Allows for easy versioning of an API by extracting the version number from the controller name and using it in the url

GlobalVersionedPrefixProvider.cs

public class GlobalVersionedPrefixProvider : DefaultDirectRouteProvider
{
    /// <summary>
    /// Global prefix, usually "api" to be prepended to the full versioned prefix
    /// </summary>
    private readonly string _prefix;

    public GlobalVersionedPrefixProvider(string prefix)
    {
        _prefix = prefix;
    }

    protected override string GetRoutePrefix(HttpControllerDescriptor controllerDescriptor)
    {
        // This will store the version of the controller, if the name contains one
        string version = null;

        // Get route prefix defined in the controller
        var existingPrefix = base.GetRoutePrefix(controllerDescriptor);

        // Extract the version number from our controller name
        int versionLocation = controllerDescriptor.ControllerName.LastIndexOf("V");
        if (versionLocation != -1)
        {
            versionLocation += "V".Length;
            version = controllerDescriptor.ControllerName.Substring(versionLocation);

            // Check if it's a valid version number
            foreach(char c in version)
            {
                if (!char.IsDigit(c) && c != 'd') // We allow 'd' as a replacement for . (dot)
                    return CreateRoutePrefix(_prefix, null, existingPrefix);
            }

            // We want the version number seperated by dots
            version = version.Replace('d', '.');
        }

        // Return the global route prefix
        return CreateRoutePrefix(_prefix, version, existingPrefix);
    }

    /// <summary>
    /// Creates a route prefix based on the given parameters
    /// </summary>
    /// <param name="prefix">The global prefix for the api, usually "api"</param>
    /// <param name="version">The version number of the controller, will be prefixed with a "v". If empty it is ignored and excluded from the url</param>
    /// <param name="existingPrefix">Prefix defined by the controller</param>
    /// <returns></returns>
    private string CreateRoutePrefix(string prefix, string version, string existingPrefix)
    {
        if (version != null)
            return string.Format("{0}/v{1}/{2}", _prefix, version, (existingPrefix ?? ""));
        else
            return string.Format("{0}/{1}", _prefix, (existingPrefix ?? ""));
    }
}