/*
 * #%L
 * Netarchivesuite - monitor
 * %%
 * Copyright (C) 2005 - 2018 The Royal Danish Library, 
 *             the National Library of France and the Austrian National Library.
 * %%
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU Lesser General Public License as
 * published by the Free Software Foundation, either version 2.1 of the
 * License, or (at your option) any later version.
 * 
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Lesser Public License for more details.
 * 
 * You should have received a copy of the GNU General Lesser Public
 * License along with this program.  If not, see
 * <http://www.gnu.org/licenses/lgpl-2.1.html>.
 * #L%
 */

package dk.netarkivet.monitor.jmx;

import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;
import java.util.ArrayList;
import java.util.Date;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Hashtable;
import java.util.List;
import java.util.Map;
import java.util.Set;

import javax.management.MBeanServer;
import javax.management.ObjectName;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import dk.netarkivet.common.distribute.monitorregistry.HostEntry;
import dk.netarkivet.common.exceptions.ArgumentNotValid;
import dk.netarkivet.common.exceptions.IOFailure;
import dk.netarkivet.common.management.SingleMBeanObject;
import dk.netarkivet.common.utils.ExceptionUtils;
import dk.netarkivet.common.utils.Settings;
import dk.netarkivet.common.utils.StringUtils;
import dk.netarkivet.monitor.MonitorSettings;
import dk.netarkivet.monitor.registry.MonitorRegistry;

/**
 * Handles the forwarding of other hosts' MBeans matching a specific regular query and interface to a given mbean
 * server. The interface should be of type T.
 *
 * @param <T> The type of object exposed through the MBeans.
 */
@SuppressWarnings({"unchecked", "rawtypes"})
public class HostForwarding<T> {

    /** The log. */
    public static final Logger log = LoggerFactory.getLogger(HostForwarding.class);

    /** List of all known and established JMX connections for this object. */
    private Map<String, Set<HostEntry>> knownJmxConnections = new HashMap<String, Set<HostEntry>>();

    /** The query to the MBeanserver to get the MBeans. */
    private final String mBeanQuery;
    /** The MBean server we register the forwarded mbeans in. */
    private final MBeanServer mBeanServer;
    /** The interface the remote mbeans should implement. */
    private final Class<T> asInterface;

    /**
     * The username for JMX read from either a System property, the overriding settings given by the installer, or the
     * default value stored in src/dk/netarkivet/monitor/settings.xml.
     */
    private String jmxUsername;

    /**
     * @return the JMX-Username
     */
    private String getJmxUsername() {
        return jmxUsername;
    }

    /**
     * Set the JMX-username with a new value. Null or empty username is not allowed.
     *
     * @param newJmxUsername New value for the JMX-username
     */
    private synchronized void setJmxUsername(String newJmxUsername) {
        ArgumentNotValid.checkNotNullOrEmpty(newJmxUsername, "String newJmxUsername");
        this.jmxUsername = newJmxUsername;
    }

    /**
     * The password for JMX read from either a System property, the overriding settings given by the installer, or the
     * default value stored in src/dk/netarkivet/monitor/settings.xml.
     */
    private String jmxPassword;

    /**
     * @return the JMX-password
     */
    private String getJmxPassword() {
        return jmxPassword;
    }

    /**
     * Set the JMX-password with a new value. Null or empty password is not allowed.
     *
     * @param newJmxPassword New value for the JMX-password
     */
    private synchronized void setJmxPassword(String newJmxPassword) {
        ArgumentNotValid.checkNotNullOrEmpty(newJmxPassword, "String newJmxPassword");
        this.jmxPassword = newJmxPassword;
    }

    /**
     * The instances of host forwardings, to ensure mbeans are only forwarded once.
     */
    private static Map<String, HostForwarding> instances = new HashMap<String, HostForwarding>();

    /** The factory used for producing connections to remote mbean servers. */
    private final JMXProxyConnectionFactory connectionFactory;

