Test-CCNumber - Uses the Luhn algorithm to test if a number is a valid credit card number or not

Test-CCNumber.ps1

Function Test-CCNumber {
<#
.SYNOPSIS
    Tests for valid credit card numbers
.DESCRIPTION
    Uses the Luhn algorithm to test if a number is a valid credit card number or not
.EXAMPLE
    PS C:\> Test-CCNumber -Number 9003085869539691
    Tests the number 9003085869539691
.EXAMPLE
    PS C:\> 4916910011471997, 2720996758722767, 342993248239546 | Test-CCNumber
    Tests the numbers 4916910011471997, 2720996758722767, 342993248239546
.NOTES
    Based off method described here: https://planetcalc.com/2464/
    See https://en.wikipedia.org/wiki/Luhn_algorithm for more information
#>
    param
    (
        # Numbers to test for valid Luhn
        [Parameter(Mandatory,ValueFromPipeline,ValueFromPipelineByPropertyName)]
        [long[]]
        $Number
    )
    Begin {
        function Test-Luhn($Number) {
            # Convert to Array
            $array = [int[]](($Number -split '') -ne '')

            # From the rightmost digit, which is the check digit, and moving left, double the value of every second digit. The check digit is not doubled; the first digit doubled is immediately to the left of the check digit. If the result of this doubling operation is greater than 9 (e.g., 8 × 2 = 16), then subtract 9 from the product (e.g., 16: 16 − 9 = 7, 18: 18 − 9 = 9).
            for ($i = $array.Count - 1; $i -ge 0; $i--) {
                if (($i -ne $array.Count - 1) -and $i % 2 -eq 0) {
                    $array[$i] = $array[$i] * 2
                    if ($array[$i] -gt 9) {
                        $array[$i] = $array[$i] - 9
                    }
                }
            }

            # Take the sum of all the digits.
            $sum = $array | Measure-Object -Sum | Select-Object -ExpandProperty Sum

            # If the total modulo 10 is equal to 0 (if the total ends in zero) then the number is valid according to the Luhn formula; else it is not valid.
            Write-Output (($sum) % 10 -eq 0)
        }
    }

    Process
    {
        foreach ($n in $Number) {
            [PSCustomObject]@{
                Number = $n
                Valid = Test-Luhn $n
            }
        }
    }
}