package e4s.tutorial;

import java.io.*;
import java.util.*;
import java.text.*;
import java.net.*;
import java.sql.*;

import e4s.html.*;
import e4s.servlet.*;
import e4s.application.sysmodule.E4ModuleSystem;

/**
 * This example illustrates the usage of a module, that is called several times
 * by the e4s framework. Each call causes the framework to create
 * a new instance of this module, so any values stored in member variables are
 * lost after each call. 
 *
 * There are workarounds throught that:
 *
 *  1) Make a variable static, but you loose the ability to hold different values
 *     for each user. Anyway, it can make sense, e.g. when using image or font 
 *     objects that are independent of the user.
 * 
 *  2) Declare the whole module as session object (see other example in this tutorial).
 *
 * Or covered here:
 *
 *  3) You can concentrate data in one or more classes (objects) and use the {@link e4s.servlet.E4ServletImplementation_Intf#setSessionObject}
 *     or {@link e4s.servlet.E4ServletImplementation_Intf#setSessionObject} which is basically also the mechanism how
 *     more complex objects (trees, sorted lists) in the e4s environment are working. 
 *
 * {@tutorial Example_PersistantModule}
 *
 * @see e4s.servlet.E4ModuleImplementation#E4ModuleImplementation(E4ServletImplementation_Intf,boolean)
 * @see Example_SessionObjects
 */
public class Example_SessionObjects extends E4ModuleImplementation
{
	public static E4Method start = null;

	private int m_test = 0;

	
	/**
	 * This is the entry point into this module.
	 * 
	 * Store the current time in two local member variables (one for the first call,
	 * and another for the last call). Place a link to the second function within this
	 * module.
	 *
	 * @param html the output to be created by this function
	 */
	public void start( HTML html )
	{
		java.util.Date first_date = (java.util.Date)getSessionObject("TUTORIAL.STARTED");
		java.util.Date last_date = (java.util.Date)getSessionObject("TUTORIAL.LASTTIME");
		
		// get call counter
		long called = getSessionObject_Long("TUTORIAL.CALLED");
		
		if (last_date == null)
		{
			html.println("This function was now called for the first time, ");
			html.println("a session object of type java.util.Date named TUTORIAL.STARTED will be stored now");
			
			// remember the time when it was first started
			setSessionObject("TUTORIAL.STARTED", new java.util.Date());
		}
		else
		{
			html.println("This function was called " + called + " times before, the first call has been at " + first_date.toString());
			html.println(" and the last call at " + last_date.toString());
			html.P();
			html.println("The local variable m_test still has a value of " + m_test + " as this module will be instantiated each call and not each session");
		}

		// remember the last date called
		setSessionObject("TUTORIAL.LASTTIME", new java.util.Date());

		// increment & store call counter
		called++;
		setSessionObject("TUTORIAL.CALLED", called);

		// this won't work the way we expect
		m_test++;
		
		// add some links
		html.P();

		// open system function to display session objects in a new window    
		A hrefList = html.A(E4ModuleSystem.listSessionObjects);
		hrefList.openInNewWindow(A.WINDOW_PARAM_RESIZE|A.WINDOW_PARAM_SCROLL);
		hrefList.println("[view objects for the current session]");

		// link again to call this function
		A hrefAgain = html.A(start);
		hrefAgain.println("[do it again]");
	}
	
}