package main

import (
	"embed"
	"fmt"
	"io/fs"
	"log"
	"net/http"
	"os"
	"path"
	"time"
)

var version = "development"

//go:embed public/*
var embeddedPublic embed.FS

// bytes of the 404.html page.
var b404 []byte

// usrIP is a good way to read the src IP this way because we trust our proxy.
// largely from: https://stackoverflow.com/a/55738279
func usrIP(r *http.Request) string {
	ip := r.Header.Get("x-forwarded-for")
	if ip == "" {
		ip = r.Header.Get("x-real-ip")
	}

	if ip == "" {
		ip = r.RemoteAddr
	}

	return ip
}

// notFound writes back 404 and the 404 page.
func notFound(w http.ResponseWriter, r *http.Request) {
	w.WriteHeader(http.StatusNotFound)
	w.Write(b404)
}

// handleNotFound allows us to override the response on e.g. 404.
// inspired by https://stackoverflow.com/a/62747667
func handleNotFound(fs http.FileSystem) http.Handler {
	fileServer := http.FileServer(fs)
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		p := r.URL.Path
		// so as not to allow path traversals.
		cleanedPath := path.Clean(p)
		_, err := fs.Open(cleanedPath)
		if os.IsNotExist(err) {
			log.Printf("Error 404 Not Found when serving path: %s, cleaned path: %s, IP: %s",
				p, cleanedPath, usrIP(r))
			notFound(w, r)
			return
		}
		fileServer.ServeHTTP(w, r)
	})
}

func main() {
	// TODO: ENV WHATPORT
	// TODO: add /ip endpoint that returns the src IP.
	f404, err := embeddedPublic.ReadFile("public/404.html")
	if err != nil {
		log.Fatalf("no 404.html in the folder, weird: %s", fmt.Errorf("err: %w", err))
	}

	b404 = f404

	root, err := fs.Sub(embeddedPublic, "public")
	if err != nil {
		log.Fatal(err)
	}

	log.Printf("Starting app built from revision '%s'\n", version)
	log.Print("Listening on :1314...")

	// https://blog.cloudflare.com/the-complete-guide-to-golang-net-http-timeouts/
	srv := http.Server{
		ReadTimeout:  15 * time.Second,
		WriteTimeout: 15 * time.Second,
		Addr:         ":1314",
		Handler:      handleNotFound(http.FS(root)),
	}

	err = srv.ListenAndServe()
	if err != nil {
		log.Fatal(err)
	}
}