package de.spieleck.servlets;

import java.io.*;
import java.util.ArrayList;
import java.util.HashMap;

import javax.servlet.*;
import javax.servlet.http.*;

/**
 * Simple Hack for a random redirection servlet.
 *
 * Setup in web.xml is as follows:
 *
 * <PRE>
 *     &lt;servlet-mapping url-pattern='rlink/*' servlet-name='rlink'/>
 *     &lt;servlet>
 *       &lt;servlet-name>rlink&lt;/servlet-name>
 *       &lt;servlet-class>de.spieleck.servlets.RandomLink&lt;/servlet-class>
 *       &lt;!-- Path to Configuration files (value is the default) -->
 *       &lt;init-param>
 *           &lt;param-name>basePath&lt;/param-name>
 *           &lt;param-value>WEB-INF/randomLinkData&lt;/param-value>
 *       &lt;/init-param>
 *       &lt;!-- Extension to path file (value is the default) -->
 *       &lt;init-param>
 *           &lt;param-name>configExt&lt;/param-name>
 *           &lt;param-value>.lst&lt;/param-value>
 *       &lt;/init-param>
 *       &lt;!-- Time to store the cookie (default one month) -->
 *       &lt;init-param>
 *           &lt;param-name>cookieTime&lt;/param-name>
 *           &lt;param-value>2678400&lt;/param-value>
 *       &lt;/init-param>
 *     &lt;/servlet>
 * </PRE>
 *
 * The servlet then accepts requests like
 * <PRE>
 *   http://yourServer/yourApp/rlink/cname
 * </PRE>
 * and looks for a configuration file at
 * <PRE>
 *    ContextPath/WEB-INF/randomLinkData/cname.lst
 * </PRE>
 * This configuraton file contains a mere list of URL's, 
 * one per line.
 * 
 * 27 Apr 2003 fixed synchronization. 
 */
public class RandomLink 
    extends HttpServlet
{
    public static final String SERVLET = "RandomLink";
    public final static String BASEPATH = "basePath";
    public final static String CONFIGEXT = "configExt";
    public final static String COOKIETIME = "cookieTime";

    /** Keep track of known Configurations */
    public static HashMap configs;

    /** Base path, where configurations are looked up from */
    protected String basePath = null;

    /** Filename extension for configuration files */
    protected String configExt = null;

    /** Expiration time for cookies. */
    protected int cookieTime = 60*60*24*31;

    public RandomLink() { }

    /**
     * Init: Pull params from web.xml.
     */
    public void init()
        throws ServletException
    {
        configs = new HashMap();
        basePath = getServletConfig().getInitParameter(BASEPATH);
        configExt = getServletConfig().getInitParameter(CONFIGEXT);
        String h = getServletConfig().getInitParameter(COOKIETIME);
        if ( h != null )
            try
            {
                cookieTime = Integer.parseInt(h);
            }
            catch ( NumberFormatException e )
            {
                e.printStackTrace();
            }
        log("Start: "+SERVLET
                +" "+BASEPATH+"="+basePath
                +" "+CONFIGEXT+"="+configExt
                +" "+COOKIETIME+"="+cookieTime
            );
        if ( configExt == null )
            configExt = ".lst";
        if ( basePath == null )
            basePath = "WEB-INF/randomLinkData";
        basePath = getServletContext().getRealPath(basePath)+"/";
    }

    /**
     * Process request, whatever type.
     */
    public void service(HttpServletRequest req, HttpServletResponse res)
        throws ServletException, IOException
    {
        // --- Obtain Configuration matching request
        String confName = req.getPathInfo();
        if ( confName == null )
            confName = "";
        else
            confName = confName.substring(1);
        Config config = getConfig(confName);
        if(config == null)
        {
            res.sendError(res.SC_EXPECTATION_FAILED, 
                                "Could not find config " + confName);
            return;
        }
        // --- Obtain next URL from either cookie or globals
        String cookieName = config.getCookieName();
        Cookie myc = null;
        Cookie[] cookies = req.getCookies();
        if ( cookies != null )
            for (int i = 0; i < cookies.length; i++ )
                if ( cookies[i].getName().equals(cookieName) )
                {
                    myc = cookies[i];
                    break;
                }
        String url = config.getNextURL(myc);
        // --- Reply, a cookie and a redirect
        myc = new Cookie(cookieName, url);
        myc.setMaxAge(cookieTime);
        res.addCookie(myc);
        res.sendRedirect(url);
    }

    /**
     * Obtain matching Configuration.
     * First try to retrieve it from HashMap if it hasn't changed
     * in between. If this fails, try to read the file.
     */
    protected synchronized Config getConfig(String cname)
    {
        Config config = (Config) configs.get(cname);
        if( config != null )
        {
            if ( ! config.isRecent() )
            {
                configs.remove(cname);
                config = null;
            }
        }
        if ( config == null )
        try
        {
            config = new Config(basePath, cname, configExt);
            configs.put(cname, config);
        }
        catch ( IOException io )
        {
            io.printStackTrace();
            return null;
        }
        return config;
    }

    /**
     *  Subclass to contain configuration data
     */
    protected static class Config
    {
        /** The file containing the configuration */
        protected File configFile;

        /** Last time the config file was changed. */
        protected long edited;

        /** Cookie sent to user for this configuration. */
        protected String cookieName;

        /** Cyclical URL-Counter, for Clients which do not accept Cookies. */
        protected int currentUrl;

        /** Alle the URLs we jump to. */
        protected String[] urls;

        public Config(String bPath, String cname, String ext)
            throws IOException
        {
            configFile = new File(bPath+cname+ext);
            readConfig();
            currentUrl = 0;
            cookieName =  "rl."+cname+"."+cname.hashCode()+".c";
        }

        public synchronized boolean isRecent()
        {
            return edited == configFile.lastModified();
        }

        public String getCookieName()
        {
            return cookieName;
        }

        public synchronized int getURLCount()
        {
            return urls.length;
        }

        public String getNextURL(Cookie myc)
        {
            int i = 0;
            if ( myc == null )
                i = nextUrlNo();
            else
            {
                String u = myc.getValue();
                for (i = 0; i < getURLCount(); i++)
                {
                    if ( u.equals(urls[i]) )
                        break;
                }
                i = (i+1) % getURLCount();
            }
            return urls[i];
        }

        protected synchronized int nextUrlNo()
        {
            currentUrl = (currentUrl + 1) % getURLCount();
            return currentUrl;
        }

        protected synchronized void readConfig()
            throws IOException
        {
            BufferedReader in = new BufferedReader(new FileReader(configFile));
            String line = in.readLine();
            ArrayList urlsa = new ArrayList(10);
            while ( line != null )
            {
                urlsa.add(line);
                line = in.readLine();
            }
            urls = new String[urlsa.size()];
            urlsa.toArray((Object[])urls);
            // Keep timestamp of change
            edited = configFile.lastModified();
        }

    }
}