function ArrayList()
{
	this.aList = []; //initialize with an empty array
}
		
ArrayList.prototype.Count = function()
{
	return this.aList.length;
}
		
ArrayList.prototype.Add = function( object )
{
	return this.aList.push( object ); //Object are placed at the end of the array
}

ArrayList.prototype.GetAt = function( index ) //Index must be a number
{
	if( index > -1 && index < this.aList.length )
		return this.aList[index];
	else
		return undefined; //Out of bound array, return undefined
}
		
ArrayList.prototype.Clear = function()
{
	this.aList = [];
}

ArrayList.prototype.RemoveAt = function ( index ) // index must be a number
{
	var m_count = this.aList.length;
				
	if ( m_count > 0 && index > -1 && index < this.aList.length ) 
	{
		switch( index )
		{
			case 0:
				this.aList.shift();
				break;
			case m_count - 1:
				this.aList.pop();
				break;
			default:
				var head   = this.aList.slice( 0, index );
				var tail   = this.aList.slice( index + 1 );
				this.aList = head.concat( tail );
				break;
		}
	}
}

ArrayList.prototype.Insert = function ( object, index )
{
	var m_count       = this.aList.length;
	var m_returnValue = -1;
				
	if ( index > -1 && index <= m_count ) 
	{
		switch(index)
		{
			case 0:
				this.aList.unshift(object);
				m_returnValue = 0;
				break;
			case m_count:
				this.aList.push(object);
				m_returnValue = m_count;
				break;
			default:
				var head      = this.aList.slice(0, index - 1);
				var tail      = this.aList.slice(index);
				this.aList    = this.aList.concat(tail.unshift(object));
				m_returnValue = index;
				break;
		}
	}
				
	return m_returnValue;
}

ArrayList.prototype.IndexOf = function( object, startIndex )
{
	var m_count       = this.aList.length;
	var m_returnValue = - 1;
				
	if ( startIndex > -1 && startIndex < m_count ) 
	{
		var i = startIndex;
					
		while( i < m_count )
		{
			if ( this.aList[i] == object )
			{
				m_returnValue = i;
				break;
			}
						
			i++;
		}
	}
				
	return m_returnValue;
}
		
		
ArrayList.prototype.LastIndexOf = function( object, startIndex )
{
	var m_count       = this.aList.length;
	var m_returnValue = - 1;
				
	if ( startIndex > -1 && startIndex < m_count ) 
	{
		var i = m_count - 1;
					
		while( i >= startIndex )
		{
			if ( this.aList[i] == object )
			{
				m_returnValue = i;
				break;
			}
						
			i--;
		}
	}
				
	return m_returnValue;
}

function Observer()
{
	this.Update = function()
	{
		return;
	}
}


function Subject()
{
	this.observers = new ArrayList();
}

Subject.prototype.Notify = function( context )
{
	var m_count = this.observers.Count();
			
	for( var i = 0; i < m_count; i++ )
		this.observers.GetAt(i).Update( context );
}

Subject.prototype.AddObserver = function( observer )
{
	if( !observer.Update )
		throw 'Wrong parameter';
	
	this.observers.Add( observer );
}

Subject.prototype.RemoveObserver = function( observer )
{
	if( !observer.Update )
		throw 'Wrong parameter';
	   
	this.observers.RemoveAt(this.observers.IndexOf( observer, 0 ));
}

function inherits(base, extension)
{
	for (var property in base)
	{
		try
		{
			extension[property] = base[property];
		}
		catch(warning)
		{
		}
	}
}	

/*
function AddObserver()
{
	var check  = document.createElement("INPUT");
	check.type = 'checkbox';
	
	inherits(new Observer(), check)
	
	check.Update = function(value)
	{
		this.checked = value;
	}
	
	mainCheck.AddObserver(check);
	
	cont.appendChild(check);
}
*/