//package com.knownspace.tools;

import java.io.CharArrayWriter;
import java.io.PrintWriter;
import java.util.StringTokenizer;
import java.util.NoSuchElementException;

public class Debug
	{
	/*
	A simple debugger to implement breakpoint assertion testing.

	Public Methods:
	---------------
	assert(booleanCondition)                //fires if booleanCondition==false
	assert(booleanCondition, messageString) //fires if booleanCondition==false
	                                        //and prints messageString

	In both cases the debugger prints the offending method's name.

	Since assert() is a static method, you can call it with "Debug.assert(...)".

	Every method should have its own assertions to test the state of its
	arguments on entry into the method.

	Set DEBUG_MODE to false when you want to turn off assertion testing.
	(Be absolutely sure that your code is working perfectly first!)
	*/

	private final static boolean FATAL_ERROR_LEVEL_SET = false;
	private final static boolean DEBUG_MODE = true;

	//number of method calls to step back in the stack to find the offending
	//method name and line number using the sun JDK
	private final static int STACK_LEVEL = 2;

	///////////////////////////////////////////////////////////////////////
	public final static void assert(boolean condition)
		{
		if (DEBUG_MODE)
			{
			if (! condition)
				printError("assertion failed in: " + getCaller(STACK_LEVEL));

			checkFatality();
			}
		}

	///////////////////////////////////////////////////////////////////////
	public final static void assert(boolean condition, String string)
		{
		if (DEBUG_MODE)
			{
			if (! condition)
				{
				printError("assertion failed: " + string);
				printError("in: " + getCaller(STACK_LEVEL));
				}

			checkFatality();
			}
		}

	///////////////////////////////////////////////////////////////////////
	private final static void printError(String string)
		{
		System.out.println(string);
		}

	///////////////////////////////////////////////////////////////////////
	private final static void checkFatality()
		{
		if (FATAL_ERROR_LEVEL_SET)
			System.exit(1);
		}

	///////////////////////////////////////////////////////////////////////
	private final static String getCaller(int callerNumber)
		{
		/*
		Determine the callerNumber'th method that called this method
		and return its name.

		NOTE: This method may not work with code compiled using a JIT
		or with a non-JDK JVM since in either case the stack trace
		format is unspecified in the language spec.

		Stack trace format assumed:
		---------------------------
		java.lang.Throwable
			at <this method's name>
			at <caller's method's name>                   (callerNumber == 1)
			at <caller's caller's method's name>          (callerNumber == 2)
			at <caller's caller's caller's method's name> (callerNumber == 3)
			<and so on for higher callerNumbers>
		*/

		if (callerNumber < 1)
			return "Debugger";

		//transform the caller number into the token number to search for
		int tokenNumber = (callerNumber * 2) + 3;

		//create a stream to catch the stack trace
		CharArrayWriter stream = new CharArrayWriter();

		//send the stack trace to the stream
		Throwable throwable = new Throwable();
		throwable.printStackTrace(new PrintWriter(stream));

		//parse the stack trace to find the callerNumber'th method call
		StringTokenizer stackTrace = new StringTokenizer(stream.toString());
		String token = "";
		try
			{
			for (int i = 0; i < tokenNumber; i++)
				token = stackTrace.nextToken();
			}
		catch (NoSuchElementException ignored)
			{
			token = "unknown";
			}

		return token;
		}
	}