package validation

import (
	"strconv"

	"github.com/go-playground/validator/v10"
)

func ValidateLicence(fl validator.FieldLevel) bool {
	fieldValue := fl.Field().String()
	if len(fieldValue) != 11 {
		return false
	}

	id, tenthChar := string(fieldValue[:9]), string(fieldValue[9])

	if tenthChar == "X" {
		tenthChar = "10"
	}
	tenthValue, _ := strconv.ParseInt(tenthChar, 10, 8)

	// for readability
	weights := []int{9, 8, 7, 6, 5, 4, 3, 2, 1}
	sum := 0

	for i := 0; i < 9; i++ {
		char := string(id[i])
		value, _ := strconv.ParseInt(char, 36, 64)
		sum += int(value) * weights[i]
	}

	calcCheckDigit := sum % 11
	if calcCheckDigit != int(tenthValue) {
		return false
	}

	return true
}