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;

namespace AcDream.App.Tests.Rendering;

/// <summary>
/// #181 — the portal-flood admitted set flaps 31↔32 on MICRON eye noise at a
/// parked camera (live: launch-176-leakfix.log, root 0x8A020142, vis flips
/// every ~100–200 frames for 517k frames; the swept eye carries ~7 µm
/// float-roundtrip noise). The flapping cell's visibility-scoped lights + the
/// union-AABB scissor rect strobe = the #176 washed-region flicker.
///
/// This replay hunts the knife edge headlessly: at the live parked eye
/// (49.15, −38.62, −3.98), sweep gazes and perturb the eye by ±0.5 mm per
/// axis; ANY admitted-set difference at sub-mm perturbation is the #181
/// instability, and the symmetric difference names the flapping cell.
/// </summary>
public class Issue181VisFlapReplayTests
{
    private const uint FacilityHub = 0x8A020000u;
    private const uint LiveRoot    = FacilityHub | 0x0142u;

    private static readonly Vector3 LiveEye = new(49.15f, -38.62f, -3.98f);

    private readonly ITestOutputHelper _out;
    public Issue181VisFlapReplayTests(ITestOutputHelper output) => _out = output;

    private static Matrix4x4 ViewProjFor(Vector3 eye, Vector3 gazeDir)
    {
        var view = Matrix4x4.CreateLookAt(eye, eye + gazeDir, Vector3.UnitZ);
        var proj = Matrix4x4.CreatePerspectiveFieldOfView(MathF.PI / 3f, 16f / 9f, 0.1f, 5000f);
        return view * proj;
    }

    private static List<uint> Flood(
        Dictionary<uint, LoadedCell> cells, uint rootId, Vector3 eye, Vector3 gazeDir)
    {
        Func<uint, LoadedCell?> lookup = id => cells.TryGetValue(id, out var c) ? c : null;
        var frame = PortalVisibilityBuilder.Build(
            cells[rootId], eye, lookup, ViewProjFor(eye, gazeDir),
            buildingMembership: null,
            drawLiftZ: PortalVisibilityBuilder.ShellDrawLiftZ);
        var result = new List<uint>(frame.OrderedVisibleCells);
        result.Sort();
        return result;
    }

    private static string CellSetString(IEnumerable<uint> ids)
        => string.Join(" ", ids.Select(id => $"{id & 0xFFFFu:X4}"));

    [Fact]
    public void Diagnostic_FlappingCellViewRegion_SliverOrLarge()
    {
        var datDir = CornerFloodReplayTests.ResolveDatDir();
        if (datDir is null) { _out.WriteLine("SKIP: no dat dir"); return; }
        using var dats = new DatCollection(datDir, DatAccessType.Read);
        var cells = Issue120ReciprocalPingPongTests.LoadAllInteriorCells(dats, FacilityHub);
        uint flapper = FacilityHub | 0x0181u;

        // The most unstable pose from the perturbation sweep.
        float yaw = 15f * MathF.PI / 180f, pitch = -20f * MathF.PI / 180f;
        var gaze = new Vector3(
            MathF.Cos(pitch) * MathF.Cos(yaw),
            MathF.Cos(pitch) * MathF.Sin(yaw),
            MathF.Sin(pitch));

        Func<uint, LoadedCell?> lookup = id => cells.TryGetValue(id, out var c) ? c : null;

        foreach (var (label, eye) in new (string, Vector3)[]
        {
            ("base      ", LiveEye),
            ("+0.5mm x  ", LiveEye + new Vector3(0.0005f, 0, 0)),
            ("-0.5mm x  ", LiveEye - new Vector3(0.0005f, 0, 0)),
            ("+5mm x    ", LiveEye + new Vector3(0.005f, 0, 0)),
            ("-5mm x    ", LiveEye - new Vector3(0.005f, 0, 0)),
            ("+2cm z    ", LiveEye + new Vector3(0, 0, 0.02f)),
            ("-2cm z    ", LiveEye - new Vector3(0, 0, 0.02f)),
        })
        {
            var frame = PortalVisibilityBuilder.Build(
                cells[LiveRoot], eye, lookup, ViewProjFor(eye, gaze),
                buildingMembership: null,
                drawLiftZ: PortalVisibilityBuilder.ShellDrawLiftZ);

