Hoping someone can assist. What I want to do is simply pass a GUID of an Umbraco media file into a Surface Controller and have it spit back the URL path. This will be called via ajax (jQuery).

var img_guid = $e.data("image-guid");
$.get("/umbraco/surface/JournalImage/GetImagePath", img_guid)
     .done(function(path) { ... }).fail(function() { ... });

I've been banging my head trying to figure out where I'm going wrong on the surface controller side. Looking at the API documentation, it looks l need to call IMediaService for passing the GUID and returning the path, but it doesn't like the fact that _services is non-static and I get an object reference error when trying to use it for getting the IMedia object.

public class JournalImageController : SurfaceController
{
    private readonly ServiceContext _services;

    public JournalImageController(IUmbracoContextAccessor umbracoContextAccessor, IUmbracoDatabaseFactory databaseFactory, ServiceContext services, AppCaches appCaches, IProfilingLogger profilingLogger, IPublishedUrlProvider publishedUrlProvider) : base(umbracoContextAccessor, databaseFactory, services, appCaches, profilingLogger, publishedUrlProvider)
    {
        _services = services;
    }

    public IActionResult GetImagePath(string guid)
    {
        string mediaPath = "fail";
        if (String.IsNullOrWhiteSpace(guid)) return mediaPath;

        Guid? gid = new Guid(guid);
        if (gid.HasValue)
        {
            IMedia mediaObj = _services.MediaService.GetById(gid.Value);
            mediaPath = mediaObj.GetUrl();
        }

        return mediaPath;
    }

}

Trying to make it static just cascades into errors within the constructor so going down that path is a dead-end. I'm not well-versed in this stuff yet, so perhaps I'm trying to make it too complicated. Most of what I've searched is Umbraco 8 and earlier, so I'm not too sure what's the most recent and efficient way to accomplish this with the current Umbraco codebase.