I need help doing a Regex.Replace with multiple results

I'm building a custom page caching utility that uses a syntax like {Substitution:GetNonCachedData} to get data that's not supposed to be cached. The solution is very similar to the built-in <@ OutputCache %> stuff but not as flexible (I don't need it to be) and, most importantly, allows the session state to be available when retrieving non-cached data.

Anyway, I have a method that replaces the tokens in the html with the result of the static method named in the {Substitution} tag.

For example my page:

<html>
    <body>
      <p>This is cached</p>
      <p>This is not: {Substitution:GetCurrentTime}</p>
    </body>
</html>

will fill in the {Substitution:GetCurrentTime} with results of a static method. Here's where the processing happens:

private static Regex SubstitutionRegex = new Regex(@"{substitution:(?<method>\w+)}", RegexOptions.IgnoreCase);

public static string WriteTemplates(string template)
{
    foreach (Match match in SubstitutionRegex.Matches(template))
    {
        var group = match.Groups["method"];
        var method = group.Value;
        var substitution = (string) typeof (Substitution).GetMethod(method).Invoke(null, null);
        template = SubstitutionRegex.Replace()
    }

    return template;

}

the variable template is the html with custom tokens in it that need to be replaced. The problem with this method is that everytime I update the template variable with the updated html the match.Index variable no longer points to the right character start because of the template now has more characters added to it.

I can come up with a solution that works by either counting characters etc or some other screwball way of doing it, but I first want to make sure there's not some easier way to achieve this with the Regex object. Anyone know how to this?

thanks!

Solution

You should call the overload of Regex.Replace that takes a MatchEvaluator delegate.

For example:

return SubstitutionRegex.Replace(template, delegate(Match match) {
    var group = match.Groups["method"];
    var method = group.Value;
    return (string) typeof (Substitution).GetMethod(method).Invoke(null, null);
});