/* SPDX-License-Identifier: GPL-2.0
 *
 * Copyright (C) 2017-2018 Jason A. Donenfeld <Jason@zx2c4.com>. All Rights Reserved.
 */

package main

import (
	"fmt"
	"os"
	"os/signal"
	"runtime"
	"strconv"
)

const (
	ExitSetupSuccess = 0
	ExitSetupFailed  = 1
)

const (
	ENV_WG_TUN_FD             = "WG_TUN_FD"
	ENV_WG_UAPI_FD            = "WG_UAPI_FD"
	ENV_WG_PROCESS_FOREGROUND = "WG_PROCESS_FOREGROUND"
)

func printUsage() {
	fmt.Printf("usage:\n")
	fmt.Printf("%s [-f/--foreground] INTERFACE-NAME\n", os.Args[0])
}

func warning() {
	shouldQuit := false

	fmt.Fprintln(os.Stderr, "WARNING WARNING WARNING WARNING WARNING WARNING WARNING")
	fmt.Fprintln(os.Stderr, "W                                                     G")
	fmt.Fprintln(os.Stderr, "W   This is alpha software. It will very likely not   G")
	fmt.Fprintln(os.Stderr, "W   do what it is supposed to do, and things may go   G")
	fmt.Fprintln(os.Stderr, "W   horribly wrong. You have been warned. Proceed     G")
	fmt.Fprintln(os.Stderr, "W   at your own risk.                                 G")
	if runtime.GOOS == "linux" {
		shouldQuit = os.Getenv("WG_I_PREFER_BUGGY_USERSPACE_TO_POLISHED_KMOD") != "1"

		fmt.Fprintln(os.Stderr, "W                                                     G")
		fmt.Fprintln(os.Stderr, "W   Furthermore, you are running this software on a   G")
		fmt.Fprintln(os.Stderr, "W   Linux kernel, which is probably unnecessary and   G")
		fmt.Fprintln(os.Stderr, "W   foolish. This is because the Linux kernel has     G")
		fmt.Fprintln(os.Stderr, "W   built-in first class support for WireGuard, and   G")
		fmt.Fprintln(os.Stderr, "W   this support is much more refined than this       G")
		fmt.Fprintln(os.Stderr, "W   program. For more information on installing the   G")
		fmt.Fprintln(os.Stderr, "W   kernel module, please visit:                      G")
		fmt.Fprintln(os.Stderr, "W           https://www.wireguard.com/install         G")
		if shouldQuit {
			fmt.Fprintln(os.Stderr, "W                                                     G")
			fmt.Fprintln(os.Stderr, "W   If you still want to use this program, against    G")
			fmt.Fprintln(os.Stderr, "W   the sage advice here, please first export this    G")
			fmt.Fprintln(os.Stderr, "W   environment variable:                             G")
			fmt.Fprintln(os.Stderr, "W   WG_I_PREFER_BUGGY_USERSPACE_TO_POLISHED_KMOD=1    G")
		}
	}
	fmt.Fprintln(os.Stderr, "W                                                     G")
	fmt.Fprintln(os.Stderr, "WARNING WARNING WARNING WARNING WARNING WARNING WARNING")

	if shouldQuit {
		os.Exit(1)
	}
}

func main() {
	warning()

	// parse arguments

	var foreground bool
	var interfaceName string
	if len(os.Args) < 2 || len(os.Args) > 3 {
		printUsage()
		return
	}

	switch os.Args[1] {

	case "-f", "--foreground":
		foreground = true
		if len(os.Args) != 3 {
			printUsage()
			return
		}
		interfaceName = os.Args[2]

	default:
		foreground = false
		if len(os.Args) != 2 {
			printUsage()
			return
		}
		interfaceName = os.Args[1]
	}

	if !foreground {
		foreground = os.Getenv(ENV_WG_PROCESS_FOREGROUND) == "1"
	}

	// get log level (default: info)

	logLevel := func() int {
		switch os.Getenv("LOG_LEVEL") {
		case "debug":
			return LogLevelDebug
		case "info":
			return LogLevelInfo
		case "error":
			return LogLevelError
		}
		return LogLevelInfo
	}()

	logger := NewLogger(
		logLevel,
		fmt.Sprintf("(%s) ", interfaceName),
	)

	logger.Debug.Println("Debug log enabled")

	// open TUN device (or use supplied fd)

	tun, err := func() (TUNDevice, error) {
		tunFdStr := os.Getenv(ENV_WG_TUN_FD)
		if tunFdStr == "" {
			return CreateTUN(interfaceName)
		}

		// construct tun device from supplied fd

		fd, err := strconv.ParseUint(tunFdStr, 10, 32)
		if err != nil {
			return nil, err
		}

		file := os.NewFile(uintptr(fd), "")
		return CreateTUNFromFile(file)
	}()

	if err != nil {
		logger.Error.Println("Failed to create TUN device:", err)
		os.Exit(ExitSetupFailed)
	}

	// open UAPI file (or use supplied fd)

	fileUAPI, err := func() (*os.File, error) {
		uapiFdStr := os.Getenv(ENV_WG_UAPI_FD)
		if uapiFdStr == "" {
			return UAPIOpen(interfaceName)
		}

		// use supplied fd

		fd, err := strconv.ParseUint(uapiFdStr, 10, 32)
		if err != nil {
			return nil, err
		}

		return os.NewFile(uintptr(fd), ""), nil
	}()

	if err != nil {
		logger.Error.Println("UAPI listen error:", err)
		os.Exit(ExitSetupFailed)
		return
	}
	// daemonize the process

	if !foreground {
		env := os.Environ()
		env = append(env, fmt.Sprintf("%s=3", ENV_WG_TUN_FD))
		env = append(env, fmt.Sprintf("%s=4", ENV_WG_UAPI_FD))
		env = append(env, fmt.Sprintf("%s=1", ENV_WG_PROCESS_FOREGROUND))
		attr := &os.ProcAttr{
			Files: []*os.File{
				nil, // stdin
				nil, // stdout
				nil, // stderr
				tun.File(),
				fileUAPI,
			},
			Dir: ".",
			Env: env,
		}

		path, err := os.Executable()
		if err != nil {
			logger.Error.Println("Failed to determine executable:", err)
			os.Exit(ExitSetupFailed)
		}

		process, err := os.StartProcess(
			path,
			os.Args,
			attr,
		)
		if err != nil {
			logger.Error.Println("Failed to daemonize:", err)
			os.Exit(ExitSetupFailed)
		}
		process.Release()
		return
	}

	// create wireguard device

	device := NewDevice(tun, logger)

	logger.Info.Println("Device started")

	// start uapi listener

	errs := make(chan error)
	term := make(chan os.Signal)

	uapi, err := UAPIListen(interfaceName, fileUAPI)

	go func() {
		for {
			conn, err := uapi.Accept()
			if err != nil {
				errs <- err
				return
			}
			go ipcHandle(device, conn)
		}
	}()

	logger.Info.Println("UAPI listener started")

	// wait for program to terminate

	signal.Notify(term, os.Kill)
	signal.Notify(term, os.Interrupt)

	select {
	case <-term:
	case <-errs:
	case <-device.Wait():
	}

	// clean up

	uapi.Close()
	device.Close()

	logger.Info.Println("Shutting down")
}