/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.apache.wicket.authorization.strategies.page;

import java.lang.ref.WeakReference;

import org.apache.wicket.Application;
import org.apache.wicket.Component;
import org.apache.wicket.Page;
import org.apache.wicket.RestartResponseAtInterceptPageException;
import org.apache.wicket.authorization.IUnauthorizedComponentInstantiationListener;
import org.apache.wicket.authorization.UnauthorizedInstantiationException;

/**
 * A very simple authorization strategy that takes a supertype (a base class or tagging interface)
 * and performs a simple authorization check by calling the abstract method isAuthorized() whenever
 * a Page class that extends or implements the supertype is about to be instantiated. If that method
 * returns true, page instantiation proceeds normally. If it returns false, the user is
 * automatically directed to the specified sign-in page for authentication, which will presumably
 * allow authorization to succeed once they have signed in.
 * <p>
 * In your Application.init() method do something like the following:
 * 
 * <pre>
 * SimplePageAuthorizationStrategy authorizationStrategy = new SimplePageAuthorizationStrategy(
 * 	MySecureWebPage.class, MySignInPage.class)
 * {
 * 	protected boolean isAuthorized()
 * 	{
 * 		// Authorize access based on user authentication in the session
 * 		return (((MySession)Session.get()).isSignedIn());
 * 	}
 * };
 * 
 * getSecuritySettings().setAuthorizationStrategy(authorizationStrategy);
 * </pre>
 * 
 * @author Eelco Hillenius
 * @author Jonathan Locke
 */
public abstract class SimplePageAuthorizationStrategy extends AbstractPageAuthorizationStrategy
{
	/**
	 * The super type (class or interface) of Pages that require authorization to be instantiated.
	 */
	private final WeakReference<Class<?>> securePageSuperTypeRef;

	/**
	 * Construct.
	 * 
	 * @param <S>
	 * 
	 * @param securePageSuperType
	 *            The class or interface supertype that indicates that a given Page requires
	 *            authorization
	 * @param signInPageClass
	 *            The sign in page class
	 */
	public <S extends Page> SimplePageAuthorizationStrategy(final Class<?> securePageSuperType,
		final Class<S> signInPageClass)
	{
		if (securePageSuperType == null)
		{
			throw new IllegalArgumentException("Secure page super type must not be null");
		}

		securePageSuperTypeRef = new WeakReference<Class<?>>(securePageSuperType);

		// Handle unauthorized access to pages
		Application.get().getSecuritySettings().setUnauthorizedComponentInstantiationListener(
			new IUnauthorizedComponentInstantiationListener()
			{
				@Override
				public void onUnauthorizedInstantiation(final Component component)
				{
					// If there is a sign in page class declared, and the
					// unauthorized component is a page, but it's not the
					// sign in page
					if (component instanceof Page)
					{
						// Redirect to page to let the user sign in
						throw new RestartResponseAtInterceptPageException(signInPageClass);
					}
					else
					{
						// The component was not a page, so throw exception
						throw new UnauthorizedInstantiationException(component.getClass());
					}
				}
			});
	}

	/**
	 * @see org.apache.wicket.authorization.strategies.page.AbstractPageAuthorizationStrategy#isPageAuthorized(java.lang.Class)
	 */
	@Override
	protected <T extends Page> boolean isPageAuthorized(final Class<T> pageClass)
	{
		if (instanceOf(pageClass, securePageSuperTypeRef.get()))
		{
			return isAuthorized();
		}

		// Allow construction by default
		return true;
	}

	/**
	 * Gets whether the current user/session is authorized to instantiate a page class which extends
	 * or implements the supertype (base class or tagging interface) passed to the constructor.
	 * 
	 * @return True if the instantiation should be allowed to proceed. False, if the user should be
	 *         directed to the application's sign-in page.
	 */
	protected abstract boolean isAuthorized();
}