/* 
 * This file is part of the Echo Web Application Framework (hereinafter "Echo").
 * Copyright (C) 2002-2009 NextApp, Inc.
 *
 * Version: MPL 1.1/GPL 2.0/LGPL 2.1
 *
 * The contents of this file are subject to the Mozilla Public License Version
 * 1.1 (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.mozilla.org/MPL/
 *
 * Software distributed under the License is distributed on an "AS IS" basis,
 * WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
 * for the specific language governing rights and limitations under the
 * License.
 *
 * Alternatively, the contents of this file may be used under the terms of
 * either the GNU General Public License Version 2 or later (the "GPL"), or
 * the GNU Lesser General Public License Version 2.1 or later (the "LGPL"),
 * in which case the provisions of the GPL or the LGPL are applicable instead
 * of those above. If you wish to allow use of your version of this file only
 * under the terms of either the GPL or the LGPL, and not to allow others to
 * use your version of this file under the terms of the MPL, indicate your
 * decision by deleting the provisions above and replace them with the notice
 * and other provisions required by the GPL or the LGPL. If you do not delete
 * the provisions above, a recipient may use your version of this file under
 * the terms of any one of the MPL, the GPL or the LGPL.
 */

package nextapp.echo2.webrender.service;

import java.io.IOException;

import nextapp.echo2.webrender.Connection;
import nextapp.echo2.webrender.Service;
import nextapp.echo2.webrender.util.GZipCompressor;
import nextapp.echo2.webrender.util.JavaScriptCompressor;
import nextapp.echo2.webrender.util.Resource;

/**
 * A service which renders <code>JavaScript</code> resource files.
 */
public class JavaScriptService 
implements Service {
    
    /**
     * Creates a new <code>JavaScript</code> service from the specified
     * resource in the <code>CLASSPATH</code>.
     * 
     * @param id the <code>Service</code> id
     * @param resourceName the <code>CLASSPATH</code> resource name containing
     *        the JavaScript content
     * @return the created <code>JavaScriptService</code>
     */
    public static JavaScriptService forResource(String id, String resourceName) {
        String content = Resource.getResourceAsString(resourceName);
        return new JavaScriptService(id, content);
    }

    /** <code>Service</code> identifier. */
    private String id;
    
    /** The JavaScript content in plain text. */
    private String content;
    
    /** The JavaScript content in GZip compressed form. */
    private byte[] gzipContent;
    
    /**
     * Creates a new <code>JavaScriptService</code>.
     * 
     * @param id the <code>Service</code> id
     * @param content the <code>JavaScript content</code>
     */
    public JavaScriptService(String id, String content) {
        super();
        this.id = id;
        this.content = JavaScriptCompressor.compress(content);
        try {
            gzipContent = GZipCompressor.compress(this.content);
        } catch (IOException ex) {
            // Should not occur.
            throw new RuntimeException("Exception compressing JavaScript source.", ex);
        }
    }
    
    /**
     * @see nextapp.echo2.webrender.Service#getId()
     */
    public String getId() {
        return id;
    }
    
    /**
     * <code>DO_NOT_CACHE</code> is returned for <code>JavaScript</code>
     * to avoid possibility of ever running out-of-date JavaScript in the
     * event an application is updated and redeployed. 
     * 
     * @see nextapp.echo2.webrender.Service#getVersion()
     */
    public int getVersion() {
        return DO_NOT_CACHE;
    }
    
    /**
     * @see nextapp.echo2.webrender.Service#service(nextapp.echo2.webrender.Connection)
     */
    public void service(Connection conn) 
    throws IOException {
        String userAgent = conn.getRequest().getHeader("user-agent");
        if (userAgent == null || userAgent.indexOf("MSIE") != -1) {
            // Due to behavior detailed Microsoft Knowledge Base Article Id 312496, 
            // all HTTP compression support is disabled for this browser.
            // Due to the fact that ClientProperties information is not necessarily 
            // available at this stage, browsers which provide deceitful user-agent 
            // headers will also be affected.
            servicePlain(conn);
        } else {
            String acceptEncoding = conn.getRequest().getHeader("accept-encoding");
            if (acceptEncoding != null && acceptEncoding.indexOf("gzip") != -1) {
                serviceGZipCompressed(conn);
            } else {
                servicePlain(conn);
            }
        }
    }
    
    /**
     * Renders the JavaScript resource using GZip encoding.
     * 
     * @param conn the relevant <code>Connection</code>
     */
    private void serviceGZipCompressed(Connection conn) 
    throws IOException {
        conn.getResponse().setContentType("text/plain");
        conn.getResponse().setHeader("Content-Encoding", "gzip");
        conn.getOutputStream().write(gzipContent);
    }
    
    /**
     * Renders the JavaScript resource WITHOUT using GZip encoding.
     * 
     * @param conn the relevant <code>Connection</code>
     */
    private void servicePlain(Connection conn) 
    throws IOException {
        conn.getResponse().setContentType("text/plain");
        conn.getWriter().print(content);
    }
}