ValidateCpf.cs

using System.Text.RegularExpressions;

namespace ApplicationsManager.Api.Application.Common.Validators;

public static class ValidateCpf
{
    public static bool IsValid(string cpf)
    {
        if (string.IsNullOrWhiteSpace(cpf))
            return false;

        cpf = new Regex(@"[.\-]").Replace(cpf, "");

        if (cpf.Length != 11)
            return false;

        var verifyingDigits = cpf[^2..].Select(x => int.Parse(x.ToString())).ToList();
        var cpfWithoutLastTwoDigits = cpf[..9].Select(x => int.Parse(x.ToString())).ToList();

        var testOne = new[] { 10, 9, 8, 7, 6, 5, 4, 3, 2 };
        var testTwo = new[] { 11, 10, 9, 8, 7, 6, 5, 4, 3, 2 };

        int verifyingDigitOne, verifyingDigitTwo;

        int[] resultOne = new int[testOne.Length], resultTwo = new int[testTwo.Length];

        for (byte i = 0; i < testOne.Length; i++)
            resultOne[i] = cpfWithoutLastTwoDigits[i] * testOne[i];

        var resultOneSum = resultOne.Sum();

        if (resultOneSum % 11 < 2)
            verifyingDigitOne = 0;
        else
            verifyingDigitOne = 11 - resultOneSum % 11;

        if (verifyingDigits[0] != verifyingDigitOne)
            return false;

        cpfWithoutLastTwoDigits.Add(verifyingDigitOne);

        for (byte i = 0; i < testTwo.Length; i++)
            resultTwo[i] = cpfWithoutLastTwoDigits[i] * testTwo[i];

        var resultTwoSum = resultTwo.Sum();

        if (resultTwoSum % 11 < 2)
            verifyingDigitTwo = 0;
        else
            verifyingDigitTwo = 11 - resultTwoSum % 11;

        return verifyingDigits[1] == verifyingDigitTwo;
    }
}