using System.Collections.Concurrent;
using System.Numerics;
using DatReaderWriter.DBObjs;
using DatReaderWriter.Enums;
using DatReaderWriter.Types;
using Plane = System.Numerics.Plane;

namespace AcDream.Core.Physics;

/// <summary>
/// Thread-safe cache of physics-relevant data extracted from GfxObj and Setup
/// dat objects during streaming. Populated by the streaming worker thread;
/// read by the physics engine on the game/render thread. ConcurrentDictionary
/// makes cross-thread access safe without a global lock.
/// </summary>
public sealed class PhysicsDataCache
{
    private readonly ConcurrentDictionary<uint, GfxObjPhysics> _gfxObj = new();
    private readonly ConcurrentDictionary<uint, SetupPhysics> _setup = new();
    private readonly ConcurrentDictionary<uint, CellPhysics> _cellStruct = new();

    /// <summary>
    /// Extract and cache the physics BSP + polygon data from a GfxObj.
    /// No-ops if the id is already cached or the GfxObj has no physics data.
    /// </summary>
    public void CacheGfxObj(uint gfxObjId, GfxObj gfxObj)
    {
        if (_gfxObj.ContainsKey(gfxObjId)) return;
        if (!gfxObj.Flags.HasFlag(GfxObjFlags.HasPhysics)) return;
        if (gfxObj.PhysicsBSP?.Root is null) return;

        _gfxObj[gfxObjId] = new GfxObjPhysics
        {
            BSP = gfxObj.PhysicsBSP,
            PhysicsPolygons = gfxObj.PhysicsPolygons,
            BoundingSphere = gfxObj.PhysicsBSP.Root.BoundingSphere,
            Vertices = gfxObj.VertexArray,
            Resolved = ResolvePolygons(gfxObj.PhysicsPolygons, gfxObj.VertexArray),
        };
    }

    /// <summary>
    /// Extract and cache the collision shape data from a Setup.
    /// No-ops if the id is already cached.
    /// </summary>
    public void CacheSetup(uint setupId, Setup setup)
    {
        if (_setup.ContainsKey(setupId)) return;
        _setup[setupId] = new SetupPhysics
        {
            CylSpheres = setup.CylSpheres ?? new(),
            Spheres = setup.Spheres ?? new(),
            Height = setup.Height,
            Radius = setup.Radius,
            StepUpHeight = setup.StepUpHeight,
            StepDownHeight = setup.StepDownHeight,
        };
    }

    /// <summary>
    /// Extract and cache the physics BSP + polygon data from a CellStruct
    /// (indoor room geometry). No-ops if the id is already cached or the
    /// CellStruct has no physics BSP.
    /// </summary>
    public void CacheCellStruct(uint envCellId, CellStruct cellStruct,
                                 Matrix4x4 worldTransform)
    {
        if (_cellStruct.ContainsKey(envCellId)) return;
        if (cellStruct.PhysicsBSP?.Root is null) return;

        Matrix4x4.Invert(worldTransform, out var inverseTransform);

        _cellStruct[envCellId] = new CellPhysics
        {
            BSP = cellStruct.PhysicsBSP,
            PhysicsPolygons = cellStruct.PhysicsPolygons,
            Vertices = cellStruct.VertexArray,
            WorldTransform = worldTransform,
            InverseWorldTransform = inverseTransform,
            Resolved = ResolvePolygons(cellStruct.PhysicsPolygons, cellStruct.VertexArray),
        };
    }

    /// <summary>
    /// Pre-resolve all physics polygons: lookup vertex positions from VertexArray
    /// and compute the face plane. Matches ACE's Polygon constructor which calls
    /// make_plane() and resolves Vertices from VertexIDs at load time.
    /// </summary>
    private static Dictionary<ushort, ResolvedPolygon> ResolvePolygons(
        Dictionary<ushort, DatReaderWriter.Types.Polygon> polys,
        VertexArray vertexArray)
    {
        var resolved = new Dictionary<ushort, ResolvedPolygon>(polys.Count);
        foreach (var (id, poly) in polys)
        {
            int numVerts = poly.VertexIds.Count;
            if (numVerts < 3) continue;

            var verts = new Vector3[numVerts];
            bool valid = true;
            for (int i = 0; i < numVerts; i++)
            {
                ushort vid = (ushort)poly.VertexIds[i];
                if (!vertexArray.Vertices.TryGetValue(vid, out var sv))
                { valid = false; break; }
                verts[i] = sv.Origin;
            }
            if (!valid) continue;

