using System;
using System.Collections.Generic;
using System.Linq;
using System.Numerics;
using AcDream.App.Rendering;
using DatReaderWriter;
using DatReaderWriter.Options;
using Xunit;
using Xunit.Abstractions;
using DatLandBlockInfo = DatReaderWriter.DBObjs.LandBlockInfo;

namespace AcDream.App.Tests.Rendering;

/// <summary>
/// #127 — per-building flood admissions are BISTABLE per frame under the
/// outdoor root (the building-flap mechanism: tower roof/edges flap, #123
/// buildings vanishing when running past). Captured live with the [viewer]
/// fwd= probe (flap-fwd-capture2.log): a ~4 cm eye wobble flips the merged
/// flood 24↔25 with a byte-identical gaze:
///   flood=25 eye=(129.051,-15.636,99.512) fwd=(-0.7565,0.5877,-0.2869)
///   flood=24 eye=(129.009,-15.610,99.503) fwd=(same)
///   flood=25 eye=(129.051,-15.642,99.514) fwd=(same)
/// (player parked at pCell=0xA9B40019, Holtburg town, A9B4-anchored world
/// frame — A9B4-local == world; A9B3 cells get a (0,-192,0) block offset.)
///
/// This harness replays the captured (eye, fwd) pairs through the
/// production outdoor pipeline — Build(outdoorNode) + per-building
/// ConstructViewBuilding merged (RetailPViewRenderer.MergeNearbyBuildingFloods
/// shape) — and DIFFS the admitted cell sets: the flipping cell names the
/// bistable admission, and the bisect along the eye segment names the knife
/// edge.
/// </summary>
public class Issue127FloodFlipReplayTests
{
    private readonly ITestOutputHelper _out;
    public Issue127FloodFlipReplayTests(ITestOutputHelper output) => _out = output;

    // The captured flip pair (A9B4-anchored world frame).
    private static readonly Vector3 EyeA = new(129.051f, -15.636f, 99.512f);
    private static readonly Vector3 EyeB = new(129.009f, -15.610f, 99.503f);
    private static readonly Vector3 Fwd = Vector3.Normalize(new Vector3(-0.7565f, 0.5877f, -0.2869f));

    private sealed record World(
        Dictionary<uint, LoadedCell> Cells,
        List<List<LoadedCell>> BuildingGroups,
        Func<uint, LoadedCell?> Lookup);

    private static void LoadLandblockBuildings(
        DatCollection dats, uint landblock, Vector3 offset,
        Dictionary<uint, LoadedCell> cells, List<List<LoadedCell>> groups)
    {
        var lbi = dats.Get<DatLandBlockInfo>(landblock | 0xFFFEu);
        if (lbi is null) return;

        // all interior cells (the lookup needs every portal-reachable cell)
        for (uint low = 0x0100u; low < 0x0100u + lbi.NumCells; low++)
        {
            uint id = landblock | low;
            try { cells[id] = CornerFloodReplayTests.LoadCell(dats, id, offset); }
            catch (InvalidOperationException) { }
        }

        // per-building groups from the bldPortal stab lists (the dat's own
        // building→cells mapping; mirrors BuildingLoader's seed+walk result)
        if (lbi.Buildings is null) return;
        foreach (var bld in lbi.Buildings)
        {
            var set = new HashSet<uint>();
            if (bld.Portals is not null)
                foreach (var bp in bld.Portals)
                    if (bp.StabList is not null)
                        foreach (ushort low in bp.StabList)
                            set.Add(landblock | low);
            var group = new List<LoadedCell>();
            foreach (uint id in set)
                if (cells.TryGetValue(id, out var c))
                    group.Add(c);
            if (group.Count > 0)
                groups.Add(group);
        }
    }

    private World? LoadWorld()
    {
        var datDir = CornerFloodReplayTests.ResolveDatDir();
        if (datDir is null) { _out.WriteLine("SKIP: dats unavailable"); return null; }

        using var dats = new DatCollection(datDir, DatAccessType.Read);
        var cells = new Dictionary<uint, LoadedCell>();
        var groups = new List<List<LoadedCell>>();
        // A9B4 = the anchor (world == local); the live gather spans the
        // streaming near window, so load a 5x5 block neighbourhood with
        // block offsets relative to the anchor.
        for (int dx = -2; dx <= 2; dx++)
        for (int dy = -2; dy <= 2; dy++)
        {
            uint lbX = (uint)(0xA9 + dx);
            uint lbY = (uint)(0xB4 + dy);
            uint lb = (lbX << 24) | (lbY << 16);
            LoadLandblockBuildings(dats, lb, new Vector3(dx * 192f, dy * 192f, 0f), cells, groups);
        }
        _out.WriteLine($"loaded {cells.Count} cells in {groups.Count} building groups");
        Func<uint, LoadedCell?> lookup = id => cells.TryGetValue(id, out var c) ? c : null;
        return new World(cells, groups, lookup);
    }

    private static Matrix4x4 ViewProjFor(Vector3 eye, Vector3 fwd, float fovY)
    {
        var view = Matrix4x4.CreateLookAt(eye, eye + fwd * 3f, Vector3.UnitZ);
        var proj = Matrix4x4.CreatePerspectiveFieldOfView(fovY, 1280f / 720f, 0.1f, 5000f);
        return view * proj;
    }

