Advanced string formatter with pattern support in C#-CodePudding

I would like to have a flexible template that can translate cases similar to:

WHnnn => WH001, WH002, WH003... (nnn is just a number indicated 3 digits)
INVyyyyMMdd => INV20220228
ORDERyyyyMMdd-nnn => ORDER20220228-007

I know that I can use the following code to achieve a specific template:

string.Format("INV{0:yyyy-MM-dd}", DateTime.Now)

Which should have the same result as case 2 above. But that's not flexible. As the customer may customize their own template as long as I can understand/support, like the third case above.

I know even for the third case, I can do something like this:

string.Format("ORDER{0:yyyy-MM-dd}-{1:d3}", DateTime.Now, 124)

But that's clumsy, as I would like the template (input) to be just like this:

ORDERyyyyMMdd-nnn

The requirement is to support all the supported patterns by string.Format in C#, but the template can be any combination of those patterns.

CodePudding user response：

I would probably use a custom formatter for this case.

Create a new class that will contain date/time & number and will implement IFormattable interface.

There is one tip: use some internal format in style INV{nnn} or INV[nnn] where only the part in {} or [] will be replaced with the value.

Otherwise there could be unwanted changes like in Inv contains 'n'. You could get output as I7v.

In your examples the N is upper case, but will it be the case even after each customisation?

Code (simplified version):

internal sealed class InvoiceNumberInfo : IFormattable
{
    private static readonly Regex formatMatcher = new Regex(@"^(?<before>.*?)\[(?<code>\w ?)\](?<after>.*)$");

    private readonly DateTime date;

    private readonly int number;

    public InvoiceNumberInfo(DateTime date, int number)
    {
        this.date = date;
        this.number = number;
    }

    public string ToString(string format, IFormatProvider formatProvider)
    {
        var output = format;
        while (true)
        {
            var match = formatMatcher.Match(output);
            if (!match.Success)
            {
                return output;
            }

            output = match.Groups["before"].Value   FormatValue(match.Groups["code"].Value)   match.Groups["after"].Value;
        }
    }

    private string FormatValue(string code)
    {
        if (code[0] == 'n')
        {
            var numberFormat = "D"   code.Length.ToString(CultureInfo.InvariantCulture);
            return this.number.ToString(numberFormat);
        }
        else
        {
            return this.date.ToString(code);
        }
    }
}

Use:

internal static class Program
{
    public static void Main(string[] args)
    {
        if (args.Length == 0)
        {
            Console.WriteLine("No format to display");
            return;
        }

        var inv = new InvoiceNumberInfo(DateTime.Now, number: 7);
        foreach (string format in args)
        {
            Console.WriteLine("Format: '{0}' is formatted as {1:"   format   "}", format, inv);
        }
    }
}

And output:

Format: 'WH[nnn]' is formatted as WH007
Format: 'INV[yyyyMMdd]' is formatted as INV20220227
Format: 'ORDER[yyyyMMdd]-[nnn]' is formatted as ORDER20220227-007

NOTE This is only a simplified version, proof of concept. Use proper error checking for your code.