    /**
     * Initialise forwarding MBeans. This will connect to all hosts mentioned in settings, and register proxy beans for
     * each bean on remote servers matching the given query. The remote beans should implement the given interface.
     *
     * @param asInterface The interface remote beans should implement.
     * @param mBeanServer The MBean server the proxy beans should be registered in.
     * @param mBeanQuery The query that returns the mbeans that should be proxied.
     */
    private HostForwarding(Class<T> asInterface, MBeanServer mBeanServer, String mBeanQuery) {
        this.mBeanServer = mBeanServer;
        this.asInterface = asInterface;
        this.mBeanQuery = mBeanQuery;
        this.connectionFactory = new CachingProxyConnectionFactory(new RmiProxyConnectionFactory());

        updateJmx();
        log.info("Constructing a HostForwarding object for query {} on Mbeanserver {}", mBeanQuery, mBeanServer);
    }

    /**
     * Get a host forwarding instance. As a side effect of this, all mbeans matching a query from remote hosts, are
     * proxied and registered in the given mbean server. Only one HostForwarding instance will be made for each query
     * string. Any subsequent call with the same query string will simply return the previously initiated instance.
     *
     * @param asInterface The interface remote mbeans should implement.
     * @param mBeanServer The MBean server to register proxy mbeans in.
     * @param query The query for which we should proxy matching mbeans on remote servers.
     * @param <T> The type of HostForwarding to return.
     * @return This host forwarding instance.
     */
    public static synchronized <T> HostForwarding getInstance(Class<T> asInterface, MBeanServer mBeanServer,
            String query) {
        if (instances.get(query) == null) {
            instances.put(query, new HostForwarding<T>(asInterface, mBeanServer, query));
        }
        HostForwarding hf = instances.get(query);
        hf.updateJmx();
        return hf;
    }

    /**
     * Gets the list of hosts and corresponding JMX ports from the monitor registry. For all unknown hosts, it registers
     * proxies to all Mbeans registered on the remote MBeanservers in the given MBeanserver.
     */
    private synchronized void updateJmx() {
        // Update username/password setting, if either of the settings
        // MonitorSettings.JMX_PASSWORD_SETTING,
        // MonitorSettings.JMX_USERNAME_SETTING have changed.

        boolean changed = updateJmxUsernameAndPassword();
        if (changed) {
            log.info(
                    "Settings '{}' and '{}' has been updated with value from a System property or one of the files: {}",
                    MonitorSettings.JMX_USERNAME_SETTING, MonitorSettings.JMX_PASSWORD_SETTING,
                    StringUtils.conjoin(",", Settings.getSettingsFiles()));
        }

        List<HostEntry> newJmxHosts = new ArrayList<HostEntry>();
        for (Map.Entry<String, Set<HostEntry>> entries : getCurrentHostEntries().entrySet()) {
            String host = entries.getKey();
            // Take a copy of the host entries, to avoid concurrent
            // modifications.
            Set<HostEntry> hostEntries = new HashSet<HostEntry>(entries.getValue());
            if (knownJmxConnections.containsKey(host)) {
                Set<HostEntry> registeredJmxPortsOnHost = knownJmxConnections.get(host);
                for (HostEntry he : hostEntries) {
                    if (!registeredJmxPortsOnHost.contains(he)) {
                        log.debug("Adding new jmx host '{}'", he);
                        newJmxHosts.add(he);
                        registeredJmxPortsOnHost.add(he);
                    } else {
                        log.trace("Updating last seen time for jmx host '{}'", he);
                        for (HostEntry existing : registeredJmxPortsOnHost) {
                            if (existing.equals(he)) {
                                existing.setTime(he.getTime());
                            }
                        }
                    }
                }
                knownJmxConnections.put(host, registeredJmxPortsOnHost);
            } else {
                log.debug("Adding new jmx hosts '{}'", hostEntries);
                newJmxHosts.addAll(hostEntries);
                knownJmxConnections.put(host, new HashSet<HostEntry>(hostEntries));
            }
        }
        if (newJmxHosts.size() > 0) {
            log.info("Found {} new JMX hosts", newJmxHosts.size());
            registerRemoteMbeans(newJmxHosts);
        }
    }

    /**
     * Update JMX username and password.
     *
     * @return true if the username and/or the password were changed.
     */
    private synchronized boolean updateJmxUsernameAndPassword() {
        boolean changed = false;

        String newJmxUsername = Settings.get(MonitorSettings.JMX_USERNAME_SETTING);

