acdream/src/AcDream.Core/Chat/ChatCommandTargetState.cs

namespace AcDream.Core.Chat;

/// <summary>
/// Presentation-independent reply/retell targets derived from the committed
/// chat transcript.
/// </summary>
/// <remarks>
/// Incoming tells carry a non-zero sender GUID and update the reply target.
/// Local outgoing tell echoes carry a zero sender GUID and place the target
/// name in <see cref="ChatEntry.Sender"/>. This is the existing retail
/// <c>@reply</c>/<c>@retell</c> behavior formerly owned by <c>ChatVM</c>.
/// </remarks>
public sealed class ChatCommandTargetState : IDisposable
{
    private readonly ChatLog _chat;
    private readonly object _gate = new();
    private string? _lastIncomingTellSender;
    private string? _lastOutgoingTellTarget;
    private bool _disposed;

    public ChatCommandTargetState(ChatLog chat)
    {
        _chat = chat ?? throw new ArgumentNullException(nameof(chat));
        _chat.EntryAppended += OnEntryAppended;
    }

    public string? LastIncomingTellSender
    {
        get
        {
            lock (_gate)
                return _lastIncomingTellSender;
        }
    }

    public string? LastOutgoingTellTarget
    {
        get
        {
            lock (_gate)
                return _lastOutgoingTellTarget;
        }
    }

    public bool IsDisposed
    {
        get
        {
            lock (_gate)
                return _disposed;
        }
    }

    /// <summary>
    /// Forget character-scoped command targets without clearing visible
    /// transcript history.
    /// </summary>
    public void ResetSession()
    {
        lock (_gate)
        {
            _lastIncomingTellSender = null;
            _lastOutgoingTellTarget = null;
        }
    }

    public void Dispose()
    {
        lock (_gate)
        {
            if (_disposed)
                return;
            _disposed = true;
            _chat.EntryAppended -= OnEntryAppended;
        }
    }

    private void OnEntryAppended(ChatEntry entry)
    {
        if (entry.Kind != ChatKind.Tell || string.IsNullOrEmpty(entry.Sender))
            return;

        lock (_gate)
        {
            if (_disposed)
                return;
            if (entry.SenderGuid != 0u)
                _lastIncomingTellSender = entry.Sender;
            else
                _lastOutgoingTellTarget = entry.Sender;
        }
    }
}