Event.cs

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using System.Text.Json;
using Fauna.Core;
using Fauna.Exceptions;
using Fauna.Mapping;
using Fauna.Serialization;
using static Fauna.Core.ResponseFields;
 
namespace Fauna.Types;
 
 
public enum EventType
{
    Add,
    Update,
    Remove,
    Status
}
 
public class Event<T> where T : notnull
{
    public EventType Type { get; private init; }
    public long TxnTime { get; private init; }
    public string Cursor { get; private init; } = null!;
    public T? Data { get; private init; }
    public QueryStats Stats { get; private init; }
 
 
    internal static Event<T> From(JsonElement json, MappingContext ctx)
    {
        var err = GetError(json);
        if (err != null)
        {
            throw new EventException(err.Value);
        }
 
        var evt = new Event<T>
        {
            TxnTime = GetTxnTime(json),
            Cursor = GetCursor(json),
            Type = GetType(json),
            Stats = GetStats(json),
            Data = GetData(json, ctx),
        };
 
        return evt;
    }
 
    internal static Event<T> From(string body, MappingContext ctx)
    {
        var json = JsonSerializer.Deserialize<JsonElement>(body);
 
        return From(json, ctx);
    }
 
    private static long GetTxnTime(JsonElement json)
    {
        if (!json.TryGetProperty(LastSeenTxnFieldName, out var elem))
        {
            return default;
        }
 
        return elem.TryGetInt64(out long i) ? i : default;
    }
 
    private static string GetCursor(JsonElement json)
    {
        if (!json.TryGetProperty(CursorFieldName, out var elem))
        {
            throw new InvalidDataException($"Missing required field: cursor - {json.ToString()}");
        }
 
        return elem.Deserialize<string>()!;
    }
 
 
    private static EventType GetType(JsonElement json)
    {
        if (!json.TryGetProperty("type", out var elem))
        {
            throw new InvalidDataException($"Missing required field: type - {json.ToString()}");
        }
 
        string? evtType = elem.Deserialize<string?>();
        EventType type = evtType switch
        {
            "add" => EventType.Add,
            "update" => EventType.Update,
            "remove" => EventType.Remove,
            "status" => EventType.Status,
            _ => throw new InvalidOperationException($"Unknown event type: {evtType}")
        };
 
        return type;
    }
 
    private static QueryStats GetStats(JsonElement json)
    {
        return json.TryGetProperty(StatsFieldName, out var elem) ? elem.Deserialize<QueryStats>() : default;
    }
 
    private static T? GetData(JsonElement json, MappingContext ctx)
    {
        if (!json.TryGetProperty(DataFieldName, out var elem))
        {
            return default;
        }
 
        var reader = new Utf8FaunaReader(elem.GetRawText());
        reader.Read();
 
        return Serializer.Generate<T>(ctx).Deserialize(ctx, ref reader);
    }
 
    private static ErrorInfo? GetError(JsonElement json)
    {
        return json.TryGetProperty(ErrorFieldName, out var elem) ? elem.Deserialize<ErrorInfo>() : null;
    }
}