        String newJmxPassword = Settings.get(MonitorSettings.JMX_PASSWORD_SETTING);

        if (jmxUsername == null || !jmxUsername.equals(newJmxUsername)) {
            setJmxUsername(newJmxUsername);
            changed = true;
        }

        if (jmxPassword == null || !jmxPassword.equals(newJmxPassword)) {
            setJmxPassword(newJmxPassword);
            changed = true;
        }

        return changed;
    }

    /**
     * Get current list of host-JMX port mappings. This lists the mappings from the registry server.
     *
     * @return current list of host-JMX port mappings.
     */
    public static Map<String, Set<HostEntry>> getCurrentHostEntries() {
        return MonitorRegistry.getInstance().getHostEntries();
    }

    /**
     * Register all remote Mbeans on the given MBeanServer. The username, and password are the same for all
     * JMX-connections. For hosts which cannot be connected to, an mbean is registered in the same domain, which tries
     * to reconnect on any invocation, and returns the status of the attempt as a string.
     *
     * @param hosts the list of remote Hosts.
     */
    private void registerRemoteMbeans(List<HostEntry> hosts) {
        for (HostEntry hostEntry : hosts) {
            log.debug("Forwarding mbeans '{}' for host: {}", this.mBeanQuery, hostEntry);
            try {
                createProxyMBeansForHost(hostEntry);
            } catch (Exception e) {
                log.warn("Failure connecting to remote JMX MBeanserver ({}). Creating an error MBean", hostEntry, e);
                try {
                    // This creates a proxy object that calls the handler on any
                    // invocation of any method on the object.
                    NoHostInvocationHandler handler = new NoHostInvocationHandler(hostEntry);
                    Class<T> proxyClass = (Class<T>) Proxy.getProxyClass(asInterface.getClassLoader(),
                            new Class[] {asInterface});
                    T noHostMBean = proxyClass.getConstructor(InvocationHandler.class).newInstance(handler);
                    SingleMBeanObject<T> singleMBeanObject = new SingleMBeanObject<T>(queryToDomain(mBeanQuery),
                            noHostMBean, asInterface, mBeanServer);
                    Hashtable<String, String> names = singleMBeanObject.getNameProperties();
                    names.put("name", "error_host_" + hostEntry.getName() + "_" + hostEntry.getJmxPort());
                    names.put("index", Integer.toString(0));
                    names.put("hostname", hostEntry.getName());
                    handler.setSingleMBeanObject(singleMBeanObject);
                    singleMBeanObject.register();
                } catch (Exception e1) {
                    log.warn("Failure registering error mbean for hostentry: {}", hostEntry, e1);
                }
            }
        }
    }

    /**
     * Connects to the given host, and lists all mbeans matching the query. For each of these mbeans, registers a
     * proxymbean, that on any invocation will connect to the remote host, and return the result of invoking the method
     * on the remote object.
     *
     * @param hostEntry The host to connect to.
     * @throws IOFailure if remote host cannot be connected to.
     */
    private synchronized void createProxyMBeansForHost(HostEntry hostEntry) {
        Set<ObjectName> remoteObjectNames;
        JMXProxyConnection connection = connectionFactory.getConnection(hostEntry.getName(), hostEntry.getJmxPort(),
                hostEntry.getRmiPort(), getJmxUsername(), getJmxPassword());

        remoteObjectNames = connection.query(mBeanQuery);
        for (ObjectName name : remoteObjectNames) {
            try {
                // This creates a proxy object that calls the handler on any
                // invocation of any method on the object.
                ProxyMBeanInvocationHandler handler = new ProxyMBeanInvocationHandler(name, hostEntry);
                Class<T> proxyClass = (Class<T>) Proxy.getProxyClass(asInterface.getClassLoader(),
                        new Class[] {asInterface});
                T mbean = proxyClass.getConstructor(InvocationHandler.class).newInstance(handler);

                SingleMBeanObject<T> singleMBeanObject = new SingleMBeanObject<T>(name, mbean, asInterface, mBeanServer);
                singleMBeanObject.register();
            } catch (Exception e) {
                log.warn("Error registering mbean", e);
            }
        }
    }

