/*
 * JBoss, Home of Professional Open Source
 * Copyright 2010, Red Hat, Inc., and individual contributors
 * by the @authors tag. See the copyright.txt in the distribution for a
 * full listing of individual contributors.
 *
 * 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.jboss.weld.contexts.cache;

import java.util.LinkedList;
import java.util.List;

/**
 * Caches beans over the life of a request, to allow for efficient bean lookups from proxies.
 * Besides, can hold any ThreadLocals to be removed at the end of the request.
 *
 * @author Stuart Douglas
 */
public class RequestScopedCache {

    private static final ThreadLocal<List<RequestScopedItem>> CACHE = new ThreadLocal<List<RequestScopedItem>>();

    private RequestScopedCache() {
    }

    public static boolean isActive() {
        return CACHE.get() != null;
    }

    private static void checkCacheForAdding(final List<RequestScopedItem> cache) {
        if (cache == null) {
            throw new IllegalStateException("Unable to add request scoped cache item when request cache is not active");
        }
    }

    public static void addItem(final RequestScopedItem item) {
        final List<RequestScopedItem> cache = CACHE.get();
        checkCacheForAdding(cache);
        cache.add(item);
    }

    public static boolean addItemIfActive(final RequestScopedItem item) {
        final List<RequestScopedItem> cache = CACHE.get();
        if (cache != null) {
            cache.add(item);
            return true;
        }
        return false;
    }

    public static boolean addItemIfActive(final ThreadLocal<?> item) {
        final List<RequestScopedItem> cache = CACHE.get();
        if (cache != null) {
            cache.add(new RequestScopedItem() {
                public void invalidate() {
                    item.remove();
                }
            });
            return true;
        }
        return false;
    }

    public static void beginRequest() {
        // if the previous request was not ended properly for some reason, make sure it is ended now
        endRequest();
        CACHE.set(new LinkedList<RequestScopedItem>());
    }

    /**
     * ends the request and clears the cache. This can be called before the request is over,
     * in which case the cache will be unavailable for the rest of the request.
     */
    public static void endRequest() {
        final List<RequestScopedItem> result = CACHE.get();
        if (result != null) {
            CACHE.remove();
            for (final RequestScopedItem item : result) {
                item.invalidate();
            }
        }
    }

    /**
     * Flushes the bean cache. The cache remains available for the rest of the request.
     */
    public static void invalidate() {
        if (isActive()) {
            endRequest();
            beginRequest();
        }
    }

}