using System;

using System.Text.Json;

using System.Text.Json.Serialization;

public class Program

{

    [JsonPolymorphic(TypeDiscriminatorPropertyName = "EventType")]

    [JsonDerivedType(typeof(EventAlpha), typeDiscriminator: nameof(EventAlpha))]

    [JsonDerivedType(typeof(EventBravo), typeDiscriminator: nameof(EventBravo))]

    public abstract class EventEnvelope

    {

        public Ulid Id { get; init; } = Ulid.NewUlid();

        public string Source { get; init; } = "Event.Source";

        public DateTime Date { get; init; } = DateTime.UtcNow;

        [JsonIgnore]

        public abstract EventEnvelope.EventData BaseData { get; }   

        public string SchemaVersion { get; init; } = "1.0";

        public abstract class EventData { } 

    }

    public class EventAlpha : EventEnvelope

    {

        public EventAlpha.EventAlphaData Data { get; init; }

        [JsonIgnore]

        public override EventEnvelope.EventData BaseData => Data;

        public class EventAlphaData : EventData

        {

            public string PropertyZulu { get; init; }

        }

    }

    public class EventBravo : EventEnvelope

    {

        public EventBravo.EventBravoData Data { get; init; }

        [JsonIgnore]

        public override EventEnvelope.EventData BaseData => Data;

        public class EventBravoData : EventData

        {

            public string PropertyYankee { get; init; }

        }

    }

​

    public static void Main()

    {

​

        var evt = new EventBravo

        {

            Data = new EventBravo.EventBravoData { PropertyYankee = "tacos rule!" }

        } as EventEnvelope;

        var serialized = JsonSerializer.Serialize(evt);

        var deserialized = JsonSerializer.Deserialize<EventEnvelope>(serialized);

        Console.WriteLine(serialized);

        Console.WriteLine(deserialized.BaseData.GetType());

        if (deserialized.BaseData is EventBravo.EventBravoData e)

        {

            Console.WriteLine(e.PropertyYankee);

        }

    }

}