package class9_Lab_Command_031_start;

import java.util.Stack;

/**
 * This is a "helper" class that handles the details of invocation of specific commands
 * @author hornick
 *
 */
public class Invoker {
	private Stack<Command> doneStack = new Stack<>();
	private Stack<Command> undoneStack = new Stack<>();

	/**
	 * tells this to execute its Command immediately
	 */
	public void invoke( Command cmd ) {
		cmd.execute();
		doneStack.push(cmd);
		undoneStack.clear();
	}

	/**
	 * tells this to undo the last Command (if possible)
	 */
	public void undo() {
		if(!doneStack.isEmpty()) {
			Command cmd = doneStack.pop();
			cmd.unexecute();
			undoneStack.push(cmd);
		}
	}

	/**
	 *
	 */
	public void redo() {
		if(!undoneStack.isEmpty()) {
			Command cmd = undoneStack.pop();
			cmd.execute();
			doneStack.push(cmd);
		}
	}

}