using System.Numerics;

namespace AcDream.App.Rendering.Walk;

/// <summary>
/// Campaign FW3.1 — the production sibling of the FW1 conformance harness's
/// <c>WalkLandscapeDatBuilder</c>
/// (tests/AcDream.App.Tests/Rendering/Walk/WalkLandscapeDatBuilder.cs): owns
/// retail's viewer-centred block grid (LScape <c>mid_radius</c> = 25 → a
/// 51×51 window, recon 2026-08-30) and its LOD ring pyramid
/// (<see cref="SideCellCountForRing"/>).
///
/// Unlike the test builder — which re-scans the whole grid from a
/// <c>DatCollection</c> on every call — this class is fed INCREMENTALLY from
/// landblock commit/retire (<see cref="PublishLandblock"/>/
/// <see cref="RetireLandblock"/>), the same lifecycle
/// <c>Wb.BuildingRegistry</c> and <c>CellVisibility</c> already follow. Each
/// landblock's z-slab and building placements are computed ONCE, on the
/// streaming worker thread, at landblock-build time
/// (<c>LandblockBuildFactory</c>/<c>WalkBuildingFactory</c>) — publishing
/// here is a pure dictionary write, no DAT or GfxObj work.
///
/// <see cref="SetViewer"/> recentres the grid on the camera's block, porting
/// the test builder's viewer-cell recompute; it goes further by also
/// reflowing the 51×51 window when the camera crosses into a different
/// landblock (the test builder never needs this — every moving fixture stays
/// within its anchor block). Reflow only touches already-published data (a
/// dictionary lookup per slot); no DAT access ever happens here.
///
/// No frame currently calls <see cref="SetViewer"/> or reads
/// <see cref="Landscape"/> — FW3.2 wires <c>RetailFrameWalk</c> into the
/// render loop. This class exists now so that wiring is additive, and so the
/// FW3.1 conformance gate can exercise the SAME assembly code path
/// production will drive.
/// </summary>
public sealed class WalkLandscapeAssembler
{
    /// <summary>Retail LScape <c>mid_radius</c> (recon 2026-08-30) — NOT
    /// acdream's streaming radius (two-tier N1/N2), which is smaller. Blocks
    /// outside the streamed window simply stay unpublished (null slots).</summary>
    public const int MidRadius = 25;

    public const int GridWidth = MidRadius * 2 + 1;

    private sealed class BlockData
    {
        public required float MaxZ;
        public required float MinZ;
        public required IReadOnlyList<WalkBuildingFactory.Entry> Buildings;
    }

    private readonly Dictionary<(int X, int Y), BlockData> _blocks = new();
    private int _viewerBlockX = int.MinValue;
    private int _viewerBlockY = int.MinValue;

    public WalkLandscape Landscape { get; } = new()
    {
        MidWidth = GridWidth,
        Blocks = new WalkLandBlock?[GridWidth * GridWidth],
        ViewerBlockX = MidRadius,
        ViewerBlockY = MidRadius,
    };

    /// <summary>Landblock commit
    /// (<c>LandblockRenderPublisher.AdvanceCompleteOne</c>'s
    /// <c>BuildingRegistryCommitted</c> step): register/replace this
    /// landblock's z-slab and building placements. If the landblock falls
    /// within the CURRENT window, the visible slot refreshes immediately.</summary>
    public void PublishLandblock(
        uint landblockId, float maxZ, float minZ,
        IReadOnlyList<WalkBuildingFactory.Entry> buildings)
    {
        (int bx, int by) = BlockCoords(landblockId);
        _blocks[(bx, by)] = new BlockData { MaxZ = maxZ, MinZ = minZ, Buildings = buildings };
        RefreshSlotIfWindowed(bx, by);
    }

    /// <summary>Landblock retirement (<c>LandblockRenderPublisher
    /// .RemoveBuildingRegistry</c>): drop this landblock's data. Safe to call
    /// on a landblock that never published (no-op).</summary>
    public void RetireLandblock(uint landblockId)
    {
        (int bx, int by) = BlockCoords(landblockId);
        _blocks.Remove((bx, by));
        RefreshSlotIfWindowed(bx, by);
    }

