package main

import (
	"errors"
	"flag"
	"io"
	"log"
	"math/rand"
	"net/http"
	"os"
	"path"
	"time"
)

const letterBytes = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ"

func init() {
	rand.Seed(time.Now().UnixNano())
}

// RandString taken from https://stackoverflow.com/a/31832326
func RandString(n int) string {
	b := make([]byte, n)
	for i := range b {
		b[i] = letterBytes[rand.Int63()%int64(len(letterBytes))]
	}
	return string(b)
}

var dataDirFlag = flag.String("dataDir", "/tmp", "directory for files")
var domainFlag = flag.String("domain", "http://localhost:8085", "base domain")
var bindFlag = flag.String("bind", ":8085", "host and port to bind")

func main() {
	flag.Parse()
	h := &Handler{
		DataDir: *dataDirFlag,
		Domain:  *domainFlag,
	}
	log.Println("listening")
	panic(http.ListenAndServe(*bindFlag, h))
}

type Handler struct {
	DataDir string
	Domain  string
}

func (h *Handler) ServeHTTP(wr http.ResponseWriter, req *http.Request) {
	if req.Method != "POST" {
		return
	}

	name := RandString(8)
	for {
		_, err := os.Stat(path.Join(h.DataDir, name))
		if errors.Is(err, os.ErrNotExist) {
			break
		}

		name = RandString(8)
	}

	file, err := os.OpenFile(path.Join(h.DataDir, name), os.O_CREATE|os.O_RDWR, 0o644)
	if err != nil {
		log.Println("error:", err)
		return
	}
	defer file.Close()
	defer req.Body.Close()

	_, err = io.Copy(file, req.Body)
	if err != nil {
		log.Println("error:", err)
		return
	}

	log.Println("uploaded as", name)
	wr.Write([]byte(h.Domain + "/" + name + "\n"))
}