            if (!frame.CellViews.TryGetValue(flapper, out var view) || view.IsEmpty)
            {
                _out.WriteLine($"{label}: 0181 NOT ADMITTED");
                continue;
            }

            // NDC shoelace area of the admitted region (screen is 4.0 NDC-units total).
            float area = 0f; int polys = 0, verts = 0;
            foreach (var vp in view.Polygons)
            {
                var v = vp.Vertices;
                polys++; verts += v.Length;
                float a = 0f;
                for (int i = 0; i < v.Length; i++)
                {
                    var p = v[i]; var q = v[(i + 1) % v.Length];
                    a += p.X * q.Y - q.X * p.Y;
                }
                area += MathF.Abs(a) * 0.5f;
            }
            _out.WriteLine(FormattableString.Invariant(
                $"{label}: 0181 admitted polys={polys} verts={verts} ndcArea={area:F4} ({area / 4f * 100f:F1}% of screen)"));
        }
    }

    [Fact]
    public void Diagnostic_SubMillimeterEyePerturbation_MustNotChangeAdmission()
    {
        var datDir = CornerFloodReplayTests.ResolveDatDir();
        if (datDir is null) { _out.WriteLine("SKIP: no dat dir"); return; }
        using var dats = new DatCollection(datDir, DatAccessType.Read);
        var cells = Issue120ReciprocalPingPongTests.LoadAllInteriorCells(dats, FacilityHub);
        Assert.True(cells.ContainsKey(LiveRoot), "live root 0x0142 not loaded");

        // ±0.5 mm per axis — an order of magnitude above the live µm noise, well
        // below anything visually meaningful.
        var perturbations = new[]
        {
            new Vector3( 0.0005f, 0, 0), new Vector3(-0.0005f, 0, 0),
            new Vector3(0,  0.0005f, 0), new Vector3(0, -0.0005f, 0),
            new Vector3(0, 0,  0.0005f), new Vector3(0, 0, -0.0005f),
        };

        int unstableGazes = 0;
        for (int yawDeg = 0; yawDeg < 360; yawDeg += 15)
        {
            foreach (float pitchDeg in new[] { 0f, -20f, -35f })
            {
                float yaw = yawDeg * MathF.PI / 180f, pitch = pitchDeg * MathF.PI / 180f;
                var gaze = new Vector3(
                    MathF.Cos(pitch) * MathF.Cos(yaw),
                    MathF.Cos(pitch) * MathF.Sin(yaw),
                    MathF.Sin(pitch));

                var baseline = Flood(cells, LiveRoot, LiveEye, gaze);
                foreach (var d in perturbations)
                {
                    var perturbed = Flood(cells, LiveRoot, LiveEye + d, gaze);
                    if (perturbed.SequenceEqual(baseline)) continue;

                    unstableGazes++;
                    var removed = baseline.Except(perturbed).ToList();
                    var added   = perturbed.Except(baseline).ToList();
                    _out.WriteLine(FormattableString.Invariant(
                        $"UNSTABLE yaw={yawDeg} pitch={pitchDeg} d=({d.X * 1000:F1},{d.Y * 1000:F1},{d.Z * 1000:F1})mm base={baseline.Count} pert={perturbed.Count} removed=[{CellSetString(removed)}] added=[{CellSetString(added)}]"));
                }
            }
        }

        _out.WriteLine($"unstable (gaze, perturbation) pairs: {unstableGazes}");
        // Diagnostic first: report, don't assert — the fix turns this into a hard pin.
    }
}