package lectures.undo_commands;
import util.annotations.WebDocuments;
import java.util.ArrayList;
import java.util.List;
@WebDocuments({"Lectures/UndoCommands.pptx", "Lectures/UndoCommands.pdf", "Videos/UndoCommands.avi"})
public class HistoryUndoer implements Undoer {
    List<Command> historyList = new ArrayList();    
    int nextCommandIndex = 0;
    public void execute (Command c) {
        while(nextCommandIndex < historyList.size()) {
              historyList.remove(nextCommandIndex); // clear redo chain
        }       
        c.execute();
        historyList.add(c); 
        nextCommandIndex++;
    }
    public void undo() {
        if (nextCommandIndex == 0)return;
        nextCommandIndex--;
        Command c = historyList.get(nextCommandIndex);
        c.undo();       
    }
    public void redo() {
        if (nextCommandIndex == historyList.size()) return;
        Command c = historyList.get(nextCommandIndex);
        c.execute();
        nextCommandIndex++;         
    }
}