extension String {
    var isValidCNH: Bool {
        let cnhLenght = 11
        if self.digitsOnly().length != cnhLenght  {
            return false
        }

        var countResult = 0
        var count = 9

        for i in 0...9 {
            countResult += (Int(String(self[self.index(from: i)])) ?? 0 - 48) * count
            count = count - 1
        }

        var dsc = 0
        var firstIdentifier = countResult % cnhLenght

        if firstIdentifier >= 10 {
            firstIdentifier = 0
            dsc = 2
        }

        countResult = 0
        count = 0

        for i in 0...8 {
            count = count + 1
            countResult += (Int(String(self[self.index(from: i)])) ?? 0 - 48) * count
        }

        let remainder = countResult % cnhLenght
        let secondIndetifier = (remainder >= 10) ? 0 : remainder - dsc
        return "\(firstIdentifier)\(secondIndetifier)" == self.substring(from: self.length - 2)
    }
 }