    // PortalBounds per group: the union AABB of the group's exit-portal
    // polygons in world space — exactly BuildingLoader's construction
    // (BuildingLoader.cs:114-144).
    private static (bool Has, Vector3 Min, Vector3 Max) PortalBoundsFor(List<LoadedCell> group)
    {
        bool has = false;
        var min = new Vector3(float.MaxValue);
        var max = new Vector3(float.MinValue);
        foreach (var cell in group)
        {
            int n = Math.Min(cell.Portals.Count, cell.PortalPolygons.Count);
            for (int i = 0; i < n; i++)
            {
                if (cell.Portals[i].OtherCellId != 0xFFFF) continue;
                var poly = cell.PortalPolygons[i];
                if (poly is null) continue;
                foreach (var v in poly)
                {
                    var world = Vector3.Transform(v, cell.WorldTransform);
                    has = true;
                    min = Vector3.Min(min, world);
                    max = Vector3.Max(max, world);
                }
            }
        }
        return (has, min, max);
    }

    // The production outdoor pipeline: full-screen outdoor root + per-building
    // exterior floods merged as a union (RetailPViewRenderer.DrawInside +
    // MergeNearbyBuildingFloods + MergeBuildingFrame), INCLUDING the gather's
    // per-building frustum pre-gate on PortalBounds (GameWindow:7542-7545) —
    // controlled by <paramref name="withPreGate"/> so the gate itself can be
    // implicated or exonerated.
    private static HashSet<uint> AdmittedCells(World w, Vector3 eye, Vector3 fwd, float fovY, bool withPreGate)
    {
        var viewProj = ViewProjFor(eye, fwd, fovY);
        var frustum = FrustumPlanes.FromViewProjection(viewProj);
        var outdoor = OutdoorCellNode.Build(0xA9B40019u);
        var pv = PortalVisibilityBuilder.Build(outdoor, eye, w.Lookup, viewProj);
        foreach (var group in w.BuildingGroups)
        {
            if (withPreGate)
            {
                var (has, min, max) = PortalBoundsFor(group);
                if (has && !FrustumCuller.IsAabbVisible(frustum, min, max))
                    continue;
            }
            var bf = PortalVisibilityBuilder.ConstructViewBuilding(group, eye, w.Lookup, viewProj);
            foreach (uint cellId in bf.OrderedVisibleCells)
            {
                if (!bf.CellViews.TryGetValue(cellId, out var srcView)) continue;
                if (pv.CellViews.TryGetValue(cellId, out var existing))
                {
                    foreach (var p in srcView.Polygons) existing.Add(p);
                    continue;
                }
                pv.CellViews[cellId] = srcView;
                pv.OrderedVisibleCells.Add(cellId);
            }
        }
        return new HashSet<uint>(pv.OrderedVisibleCells);
    }

    /// <summary>
    /// Reproduce + name: the captured 4 cm pair must admit the SAME cell set
    /// (a stable world does not flap a building interior for a 4 cm eye
    /// wobble at identical gaze). The diff names the bistable cell(s); the
    /// bisect prints the knife-edge location and transition count.
    /// </summary>
    [Fact]
    public void CapturedFlipPair_AdmissionIsStable()
    {
        var w = LoadWorld();
        if (w is null) return;

        foreach (bool preGate in new[] { false, true })
        foreach (float fov in new[] { MathF.PI / 3f, 1.2f, MathF.PI / 2f, 0.9f })
        {
            var a = AdmittedCells(w, EyeA, Fwd, fov, preGate);
            var b = AdmittedCells(w, EyeB, Fwd, fov, preGate);
            var onlyA = a.Except(b).OrderBy(x => x).ToList();
            var onlyB = b.Except(a).OrderBy(x => x).ToList();
            _out.WriteLine(FormattableString.Invariant(
                $"preGate={preGate} fov={fov:F2}: |A|={a.Count} |B|={b.Count} onlyA=[{string.Join(",", onlyA.Select(x => $"0x{x:X8}"))}] onlyB=[{string.Join(",", onlyB.Select(x => $"0x{x:X8}"))}]"));

            if (onlyA.Count == 0 && onlyB.Count == 0) continue;

            // bisect the segment: count admission transitions per flipping cell
            foreach (uint cell in onlyA.Concat(onlyB))
            {
                int transitions = 0;
                bool? prev = null;
                for (int i = 0; i <= 40; i++)
                {
                    var eye = Vector3.Lerp(EyeA, EyeB, i / 40f);
                    bool admitted = AdmittedCells(w, eye, Fwd, fov, preGate).Contains(cell);
                    if (prev.HasValue && admitted != prev.Value) transitions++;
                    prev = admitted;
                }
                _out.WriteLine(FormattableString.Invariant(
                    $"  cell 0x{cell:X8}: {transitions} admission transition(s) along the 4 cm segment"));
            }

            Assert.Fail($"flood admission differs across the captured 4 cm pair (preGate={preGate}, fov={fov:F2}) — see output for the flipping cells");
        }
    }
}