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Contains the core Hudson code and view files to render HTML.
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/*******************************************************************************
 *
 * Copyright (c) 2004-2009 Oracle Corporation.
 *
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License v1.0
 * which accompanies this distribution, and is available at
 * http://www.eclipse.org/legal/epl-v10.html
 *
 * Contributors:
 * 
*    Kohsuke Kawaguchi
 *
 *
 *******************************************************************************/ 

package hudson.model;

import hudson.ExtensionPoint;
import hudson.ExtensionList;
import hudson.Extension;
import hudson.ExtensionPoint.LegacyInstancesAreScopedToHudson;
import hudson.triggers.SCMTrigger;
import hudson.triggers.TimerTrigger;

import java.util.Set;
import java.io.IOException;

import org.kohsuke.stapler.StaplerRequest;
import org.kohsuke.stapler.StaplerResponse;

/**
 * Checks the health of a subsystem of Hudson and if there's something that
 * requires administrator's attention, notify the administrator.
 *
 * How to implement?
  Plugins who wish to contribute such
 * notifications can implement this class and put {@link Extension} on it to
 * register it to Hudson.
 *
 * 
 Once installed, it's the implementor's responsibility to perform
 * monitoring and activate/deactivate the monitor accordingly. Sometimes this
 * can be done by updating a flag from code (see {@link SCMTrigger} for one such
 * example), while other times it's more convenient to do so by running some
 * code periodically (for this, use {@link TimerTrigger#timer})
 *
 * 
 {@link AdministrativeMonitor}s are bound to URL by
 * {@link Hudson#getAdministrativeMonitor(String)}. See {@link #getUrl()}.
 *
 * 
Views
  message.jelly
  If {@link #isActivated()}
 * returns true, Hudson will use the message.jelly view of this object
 * to render the warning text. This happens in the
 * http://SERVER/hudson/manage page. This view should typically render
 * a DIV box with class='error' or class='warning' with a human-readable text
 * inside it. It often also contains a link to a page that provides more details
 * about the problem. 
 
 *
 * @author Kohsuke Kawaguchi
 * @since 1.273
 * @see Hudson#administrativeMonitors
 */
@LegacyInstancesAreScopedToHudson
public abstract class AdministrativeMonitor extends AbstractModelObject implements ExtensionPoint {

    /**
     * Human-readable ID of this monitor, which needs to be unique within the
     * system.
     *
     *  This ID is used to remember persisted setting for this monitor, so
     * the ID should remain consistent beyond the Hudson JVM lifespan.
     */
    public final String id;

    protected AdministrativeMonitor(String id) {
        this.id = id;
    }

    protected AdministrativeMonitor() {
        this.id = this.getClass().getName();
    }

    /**
     * Returns the URL of this monitor, relative to the context path, like
     * "administrativeMonitor/foobar".
     */
    public String getUrl() {
        return "administrativeMonitor/" + id;
    }

    public String getDisplayName() {
        return id;
    }

    public final String getSearchUrl() {
        return getUrl();
    }

    /**
     * Mark this monitor as disabled, to prevent this from showing up in the UI.
     */
    public void disable(boolean value) throws IOException {
        Hudson hudson = Hudson.getInstance();
        Set set = hudson.disabledAdministrativeMonitors;
        if (value) {
            set.add(id);
        } else {
            set.remove(id);
        }
        hudson.save();
    }

    /**
     * Returns true if this monitor {@link #disable(boolean) isn't disabled}
     * earlier.
     *
     * 
 This flag implements the ability for the admin to say "no thank you"
     * to the monitor that he wants to ignore.
     */
    public boolean isEnabled() {
        return !Hudson.getInstance().disabledAdministrativeMonitors.contains(id);
    }

    /**
     * Returns true if this monitor is activated and wants to produce a warning
     * message.
     *
     *  This method is called from the HTML rendering thread, so it should
     * run efficiently.
     */
    public abstract boolean isActivated();

    /**
     * URL binding to disable this monitor.
     */
    public void doDisable(StaplerRequest req, StaplerResponse rsp) throws IOException {
        Hudson.getInstance().checkPermission(Hudson.ADMINISTER);
        disable(true);
        rsp.sendRedirect2(req.getContextPath() + "/manage");
    }

    /**
     * All registered {@link AdministrativeMonitor} instances.
     */
    public static ExtensionList all() {
        return Hudson.getInstance().getExtensionList(AdministrativeMonitor.class);
    }
}