/*
 * ServerMonitor.java
 *
 * Created on April 29, 2004, 12:40 PM
 *
 *  Copyright 2004 Andrew Kaluzniacki. All Rights Reserved.
 *  http://drewk.net
 *
 *
 *  ToDO: handle many hosts - initialize by config file - propertiesfile maybe
 */

/**
 *
 * @author  drew
 */

import java.io.IOException;
import java.io.OutputStreamWriter;
import java.io.PrintWriter;
import java.net.Socket;
import java.net.UnknownHostException;
import java.net.URL;
import java.net.URLConnection;
import java.util.Date;

/**
 * ServerMonitor is a class for monitoring a server by checking to see if a
 * Socket connection can be made to named host at a specific port.
 */
public class ServerMonitor {
    
    private String host = null;
    private int port = 0;
    private String errorString = null;
    private boolean sentMail = false;
    
    /**
     * Creates a new instance of ServerMonitor
     * @param host name of host to monitor
     * @param port port on host to be monitored
     */
    public ServerMonitor(String host, int port) {
        this.host = host;
        this.port = port;
    }
    
    /**
     * Check if a socket connection can be made to host:port
     * @return true if connection made.
     * false if no connection, and errorString is set to reason.
     */
    public boolean checkServer() {
        
        Socket socket = null;
        
        boolean retValue = false;
        errorString = "Success";
        
        try {
            socket = new Socket(host, port);
            retValue = true;
        } catch (UnknownHostException e) {
            errorString = "Unknown host exception:" + host;
        } catch (IOException e) {
            errorString = "IOException connecting to:" + host;
        }
        
        if (socket != null) {
            try {
                socket.close();
            }  catch (IOException e) {
                System.out.println("IOException closing socket:" + e);
            }
        }
        
        return retValue;
    }
    
    /**
     * Send email to notify administrator of failure.
     * This is only done once.
     */
    public void emailAdmin(String adminEmail, String smtpHost) {
        
        if (sentMail) { // only once
            return;
        }
        
        sentMail = true;
        
        System.out.println("Sending mail to admin.");
        
        try {
            System.getProperties().put("mail.host", smtpHost);
            URL u = new URL("mailto:" + adminEmail);
            URLConnection c = u.openConnection();
            c.setDoInput(false);
            c.setDoOutput(true);
            c.connect();
            PrintWriter mail_out =
            new PrintWriter(new OutputStreamWriter(c.getOutputStream() ) );
            
            mail_out.println("To:" + adminEmail);
            mail_out.println("Subject:[Server Monitor] " + host);
            mail_out.println();
            
            mail_out.println("Check the log. This will be the only message until you restart ServerMonitor.");
            mail_out.close();
        } catch (Exception e) {
            System.out.println("ERROR: unable to send mail. " + e);
            sentMail = false;
        }
        
    }
    
    
    /**
     * Returns a string describing the result of last call to checkServer
     * @return status string
     */
    public String getError() { return errorString; }
    
    /**
     * Run the ServerMonitor
     * @param args the command line arguments - none<br>
     *  Arguments are passed as system properties.<br>
     *  sm.host<br>
     *  sm.port<br>
     *  sm.interval [minutes]<br>
     *  sm.refHost<br>
     *  sm.refPort<br>
     *  sm.adminEmail<br>
     *  sm.smtpHost<br>
     *
     * @throws InterruptedException only if the call to sleep is interupted.
     */
    public static void main(String[] args) throws InterruptedException {
         
        
        String host = System.getProperty("sm.host", "localhost");
        
        int port = Integer.getInteger("sm.port", 80).intValue();
   
        int intervalMinutes = Integer.getInteger("sm.interval", 10).intValue();
        
        String refHost = System.getProperty("sm.refHost", "localhost");
        
        int refPort = Integer.getInteger("sm.refPort", 80).intValue();
            
        String adminEmail = System.getProperty("sm.adminEmail", "root@localhost");
        
        String smtpHost = System.getProperty("sm.smtpHost", "localhost");
 
        
        System.out.println("Starting ServerMonitor. host:" + host + " port:" +
        port + " refHost:" + refHost + " refPort:" +
        refPort + " interval:" + intervalMinutes +
        " adminEmail:" + adminEmail + " smtpHost:" + smtpHost);
        
        ServerMonitor sm = new ServerMonitor(host, port);
        ServerMonitor rm = new ServerMonitor(refHost , refPort);
        
        
        while (true) {
            Date date = new Date();
            if (sm.checkServer()) {
                System.out.println( "[" + date + "] " + host +
                " seems to be running.");
            } else {
                System.out.println( "[" + date + "] Error: " + host +
                " not reachable. " + sm.getError());
                if (rm.checkServer()) {
                    System.out.println( "     Checking reference host. " + refHost +
                    " seems to be running.");
                } else {
                    System.out.println( "     Checking reference host.  Error: " +
                    refHost + " not reachable. " + rm.getError());
                }
                
                sm.emailAdmin(adminEmail, smtpHost);
            }
            long millis = intervalMinutes * ( 60 * 1000 );
            Thread.sleep(millis);
        }
    }
}