package example8_1_AfterClass;

import java.util.Deque;
import java.util.LinkedList;

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

	/**
	 * constructor
	 */
	public Invoker() {
	}
	
	/**
	 * tells this to execute its Command immediately
	 */
	public boolean invoke( Command command ) {
        boolean status;
        if(command instanceof UndoCommand) {
            status = undo();
        } else {
//            new Invoker().invoke(command);
            status = command.execute();
            if(status) {
                stack.push(command);
            }
        }
        return status;
	}

	/**
	 * tells this to undo the last Command (if possible)
	 */
	public boolean undo() {
        boolean status;
        Command lastCommand = stack.pollFirst();
        if(null != lastCommand) {
            status = lastCommand.unexecute();
        } else {
            status = false;
        }
        return status;
	}

}