package main

import (
	"bytes"
	"compress/gzip"
	"fmt"
	"golang.org/x/net/http2"
	"golang.org/x/net/http2/h2c"
	"io/ioutil"
	"net/http"
	"net/http/httputil"
	"strconv"
	"time"
)

func ForwardAnalytics(req *http.Request) {
	req.URL.Scheme = "https"
	req.URL.Host = "www.google-analytics.com"
	req.Host = "www.google-analytics.com"
	req.URL.Path = "/analytics.js"
	req.Header.Set("Accept-Encoding", "gzip")
}

func ModifyAnalytics(r *http.Response) error {
	bytesFromBody, err := ioutil.ReadAll(r.Body)
	defer r.Body.Close()
	if err != nil {
		return nil
	}
	if r.Header.Get("Content-Encoding") == "gzip" {
		gzipReader, err := gzip.NewReader(bytes.NewBuffer(bytesFromBody))
		if err != nil {
			return nil
		}
		defer gzipReader.Close()
		readableBytes, err := ioutil.ReadAll(gzipReader)
		var b bytes.Buffer
		gzipWriter, err := gzip.NewWriterLevel(&b, gzip.DefaultCompression)
		if err != nil {
			return nil
		}
		defer gzipWriter.Close()
		writtenLen, err := gzipWriter.Write(readableBytes)
		fmt.Println("Wrote ", writtenLen)
		if err != nil {
			return nil
		}
		r.ContentLength = int64(len(readableBytes))
		r.Header.Set("Content-Length", strconv.FormatInt(int64(len(readableBytes)), 10))
		r.Body = ioutil.NopCloser(&b)

		return nil
	} else {
		return nil
	}
}


func handleProxy(w http.ResponseWriter, req *http.Request) {
	proxy := httputil.ReverseProxy{
		Director: ForwardAnalytics
	}
	proxy.ModifyResponse = ModifyAnalytics
	proxy.ServeHTTP(w, req)

}

func main() {
	h2s := &http2.Server{
		IdleTimeout: 20 * time.Second,
	}
	mux := http.NewServeMux()
	mux.HandleFunc( "/", handleProxy)
	s := &http.Server{
		ReadHeaderTimeout: 20 * time.Second,
		ReadTimeout:       10 * time.Second,
		WriteTimeout:      30 * time.Second,
		Addr:              "localhost:8456",
		Handler:           h2c.NewHandler(mux, h2s),
	}
	s.ListenAndServe()
}