// PortalVisibilityBuilder.cs
//
// Phase A8.F: recursive portal-clip visibility (the builder). Port of retail
// PView::ConstructView (decomp:433750) -> ClipPortals (433572) -> AddViewToPortals
// (433446). Walks the portal graph from the camera cell, accumulating a per-cell
// screen-space CellView; exit portals union their clipped region into OutsideView.
// GL-free; unit-tested without a GPU context.
using System;
using System.Collections.Generic;
using System.Numerics;

namespace AcDream.App.Rendering;

/// <summary>Per-frame output of the portal-frame BFS.</summary>
public sealed class PortalVisibilityFrame
{
    /// <summary>Screen region (NDC) where outdoor terrain/scenery may draw — exit portals
    /// recursively clipped to their portal chain. The cellar-flap fix.</summary>
    public CellView OutsideView { get; } = new();

    /// <summary>Per-cell accumulated clip region, keyed by full cell id (wire-in #2).</summary>
    public Dictionary<uint, CellView> CellViews { get; } = new();

    /// <summary>Entry clip regions for other buildings reached through our portals, keyed by the
    /// neighbour cell id that left the camera building's cell set (wire-in #3 / Step 5).</summary>
    public Dictionary<uint, CellView> CrossBuildingViews { get; } = new();
}

public static class PortalVisibilityBuilder
{
    // Per-cell re-processing bound. NOTE: this cap is the actual termination mechanism for
    // cyclic portal graphs, NOT merely a safety net — the re-enqueue-on-growth guard below is
    // a near-no-op because CellView.Add never dedupes, so a cell almost always "grows". Retail
    // instead converges via an update_count / set_view(...,i) slice watermark (decomp: AddToCell
    // 433050 esi[0x11], InitCell timestamp, AddViewToPortals 433446). Consequences vs retail:
    // (a) a cell reachable through >4 contributing portals under-counts; (b) duplicate polygons
    // accumulate on cyclic/multi-path graphs (correctness survives — stencil marks are idempotent
    // — but it is per-frame cost). Both bite only on dungeon-scale cyclic/hub graphs; a cottage
    // cellar is a short chain where each cell is visited once. The faithful fixpoint port is filed
    // as a fast-follow (docs/ISSUES.md) before A8.F is relied on for dungeons.
    private const int MaxReprocessPerCell = 4;
    private const float PortalSideEpsilon = 0.01f; // matches CellVisibility.PointInCellEpsilon

    // TEMP diagnostic (Phase A8.F visual-gate triage; strip after): ACDREAM_A8_DUMP_PV=1 dumps the
    // local→NDC→clipped portal geometry for the first 2 Build calls per distinct camera cell.
    private static readonly bool s_pvDump =
        Environment.GetEnvironmentVariable("ACDREAM_A8_DUMP_PV") == "1";
    private static readonly Dictionary<uint, int> s_pvDumpCount = new();

    /// <param name="lookup">Resolve a full cell id to its LoadedCell, or null if not loaded.</param>
    /// <param name="buildingMembership">Optional: true if a cell id is in the camera building's cell
    /// set. When provided, a neighbour OUTSIDE the set routes to CrossBuildingViews instead of
    /// continuing the in-building BFS. Pass null to treat all reachable cells as in-building.</param>
    public static PortalVisibilityFrame Build(
        LoadedCell cameraCell,
        Vector3 cameraPos,
        Func<uint, LoadedCell?> lookup,
        Matrix4x4 viewProj,
        Func<uint, bool>? buildingMembership = null)
    {
        var frame = new PortalVisibilityFrame();
        if (cameraCell == null) return frame;

        // Interior portals never cross landblocks (same invariant as CellVisibility.GetVisibleCells);
        // building-boundary crossings are handled separately via the buildingMembership escape hatch.
        uint lbMask = cameraCell.CellId & 0xFFFF0000u;

        frame.CellViews[cameraCell.CellId] = CellView.FullScreen();
        var processCount = new Dictionary<uint, int>();
        var queue = new Queue<LoadedCell>();
        queue.Enqueue(cameraCell);

