SVSimServer/SVSim.BattleNode/Protocol/MsgEnvelope.cs

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

namespace SVSim.BattleNode.Protocol;

/// <summary>
/// The shared envelope on every encrypted msg / synchronize frame. Body is opaque
/// (Dictionary&lt;string, object?&gt;) because shape varies per Uri — typed register-action
/// models come in a later slice.
/// </summary>
public sealed record MsgEnvelope(
    NetworkBattleUri Uri,
    long ViewerId,
    string Uuid,
    string? Bid,
    int Try,
    EmitCategory Cat,
    long? PubSeq,
    long? PlaySeq,
    Dictionary<string, object?> Body)
{
    private static readonly JsonSerializerOptions Options = CreateOptions();

    private static readonly HashSet<string> ReservedEnvelopeKeys = new()
    {
        "uri", "viewerId", "uuid", "bid", "try", "cat", "pubSeq", "playSeq",
    };

    private static JsonSerializerOptions CreateOptions()
    {
        var opt = new JsonSerializerOptions
        {
            // Wire-key casing here is bare camelCase — NOT EmulatedEntrypoint's snake_case policy.
            DefaultIgnoreCondition = JsonIgnoreCondition.WhenWritingNull,
            PropertyNamingPolicy = JsonNamingPolicy.CamelCase,
        };
        opt.Converters.Add(new JsonStringEnumConverter());
        return opt;
    }

    public static string ToJson(MsgEnvelope env)
    {
        var doc = new Dictionary<string, object?>
        {
            ["uri"] = env.Uri.ToString(),
            ["viewerId"] = env.ViewerId,
            ["uuid"] = env.Uuid,
            ["try"] = env.Try,
            ["cat"] = (int)env.Cat,
        };
        if (env.Bid is not null) doc["bid"] = env.Bid;
        if (env.PubSeq.HasValue) doc["pubSeq"] = env.PubSeq.Value;
        if (env.PlaySeq.HasValue) doc["playSeq"] = env.PlaySeq.Value;
        foreach (var (k, v) in env.Body)
        {
            if (ReservedEnvelopeKeys.Contains(k))
                throw new ArgumentException(
                    $"Body key '{k}' collides with a reserved envelope field. Move it to a typed field on MsgEnvelope.",
                    nameof(env));
            doc[k] = v;
        }
        return JsonSerializer.Serialize(doc, Options);
    }

    public static MsgEnvelope FromJson(string json)
    {
        using var doc = JsonDocument.Parse(json);
        var root = doc.RootElement;

        var uri = Enum.Parse<NetworkBattleUri>(root.GetProperty("uri").GetString()!);
        var viewerId = root.GetProperty("viewerId").GetInt64();
        var uuid = root.GetProperty("uuid").GetString()!;
        var bid = root.TryGetProperty("bid", out var bidEl) ? bidEl.GetString() : null;
        var @try = root.TryGetProperty("try", out var tryEl) ? tryEl.GetInt32() : 0;
        var cat = root.TryGetProperty("cat", out var catEl) ? (EmitCategory)catEl.GetInt32() : EmitCategory.Battle;
        var pubSeq = root.TryGetProperty("pubSeq", out var psEl) ? psEl.GetInt64() : (long?)null;
        var playSeq = root.TryGetProperty("playSeq", out var plsEl) ? plsEl.GetInt64() : (long?)null;

        var body = new Dictionary<string, object?>();
        foreach (var prop in root.EnumerateObject())
        {
            if (ReservedEnvelopeKeys.Contains(prop.Name)) continue;
            body[prop.Name] = ToObject(prop.Value);
        }

        return new MsgEnvelope(uri, viewerId, uuid, bid, @try, cat, pubSeq, playSeq, body);
    }

    private static object? ToObject(JsonElement el) => el.ValueKind switch
    {
        JsonValueKind.String => el.GetString(),
        // Extracted to a helper because writing the conditional inline as
        //   el.TryGetInt64(out var l) ? l : el.GetDouble()
        // unifies the conditional's branches to the common implicit-convertible type. long→double
        // is implicit; so the result type collapses to double and the long value silently widens.
        // Downstream OfType<long> filters then drop the (now boxed-double) entries, which broke
        // the mulligan idxList extraction. Separate method returns object explicitly so each
        // branch boxes its own runtime type.
        JsonValueKind.Number => ParseNumber(el),
        JsonValueKind.True => true,
        JsonValueKind.False => false,
        JsonValueKind.Null => null,
        JsonValueKind.Array => el.EnumerateArray().Select(ToObject).ToList(),
        JsonValueKind.Object => el.EnumerateObject().ToDictionary(p => p.Name, p => ToObject(p.Value)),
        _ => el.GetRawText(),
    };

    private static object ParseNumber(JsonElement el)
    {
        if (el.TryGetInt64(out var l)) return l;
        return el.GetDouble();
    }
}