refactor(jsonapi-exception-filter): use exception factory

Author: jaredcnance

src/JsonApiDotNetCore/Internal/JsonApiExceptionFactory.cs

@@ -0,0 +1,22 @@
+using System;
+using System.Linq;
+
+namespace JsonApiDotNetCore.Internal
+{
+    public static class JsonApiExceptionFactory
+    {
+        public static JsonApiException GetException(Exception exception)
+        {
+            var exceptionType = exception.GetType().ToString().Split('.').Last();
+            switch(exceptionType)
+            {
+                case "JsonApiException":
+                    return (JsonApiException)exception;
+                case "InvalidCastException":
+                    return new JsonApiException("409", exception.Message);
+                default:
+                    return new JsonApiException("500", exception.Message);
+            }
+        }
+    }
+}

src/JsonApiDotNetCore/Middleware/JsonApiExceptionFilter.cs

@@ -19,11 +19,8 @@ public void OnException(ExceptionContext context)
         {
             _logger?.LogError(new EventId(), context.Exception, "An unhandled exception occurred during the request");
 
-            var jsonApiException = context.Exception as JsonApiException;
+            var jsonApiException = JsonApiExceptionFactory.GetException(context.Exception);
 
-            if(jsonApiException == null)
-                jsonApiException = new JsonApiException("500", context.Exception.Message);
-
             var error = jsonApiException.GetError();
             var result = new ObjectResult(error);
             result.StatusCode = Convert.ToInt16(error.Status);