package main

import (
	"encoding/json"
	"fmt"
	"log"
	"net/http"
	"net/url"
	"os"
	"regexp"
	"strings"
	"sync"
	"time"
)

var (
	long           = regexp.MustCompile(`(.{72}\S*)\s+`)
	file, requests *os.File
	m              sync.Mutex
)

func wrap(s string) string {
	return strings.ReplaceAll(long.ReplaceAllString(
		strings.ReplaceAll(s, "\r", ""), "$1\n"), "\n", "\n ")
}

func handler(w http.ResponseWriter, r *http.Request) {
	defer r.Body.Close()
	if err := r.ParseForm(); err != nil {
		w.WriteHeader(http.StatusBadRequest)
		return
	}
	text := r.FormValue("text")
	if len(text) > 64<<10 {
		w.WriteHeader(http.StatusBadRequest)
		return
	}

	m.Lock()
	defer m.Unlock()

	j, _ := json.Marshal(struct {
		URI     string
		Headers http.Header
		Form    url.Values
	}{
		URI:     r.RequestURI,
		Headers: r.Header,
		Form:    r.Form,
	})

	if s, err := file.Stat(); err != nil {
		log.Fatalln(err)
	} else if s.Size()+int64(len(text)) > 64<<20 {
		w.WriteHeader(http.StatusInternalServerError)
	} else if r.Form.Has("submit") {
		// <input type="submit"> should not be named, and thus received.
		//
		// If this is not enough to filter out most spammers, consider also:
		//  - Header: "Origin" should not be missing for POST.
		//  - Header: "Accept" should not be "*/*".
		//  - Header: "Accept-Language" and "Accept-Encoding" should be present.
		//  - Form: _charset_ should not be kept verbatim,
		//    seeing as Safari/Chromium/Firefox all pass UTF-8,
		//    in accordance with HTML5.
		w.WriteHeader(http.StatusTeapot)
	} else {
		fmt.Fprintf(file, "%s %s\n %s\n",
			time.Now().Local().Format(time.RFC1123), r.RequestURI, wrap(text))
		if err := file.Sync(); err != nil {
			log.Fatalln(err)
		}

		// To help filter out spammers.
		fmt.Fprintf(requests, "%s\n", j)
		if err := requests.Sync(); err != nil {
			log.Fatalln(err)
		}

		fmt.Fprintln(w, "Saved.")
	}
}

func main() {
	if len(os.Args) != 3 {
		log.Fatalf("Usage: %s BIND DB\n", os.Args[0])
	}

	var err error
	if file, err = os.OpenFile(os.Args[2],
		os.O_CREATE|os.O_APPEND|os.O_WRONLY, 0644); err != nil {
		log.Fatalln(err)
	}
	if requests, err = os.OpenFile(os.Args[2]+".requests",
		os.O_CREATE|os.O_APPEND|os.O_WRONLY, 0644); err != nil {
		log.Fatalln(err)
	}

	http.HandleFunc("/", handler)
	log.Fatalln(http.ListenAndServe(os.Args[1], nil))
}