//
//  ========================================================================
//  Copyright (c) 1995-2020 Mort Bay Consulting Pty Ltd and others.
//  ------------------------------------------------------------------------
//  All rights reserved. This program and the accompanying materials
//  are made available under the terms of the Eclipse Public License v1.0
//  and Apache License v2.0 which accompanies this distribution.
//
//      The Eclipse Public License is available at
//      http://www.eclipse.org/legal/epl-v10.html
//
//      The Apache License v2.0 is available at
//      http://www.opensource.org/licenses/apache2.0.php
//
//  You may elect to redistribute this code under either of these licenses.
//  ========================================================================
//

package org.eclipse.jetty.servlets;

import java.io.IOException;
import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;
import java.util.regex.Matcher;
import java.util.regex.Pattern;
import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.http.HttpServletRequest;

/* ------------------------------------------------------------ */
/** User Agent Filter.
 * <p>
 * This filter allows efficient matching of user agent strings for
 * downstream or extended filters to use for browser specific logic.
 * </p>
 * <p>
 * The filter is configured with the following init parameters:
 * <dl>
 * <dt>attribute</dt><dd>If set, then the request attribute of this name is set with the matched user agent string</dd>
 * <dt>cacheSize</dt><dd>The size of the user-agent cache, used to avoid reparsing of user agent strings. The entire cache is flushed
 * when this size is reached</dd>
 * <dt>userAgent</dt><dd>A regex {@link Pattern} to extract the essential elements of the user agent.
 * The concatenation of matched pattern groups is used as the user agent name</dd>
 * <dl>
 * An example value for pattern is <code>(?:Mozilla[^\(]*\(compatible;\s*+([^;]*);.*)|(?:.*?([^\s]+/[^\s]+).*)</code>. These two
 * pattern match the common compatibility user-agent strings and extract the real user agent, failing that, the first
 * element of the agent string is returned.
 *
 *
 */
public class UserAgentFilter implements Filter
{
    private static final String __defaultPattern = "(?:Mozilla[^\\(]*\\(compatible;\\s*+([^;]*);.*)|(?:.*?([^\\s]+/[^\\s]+).*)";
    private Pattern _pattern = Pattern.compile(__defaultPattern);
    private Map<String, String> _agentCache = new ConcurrentHashMap<String, String>();
    private int _agentCacheSize=1024;
    private String _attribute;

    /* ------------------------------------------------------------ */
    /* (non-Javadoc)
     * @see javax.servlet.Filter#destroy()
     */
    public void destroy()
    {
    }

    /* ------------------------------------------------------------ */
    /* (non-Javadoc)
     * @see javax.servlet.Filter#doFilter(javax.servlet.ServletRequest, javax.servlet.ServletResponse, javax.servlet.FilterChain)
     */
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException
    {
        if (_attribute!=null && _pattern!=null)
        {
            String ua=getUserAgent(request);
            request.setAttribute(_attribute,ua);
        }
        chain.doFilter(request,response);
    }

    /* ------------------------------------------------------------ */
    /* (non-Javadoc)
     * @see javax.servlet.Filter#init(javax.servlet.FilterConfig)
     */
    public void init(FilterConfig filterConfig) throws ServletException
    {
        _attribute=filterConfig.getInitParameter("attribute");

        String p=filterConfig.getInitParameter("userAgent");
        if (p!=null)
            _pattern=Pattern.compile(p);

        String size=filterConfig.getInitParameter("cacheSize");
        if (size!=null)
            _agentCacheSize=Integer.parseInt(size);
    }

    /* ------------------------------------------------------------ */
    public String getUserAgent(ServletRequest request)
    {
        String ua=((HttpServletRequest)request).getHeader("User-Agent");
        return getUserAgent(ua);
    }

    /* ------------------------------------------------------------ */
    /** Get UserAgent.
     * The configured agent patterns are used to match against the passed user agent string.
     * If any patterns match, the concatenation of pattern groups is returned as the user agent
     * string. Match results are cached.
     * @param ua A user agent string
     * @return The matched pattern groups or the original user agent string
     */
    public String getUserAgent(String ua)
    {
        if (ua == null)
            return null;

        String tag = _agentCache.get(ua);

        if (tag == null)
        {
            if (_pattern != null)
            {
                Matcher matcher = _pattern.matcher(ua);
                if (matcher.matches())
                {
                    if (matcher.groupCount() > 0)
                    {
                        for (int g = 1; g <= matcher.groupCount(); g++)
                        {
                            String group = matcher.group(g);
                            if (group != null)
                                tag = tag == null ? group : tag + group;
                        }
                    }
                    else
                    {
                        tag = matcher.group();
                    }
                }
            }

            if (tag == null)
                tag = ua;

            if (_agentCache.size() >= _agentCacheSize)
                _agentCache.clear();
            _agentCache.put(ua, tag);
        }

        return tag;
    }
}
