using System.Collections.Generic;
using System.Numerics;

namespace AcDream.App.Rendering.Wb;

/// <summary>
/// Phase A8 (2026-05-26): a logical building — one or more EnvCells linked
/// via the dat-level <c>LandBlockInfo.Buildings</c> entry. Building shells (cottage
/// walls, inn walls — <c>IsBuildingShell=true</c> entities) render unconditionally
/// when the camera is inside this building's cells. The exit portal polygons
/// are stencil-marked so outdoor visibility leaks through portal silhouettes
/// only.
///
/// <para>Step 5 (cross-building visibility via 3-stencil-bit pipeline) uses
/// the occlusion-query state to skip rendering when the building's portals
/// weren't visible last frame.</para>
///
/// <para>WB reference: <c>WorldBuilder.Shared/Services/PortalService.cs</c>
/// (<c>BuildingPortalGroup</c>) and <c>PortalRenderManager.cs</c> step-5 lifecycle.
/// Retail reference: <c>docs/research/named-retail/acclient.h:32035</c>
/// (<c>BuildInfo</c>) + <c>32094</c> (<c>CBldPortal</c>).</para>
/// </summary>
public sealed class Building
{
    /// <summary>Unique within a landblock; allocated sequentially by <see cref="BuildingLoader"/>
    /// starting at 1 (0 is reserved for "no building" semantics on <c>LoadedCell</c>).</summary>
    public required uint BuildingId { get; init; }

    /// <summary>The EnvCells this building owns. Includes all cells reachable
    /// from the building's entry portals via interior portals (no exit portals).
    /// Populated by <see cref="BuildingLoader.Build"/> via BFS over
    /// <see cref="AcDream.App.Rendering.LoadedCell.Portals"/>.</summary>
    public required HashSet<uint> EnvCellIds { get; init; }

    /// <summary>Exit portal polygons in world space (each polygon is a triangle
    /// fan from vertex 0). Stencil-marked + far-depth-punched at Steps 1+2 of
    /// WB's RenderInsideOut pipeline (RR7). Collected during
    /// <see cref="BuildingLoader.Build"/> Step C by transforming cell-local portal
    /// polygon vertices via <see cref="AcDream.App.Rendering.LoadedCell.WorldTransform"/>.</summary>
    public required IReadOnlyList<Vector3[]> ExitPortalPolygons { get; init; }

    // -------------------------------------------------------------------------
    // Step 5 occlusion-query state (mutable, per-frame, RR9 scope).
    // -------------------------------------------------------------------------

    /// <summary>GL query object handle; lazily created on first use by the
    /// Step 5 occlusion-query pass (RR9). 0 = not yet created.</summary>
    public uint QueryId;

    /// <summary>True after the first <c>BeginQuery</c> call; controls whether the
    /// read-back path is safe to execute on the next frame.</summary>
    public bool QueryStarted;

    /// <summary>Previous-frame query result. When false, the building's interior
    /// render is skipped (Step 5 early-out in RR9 + RR11).</summary>
    public bool WasVisible;
}