/*
 * 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.util.xml;

import java.io.IOException;
import java.io.InputStream;
import java.util.HashMap;
import java.util.Map;

import javax.servlet.Filter;

import org.apache.wicket.util.lang.Args;
import org.xml.sax.EntityResolver;
import org.xml.sax.InputSource;
import org.xml.sax.SAXException;

/**
 * entity resolver that tries to locate a document type definition (DTD) using a set of custom
 * entity resolvers
 * 
 * @author pete
 */
public class CustomEntityResolver implements EntityResolver
{
        private final Map<EntityKey, EntityLocator> entities = new HashMap<>(3);

        /**
         * get default instances of custom entity resolver with preloaded well-known entities
         * 
         * @return instance of resolver
         */
        public static CustomEntityResolver getPreloaded()
        {
                CustomEntityResolver resolver = new CustomEntityResolver();

                resolver.put(new EntityKey("-//Sun Microsystems, Inc.//DTD Web Application 2.3//EN",
                        "http://java.sun.com/dtd/web-app_2_3.dtd"), new ServletApiEntityLocator(
                        "web-app_2_3.dtd"));

                return resolver;
        }

        /**
         * add custom entity resolver
         * 
         * @param key
         *            key for lookup (contains id and url)
         * @param locator
         *            locator for looking up entity
         */
        public void put(final EntityKey key, final EntityLocator locator)
        {
                Args.notNull(key, "key");
                Args.notNull(locator, "locator");
                entities.put(key, locator);
        }

        @Override
        public InputSource resolveEntity(final String id, final String url) throws SAXException,
                IOException
        {
                for (Map.Entry<EntityKey, EntityLocator> entry : entities.entrySet())
                {
                        if (entry.getKey().id.equals(id) || entry.getKey().url.equals(url))
                        {
                                return entry.getValue().locateInputSource();
                        }
                }

                return null;
        }

        /**
         * key for entity
         * <p/>
         * consists of id + url
         */
        public static class EntityKey
        {
                private final String id;
                private final String url;

                private EntityKey(final String id, final String url)
                {
                        Args.notEmpty(id, "id");
                        Args.notEmpty(url, "url");
                        this.id = id;
                        this.url = url;
                }

                @Override
                public boolean equals(final Object o)
                {
                        if (this == o)
                        {
                                return true;
                        }
                        if (!(o instanceof EntityKey))
                        {
                                return false;
                        }

                        EntityKey key = (EntityKey)o;

                        if (!id.equals(key.id))
                        {
                                return false;
                        }

                        return url.equals(key.url);
                }

                @Override
                public int hashCode()
                {
                        int result = id.hashCode();
                        result = 31 * result + url.hashCode();
                        return result;
                }
        }

        /**
         * entity locator
         * <p/>
         * manages locating an entity
         */
        public static interface EntityLocator
        {
                /**
                 * @return input source
                 * @throws SAXException
                 * @throws IOException
                 */
                InputSource locateInputSource() throws SAXException, IOException;
        }

        /**
         * entity locator for resources inside servlet-api.jar
         */
        public static class ServletApiEntityLocator implements EntityLocator
        {
                private final String name;

                private ServletApiEntityLocator(final String name)
                {
                        this.name = name;
                }

                /**
                 * resolve servlet api resource, where e.g. 'web-app_2_3.dtd' is located
                 * 
                 * @return input source
                 */
                @Override
                public InputSource locateInputSource()
                {
                        InputStream stream = Filter.class.getResourceAsStream("resources/" + name);

                        if (stream == null)
                        {
                                return null;
                        }

                        return new InputSource(stream);
                }
        }
}