        bool pvDump = false;
        if (s_pvDump)
        {
            lock (s_pvDumpCount)
            {
                s_pvDumpCount.TryGetValue(cameraCell.CellId, out int dc);
                if (dc < 2) { s_pvDumpCount[cameraCell.CellId] = dc + 1; pvDump = true; }
            }
            if (pvDump)
            {
                Console.WriteLine($"[pv-dump] camCell=0x{cameraCell.CellId:X8} portals={cameraCell.Portals.Count} polyLists={cameraCell.PortalPolygons.Count} vp[M11={viewProj.M11:F3} M22={viewProj.M22:F3} M33={viewProj.M33:F3} M34={viewProj.M34:F3} M43={viewProj.M43:F3} M44={viewProj.M44:F3}]");
                // Camera-cell portal census (A8.F triage 2026-05-29): report, for EVERY
                // portal, the exact inputs the BFS guards read — BEFORE the guards run, so
                // a portal the loop silently `continue`s past is still visible here. An
                // empty OUTSIDEVIEW can then be traced to the precise gate: polyLen<3 (empty
                // polygon from BuildLoadedCell), interiorSide=false (camera back-facing the
                // portal — a legitimately-empty result, not a bug), or (if both OK) a
                // downstream projection/clip failure shown by the EXIT-PROJ/EXIT-CLIP lines.
                for (int ci = 0; ci < cameraCell.Portals.Count; ci++)
                {
                    int plen = ci < cameraCell.PortalPolygons.Count
                        ? (cameraCell.PortalPolygons[ci]?.Length ?? -1) : -2;
                    bool hasPlane = ci < cameraCell.ClipPlanes.Count;
                    bool interiorSide = !hasPlane || CameraOnInteriorSide(cameraCell, ci, cameraPos);
                    var n = hasPlane ? cameraCell.ClipPlanes[ci].Normal : Vector3.Zero;
                    Console.WriteLine($"[pv-dump]   CAMPORTAL[{ci}] other=0x{cameraCell.Portals[ci].OtherCellId:X4} polyLen={plen} hasPlane={hasPlane} interiorSide={interiorSide} planeN=({n.X:F3},{n.Y:F3},{n.Z:F3})");
                }
            }
        }

        while (queue.Count > 0)
        {
            var cell = queue.Dequeue();
            if (!frame.CellViews.TryGetValue(cell.CellId, out var currentView) || currentView.IsEmpty)
                continue;

            processCount.TryGetValue(cell.CellId, out int pc);
            if (pc >= MaxReprocessPerCell) continue;
            processCount[cell.CellId] = pc + 1;

            for (int i = 0; i < cell.Portals.Count; i++)
            {
                if (i >= cell.PortalPolygons.Count) continue;
                var poly = cell.PortalPolygons[i];
                if (poly == null || poly.Length < 3) continue;

                bool dx = pvDump && cell.Portals[i].OtherCellId == 0xFFFF;

                // Portal-side test: only traverse a portal the camera is on the interior side of
                // (mirrors CellVisibility.GetVisibleCells + retail's 'seen' flag). Culls back-facing
                // portals so we never feed a degenerate/wrong-facing projection downstream.
                if (i < cell.ClipPlanes.Count && !CameraOnInteriorSide(cell, i, cameraPos))
                {
                    if (dx) Console.WriteLine($"[pv-dump]   EXIT-CULLED(side) cell=0x{cell.CellId:X8} p{i} localN={poly.Length} hasClipPlane={(i < cell.ClipPlanes.Count)}");
                    continue;
                }

                // Project to NDC, then normalize to CCW for the CCW-only ScreenPolygonClip
                // (ProjectToNdc preserves input winding; portal dat polygons may be CW).
                Vector2[] portalNdc = PortalProjection.ProjectToNdc(poly, cell.WorldTransform, viewProj);
                if (dx) Console.WriteLine($"[pv-dump]   EXIT-PROJ cell=0x{cell.CellId:X8} p{i} localN={poly.Length} ndcN={portalNdc.Length} local0=({poly[0].X:F2},{poly[0].Y:F2},{poly[0].Z:F2}) ndc=[{string.Join(" ", System.Array.ConvertAll(portalNdc, v => $"({v.X:F2},{v.Y:F2})"))}]");
                if (portalNdc.Length < 3) continue;
                EnsureCcw(portalNdc);

