PowerShell custom argument transformation attribute for DateTime

customArgumenTransformationAttribute_DateTime.ps1

class DateTransformAttribute : System.Management.Automation.ArgumentTransformationAttribute {
   
    # property to take additional format strings for transformations
    [string[]]$AdditionalFormatStrings 

    # default constructor:
    DateTransformAttribute() : base() { }

    # 2nd constructor with parameter AdditionalFormatStrings
    DateTransformAttribute([string[]]$AdditionalFormatStrings) : base() {
        $this.AdditionalFormatStrings = $AdditionalFormatStrings
    }

    # Transform() method is called whenever there is a variable or parameter assignment.

    [object] Transform([System.Management.Automation.EngineIntrinsics]$engineIntrinsics, [object] $inputData) {
        if ($inputData -as [datetime]) {
            # return as-is:
            return ($inputData -as [datetime])
        }
        # get the provided format strings first for them to take precedence
        $dateFormatStrings = $this.AdditionalFormatStrings
        # add the static date format strings
        $dayFirstFormats = 'd/M h:mtt', 'dd/MM hh:mmtt', 'dd/MM hh:mm:ss tt'
        # add same with '.' as delimiter
        $dayFirstFormats = $dayFirstFormats.foreach{ $_; $_.Replace('/', '.') }
        $monthFirstFormats = 'M/d h:mtt', 'MM/dd hh:mmtt', 'MM/dd hh:mm:ss tt'
        # check if the local date is in M/d or d/M format
        # check for this format first
        if ('14/6' -as [datetime]) { 
            # local date is d/M
            $dateFormatStrings += $dayFirstFormats + $monthFirstFormats
        }
        else {
            $dateFormatStrings += $monthFirstFormats + $dayFirstFormats
        }
        
        #try to convert a provided string with ParseExact using the different format strings
        if ($inputData -is [string]) {
            foreach ($format in $dateFormatStrings) {
                try {
                    $newDate = [datetime]::ParseExact($inputData, $format, $Null)
                }
                catch {
                    # if the conversion attempt fails keep trying the other formats
                    continue
                }
                # if the conversion succeeds return the date
                if ($newDate) { return $newDate }
            }
        }
        
        # conversion faild throw an exception.
        throw [System.InvalidOperationException]::new('No valid date time.')
    }
}