    /**
     * Returns the domain from a given query. Used for constructing an error-mbean-name on connection trouble.
     *
     * @param aMBeanQuery The query to return the domain from.
     * @return the domain from a given query.
     */
    private String queryToDomain(String aMBeanQuery) {
        return aMBeanQuery.replaceAll(":.*$", "");
    }

    /**
     * Get the mbean server that proxies to remote mbeans are registered in.
     *
     * @return The mbean server with proxy mbeans.
     */
    public MBeanServer getMBeanServer() {
        return mBeanServer;
    }

    /**
     * An invocation handler for the mbeans registered when a host does not respond. This handler will on any invocation
     * attempt to reconnect, and then return a string with the result. Unsuccessfully connecting, it will unregister the
     * mbean.
     */
    private class NoHostInvocationHandler implements InvocationHandler {
        /** The mbean this invocation handler handles. */
        private SingleMBeanObject singleMBeanObject;
        /** The host we should retry connecting to. */
        private HostEntry hostEntry;

        /**
         * Make a new invocation handler for showing errors and retrying connect.
         *
         * @param hostEntry The host to retry connecting to.
         */
        public NoHostInvocationHandler(HostEntry hostEntry) {
            this.hostEntry = hostEntry;
        }

        /**
         * Remembers the mbean this invocation handler is registered in. Should always be called before actually
         * registering the mbean.
         *
         * @param singleMBeanObject The mbean this object handles.
         */
        public void setSingleMBeanObject(SingleMBeanObject singleMBeanObject) {
            this.singleMBeanObject = singleMBeanObject;
        }

        /**
         * Retries connecting to the host. On success, returns a string with success, and unregisters. On failure,
         * returns a string with failure.
         *
         * @param proxy The error mbean that invoked this, ignored.
         * @param method The method attempted invoked, ignored.
         * @param args The arguments for the method, ignored.
         * @return A string with success or failure.
         * @throws Throwable Shouldn't throw exceptions.
         */
        public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
            try {
                createProxyMBeansForHost(hostEntry);
                singleMBeanObject.unregister();
                return "Now proxying JMX beans for host '" + hostEntry.getName() + ":" + hostEntry.getJmxPort() + "'";
            } catch (Exception e) {
                // Still unable to connect. Oh well.
                return "[" + new Date() + "] Unable to proxy JMX beans on host '" + hostEntry.getName() + ":"
                        + hostEntry.getJmxPort() + "', last seen active at '" + hostEntry.getTime() + "'\n"
                        + ExceptionUtils.getStackTrace(e);
            }
        }
    }

    /** An invocation handler that forwards invocations to a remote mbean. */
    private class ProxyMBeanInvocationHandler implements InvocationHandler {
        /** The name of the remote mbean. */
        private final ObjectName name;
        /** The host for the remote mbean. */
        private final HostEntry hostEntry;

        /**
         * Make a new forwarding mbean handler.
         *
         * @param name The name of the remote mbean.
         * @param hostEntry The host for the remote mbean.
         */
        public ProxyMBeanInvocationHandler(ObjectName name, HostEntry hostEntry) {
            this.name = name;
            this.hostEntry = hostEntry;
        }

        /**
         * Initialises a connection to a remote bean. Then invokes the method on that bean.
         *
         * @param proxy This proxying object. Ignored.
         * @param method The method invoked. This is called on the remote mbean.
         * @param args The arguments to the method. These are given to the remote mbean.
         * @return Whatever the remote mbean returns.
         * @throws IOFailure On trouble establishing the connection.
         * @throws javax.management.RuntimeMBeanException On exceptions in the mbean invocations.
         * @throws Throwable What ever the remote mbean has thrown.
         */
        public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
            // establish or reestablish mbean.
            JMXProxyConnection connection;
            try {
                connection = connectionFactory.getConnection(hostEntry.getName(), hostEntry.getJmxPort(),
                        hostEntry.getRmiPort(), getJmxUsername(), getJmxPassword());
            } catch (Exception e) {
                throw new IOFailure("Could not connect to host '" + hostEntry.getName() + ":" + hostEntry.getJmxPort()
                        + "', last seen active at '" + hostEntry.getTime() + "'\n", e);
            }
            // call remote method.
            T mBean = connection.createProxy(name, asInterface);
            return method.invoke(mBean, args);
        }
    }

}