package daoannotation;

import java.lang.annotation.AnnotationFormatError;
import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;

public class DaoProxyFactory {

  @SuppressWarnings("unchecked")
	public static <T> T newRoleDaoProxy(Class<T> dao) {
		Implement implAnnotation = dao.getAnnotation(Implement.class);
		
		if (implAnnotation == null) {
			throw new AnnotationFormatError("this is no annotation for this interface: " + 
					dao.getSimpleName().toString());
		}
		
		BaseDao implClass = null;
		
		try {
			implClass = implAnnotation.value().newInstance();
		} catch (Exception e) {
			throw new RuntimeException("this interface cannot be instanized!", e);
		}
		
		return (T) Proxy.newProxyInstance(
				DaoProxyFactory.class.getClassLoader(), 
				new Class<?>[] { dao }, 
				new RoleInovationHandler(implClass));
		
	}
	
	private static final class RoleInovationHandler implements InvocationHandler {
		private BaseDao target;
		
		public RoleInovationHandler(BaseDao target) {
			this.target = target;
		}
		
		@Override
		public Object invoke(Object proxy, Method method, Object[] args)
				throws Throwable {
			Permission permitAnnotation = method.getAnnotation(Permission.class);
			
			outter:
			if (permitAnnotation != null) {
				Role currentRole = RoleContext.INSTANCE.getCurrentRole();
				
				for (Role role : permitAnnotation.value()) {
					if (role.equals(currentRole)) {
						break outter;
					}
				}
				
				throw new SecurityException("user is not allowed to this operation!");
				
			}
			return method.invoke(target, args);
		}
		
	}
	
	public static void main(String[] args) {
		UserDao userDao = DaoProxyFactory.newRoleDaoProxy(UserDao.class);
		userDao.save();
		userDao.delete();
		//userDao.query();
	}
}