update/backup.go

package main

import (
	"bufio"
	"errors"
	"fmt"
	"io/fs"
	"log"
	"os"
	"os/exec"
	"strings"
)

func parseEnvironment(key string) string {
	value := os.Getenv(key)
	if value == "" {
		log.Panicf("%s is not set\n", key)
	}
	if _, err := os.Stat(value); err != nil {
		if errors.Is(err, fs.ErrNotExist) {
			log.Panicf("%s does not point to a valid path\n", key)
		}
		log.Panicf("trying to stat %s produced an unkown error\n", value)
	}
	return value
}

func parsePacmanConf() string {
	var path string

	file, err := os.Open("/etc/pacman.conf")
	if err != nil {
		log.Panicln(err)
	}
	defer func() {
		if err := file.Close(); err != nil {
			log.Panicln(err)
		}
	}()

	scanner := bufio.NewScanner(file)
	for scanner.Scan() {
		line := scanner.Text()
		if !strings.Contains(line, "DBPath") {
			continue
		}
		path = strings.TrimSpace(strings.Split(line, "=")[1])
		break
	}

	if _, err := os.Stat(path); err != nil {
		if errors.Is(err, fs.ErrNotExist) {
			log.Panicln("DBPath in /etc/pacman.conf does not point to a valid path")
		}
		log.Panicf("trying to stat %s produced an unkown error\n", path)
	}

	return fmt.Sprintf("%s%s", path, "local")
}

func preBackup() {
	pacmanDb := parsePacmanConf()
	log.Printf("pacmanDb: %s\n", pacmanDb)
	tmpPath := "/tmp/update/pre_backup"

	output, err := exec.Command("pacman",  "--verbose", "--query").Output()
	if err != nil {
		log.Panicln(err)
	}

	err = os.MkdirAll(tmpPath, 0755)

	err = os.WriteFile(fmt.Sprintf("%s/%s", tmpPath, "pre_pacman.txt"), output, 0644)
	if err != nil {
		log.Panicln(err)
	}

	defer func() {
		if r := recover(); r != nil {
			err := os.RemoveAll(tmpPath)
			if err != nil {
				log.Fatal(err)
			}

			err = CopyDir(pacmanDb, fmt.Sprintf("%s/%s", tmpPath, pacmanDb))
			if err != nil {
				log.Panicln(err)
			}

			log.Println("recovered successfully")
		}
	}()

	err = CopyDir(pacmanDb, fmt.Sprintf("%s/%s", tmpPath, pacmanDb))
	if err != nil {
		log.Panicln(err)
	}
}

func postBackup() {
	/*
	 * basic logic for post:
	 * create new pkg list and delete all lines which are the same as pre
	 */
	panic("unimplemented")
}

func main() {
	// backup_dir := parseEnvironment("UPDATE_BACKUP_DIR")
	cmdlineArg := os.Args[1]
	log.Printf("cmdlineArg: %s\n", cmdlineArg)

	if cmdlineArg == "pre" {
		preBackup()
	} else if cmdlineArg == "post" {
		postBackup()
	} else {
		log.Panicf("invalid cmdline argument. supplied value was: %s\n", cmdlineArg)
	}
}