/*
 * Copyright 2013 Red Hat, Inc.
 *
 * This file is part of Thermostat.
 *
 * Thermostat is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published
 * by the Free Software Foundation; either version 2, or (at your
 * option) any later version.
 *
 * Thermostat 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 Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with Thermostat; see the file COPYING.  If not see
 * <http://www.gnu.org/licenses/>.
 *
 * Linking this code with other modules is making a combined work
 * based on this code.  Thus, the terms and conditions of the GNU
 * General Public License cover the whole combination.
 *
 * As a special exception, the copyright holders of this code give
 * you permission to link this code with independent modules to
 * produce an executable, regardless of the license terms of these
 * independent modules, and to copy and distribute the resulting
 * executable under terms of your choice, provided that you also
 * meet, for each linked independent module, the terms and conditions
 * of the license of that module.  An independent module is a module
 * which is not derived from or based on this code.  If you modify
 * this code, you may extend this exception to your version of the
 * library, but you are not obligated to do so.  If you do not wish
 * to do so, delete this exception statement from your version.
 */

package com.redhat.thermostat.vm.gc.agent.internal;

import java.net.URISyntaxException;
import java.util.HashMap;
import java.util.Map;
import java.util.logging.Level;
import java.util.logging.Logger;

import sun.jvmstat.monitor.HostIdentifier;
import sun.jvmstat.monitor.MonitorException;
import sun.jvmstat.monitor.MonitoredHost;
import sun.jvmstat.monitor.MonitoredVm;
import sun.jvmstat.monitor.VmIdentifier;
import sun.jvmstat.monitor.event.VmListener;

import com.redhat.thermostat.agent.VmStatusListener;
import com.redhat.thermostat.agent.VmStatusListenerRegistrar;
import com.redhat.thermostat.backend.Backend;
import com.redhat.thermostat.backend.BackendID;
import com.redhat.thermostat.backend.BackendsProperties;
import com.redhat.thermostat.common.Version;
import com.redhat.thermostat.common.utils.LoggingUtils;
import com.redhat.thermostat.vm.gc.common.VmGcStatDAO;

public class VmGcBackend extends Backend implements VmStatusListener {

    private static final Logger LOGGER = LoggingUtils.getLogger(VmGcBackend.class);

    private final VmGcStatDAO vmGcStats;
    private final VmStatusListenerRegistrar registerer;

    private final Map<Integer, VmAndListener> registeredListeners = new HashMap<>();
    private MonitoredHost host;
    private boolean started;

    public VmGcBackend(VmGcStatDAO vmGcStatDAO, Version version, VmStatusListenerRegistrar registerer) {
        super(new BackendID("VM GC Backend", VmGcBackend.class.getName()));
        this.vmGcStats = vmGcStatDAO;
        this.registerer = registerer;
        
        setConfigurationValue(BackendsProperties.VENDOR.name(), "Red Hat, Inc.");
        setConfigurationValue(BackendsProperties.DESCRIPTION.name(), "Gathers garbage collection statistics about a JVM");
        setConfigurationValue(BackendsProperties.VERSION.name(), version.getVersionNumber());
        
        try {
            HostIdentifier hostId = new HostIdentifier((String) null);
            host = MonitoredHost.getMonitoredHost(hostId);
        } catch (MonitorException me) {
            LOGGER.log(Level.WARNING, "Problems with connecting jvmstat to local machine", me);
        } catch (URISyntaxException use) {
            LOGGER.log(Level.WARNING, "Failed to create host identifier", use);
        }
    }

    // Methods from Backend

    @Override
    public boolean activate() {
        if (!started) {
            registerer.register(this);
            started = true;
        }
        return started;
    }

    @Override
    public boolean deactivate() {
        if (started) {
            registerer.unregister(this);
            started = false;
        }
        return !started;
    }
    
    @Override
    public boolean isActive() {
        return started;
    }

    @Override
    public String getConfigurationValue(String key) {
        return null;
    }

    @Override
    public boolean attachToNewProcessByDefault() {
        return true;
    }

    @Override
    public int getOrderValue() {
        return ORDER_MEMORY_GROUP + 20;
    }

    // Methods from VmStatusListener

    @Override
    public void vmStatusChanged(Status newStatus, int pid) {
        switch (newStatus) {
        case VM_STARTED:
            /* fall-through */
        case VM_ACTIVE:
            vmStarted(pid);
            break;
        case VM_STOPPED:
            vmStopped(pid);
            break;
        }
    }

    private void vmStarted(int pid) {
        if (attachToNewProcessByDefault()) {
            try {
                MonitoredVm vm = host.getMonitoredVm(host.getHostIdentifier().resolve(new VmIdentifier(String.valueOf(pid))));
                if (vm != null) {
                    VmGcVmListener listener = new VmGcVmListener(vmGcStats, pid);
                    vm.addVmListener(listener);
                    registeredListeners.put(pid, new VmAndListener(vm, listener));
                    LOGGER.finer("Attached VmListener for VM: " + pid);
                } else {
                    LOGGER.warning("could not connect to vm " + pid);
                }
            } catch (MonitorException me) {
                LOGGER.log(Level.WARNING, "could not connect to vm " + pid, me);
            } catch (URISyntaxException e) {
                throw new AssertionError("The URI for the monitored vm must be valid, but it is not.");
            }
        }
    }

    private void vmStopped(int pid) {
        VmAndListener tuple = registeredListeners.remove(pid);
        if (tuple == null) {
            LOGGER.warning("received vm stopped for an unknown VM");
            return;
        }

        MonitoredVm vm = tuple.vm;
        VmListener listener = tuple.listener;
        try {
            if (listener != null) {
                vm.removeVmListener(listener);
            }
        } catch (MonitorException e) {
            LOGGER.log(Level.WARNING, "can't remove vm listener", e);
        }
        vm.detach();
    }

    /*
     * For testing purposes only.
     */
    void setHost(MonitoredHost host) {
        this.host = host;
    }

    private static class VmAndListener {
        private MonitoredVm vm;
        private VmListener listener;

        public VmAndListener(MonitoredVm vm, VmListener listener) {
            this.vm = vm;
            this.listener = listener;
        }

    }
}