web api 2 attribute based route generation

Using the algorithms described here, I opted to using ApiExplorer to fetch out the routes that match a given set of values.

Example of usage:

[RoutePrefix( "api/v2/test" )]
public class EntityController : ApiController {
    [Route( "" )]
    public IEnumerable<Entity> GetAll() {
        // ...
    }

    [Route( "{id:int}" )]
    public Entity Get( int id ) {
        // ...
    }

    // ... stuff

    [HttpGet]
    [Route( "{id:int}/children" )]
    public IEnumerable[Child] Children( int id ) {
        // ...
    }
}

///
/// elsewhere
///

// outputs: api/v2/test/5
request.HttpRouteUrl( HttpMethod.Get, new {
    controller = "entity",
    id = 5
} )

// outputs: api/v2/test/5/children
request.HttpRouteUrl( HttpMethod.Get, new {
    controller = "entity",
    action = "children",
    id = 5
} )

Here's the implementation:

public static class HttpRouteUrlExtension {
    private const string HttpRouteKey = "httproute";

    private static readonly Type[] SimpleTypes = new[] {
        typeof (DateTime), 
        typeof (Decimal), 
        typeof (Guid), 
        typeof (string), 
        typeof (TimeSpan)
    };

    public static string HttpRouteUrl( this HttpRequestMessage request, HttpMethod method, object routeValues ) {
        return HttpRouteUrl( request, method, new HttpRouteValueDictionary( routeValues ) );
    }

    public static string HttpRouteUrl( this HttpRequestMessage request, HttpMethod method, IDictionary<string, object> routeValues ) {
        if ( routeValues == null ) {
            throw new ArgumentNullException( "routeValues" );
        }

        if ( !routeValues.ContainsKey( "controller" ) ) {
            throw new ArgumentException( "'controller' key must be provided", "routeValues" );
        }

        routeValues = new HttpRouteValueDictionary( routeValues );
        if ( !routeValues.ContainsKey( HttpRouteKey ) ) {
            routeValues.Add( HttpRouteKey, true );
        }

        string controllerName = routeValues[ "controller" ].ToString();
        routeValues.Remove( "controller" );

        string actionName = string.Empty;
        if ( routeValues.ContainsKey( "action" ) ) {
            actionName = routeValues[ "action" ].ToString();
            routeValues.Remove( "action" );
        }

        IHttpRoute[] matchedRoutes = request.GetConfiguration().Services
                                            .GetApiExplorer().ApiDescriptions
                                            .Where( x => x.ActionDescriptor.ControllerDescriptor.ControllerName.Equals( controllerName, StringComparison.OrdinalIgnoreCase ) )
                                            .Where( x => x.ActionDescriptor.SupportedHttpMethods.Contains( method ) )
                                            .Where( x => string.IsNullOrEmpty( actionName ) || x.ActionDescriptor.ActionName.Equals( actionName, StringComparison.OrdinalIgnoreCase ) )
                                            .Select( x => new {
                                                route = x.Route,
                                                matches = x.ActionDescriptor.GetParameters()
                                                           .Count( p => ( !p.IsOptional ) &&
                                                                   ( p.ParameterType.IsPrimitive || SimpleTypes.Contains( p.ParameterType ) ) &&
                                                                   ( routeValues.ContainsKey( p.ParameterName ) ) &&
                                                                   ( routeValues[ p.ParameterName ].GetType() == p.ParameterType ) )
                                            } )
                                            .Where(x => x.matches > 0)
                                            .OrderBy( x => x.route.DataTokens[ "order" ] )
                                            .ThenBy( x => x.route.DataTokens[ "precedence" ] )
                                            .ThenByDescending( x => x.matches )
                                            .Select( x => x.route )
                                            .ToArray();

        if ( matchedRoutes.Length > 0 ) {
            IHttpVirtualPathData pathData = matchedRoutes[ 0 ].GetVirtualPath( request, routeValues );

            if ( pathData != null ) {
                return new Uri( new Uri( httpRequestMessage.RequestUri.GetLeftPart( UriPartial.Authority ) ), pathData.VirtualPath ).AbsoluteUri;
            }
        }

        return null;
    }
}