    /// <summary>Recentres the grid on the camera's block and updates the
    /// sub-block cell offsets (retail's viewer recentre —
    /// <c>WalkLandscapeDatBuilder.SetViewer</c>'s port). When the camera's
    /// block hasn't changed since the last call, this only updates
    /// <see cref="WalkLandscape.ViewerCellX"/>/<see cref="WalkLandscape.ViewerCellY"/>
    /// — zero allocation, matching the test builder's lightweight path. A
    /// block crossing additionally reflows the 51×51 window from already-
    /// published data (a bounded, allocation-free dictionary-lookup pass —
    /// no DAT/GfxObj work, which already happened at publish time).</summary>
    public void SetViewer(uint cameraCellId, Vector3 cameraOrigin)
    {
        int cameraBlockX = (int)(cameraCellId >> 24);
        int cameraBlockY = (int)((cameraCellId >> 16) & 0xFF);
        if (cameraBlockX != _viewerBlockX || cameraBlockY != _viewerBlockY)
        {
            _viewerBlockX = cameraBlockX;
            _viewerBlockY = cameraBlockY;
            RebuildWindow();
        }

        uint low = cameraCellId & 0xFFFFu;
        if (low >= 1 && low <= 0x40)
        {
            int cellIndex = (int)low - 1;
            Landscape.ViewerCellX = cellIndex / 8;
            Landscape.ViewerCellY = cellIndex % 8;
        }
        else
        {
            // Interior camera: derive the outside-projected landcell from
            // the camera origin, matching the test builder's fallback
            // (Position::get_outside_cell_id via SmartBox::RenderNormalMode's
            // seen_outside arm).
            Landscape.ViewerCellX = Math.Clamp((int)MathF.Floor(cameraOrigin.X / 24f), 0, 7);
            Landscape.ViewerCellY = Math.Clamp((int)MathF.Floor(cameraOrigin.Y / 24f), 0, 7);
        }
    }

    /// <summary><c>ring &lt;= 1 ? 8 : ring == 2 ? 4 : ring &lt;= 4 ? 2 : 1</c>
    /// — the live-observed resolution pyramid (recon 2026-08-30): 8×8 in the
    /// 3×3 core, 4×4 at ring 2, 2×2 at rings 3–4, 1×1 beyond. Buildings only
    /// attach at full resolution (ring ≤ 1) — the traces show no BLD beyond
    /// ±1 block.</summary>
    internal static int SideCellCountForRing(int ring)
        => ring <= 1 ? 8 : ring == 2 ? 4 : ring <= 4 ? 2 : 1;

    internal static int RingOf(int gridX, int gridY)
        => Math.Max(Math.Abs(gridX - MidRadius), Math.Abs(gridY - MidRadius));

    private void RebuildWindow()
    {
        for (int gx = 0; gx < GridWidth; gx++)
        {
            for (int gy = 0; gy < GridWidth; gy++)
            {
                int bx = _viewerBlockX + gx - MidRadius;
                int by = _viewerBlockY + gy - MidRadius;
                Landscape.Blocks[gx * GridWidth + gy] = BuildSlot(bx, by, gx, gy);
            }
        }
    }

    private void RefreshSlotIfWindowed(int bx, int by)
    {
        if (_viewerBlockX == int.MinValue)
            return;   // SetViewer has never run — no window to refresh yet.
        int gx = bx - _viewerBlockX + MidRadius;
        int gy = by - _viewerBlockY + MidRadius;
        if (gx < 0 || gx >= GridWidth || gy < 0 || gy >= GridWidth)
            return;
        Landscape.Blocks[gx * GridWidth + gy] = BuildSlot(bx, by, gx, gy);
    }

    private WalkLandBlock? BuildSlot(int bx, int by, int gx, int gy)
    {
        if (bx < 0 || bx > 0xFF || by < 0 || by > 0xFF)
            return null;
        if (!_blocks.TryGetValue((bx, by), out BlockData? data))
            return null;

        int sideCellCount = SideCellCountForRing(RingOf(gx, gy));
        var block = new WalkLandBlock
        {
            // Additive (Campaign FW3.2b-1): same (bx<<24 | by<<16) encoding
            // BlockCoords decodes below — see WalkLandBlock.LandblockId.
            LandblockId = (uint)bx << 24 | (uint)by << 16,
            SideCellCount = sideCellCount,
            MaxZ = data.MaxZ,
            MinZ = data.MinZ,
        };
        block.EnsureCellArrays();

        if (sideCellCount == 8)
        {
            foreach (WalkBuildingFactory.Entry entry in data.Buildings)
            {
                int cellIndex = (int)(entry.Building.PositionCellId & 0xFFFFu) - 1;
                if (cellIndex >= 0 && cellIndex < 64)
                    block.CellBuildings[cellIndex] = entry.Building;
            }
        }
        return block;
    }

    private static (int X, int Y) BlockCoords(uint landblockId)
        => ((int)((landblockId >> 24) & 0xFFu), (int)((landblockId >> 16) & 0xFFu));
}