using System.Text.Json;
using System.Text.Json.Serialization;

namespace AVEVA.Historian.Client.StoreForward;

/// <summary>
/// Shared JSON settings for persisting <see cref="HistorianOutboxEntry"/> envelopes. The custom
/// <see cref="ObjectConverter"/> normalizes <c>HistorianEvent.Properties</c> values (typed
/// <see cref="object"/>) back to plain CLR scalars on read instead of leaving raw
/// <see cref="JsonElement"/>s, so a rehydrated event matches what the producer enqueued.
/// </summary>
internal static class OutboxJson
{
    public static readonly JsonSerializerOptions Options = CreateOptions();

    private static JsonSerializerOptions CreateOptions()
    {
        var options = new JsonSerializerOptions
        {
            WriteIndented = false,
            DefaultIgnoreCondition = JsonIgnoreCondition.WhenWritingNull,
        };
        options.Converters.Add(new ObjectConverter());
        return options;
    }

    private sealed class ObjectConverter : JsonConverter<object?>
    {
        public override object? Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)
        {
            switch (reader.TokenType)
            {
                case JsonTokenType.Null:
                    return null;
                case JsonTokenType.String:
                    return reader.GetString();
                case JsonTokenType.True:
                    return true;
                case JsonTokenType.False:
                    return false;
                case JsonTokenType.Number:
                    return reader.TryGetInt64(out long l) ? l : reader.GetDouble();
                default:
                    using (JsonDocument doc = JsonDocument.ParseValue(ref reader))
                    {
                        return doc.RootElement.GetRawText();
                    }
            }
        }

        public override void Write(Utf8JsonWriter writer, object? value, JsonSerializerOptions options)
        {
            if (value is null)
            {
                writer.WriteNullValue();
                return;
            }

            // Serialize by runtime type so scalars use their own converters (no re-entry into this one).
            JsonSerializer.Serialize(writer, value, value.GetType(), options);
        }
    }
}