package pkg

import (
	"encoding/json"
	"errors"
	"os"
	"os/exec"
	"path/filepath"
	"strings"
)

var ErrUnknownDistribution = errors.New("unknown linux distribution")
var ErrNoCandidateInstalled = errors.New("no package-manager candidate installed")
var ErrNoDriverFound = errors.New("no driver found for the package manager")

func Load() (PackageManager, error) {

	// 1. get distro name
	out, err := exec.Command("lsb_release", "-is").Output()
	if err != nil {
		return nil, err
	}

	distro := strings.ToLower(strings.Trim(string(out), " \n\t"))

	// 2. load config file
	driverTable := filepath.Join(os.Getenv("GOPATH"), "src/git.xdrm.io/xdrm-brackets/nix-amer/meta/pkg-drivers.json")
	file, err := os.Open(driverTable)
	if err != nil {
		return nil, err
	}
	defer file.Close()

	// 3. Parse json
	table := make(map[string][]string)
	decoder := json.NewDecoder(file)
	if err := decoder.Decode(&table); err != nil {
		return nil, err
	}
	decoder = nil

	// 4. Get available package-manager list for distro
	available, exists := table[distro]
	if !exists || len(available) < 1 {
		return nil, ErrUnknownDistribution
	}

	// 5. Check each available package-manager in order
	selected := ""
	for _, current := range available {
		if exec.Command("which", current).Run() == nil {
			selected = current
			break
		}
	}

	// no candidate installed
	if len(selected) < 1 {
		return nil, ErrNoCandidateInstalled
	}

	// 6. Instanciate
	switch selected {
	case "apt-get":
		return new(Apt), nil
	case "apk":
		return new(Apk), nil
	case "eopkg":
		return new(Eopkg), nil
	case "pacman":
		return new(Pacman), nil
	case "dnf":
		return new(Dnf), nil
	case "yum":
		return new(Yum), nil
	}

	return nil, ErrNoDriverFound

}