/*
paster -- paste service
Copyright (C) 2021-2022 Sergey Matveev <stargrave@stargrave.org>

This program is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, version 3 of the License.

This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public License
along with this program.  If not, see <http://www.gnu.org/licenses/>.
*/

package main

import (
	"bufio"
	"bytes"
	"crypto/rand"
	"crypto/sha512"
	_ "embed"
	"encoding/base32"
	"encoding/hex"
	"flag"
	"fmt"
	"html/template"
	"io"
	"os"
	"strconv"
)

var (
	//go:embed asciicast.tmpl
	ASCIICastHTMLTmplRaw string
	ASCIICastHTMLTmpl    = template.Must(template.New("asciicast").Parse(
		ASCIICastHTMLTmplRaw,
	))
)

func fatal(s string) {
	fmt.Println(s)
	os.Exit(1)
}

func asciicastHTML(playerPath, cast string) error {
	var buf bytes.Buffer
	err := ASCIICastHTMLTmpl.Execute(&buf, struct {
		PlayerPath string
		Cast       string
	}{
		PlayerPath: playerPath,
		Cast:       cast,
	})
	if err != nil {
		return err
	}
	fn := cast + ".html"
	fd, err := os.OpenFile(fn, os.O_WRONLY|os.O_CREATE|os.O_EXCL, os.FileMode(0666))
	if err != nil {
		return err
	}
	if _, err = fd.Write(buf.Bytes()); err != nil {
		os.Remove(fn)
		return err
	}
	return fd.Close()
}

func main() {
	maxSize := flag.Uint64("max-size", 1<<20, "Maximal upload size")
	asciicastPath := flag.String("asciicast-path", "", "Generate HTMLs for .cast asciicasts, specify \"asciinema-player-v2.6.1\"")
	flag.Usage = func() {
		fmt.Fprintf(os.Stderr, "Usage: paster [options] URL [...]\n")
		flag.PrintDefaults()
	}
	flag.Parse()
	if len(flag.Args()) == 0 {
		flag.Usage()
		os.Exit(1)
	}
	var fn string
	r := bufio.NewReader(os.Stdin)
	b, err := r.ReadByte()
	if err != nil {
		fatal(err.Error())
	}
	if b != 'd' {
		fatal("bad bencode: no dictionary start")
	}
	buf := make([]byte, 21)
	ext := ".txt"
	var size uint64
AnotherKey:
	if _, err = io.ReadFull(r, buf[:3]); err != nil {
		fatal(err.Error())
	}
	switch s := string(buf[:3]); s {
	case "1:e":
		if _, err = io.ReadFull(r, buf[:2]); err != nil {
			fatal(err.Error())
		}
		if buf[1] != ':' {
			fatal(`bad bencode: invalid "e" format`)
		}
		extLen, err := strconv.Atoi(string(buf[:1]))
		if err != nil {
			fatal(err.Error())
		}
		if _, err = io.ReadFull(r, buf[:extLen]); err != nil {
			fatal(err.Error())
		}
		ext = "." + string(buf[:extLen])
		goto AnotherKey
	case "1:v":
		n, err := r.Read(buf)
		if err != nil {
			fatal(err.Error())
		}
		i := bytes.IndexByte(buf[:n], ':')
		if i == -1 {
			fatal(`bad bencode: invalid "v" length`)
		}
		size, err = strconv.ParseUint(string(buf[:i]), 10, 64)
		if err != nil {
			fatal(err.Error())
		}
		if size == 0 {
			fatal("empty paste")
		}
		if size > *maxSize {
			fatal("too big")
		}
		buf = buf[i+1 : n]
	default:
		fatal("bad bencode: invalid key")
	}
	rnd := make([]byte, 12)
	if _, err = io.ReadFull(rand.Reader, rnd); err != nil {
		fatal(err.Error())
	}
	fn = "." + base32.StdEncoding.WithPadding(base32.NoPadding).EncodeToString(rnd) + ext
	fd, err := os.OpenFile(fn, os.O_RDWR|os.O_CREATE|os.O_EXCL, os.FileMode(0666))
	if err != nil {
		fatal(err.Error())
	}
	h := sha512.New()
	bfd := bufio.NewWriter(fd)
	mr := io.MultiReader(bytes.NewReader(buf), r)
	mw := io.MultiWriter(bfd, h)
	if _, err = io.CopyN(mw, mr, int64(size-1)); err != nil {
		goto Failed
	}
	if len(buf) == 0 {
		buf = append(buf, 0)
	} else {
		buf = buf[:1]
	}
	if _, err = mr.Read(buf); err != nil {
		goto Failed
	}
	if _, err = mw.Write(buf); err != nil {
		goto Failed
	}
	if (ext == ".txt" || ext == ".url") && buf[0] != '\n' {
		if err = bfd.WriteByte('\n'); err != nil {
			goto Failed
		}
	}
	if _, err = mr.Read(buf); err != nil {
		goto Failed
	}
	if buf[0] != 'e' {
		os.Remove(fn)
		fatal("bad bencode: no dictionary end")
	}
	if err = bfd.Flush(); err != nil {
		goto Failed
	}
	if err = fd.Close(); err != nil {
		goto Failed
	}
	if err = os.Rename(fn, fn[1:]); err != nil {
		goto Failed
	}
	for _, u := range flag.Args() {
		fmt.Println(u + fn[1:])
	}
	fmt.Println("SHA512/2:", hex.EncodeToString(h.Sum(nil)[:512/2/8]))
	if ext == ".cast" && *asciicastPath != "" {
		if err = asciicastHTML(*asciicastPath, fn[1:]); err != nil {
			goto Failed
		}
		for _, u := range flag.Args() {
			fmt.Println(u + fn[1:] + ".html")
		}
	}
	fmt.Fprintf(
		os.Stderr,
		"[%s]:%s %s %d\n",
		os.Getenv("TCPREMOTEIP"),
		os.Getenv("TCPREMOTEPORT"),
		fn[1:], size,
	)
	return
Failed:
	os.Remove(fn)
	fatal(err.Error())
}