            // Compute plane normal using ACE's make_plane algorithm:
            // fan cross-product accumulation + normalization.
            var normal = Vector3.Zero;
            for (int i = 1; i < numVerts - 1; i++)
            {
                var v1 = verts[i] - verts[0];
                var v2 = verts[i + 1] - verts[0];
                normal += Vector3.Cross(v1, v2);
            }
            float len = normal.Length();
            if (len < 1e-8f) continue;
            normal /= len;

            // D = -(average dot(normal, vertex))
            float dotSum = 0f;
            for (int i = 0; i < numVerts; i++)
                dotSum += Vector3.Dot(normal, verts[i]);
            float d = -(dotSum / numVerts);

            resolved[id] = new ResolvedPolygon
            {
                Vertices = verts,
                Plane = new Plane(normal, d),
                NumPoints = numVerts,
                SidesType = poly.SidesType,
            };
        }
        return resolved;
    }

    public GfxObjPhysics? GetGfxObj(uint id) => _gfxObj.TryGetValue(id, out var p) ? p : null;
    public SetupPhysics? GetSetup(uint id) => _setup.TryGetValue(id, out var p) ? p : null;
    public CellPhysics? GetCellStruct(uint id) => _cellStruct.TryGetValue(id, out var p) ? p : null;
    public int GfxObjCount => _gfxObj.Count;
    public int SetupCount => _setup.Count;
    public int CellStructCount => _cellStruct.Count;
}

/// <summary>
/// A physics polygon with pre-resolved vertex positions and pre-computed plane.
/// ACE pre-computes these in its Polygon constructor; we do it at cache time
/// to avoid per-collision-test vertex lookups.
/// </summary>
public sealed class ResolvedPolygon
{
    public required Vector3[] Vertices { get; init; }
    public required Plane Plane { get; init; }
    public required int NumPoints { get; init; }
    public required CullMode SidesType { get; init; }
}

/// <summary>Cached physics data for a single GfxObj part.</summary>
public sealed class GfxObjPhysics
{
    public required PhysicsBSPTree BSP { get; init; }
    public required Dictionary<ushort, Polygon> PhysicsPolygons { get; init; }
    public Sphere? BoundingSphere { get; init; }
    public required VertexArray Vertices { get; init; }

    /// <summary>
    /// Pre-resolved polygon data with vertex positions and computed planes.
    /// Populated once at cache time so BSP queries don't pay per-test lookup cost.
    /// </summary>
    public required Dictionary<ushort, ResolvedPolygon> Resolved { get; init; }
}

/// <summary>Cached collision shape data for a Setup (character/creature capsule).</summary>
public sealed class SetupPhysics
{
    public List<CylSphere> CylSpheres { get; init; } = new();
    public List<Sphere> Spheres { get; init; } = new();
    public float Height { get; init; }
    public float Radius { get; init; }
    public float StepUpHeight { get; init; }
    public float StepDownHeight { get; init; }
}

/// <summary>
/// Cached physics data for an indoor cell's room geometry (CellStruct).
/// Used for wall/floor/ceiling collision in EnvCells.
/// ACE: EnvCell.find_env_collisions queries CellStructure.PhysicsBSP.
/// </summary>
public sealed class CellPhysics
{
    public required PhysicsBSPTree BSP { get; init; }
    public required Dictionary<ushort, Polygon> PhysicsPolygons { get; init; }
    public required VertexArray Vertices { get; init; }
    public Matrix4x4 WorldTransform { get; init; }
    public Matrix4x4 InverseWorldTransform { get; init; }

    /// <summary>
    /// Pre-resolved polygon data with vertex positions and computed planes.
    /// </summary>
    public required Dictionary<ushort, ResolvedPolygon> Resolved { get; init; }
}