/*
 * $Id$
 *
 * 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.struts2.util;

import java.util.Collection;
import java.util.Collections;
import java.util.Map;
import java.util.Set;

import javax.servlet.jsp.PageContext;

import org.apache.struts2.ServletActionContext;


/**
 * A Map that holds 4 levels of scope.
 * <p/>
 * The scopes are the ones known in the web world.:
 * <ul>
 *   <li>Page scope</li>
 *   <li>Request scope</li>
 *   <li>Session scope</li>
 *   <li>Application scope</li>
 * </ul>
 * A object is searched in the order above, starting from page and ending at application scope.
 *
 */
public class AttributeMap implements Map {

    protected static final String UNSUPPORTED = "method makes no sense for a simplified map";


    Map context;


    public AttributeMap(Map context) {
        this.context = context;
    }


    public boolean isEmpty() {
        throw new UnsupportedOperationException(UNSUPPORTED);
    }

    public void clear() {
        throw new UnsupportedOperationException(UNSUPPORTED);
    }

    public boolean containsKey(Object key) {
        return (get(key) != null);
    }

    public boolean containsValue(Object value) {
        throw new UnsupportedOperationException(UNSUPPORTED);
    }

    public Set entrySet() {
        return Collections.EMPTY_SET;
    }

    public Object get(Object key) {
        PageContext pc = getPageContext();

        if (pc == null) {
            Map request = (Map) context.get("request");
            Map session = (Map) context.get("session");
            Map application = (Map) context.get("application");

            if ((request != null) && (request.get(key) != null)) {
                return request.get(key);
            } else if ((session != null) && (session.get(key) != null)) {
                return session.get(key);
            } else if ((application != null) && (application.get(key) != null)) {
                return application.get(key);
            }
        } else {
            try{
                return pc.findAttribute(key.toString());
            }catch (NullPointerException npe){
                return null;
            }
        }

        return null;
    }

    public Set keySet() {
        return Collections.EMPTY_SET;
    }

    public Object put(Object key, Object value) {
        PageContext pc = getPageContext();
        if (pc != null) {
            pc.setAttribute(key.toString(), value);
        }

        return null;
    }

    public void putAll(Map t) {
        throw new UnsupportedOperationException(UNSUPPORTED);
    }

    public Object remove(Object key) {
        throw new UnsupportedOperationException(UNSUPPORTED);
    }

    public int size() {
        throw new UnsupportedOperationException(UNSUPPORTED);
    }

    public Collection values() {
        return Collections.EMPTY_SET;
    }

    private PageContext getPageContext() {
        return (PageContext) context.get(ServletActionContext.PAGE_CONTEXT);
    }
}
