package main

import (
	"bytes"
	"encoding/json"
	"flag"
	"io"
	"log"
	"net/http"
	"net/url"
	"os"
	"strconv"
	"strings"
	"text/template"
	"time"
)

func main() {
	fs := flag.NewFlagSet(os.Args[0], flag.ContinueOnError)
	p := fs.Int("p", 28080, "port")
	t := fs.String("t", "{{ . }}", "template")
	y := fs.String("y", "http://localhost:41912", "target")
	if err := fs.Parse(os.Args[1:]); err != nil {
		panic(err)
	}

	tmpl, err := template.New("").Parse(*t)
	if err != nil {
		panic(err)
	}

	u, err := url.Parse(*y)
	if err != nil {
		panic(err)
	}

	c := &http.Client{
		Timeout: time.Minute,
		Transport: &http.Transport{
			DisableKeepAlives: true,
		},
	}

	handle := func(w http.ResponseWriter, r *http.Request) error {
		var v interface{}
		if err := json.NewDecoder(r.Body).Decode(&v); err != nil {
			return err
		}
		buff := bytes.NewBuffer(nil)
		if err := tmpl.Execute(buff, v); err != nil {
			return err
		}

		log.Printf("%+v => %s => %s", v, buff.Bytes(), u.String())

		req, err := http.NewRequest(r.Method, u.String(), io.NopCloser(buff))
		if err != nil {
			return err
		}
		req = req.WithContext(r.Context())
		for k, v := range r.Header {
			switch strings.ToLower(k) {
			case "content-length":
			default:
				req.Header.Set(k, v[0])
				for _, v := range v[1:] {
					req.Header.Add(k, v)
				}
			}
		}
		resp, err := c.Do(req)
		if err != nil {
			return err
		}
		defer resp.Body.Close()

		for k, v := range resp.Header {
			w.Header().Set(k, v[0])
			for _, v := range v[1:] {
				w.Header().Add(k, v)
			}
		}
		w.WriteHeader(resp.StatusCode)
		io.Copy(w, resp.Body)

		return nil
	}
	log.Println("listening on", *p)
	if err := http.ListenAndServe(":"+strconv.Itoa(*p), http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		if err := handle(w, r); err != nil {
			http.Error(w, err.Error(), http.StatusBadRequest)
		}
	})); err != nil {
		panic(err)
	}
}