import java.io.IOException;
import java.net.URL;

import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.annotation.WebFilter;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletRequestWrapper;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpServletResponseWrapper;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;

/**
 * Реализация CORS фильтра по спецификации
 * https://developer.mozilla.org/ru/docs/Web/HTTP/CORS
 *
 * @author stranger
 *
 */
@WebFilter("/*")
public class CorsFilter implements javax.servlet.Filter {
    private static final String ALLOWED_METHODS = "GET, POST, PUT, DELETE, OPTIONS, HEAD";
    private Log log = LogFactory.getLog(CorsFilter.class);

    @Override
    public void init(FilterConfig filterConfig) throws ServletException {
        if (log.isInfoEnabled()) {
            log.info("CorsFilter initialized");
        }
    }

    @Override
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain)
            throws IOException, ServletException {
        try {
            if (request instanceof HttpServletRequest && response instanceof HttpServletResponse) {
                final HttpServletRequestWrapper requestWrapper = new HttpServletRequestWrapper(
                        (HttpServletRequest) request);
                final String httpRequestUrl = requestWrapper.getRequestURL().toString();
                final String httpQueryString = requestWrapper.getQueryString();
                if (log.isDebugEnabled()) {
                    log.debug(String.format("%s?%s", httpRequestUrl, httpQueryString));
                }
                final String httpOrigin = requestWrapper.getHeader("origin");
                if (httpOrigin != null && !httpOrigin.isEmpty()) {
                    final URL httpOriginUrl = new URL(httpOrigin);
                    final String httpOriginHost = httpOriginUrl.getHost();
                    if (isAllowedOriginHost(httpOriginHost)) {
                        if (log.isInfoEnabled()) {
                            log.info(String.format("The %s http header origin is allowed", httpOrigin));
                        }
                        final HttpServletResponseWrapper responseWrapper = new HttpServletResponseWrapper(
                                (HttpServletResponse) response);
                        responseWrapper.setHeader("Access-Control-Allow-Origin", httpOrigin);
                        if ("OPTIONS".equals(requestWrapper.getMethod())) {
                            final String accessControlRequestHeaders = requestWrapper.getHeader("Access-Control-Request-Headers");
                            if(accessControlRequestHeaders != null ) {
                                responseWrapper.setHeader("Access-Control-Allow-Headers", accessControlRequestHeaders);
                            }
                            responseWrapper.setHeader("Access-Control-Allow-Methods", ALLOWED_METHODS);
                            responseWrapper.setHeader("Access-Control-Allow-Credentials", "true");
                            responseWrapper.setHeader("Access-Control-Max-Age", "86400");
                            responseWrapper.setStatus(204);
                            if (log.isInfoEnabled()) {
                                log.info(String.format("The CORS preflighted request (OPTIONS) for the %s origin [Access-Control-Request-Headers: %s] succeeded", httpOrigin, accessControlRequestHeaders));
                            }
                            return;
                        }
                    } else {
                        if (log.isWarnEnabled()) {
                            log.warn(String.format("The %s http header origin is not allowed and CORS request has been rejected", httpOrigin));
                        }
                    }
                }
                if (log.isDebugEnabled()) {
                    log.debug(String.format("%s?%s finished", httpRequestUrl, httpQueryString));
                }

            }
            chain.doFilter(request, response);
        } catch (Exception e) {
            log.error("Failed", e);
            chain.doFilter(request, response);
        }
    }

    @Override
    public void destroy() {
        if (log.isInfoEnabled()) {
            log.info("Destoyed");
        }
    }

    public static boolean isAllowedOriginHost(String httpOriginHost) {
        if( httpOriginHost != null ) {
            if( "localhost".equalsIgnoreCase(httpOriginHost) ) {
                return true;
            } else
            if( httpOriginHost.equals("127.0.0.1") ) {
                return true;
            } else
            if( httpOriginHost.startsWith("10.") ) {
                return true;
            } else
            if( httpOriginHost.startsWith("100.") ) {
                String parts[] = httpOriginHost.split("/.");
                if( parts.length == 4 ) {
                    int d = Integer.valueOf(parts[2]);
                    return 64 <= d && d <= 127;
                }
            } else
            if( httpOriginHost.startsWith("172.") ) {
                String parts[] = httpOriginHost.split("/.");
                if( parts.length == 4 ) {
                    int d = Integer.valueOf(parts[2]);
                    return 16 <= d && d <= 31;
                }
            } else
            if( httpOriginHost.startsWith("192.168.") ) {
                return true;
            }
        }
        return false;
    }



}