// Helper script for remote gdb
// Copyright (C) 2017 Moritz Bitsch
//
// 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, either version 3 of the License, or
// (at your option) any later version.
//
// 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"
	"flag"
	"fmt"
	"io"
	"os"
	"path"
	"strconv"
	"strings"

	"golang.org/x/crypto/ssh"
)

var (
	optUser     = flag.String("user", "default", "username for ssh user")
	optPassword = flag.String("pass", "", "password")
	optGdbPort  = flag.Uint("port", 10001, "remote gdb port to use")
)

func main() {
	flag.Usage = func() {
		fmt.Fprintf(os.Stderr, "Usage: %s [OPTIONS] hostname program args\n", os.Args[0])
		flag.PrintDefaults()
	}

	flag.Parse()

	if flag.NArg() < 2 {
		flag.Usage()
		os.Exit(2)
	}

	connection, err := createConnection(flag.Arg(0), *optUser, *optPassword)
	if err != nil {
		fmt.Fprintf(os.Stderr, "Can't connect to host: %s", err.Error())
		os.Exit(1)
	}
	defer connection.Close()

	err = deployFile(connection, flag.Arg(1), "/tmp/"+path.Base(flag.Arg(1)), "0755")
	if err != nil {
		fmt.Fprintf(os.Stderr, "Can't deploy file: %s", err.Error())
		os.Exit(1)
	}

	session, err := startGDB(connection, "/tmp/"+path.Base(flag.Arg(1)))
	if err != nil {
		fmt.Fprintf(os.Stderr, "Can't start gdb: %s", err.Error())
		os.Exit(1)
	}
	defer session.Close()
}

func startGDB(client *ssh.Client, remoteCommand string) (*ssh.Session, error) {
	session, err := client.NewSession()
	if err != nil {
		return nil, err
	}

	output, err := session.StderrPipe()
	if err != nil {
		return nil, err
	}

	err = session.Start("exec nohup gdbserver --once :" + strconv.Itoa(int(*optGdbPort)) + " " + remoteCommand)
	if err != nil {
		return nil, err
	}

	reader := bufio.NewReader(output)

	for line, err := reader.ReadString('\n'); err == nil; line, err = reader.ReadString('\n') {
		if strings.HasPrefix(line, "Listening on port") {
			println(line)
			break
		}
	}

	return session, nil
}

func deployFile(client *ssh.Client, localPath, remotePath string, permissions string) error {
	fmt.Printf("Deploy: %s -> %s\n", localPath, remotePath)

	reader, err := os.Open(localPath)
	if err != nil {
		return err
	}
	defer reader.Close()

	st, err := reader.Stat()
	if err != nil {
		return err
	}

	session, err := client.NewSession()
	if err != nil {
		return err
	}
	defer session.Close()

	writer, _ := session.StdinPipe()

	go func() {
		fmt.Fprintf(writer, "C%s %d %s\n", permissions, st.Size(), path.Base(remotePath))
		io.Copy(writer, reader)
		writer.Write([]byte{0x00})
		writer.Close()
	}()

	return session.Run("/usr/bin/scp -t " + path.Dir(remotePath))
}

func createConnection(host string, username string, password string) (*ssh.Client, error) {
	config := &ssh.ClientConfig{
		User: username,
		Auth: []ssh.AuthMethod{
			ssh.Password(password),
		},
		HostKeyCallback: ssh.InsecureIgnoreHostKey(),
	}

	return ssh.Dial("tcp", host, config)
}