package efivar

import (
	"bytes"
	"errors"
	"fmt"
	"io/ioutil"
	"os"
	"os/exec"
	"strconv"
	"strings"

	"github.com/google/uuid"
)

// const efiVarDir = "/sys/firmware/efi/efivars"
const execPath = "/usr/bin/efivar"

var VendorID = uuid.MustParse("638a24ce-a0ce-4908-8152-b2a4e8b2f29d")

const (
	VarBootUUID  = "HTTP_BOOT_UUID"
	VarBootPort  = "HTTP_BOOT_MCAST_PORT"
	VarBootGroup = "HTTP_BOOT_MCAST_GROUP"
	VarBootIP    = "HTTP_BOOT_IP"
)

var ErrNotFound = errors.New("variable not found")

func toFullVarName(gid uuid.UUID, varName string) string {
	return strings.Join([]string{gid.String(), varName}, "-")
}

func numSliceToBytes(in []string) ([]byte, error) {
	res := []byte{}
	for i, n := range in {
		strippedN := strings.TrimSpace(n)
		if len(strippedN) == 0 {
			continue
		}
		intN, err := strconv.Atoi(strippedN)
		if err != nil {
			return nil, fmt.Errorf("invalid number %s at index %d", n, i)
		}
		if intN < 0 || intN > 255 {
			return nil, fmt.Errorf("value %d at index %d out of range", intN, i)
		}
		res = append(res, byte(intN))
	}
	return res, nil
}

func GetVar(gid uuid.UUID, varName string) ([]byte, error) {
	cmd := exec.Command(execPath, "-n", toFullVarName(gid, varName), "-d")
	var outBuf, errBuf bytes.Buffer
	cmd.Stdout = &outBuf
	cmd.Stderr = &errBuf

	err := cmd.Run()
	var exitErr exec.ExitError
	e := &exitErr
	if err != nil && !errors.As(err, &e) {
		return nil, err
	}
	if cmd.ProcessState.ExitCode() != 0 {
		stderr := errBuf.String()
		if strings.Contains(stderr, "No such file or directory") {
			return nil, ErrNotFound
		}
		return nil, fmt.Errorf("error getting variable, returncode %d, stderr %q", cmd.ProcessState.ExitCode(), stderr)
	}

	nums := strings.Split(outBuf.String(), " ")
	return numSliceToBytes(nums)
}

func SetVar(gid uuid.UUID, varName string, value []byte) error {
	tmpVarFile, err := os.CreateTemp("/tmp", "efitmpvar")
	if err != nil {
		return fmt.Errorf("failed to create tmp file to write variable: %w", err)
	}
	defer tmpVarFile.Close()
	defer os.Remove(tmpVarFile.Name())

	if err := ioutil.WriteFile(tmpVarFile.Name(), value, 0o500); err != nil {
		return fmt.Errorf("failed to write variable value to tmp file: %w", err)
	}

	cmd := exec.Command(execPath, "-n", toFullVarName(gid, varName), "-w", "-f", tmpVarFile.Name())
	var errBuf bytes.Buffer
	cmd.Stderr = &errBuf

	err = cmd.Run()
	var exitErr exec.ExitError
	e := &exitErr
	if err != nil && !errors.As(err, &e) {
		return err
	}
	if cmd.ProcessState.ExitCode() != 0 {
		stderr := errBuf.String()
		return fmt.Errorf("error setting variable, returncode %d, stderr %q", cmd.ProcessState.ExitCode(), stderr)
	}
	return nil
}