AX-Copilot-Codex/src/AxCopilot/Views/ChatWindow.TranscriptRenderPlanner.cs

using AxCopilot.Models;

namespace AxCopilot.Views;

public partial class ChatWindow
{
    private sealed class TranscriptRenderPlan
    {
        public required List<(string Key, DateTime Timestamp, int Order, Action Render)> VisibleTimeline { get; init; }
        public required List<string> NewKeys { get; init; }
        public required bool ShowHistory { get; init; }
        public required int HiddenCount { get; init; }
        public required bool CanIncremental { get; init; }
        public required int PreviousLiveCount { get; init; }
        public required int PreviousStableCount { get; init; }
    }

    private TranscriptRenderPlan BuildTranscriptRenderPlan(
        ChatConversation conv,
        IReadOnlyList<ChatMessage> visibleMessages,
        IReadOnlyList<ChatExecutionEvent> visibleEvents)
    {
        var orderedTimeline = BuildTimelineRenderActions(visibleMessages, visibleEvents);
        var effectiveRenderLimit = GetActiveTimelineRenderLimit();
        var hiddenCount = Math.Max(0, orderedTimeline.Count - effectiveRenderLimit);

        // B-1: 스트리밍 중 hiddenCount 안정화 — 감소만 차단하여 prefix 키 불일치 방지
        // 스트리밍 시 GetActiveTimelineRenderLimit()가 더 작은 값을 반환하면
        // hiddenCount가 변동하여 visible 범위가 밀리고 인크리멘탈 렌더가 항상 실패함
        if (_isStreaming && _lastRenderedHiddenCount >= 0 && hiddenCount < _lastRenderedHiddenCount)
            hiddenCount = _lastRenderedHiddenCount;

        var visibleTimeline = hiddenCount > 0
            ? orderedTimeline.GetRange(hiddenCount, orderedTimeline.Count - hiddenCount)
            : orderedTimeline;

        var newKeys = new List<string>(visibleTimeline.Count);
        foreach (var item in visibleTimeline)
            newKeys.Add(item.Key);

        // B-2: _agentLiveContainer가 transcript에 있어도 인크리멘탈 허용
        // 라이브 컨테이너는 인크리멘탈 렌더 시 임시 분리 후 재삽입하므로
        // expectedChildCount에 포함하고 canIncremental 조건에서 제외
        var liveContainerInTranscript = _agentLiveContainer != null && ContainsTranscriptElement(_agentLiveContainer);
        var expectedChildCount = _lastRenderedTimelineKeys.Count
            + (_lastRenderedHiddenCount > 0 ? 1 : 0)
            + (liveContainerInTranscript ? 1 : 0);
        var canIncremental = _lastRenderedTimelineKeys.Count > 0
            && newKeys.Count >= _lastRenderedTimelineKeys.Count
            && _lastRenderedHiddenCount == hiddenCount
            && GetTranscriptElementCount() == expectedChildCount;

        var previousLiveCount = 0;
        if (canIncremental)
        {
            for (var i = _lastRenderedTimelineKeys.Count - 1; i >= 0; i--)
            {
                if (_lastRenderedTimelineKeys[i].StartsWith("_live_", StringComparison.Ordinal))
                    previousLiveCount++;
                else
                    break;
            }
        }

        return new TranscriptRenderPlan
        {
            VisibleTimeline = visibleTimeline,
            NewKeys = newKeys,
            ShowHistory = conv.ShowExecutionHistory,
            HiddenCount = hiddenCount,
            CanIncremental = canIncremental,
            PreviousLiveCount = previousLiveCount,
            PreviousStableCount = _lastRenderedTimelineKeys.Count - previousLiveCount,
        };
    }
}