AmirSoleimani/IRValidator

package validate

import (
    "errors"
    "strconv"
)

var firstNumValid = [3]uint8{
    54, //6
    53, //5
    42, //4
}

//CardNumber card number validation
func CardNumber(value string) error {
    // check length
    if len(value) != 16 {
        return errors.New("card length < 16 :)")
    }

    // check #1 > first number
    err := checkFirstCardNumber(value[0])
    if err != nil {
        return err
    }

    // check #2 > calcualte *slices < 10
    sum := calculateCardNumbers(&value)

    // check #3 > %10 = 0
    if sum%10 != 0 {
        return errors.New("card number is not valid")
    }

    return nil
}

//checkFirstCardNumber first number in cardnum
func checkFirstCardNumber(firstNum uint8) error {
    for _, v := range firstNumValid {
        if v == firstNum {
            return nil
        }
    }

    return errors.New("first number isn`t valid")
}

//calculateCardNumbers Yo
func calculateCardNumbers(valueSlices *string) (sum uint64) {
    for i := 0; i < len(*valueSlices); i++ {
        v, _ := strconv.ParseUint(string((*valueSlices)[i]), 10, 8)
        var x uint64
        if i%2 == 0 {
            if x = v * 2; x >= 10 {
                x -= 9
            }
        } else {
            x = v
        }
        sum += x
    }

    return sum
}