/*
SGBlog -- Git-based CGI blogging engine
Copyright (C) 2020 Sergey Matveev <stargrave@stargrave.org>

This program is free software: you can redistribute it and/or modify
it under the terms of the GNU Affero 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 Affero General Public License
along with this program.  If not, see <http://www.gnu.org/licenses/>.
*/

// Git-based CGI blogging engine email to comments adder
package main

import (
	"bytes"
	"crypto/sha1"
	"encoding/hex"
	"flag"
	"fmt"
	"io/ioutil"
	"log"
	"net/mail"
	"os"
	"os/exec"
	"strconv"
	"strings"
	"syscall"
	"time"

	"go.cypherpunks.ru/netstring/v2"
)

const WhenFmt = "2006-01-02 15:04:05Z07:00"

func main() {
	gitCmd := flag.String("git-cmd", "/usr/local/bin/git", "Path to git executable")
	gitDir := flag.String("git-dir", "", "Path to .git repository")
	notesRef := flag.String("ref", "comments", "notes reference name")
	umask := flag.String("umask", "027", "umask value")
	dryRun := flag.Bool("dryrun", false, "Show comment, do not add")
	flag.Parse()
	uid := syscall.Geteuid()
	if err := syscall.Setuid(uid); err != nil {
		log.Fatal(err)
	}
	umaskInt, err := strconv.ParseUint(*umask, 8, 16)
	if err != nil {
		panic(err)
	}
	syscall.Umask(int(umaskInt))

	msg, err := mail.ReadMessage(os.Stdin)
	if err != nil {
		log.Fatal(err)
	}
	subj, r, err := parseEmail(msg)
	if err != nil {
		log.Fatal(err)
	}
	body, err := ioutil.ReadAll(r)
	if err != nil {
		log.Fatal(err)
	}
	from := msg.Header.Get("From")
	if from == "" {
		log.Fatal("From is missing")
	}
	if len(body) == 0 {
		log.Fatal("no body")
	}

	subj = strings.TrimPrefix(subj, "Re: ")
	if h, err := hex.DecodeString(subj); err != nil || len(h) != sha1.Size {
		os.Exit(0)
	}
	fromCols := strings.Fields(from)
	if len(fromCols) == 1 {
		if idx := strings.Index(from, "@"); idx != -1 {
			from = strings.Trim(from[:idx], "<>")
		}
	} else {
		from = strings.Join(fromCols[:len(fromCols)-1], " ")
	}

	cmd := exec.Command(
		*gitCmd, "--git-dir", *gitDir,
		"notes", "--ref", *notesRef, "show", subj,
	)
	note, _ := cmd.Output()
	note = bytes.TrimSuffix(note, []byte{'\n'})

	// Remove trailing whitespaces, because git-notes-add will remove
	// them anyway, and we have to know exact bytes count
	lines := strings.Split(string(body), "\n")
	for i, line := range lines {
		lines[i] = strings.TrimRight(line, " ")
	}
	for lines[len(lines)-1] == "" {
		lines = lines[:len(lines)-1]
	}

	buf := bytes.NewBuffer(note)
	w := netstring.NewWriter(buf)
	w.WriteChunk([]byte(fmt.Sprintf(
		"From: %s\nDate: %s\n\n%s",
		from,
		time.Now().Format(WhenFmt),
		strings.Join(lines, "\n"),
	)))

	if *dryRun {
		fmt.Print(buf.String())
		os.Exit(0)
	}

	cmd = exec.Command(
		*gitCmd, "--git-dir", *gitDir,
		"notes", "--ref", *notesRef, "add",
		"-F", "-", "-f", subj,
	)
	cmd.Stdin = buf
	if err = cmd.Run(); err != nil {
		log.Fatal(err)
	}
}