thread.",
                                    nextRefreshDate, expiryDate);
                            return;
                        }
                    }
                    if (now < nextRefresh) {
                        Date until = new Date(nextRefresh);
                        log.info("TGT refresh sleeping until: {}", until);
                        try {
                            Thread.sleep(nextRefresh - now);
                        } catch (InterruptedException ie) {
                            log.warn("TGT renewal thread has been interrupted and will exit.");
                            return;
                        }
                    } else {
                        log.error("NextRefresh: {} is in the past: exiting refresh thread. Check"
                                + " clock sync between this host and KDC - (KDC's clock is likely ahead of this host)."
                                + " Manual intervention will be required for this client to successfully authenticate."
                                + " Exiting refresh thread.", nextRefreshDate);
                        return;
                    }
                    if (isUsingTicketCache) {
                        String kinitArgs = "-R";
                        int retry = 1;
                        while (retry >= 0) {
                            try {
                                log.debug("Running ticket cache refresh command: {} {}", kinitCmd, kinitArgs);
                                Shell.execCommand(kinitCmd, kinitArgs);
                                break;
                            } catch (Exception e) {
                                if (retry > 0) {
                                    --retry;
                                    // sleep for 10 seconds
                                    try {
                                        Thread.sleep(10 * 1000);
                                    } catch (InterruptedException ie) {
                                        log.error("Interrupted while renewing TGT, exiting Login thread");
                                        return;
                                    }
                                } else {
                                    log.warn("Could not renew TGT due to problem running shell command: '" + kinitCmd
                                            + " " + kinitArgs + "'" + "; exception was: " + e + ". Exiting refresh thread.", e);
                                    return;
                                }
                            }
                        }
                    }
                    try {
                        int retry = 1;
                        while (retry >= 0) {
                            try {
                                reLogin();
                                break;
                            } catch (LoginException le) {
                                if (retry > 0) {
                                    --retry;
                                    // sleep for 10 seconds.
                                    try {
                                        Thread.sleep(10 * 1000);
                                    } catch (InterruptedException e) {
                                        log.error("Interrupted during login retry after LoginException:", le);
                                        throw le;
                                    }
                                } else {
                                    log.error("Could not refresh TGT for principal: " + principal + ".", le);
                                }
                            }
                        }
                    } catch (LoginException le) {
                        log.error("Failed to refresh TGT: refresh thread exiting now.", le);
                        return;
                    }
                }
            }
        }, true);
    }

    public void startThreadIfNeeded() {
        // thread object 't' will be null if a refresh thread is not needed.
        if (t != null) {
            t.start();
        }
    }

    public void shutdown() {
        if ((t != null) && (t.isAlive())) {
            t.interrupt();
            try {
                t.join();
            } catch (InterruptedException e) {
                log.warn("Error while waiting for Login thread to shutdown: " + e, e);
            }
        }
    }

    public Subject subject() {
        return subject;
    }

    private synchronized LoginContext login(final String loginContextName) throws LoginException {
        String jaasConfigFile = System.getProperty(JaasUtils.JAVA_LOGIN_CONFIG_PARAM);
        if (jaasConfigFile == null) {
            log.debug("System property '" + JaasUtils.JAVA_LOGIN_CONFIG_PARAM + "' is not set, using default JAAS configuration.");
        }
        AppConfigurationEntry[] configEntries = Configuration.getConfiguration().getAppConfigurationEntry(loginContextName);
        if (configEntries == null) {
            String errorMessage = "Could not find a '" + loginContextName + "' entry in the JAAS configuration. System property '" +
                JaasUtils.JAVA_LOGIN_CONFIG_PARAM + "' is " + (jaasConfigFile == null ? "not set" : jaasConfigFile);
            throw new IllegalArgumentException(errorMessage);
        }

        LoginContext loginContext = new LoginContext(loginContextName, callbackHandler);
        loginContext.login();
        log.info("Successfully logged in.");
        return loginContext;
    }

    private long getRefreshTime(KerberosTicket tgt) {
        long start = tgt.getStartTime().getTime();
        long expires = tgt.getEndTime().getTime();
        log.info("TGT valid starting at: {}", tgt.getStartTime());
        log.info("TGT expires: {}", tgt.getEndTime());
        long proposedRefresh = start + (long) ((expires - start) *
                (ticketRenewWindowFactor + (ticketRenewJitter * RNG.nextDouble())));

        if (proposedRefresh > expires)
            // proposedRefresh is too far in the future: it's after ticket expires: simply return now.
            return currentWallTime();
        else
            return proposedRefresh;
    }

    private synchronized KerberosTicket getTGT() {
        Set<KerberosTicket> tickets = subject.getPrivateCredentials(KerberosTicket.class);
        for (KerberosTicket ticket : tickets) {
            KerberosPrincipal server = ticket.getServer();
            if (server.getName().equals("krbtgt/" + server.getRealm() + "@" + server.getRealm())) {
                log.debug("Found TGT {}.", ticket);
                return ticket;
            }
        }
        return null;
    }

    private boolean hasSufficientTimeElapsed() {
        long now = currentElapsedTime();
        if (now - lastLogin < minTimeBeforeRelogin) {
            log.warn("Not attempting to re-login since the last re-login was attempted less than {} seconds before.",
                    minTimeBeforeRelogin / 1000);
            return false;
        }
        return true;
    }

    /**
     * Re-login a principal. This method assumes that {@link #login(String)} has happened already.
     * @throws javax.security.auth.login.LoginException on a failure
     */
    private synchronized void reLogin() throws LoginException {
        if (!isKrbTicket) {
            return;
        }
        if (login == null) {
            throw new LoginException("Login must be done first");
        }
        if (!hasSufficientTimeElapsed()) {
            return;
        }
        log.info("Initiating logout for {}", principal);
        synchronized (Login.class) {
            // register most recent relogin attempt
            lastLogin = currentElapsedTime();
            //clear up the kerberos state. But the tokens are not cleared! As per
            //the Java kerberos login module code, only the kerberos credentials
            //are cleared
            login.logout();
            //login and also update the subject field of this instance to
            //have the new credentials (pass it to the LoginContext constructor)
            login = new LoginContext(loginContextName, subject);
            log.info("Initiating re-login for {}", principal);
            login.login();
        }
    }

    private long currentElapsedTime() {
        return time.nanoseconds() / 1000000;
    }

    private long currentWallTime() {
        return time.milliseconds();
    }

}