package main

import (
	"context"
	"fmt"
	"log"
	"net/http"
	"net/http/httputil"
	"net/url"
	"os"
	"os/signal"
	"strings"

	"tailscale.com/tsnet"
)

func must[T any](t T, err error) T {
	if err != nil {
		panic(err)
	}
	return t
}

func main() {
	var servers []*http.Server

	upstreamsConfig := os.Getenv("UPSTREAMS")
	hosts := strings.Split(upstreamsConfig, ",")
	if upstreamsConfig == "" || len(hosts) == 0 {
		log.Fatalf("set UPSTREAMS in environment like 'dockerhost:7400,otherdocker:80'")
	}

	for _, upstream := range hosts {
		hostname, port, ok := strings.Cut(upstream, ":")
		if hostname == "" {
			// parsing error, just skip it
			continue
		}
		if !ok || port == "" {
			// default to 80
			port = "80"
		}
		s := &tsnet.Server{
			Dir:      "/.config/" + hostname,
			Hostname: hostname,
			Logf: func(s string, a ...any) { // silence most tsnet logs
				if strings.HasPrefix(s, "To start this tsnet server") {
					log.Printf(s, a...)
				}
			},
		}
		defer s.Close()

		ln, err := s.Listen("tcp", ":80")
		if err != nil {
			fmt.Printf("%+v\n", err)
			return
		}
		defer ln.Close()

		srv := &http.Server{
			Handler: httputil.NewSingleHostReverseProxy(
				must(url.Parse("http://" + hostname + ":" + port + "/")),
			),
		}
		servers = append(servers, srv)
		// start server
		go func() {
			err = srv.Serve(ln)
			fmt.Printf("%+v\n", err)
		}()
	}

	sigint := make(chan os.Signal, 1)
	signal.Notify(sigint, os.Interrupt)
	<-sigint
	for _, server := range servers {
		if err := server.Shutdown(context.Background()); err != nil {
			log.Printf("HTTP server Shutdown: %v", err)
		}
	}
}