using System.Collections.Generic;

namespace AcDream.App.Rendering.Wb;

/// <summary>
/// Phase A8 (2026-05-28): EnvCell-scoped visibility snapshot. Direct port of
/// WB's <c>VisibilitySnapshot</c> at
/// <c>references/WorldBuilder/Chorizite.OpenGLSDLBackend/Lib/VisibilitySnapshot.cs:1-36</c>,
/// narrowed to the fields <see cref="EnvCellRenderer"/> actually consumes
/// (<c>BatchedByCell</c> + <c>VisibleLandblocks</c> + <c>PostPreparePoolIndex</c>).
/// The scenery-side <c>VisibleGroups</c> / <c>VisibleGfxObjIds</c> /
/// <c>IntersectingLandblocks</c> are dropped — we render scenery through
/// <see cref="WbDrawDispatcher"/>, not through this snapshot.
///
/// <para>Used as an immutable snapshot atomically swapped under the
/// renderer's render lock so PrepareRenderBatches (worker-driven) and
/// Render (render-thread-driven) can't race on a half-populated dict.</para>
/// </summary>
public sealed class EnvCellVisibilitySnapshot
{
    /// <summary>Landblocks fully or partially inside the frustum at prepare time.</summary>
    public List<EnvCellLandblock> VisibleLandblocks { get; init; } = new();

    /// <summary>
    /// Grouped instance data by full 32-bit cell id.
    /// Outer key: <c>CellId</c>. Inner key: <c>GfxObjId</c> (ulong; bit 33 set for
    /// deduplicated cell geometry per <see cref="EnvCellRenderer.GetEnvCellGeomId"/>).
    /// Value: list of per-instance transforms (one per cell or per static object
    /// inside that cell).
    /// </summary>
    public Dictionary<uint, Dictionary<ulong, List<InstanceData>>> BatchedByCell { get; init; } = new();

    /// <summary>
    /// Pool-index high-water mark after PrepareRenderBatches' merge phase.
    /// Mirrors WB <c>VisibilitySnapshot.PostPreparePoolIndex</c> at
    /// <c>references/WorldBuilder/.../VisibilitySnapshot.cs:31</c>.
    /// <para>Read by <see cref="EnvCellRenderer.Render"/> to set the pool
    /// cursor to a safe region past the snapshot's owned lists, so any
    /// <c>GetPooledList</c> calls inside Render don't trample data the
    /// snapshot still references. Dropping this field caused the post-Wave-5
    /// visual chaos — see
    /// <c>docs/research/2026-05-28-a8-env-cell-renderer-audit-findings.md</c>.</para>
    /// </summary>
    public int PostPreparePoolIndex { get; init; }

    /// <summary>True when no visible cells were produced this prepare cycle.</summary>
    public bool IsEmpty => VisibleLandblocks.Count == 0 && BatchedByCell.Count == 0;
}