                // Intersect the portal opening with every polygon of the current cell's view.
                var clippedRegion = new List<ViewPolygon>();
                foreach (var vp in currentView.Polygons)
                {
                    var clipped = ScreenPolygonClip.Intersect(portalNdc, vp.Vertices);
                    if (clipped.Length >= 3) clippedRegion.Add(new ViewPolygon(clipped));
                }
                if (dx) Console.WriteLine($"[pv-dump]   EXIT-CLIP cell=0x{cell.CellId:X8} p{i} currentViewPolys={currentView.Polygons.Count} clipResult={clippedRegion.Count}");
                if (clippedRegion.Count == 0) continue; // portal not visible through this chain

                var portal = cell.Portals[i];

                if (portal.OtherCellId == 0xFFFF)
                {
                    if (pvDump)
                    {
                        Console.WriteLine($"[pv-dump]   EXIT cell=0x{cell.CellId:X8} p{i} localN={poly.Length} ndcN={portalNdc.Length} clipPolys={clippedRegion.Count}");
                        Console.WriteLine($"[pv-dump]     local=[{string.Join(" ", System.Array.ConvertAll(poly, v => $"({v.X:F2},{v.Y:F2},{v.Z:F2})"))}]");
                        Console.WriteLine($"[pv-dump]     ndc=[{string.Join(" ", System.Array.ConvertAll(portalNdc, v => $"({v.X:F3},{v.Y:F3})"))}]");
                        foreach (var cp in clippedRegion)
                            Console.WriteLine($"[pv-dump]     clipped({cp.Vertices.Length})=[{string.Join(" ", System.Array.ConvertAll((Vector2[])cp.Vertices, v => $"({v.X:F3},{v.Y:F3})"))}]");
                    }
                    // Exit portal -> outdoors visible through this (clipped) opening.
                    foreach (var cp in clippedRegion) frame.OutsideView.Add(cp);
                    continue;
                }

                // TODO(A8.F): neighbour-side OtherPortalClip (decomp:433524) — also clip the
                // interior portal against the neighbour's matching portal polygon. Not implemented
                // here; add if multi-cell conformance shows over-inclusion.
                uint neighbourId = lbMask | portal.OtherCellId;

                // Cross-building boundary: route to CrossBuildingViews, don't continue in-building BFS.
                if (buildingMembership != null && !buildingMembership(neighbourId))
                {
                    var xview = GetOrCreate(frame.CrossBuildingViews, neighbourId);
                    foreach (var cp in clippedRegion) xview.Add(cp);
                    continue;
                }

                var neighbour = lookup(neighbourId);
                if (neighbour == null) continue;

                // Union the clipped region into the neighbour's view; (re)enqueue if it grew.
                var nview = GetOrCreate(frame.CellViews, neighbourId);
                int before = nview.Polygons.Count;
                foreach (var cp in clippedRegion) nview.Add(cp);
                if (nview.Polygons.Count > before)
                    queue.Enqueue(neighbour);
            }
        }

        if (pvDump)
            Console.WriteLine($"[pv-dump] OUTSIDEVIEW polys={frame.OutsideView.Polygons.Count} bfsCellViews={frame.CellViews.Count} crossBldg={frame.CrossBuildingViews.Count}");

        return frame;
    }

    // Mirrors CellVisibility's portal-side test (InsideSide convention).
    private static bool CameraOnInteriorSide(LoadedCell cell, int portalIndex, Vector3 cameraPos)
    {
        var plane = cell.ClipPlanes[portalIndex];
        if (plane.Normal.LengthSquared() < 1e-8f) return true; // no usable plane → allow
        var localCam = Vector3.Transform(cameraPos, cell.InverseWorldTransform);
        float dot = Vector3.Dot(plane.Normal, localCam) + plane.D;
        return plane.InsideSide == 0 ? dot >= -PortalSideEpsilon : dot <= PortalSideEpsilon;
    }

    // Reverse vertex order in place if the polygon is wound clockwise (signed area < 0).
    private static void EnsureCcw(Vector2[] poly)
    {
        float area2 = 0f;
        for (int i = 0; i < poly.Length; i++)
        {
            var p = poly[i]; var q = poly[(i + 1) % poly.Length];
            area2 += p.X * q.Y - q.X * p.Y;
        }
        if (area2 < 0f) Array.Reverse(poly);
    }

    private static CellView GetOrCreate(Dictionary<uint, CellView> map, uint key)
    {
        if (!map.TryGetValue(key, out var v)) { v = new CellView(); map[key] = v; }
        return v;
    }
}