Formatting TFN and ABN

I'm not entirely sure if I've mentioned this before BUT I happen to LOVE extension methods.

Extension methods enable you to "add" methods to existing types without creating a new derived type, recompiling, or otherwise modifying the original type. Extension methods are a special kind of static method, but they are called as if they were instance methods on the extended type. For client code written in C# and Visual Basic, there is no apparent difference between calling an extension method and the methods that are actually defined in a type.

I recently had to write some of them up for Formating TFN and ABNs.

Here are the TfnAbnExtnesion Methods. (I could have also used regular expression to accomplish this but I chose to keep it simple/maintainable.)

 
public static class TfnAbnExtensions
{
    /// <summary>
    /// Formats the TFN.
    /// If the length is 9 char, return XXX XXX XXX
    /// If the length is 8 char, return XXX XXX XX
    /// </summary>
    /// <param name="tfn">The TFN.</param>
    /// <returns></returns>
    public static string FormatTfn(this string tfn)
    {
        // Ignore null/empty strings
        if (string.IsNullOrWhiteSpace(tfn))
        {
            return string.Empty;
        }

        // Remove any existing whitespaces
        var newtfn = tfn.UnFormatAbnTfn();
            
        var result = string.Empty;
        var tfnCharArray = newtfn.ToCharArray();

        for (int i = 0; i < tfnCharArray.Length; i++)
        {
            if (i % 3 == 0 && i != 0)
            {
                result += " ";
            }

            result += tfnCharArray[i].ToString(CultureInfo.InvariantCulture);
        }

        return result;
    }


    /// <summary>
    /// Formats the ABN.
    /// </summary>
    /// <param name="abn">The ABN.</param>
    /// <returns></returns>
    public static string FormatAbn(this string abn)
    {
        // Ignore null/empty strings
        if (string.IsNullOrWhiteSpace(abn))
        {
            return string.Empty;
        }

        // Un-format the ABN
        var newtfn = abn.UnFormatAbnTfn();
            
        var result = string.Empty;
        var abnCharArray = newtfn.ToCharArray();
        var tempCounter = 0;

        for (int i = 0; i < abnCharArray.Length; i++)
        {
            // Second character & then every 3rd char
            if (i == 2 || tempCounter == 3)
            {
                result += " ";
                tempCounter = 0;
            }

            tempCounter++;
            result += abnCharArray[i].ToString(CultureInfo.InvariantCulture);
        }

        return result;
    }


    /// <summary>
    /// Un formats the ABN or TFN by removing blank spaces
    /// </summary>
    /// <param name="abnTfn">The ABN or TFN.</param>
    /// <returns></returns>
    public static string UnFormatAbnTfn(this string abnTfn)
    {
        return string.IsNullOrWhiteSpace(abnTfn) ? abnTfn :
            abnTfn
            .Replace(" ", string.Empty)
            .Replace("-", string.Empty)
            .Replace("/", string.Empty);
    }
    
}

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References: Extension Methods (C# Programming Guide)

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