rem
	History module
end rem

Function CanUndo:Byte()
	Return Not undoList.IsEmpty()
End Function

Function Undo()
	If undoList.IsEmpty() Then Return
	Local h:THistory = THistory(undoList.RemoveLast())
	h.Undo()
	redoList.AddFirst(h)
End Function

Function CanRedo:Byte()
	Return Not redoList.IsEmpty()
End Function

Function Redo()
	If redoList.IsEmpty() Then Return
	Local h:THistory = THistory(redoList.RemoveFirst())
	h.Redo()
	undoList.AddLast(h)
End Function

Type THistory Abstract
	Method New()
		If Not redoList.IsEmpty()
			redoList = New TList
		End If
		undoList.AddLast(Self)
		If undoList.Count() > MAX_HISTORY
			undoList.RemoveFirst()
		End If
	End Method
	
	Method Undo() Abstract
	Method Redo() Abstract
End Type

Const MAX_HISTORY:Int = 100

Global undoList:TList = New TList
Global redoList:TList = New TList