/*
 * Copyright 2005-2010 the original author or authors.
 * 
 * Licensed 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.wamblee.security.authorization.jpa;

import javax.persistence.EntityManager;
import javax.persistence.NoResultException;
import javax.persistence.NonUniqueResultException;

import org.wamblee.persistence.JpaMergeSupport;
import org.wamblee.security.authorization.AbstractAuthorizationService;
import org.wamblee.security.authorization.AbstractAuthorizationRule;
import org.wamblee.security.authorization.AuthorizationRule;
import org.wamblee.security.authorization.AuthorizationService;
import org.wamblee.security.authorization.DefaultAuthorizationService;
import org.wamblee.security.authorization.Operation;
import org.wamblee.usermgt.UserAccessor;

/**
 * Authorization service with persistent storage. This is a wrapper for
 * {@link org.wamblee.security.authorization.DefaultAuthorizationService} which
 * refreshes the state of the service at certain time intervals.
 * 
 * @author Erik Brakkee
 */
public class JpaAuthorizationService implements AuthorizationService {

    /**
     * Authorization service to use.
     */
    private AuthorizationService service;

    /**
     * Hibernate template to use.
     */
    private EntityManager entityManager;

    /**
     * User accessor.
     */
    private UserAccessor userAccessor;

    /**
     * Name of the service.
     */
    private String name;

    /**
     * Refresh interval in milliseconds.
     */
    private final long refreshInterval;

    /**
     * Last refresh time.
     */
    private long lastRefreshTime;

    /**
     * Constructs the persistent service.
     * 
     * @param aName
     *            Name of the service.
     * @param aEntityManager
     *            Entity manager.
     * @param aAccessor
     *            User accessor.
     * @param aRefresh
     *            Whether or not to refresh the state of the service at the
     *            start of every operation.
     */
    public JpaAuthorizationService(String aName, EntityManager aEntityManager,
        UserAccessor aAccessor, long aRefreshInterval) {
        entityManager = aEntityManager;
        refreshInterval = aRefreshInterval;
        lastRefreshTime = System.currentTimeMillis();
        userAccessor = aAccessor;
        name = aName;
    }
    
    @Override
    public void setUserAccessor(UserAccessor aUserAccessor) {
        userAccessor = aUserAccessor;   
    }

    /**
     * Initialize service if needed.
     * 
     */
    private void initialize() {
        if (service == null) {
            refreshByReload();
        }
    }

    private void refreshByReload() {
        try {
            service = entityManager.createNamedQuery(
                AbstractAuthorizationService.QUERY_FIND_BY_NAME,
                AbstractAuthorizationService.class).setParameter(
                    AbstractAuthorizationService.NAME_PARAM, name).getSingleResult();
            service.setUserAccessor(userAccessor);
        } catch (NonUniqueResultException e) {
            throw new IllegalArgumentException(
                "Returned more than one service for name '" + name + "'");
        } catch (NoResultException e) {
            service = new DefaultAuthorizationService(userAccessor, name);
            entityManager.persist(service);
        }
    }

    /*
     * (non-Javadoc)
     * 
     * @see
     * org.wamblee.security.authorization.AuthorizationService#isAllowed(java
     * .lang.Object, org.wamblee.security.authorization.Operation)
     */
    public boolean isAllowed(Object aResource, Operation aOperation) {
        initialize();
        refresh();

        return service.isAllowed(aResource, aOperation);
    }

    /*
     * (non-Javadoc)
     * 
     * @see org.wamblee.security.authorization.AuthorizationService#check(T,
     * org.wamblee.security.authorization.Operation)
     */
    public <T> T check(T aResource, Operation aOperation) {
        initialize();
        refresh();

        return service.check(aResource, aOperation);
    }

    /*
     * (non-Javadoc)
     * 
     * @see org.wamblee.security.authorization.AuthorizationService#getRules()
     */
    public AuthorizationRule[] getRules() {
        initialize();
        refresh();

        return service.getRules();
    }

    /*
     * (non-Javadoc)
     * 
     * @see
     * org.wamblee.security.authorization.AuthorizationService#appendRule(org
     * .wamblee.security.authorization.AuthorizationRule)
     */
    public void appendRule(AuthorizationRule aRule) {
        initialize();
        refresh();
        service.appendRule(aRule);
        save();
    }

    /*
     * (non-Javadoc)
     * 
     * @see
     * org.wamblee.security.authorization.AuthorizationService#removeRule(int)
     */
    public void removeRule(int aIndex) {
        initialize();
        refresh();
        service.removeRule(aIndex);
        save();
    }

    /*
     * (non-Javadoc)
     * 
     * @see
     * org.wamblee.security.authorization.AuthorizationService#insertRuleAfter
     * (int, org.wamblee.security.authorization.AuthorizationRule)
     */
    public void insertRuleAfter(int aIndex, AuthorizationRule aRule) {
        initialize();
        refresh();
        service.insertRuleAfter(aIndex, aRule);
        save();
    }

    /**
     * Refreshes the state of the service through hibernate.
     */
    private synchronized void refresh() {
        long time = System.currentTimeMillis();

        if ((time - lastRefreshTime) > refreshInterval) {
            refreshByReload();
            lastRefreshTime = time;
        }
    }

    /**
     * Saves any changes to the service state if necessary.
     */
    private void save() {
        AuthorizationService merged = entityManager.merge(service);
        entityManager.flush();
        JpaMergeSupport.merge(merged, service);
    }
}