public class CloudEvent(Uri source, string type = "ms.aio.telemetry", string specversion = "1.0")
{
    private string? _id = null!;
    public Uri? Source { get => source; }
    public string SpecVersion { get => specversion;  }
    public string Type { get => type;  }
    public string? Id { get => _id; internal set => _id = value; } // although id is required, we want update it in the same instance from the sender.

    // optional 
    private string? _dataContentType;
    private string? _dataSchema;
    private string? _subject;
    private DateTime? _time;
    public DateTime? Time { get => _time; internal set => _time = value; }
    public string? DataContentType { get => _dataContentType; internal set => _dataContentType = value; }
    public string? Subject { get => _subject; internal set => _subject = value; }
    public string? DataSchema { get => _dataSchema; set => _dataSchema = value; }
}

public static partial class MqttApplicationMessageBuilderExtension
{
    public static MqttApplicationMessageBuilder WithCloudEvents(this MqttApplicationMessageBuilder mb, CloudEvent md)
    {
        mb.WithUserProperty(nameof(md.SpecVersion).ToLowerInvariant(), md.SpecVersion)
          .WithUserProperty(nameof(md.Id).ToLowerInvariant(), md.Id!.ToString())
          .WithUserProperty(nameof(md.Type).ToLowerInvariant(), md.Type)
          .WithUserProperty(nameof(md.Source).ToLowerInvariant(), md.Source!.ToString());

        if (md.Time is not null)
        {
            mb.WithUserProperty(nameof(md.Time).ToLowerInvariant(), md.Time!.Value.ToString("O"));
        }

        if (md.Subject is not null)
        {
            mb.WithUserProperty(nameof(md.Subject).ToLowerInvariant(), md.Subject);
        }

        if (md.DataContentType is not null)
        {
            mb.WithUserProperty(nameof(md.DataContentType).ToLowerInvariant(), md.DataContentType);
        }

        if (md.DataSchema is not null)
        {
            mb.WithUserProperty(nameof(md.DataSchema).ToLowerInvariant(), md.DataSchema);
        }
        
        return mb;
    }
}