package licensing

import (
	"crypto/sha256"
	"encoding/hex"
	"errors"
	"fmt"
	"strings"
)

const machineHashDomain = "softbox.machine-hash.v1\x00"

// ErrInvalidMachineGUID reports a missing or malformed Windows MachineGuid.
// It intentionally contains no source value.
var ErrInvalidMachineGUID = errors.New("machine GUID is invalid")

// DeriveMachineHash returns the v1, machine-bound license hash for a normalized
// Windows MachineGuid and the Windows directory volume serial number. It never
// persists either source identifier.
func DeriveMachineHash(machineGUID string, systemVolumeSerial uint32) (string, error) {
	normalizedGUID, err := normalizeMachineGUID(machineGUID)
	if err != nil {
		return "", err
	}

	input := machineHashDomain + normalizedGUID + "\x00" + fmt.Sprintf("%08x", systemVolumeSerial)
	sum := sha256.Sum256([]byte(input))
	return hex.EncodeToString(sum[:]), nil
}

func normalizeMachineGUID(value string) (string, error) {
	value = strings.TrimSpace(value)
	if len(value) != 36 {
		return "", ErrInvalidMachineGUID
	}

	for index := 0; index < len(value); index++ {
		character := value[index]
		if character > 0x7f {
			return "", ErrInvalidMachineGUID
		}
		if index == 8 || index == 13 || index == 18 || index == 23 {
			if character != '-' {
				return "", ErrInvalidMachineGUID
			}
			continue
		}
		if !isASCIHex(character) {
			return "", ErrInvalidMachineGUID
		}
	}

	return strings.ToLower(value), nil
}

func isASCIHex(character byte) bool {
	return character >= '0' && character <= '9' ||
		character >= 'a' && character <= 'f' ||
		character >= 'A' && character <= 'F'
}