package com.acme.filter;

import javax.servlet.FilterChain;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpServletRequest;
import java.io.ByteArrayOutputStream;
import java.io.OutputStream;
import java.io.IOException;
import java.util.zip.GZIPOutputStream;
import java.util.Enumeration;


public class GZIPFilter extends GenericFilter
{

    public GZIPFilter() {}

    public void doFilter(final ServletRequest request, final ServletResponse response, FilterChain chain) throws IOException, ServletException
    {
        HttpServletResponse httpResponse = (HttpServletResponse) response;
        HttpServletRequest httpRequest=(HttpServletRequest) request;
        GenericResponseWrapper wrapper = new GenericResponseWrapper(httpResponse);
        chain.doFilter(request, wrapper);
        OutputStream out = response.getOutputStream();
        if (!isCached(wrapper) && !isIncluded(request) && accepts(httpRequest,"gzip"))
        {
            ByteArrayOutputStream compressed = new ByteArrayOutputStream();
            GZIPOutputStream gzout = new GZIPOutputStream(compressed);
            gzout.write(wrapper.getData());
            gzout.flush();
            gzout.close();
            httpResponse.setHeader("Content-Encoding", "gzip");
            out.write(compressed.toByteArray());
            response.setContentLength(compressed.size());
        }
        else
        {
            out.write(wrapper.getData());
        }
        out.flush();
        out.close();
    }

    protected boolean isIncluded(ServletRequest request)
    {
        String uri = (String) request.getAttribute("javax.servlet.include.request_uri");
        if (uri == null)
        {
            return false;
        }
        else
        {
            return true;
        }
    }

    protected boolean isCached(GenericResponseWrapper wrapper)
    {
        if (wrapper.getData().length > 0)
        {
            return false;
        }
        else
        {
            return true;
        }
    }

    protected boolean accepts(HttpServletRequest request, String name)
    {
        return headerContains(request,"Accept-Encoding",name);
    }



    protected boolean headerContains(HttpServletRequest request, String header, String value)
    {
       Enumeration accepted=request.getHeaders(header);
        while(accepted.hasMoreElements())
        {
            String headerValue=(String)accepted.nextElement();
            if(headerValue.indexOf(value)!=-1)
            {
                return true;
            }
        }
        return false;
    }

}