// Веб-сервер для смены пароля на почтовый ящик @sch9.ru
//
// Copyright (c) 2025 Nikita Osokin.
//
// Redistribution and use in source and binary forms, with or without modification, are permitted
// provided that the following conditions are met:
// 1. Redistributions of source code must retain the above copyright notice, this list of
//    conditions and the following disclaimer.
// 2. Redistributions in binary form must reproduce the above copyright notice, this list of
//    conditions and the following disclaimer in the documentation and/or other materials provided
//    with the distribution.
//
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR
// IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY
// AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR
// CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
// CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
// SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR
// OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
// POSSIBILITY OF SUCH DAMAGE.

package main

import (
	"io"
	"log"
	"net/http"
	"os"
	"os/exec"
	"strconv"
	"strings"
	"sync"
)

var status404_text	[]byte
var index_text		[]byte
var passwd_file_mutex	sync.Mutex

func validate_chpasswd_input(reader io.Reader) ([]byte, bool) {
	buf := make([]byte, 2049 * 4)
	l, _ := reader.Read(buf)

	eof_check := make([]byte, 1)
	n, err := reader.Read(eof_check)
	if n != 0 || err != io.EOF {
		return nil, false
	}

	i := 0
	lines_found := 0
	line_start := 0
	for i < l {
		if buf[i] == '\n' {
			if(i + 1 - line_start > 2049 || i + 1 - line_start == 1) {
				return nil, false
			}

			line_start = i + 1
			lines_found++
			if(lines_found == 4) {
				break
			}
		}

		i++
	}

	if lines_found != 4 || i + 1 != l {
		return nil, false
	}
	return buf, true
}

func handle_request(writer http.ResponseWriter, request *http.Request) {
	if request.URL.Path != "/" {
		writer.WriteHeader(http.StatusNotFound)
		writer.Write(status404_text)
	} else {
		if request.Method == http.MethodGet {
			writer.Write(index_text)
		} else if request.Method == http.MethodPost {
			passwd_file_mutex.Lock()

			lines, could_read := validate_chpasswd_input(request.Body)
			if !could_read {
				writer.WriteHeader(http.StatusBadRequest)
				writer.Write([]byte("250")) // -6, INVALID_INPUT

				passwd_file_mutex.Unlock()
				return
			}

			chpasswd := exec.Command("./chpasswd", "./chpasswd")
			chpasswd.Stdin = strings.NewReader(string(lines))
			chpasswd_res := chpasswd.Run()
			if chpasswd_res != nil {
				writer.WriteHeader(http.StatusBadRequest)
				writer.Write([]byte(strconv.Itoa(chpasswd_res.(*exec.ExitError).ExitCode())))

				passwd_file_mutex.Unlock()
				return
			}

			update := exec.Command("/sbin/smtpctl", "update", "table", "creds")
			update_res := update.Run()
			if update_res != nil {
				writer.WriteHeader(http.StatusBadRequest)
				writer.Write([]byte("255")) // -1, INTERNAL_ERROR

				passwd_file_mutex.Unlock()
				return
			}
 
			writer.Write([]byte("0"))

			passwd_file_mutex.Unlock()
			return
		} else {
			writer.WriteHeader(http.StatusNotImplemented)
		}
	}
}

func handle_favicon(writer http.ResponseWriter, request *http.Request) {
	writer.WriteHeader(http.StatusNotFound)
}

func get_file_text(name string) []byte {
	var err error

	file, err := os.Open(name)
	if err != nil {
		log.Fatal(err)
	}

	file_stat, err := file.Stat()
	if err != nil {
		file.Close()
		log.Fatal(err)
	}
	text := make([]byte, file_stat.Size())

	_, err = file.Read(text);
	if err != nil {
		file.Close()
		log.Fatal(err)
	}

	file.Close()
	return text
}

func main() {
	index_text = get_file_text("index.html")
	status404_text = get_file_text("404.html")

	http.HandleFunc("/favicon.ico", handle_favicon)
	http.HandleFunc("/", handle_request)
	http.ListenAndServe(":62272", nil)
}