Resolve enum from a custom attribute property search

Question

I have the following enum used in CallForm FormDialog:

public enum CallTimeOptions
{
    [Describe("tonight")]
    [Terms("tonight", "this evening", "pm", "this pm")]
    Tonight = 1,

    [Describe("tomorrow morning")]
    [Terms("tomorrow morning", "tomorrow am", "am")]
    TomorrowMorning,

    [Describe("tomorrow noon time")]
    [Terms("tomorrow noon time", "tomorrow noon", "tomorrow lunch", "lunch")]
    TomorrowNoonTime,

    [Describe("tomorrow evening")]
    [Terms("tomorrow evening", "tomorrow pm", "tomorrow night")]
    TomorrowEvening

};

I am calling my CallForm from a LUIS intent that can have a datetimeV2 so something like this:

[LuisIntent("Call")]
public async Task Call(IDialogContext context, LuisResult result)
{
    EntityRecommendation entityRecommendation;

    if (result.TryFindEntity("builtin.datetimeV2.datetimerange", out entityRecommendation))
    {
        context.UserData.SetValue<string>(ContextKeys.CallTimeOption, entityRecommendation.Entity);

    }   

    context.UserData.Call(new CallForm(), CallFormResumeAfter);          
}

Then I want to prefill it in StartAsync of CallForm but don't know how...

public async Task StartAsync(IDialogContext context)
{
    var state = new CallTimeForm();           
    string calltime;

    if(context.UserData.TryGetValue(ContextKeys.CallTimeOption, out calltime))
    {
        state.PreferredCallTime = -- is there a way to match calltime with CallTimeOptions ? --
    }

     var form = new FormDialog<CallTimeForm>(
                                  state,
                                  BuildForm,
                                  FormOptions.PromptInStart);

        context.Call(form, this.AfterBuildForm);
}

Answer 1

An example of how to do this is via reflection and Attribute.GetCustomAttribute

Retrieves a custom attribute of a specified type applied to an assembly, module, type member, or method parameter.

method

public static class EnumEx
{
   public static T GetValueFromTerms<T>(string value)
   {
      var type = typeof(T);
      if (!type.IsEnum)
      {
         throw new InvalidOperationException();
      }

      foreach (var field in type.GetFields())
      {
         if (Attribute.GetCustomAttribute(field, typeof(TermsAttribute)) is TermsAttribute attribute)
         {
            // Search your attribute array or properties here
            // Depending on the structure of your attribute 
            // you will need to change this if Conidition
            if (attribute.ContainsTerms(value))
            {
               return (T)field.GetValue(null);
            }
         }
         else
         {
            if (field.Name == value)
            {
               return (T)field.GetValue(null);
            }
         }
      }
      throw new ArgumentException("Not found.", nameof(value));
      // or return default(T);
   }
}

Usage

var callTimeOptions = EnumEx.GetValueFromTerms<CallTimeOptions>("tomorrow noon time");

However, I think you are not going about this the right way.

A more future proofed system would be to use a Dictionary<string,CallTimeOptions> to look up search terms and map them to enums.

I know attributes seems neat and might work well if you arnt going to expand this much, however a dictionary could be loaded form db or file, and it might just be easier to maintain (depending on your requirements)