package de.is24.infrastructure.gridfs.http.web.filter;

import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletOutputStream;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletRequestWrapper;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpServletResponseWrapper;
import java.io.IOException;
import java.io.OutputStreamWriter;
import java.io.PrintWriter;
import java.io.UnsupportedEncodingException;

/**
 * Code from http://axelfontaine.com/blog/http-head.html
 */
public class HttpHeadFilter implements Filter {
  public void init(FilterConfig filterConfig) throws ServletException {
  }

  public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
    HttpServletRequest httpServletRequest = (HttpServletRequest) request;

    if (isHttpHead(httpServletRequest)) {
      HttpServletResponse httpServletResponse = (HttpServletResponse) response;
      NoBodyResponseWrapper noBodyResponseWrapper = new NoBodyResponseWrapper(httpServletResponse);

      chain.doFilter(new ForceGetRequestWrapper(httpServletRequest), noBodyResponseWrapper);
      noBodyResponseWrapper.setContentLength();
    } else {
      chain.doFilter(request, response);
    }
  }

  public void destroy() {
  }

  private boolean isHttpHead(HttpServletRequest request) {
    return "HEAD".equals(request.getMethod());
  }

  private class ForceGetRequestWrapper extends HttpServletRequestWrapper {
    public ForceGetRequestWrapper(HttpServletRequest request) {
      super(request);
    }

    public String getMethod() {
      return "GET";
    }
  }

  private class NoBodyResponseWrapper extends HttpServletResponseWrapper {
    private final NoBodyOutputStream noBodyOutputStream = new NoBodyOutputStream();
    private PrintWriter writer;

    public NoBodyResponseWrapper(HttpServletResponse response) {
      super(response);
    }

    public ServletOutputStream getOutputStream() throws IOException {
      return noBodyOutputStream;
    }

    public PrintWriter getWriter() throws UnsupportedEncodingException {
      if (writer == null) {
        writer = new PrintWriter(new OutputStreamWriter(noBodyOutputStream, getCharacterEncoding()));
      }

      return writer;
    }

    void setContentLength() {
      super.setContentLength(noBodyOutputStream.getContentLength());
    }
  }

  private class NoBodyOutputStream extends ServletOutputStream {
    private int contentLength = 0;

    int getContentLength() {
      return contentLength;
    }

    public void write(int b) {
      contentLength++;
    }

    public void write(byte[] buf, int offset, int len) throws IOException {
      contentLength += len;
    }
  }
}