using System.Collections.Generic;
using UnityEngine;

/// <summary>
/// Editor-baked solid/enclosed voxel volume for a single (typically non-convex, non-watertight)
/// environment mesh. Runtime lookup is an O(1) grid test, so <see cref="ConcealmentMeter"/> can
/// treat furniture as "embeddable" without per-voxel raycast parity (unreliable on the open-shell
/// furniture meshes of asset kits).
///
/// The bake marks a voxel INSIDE when either classifier fires: generalized winding number &gt; 0.5
/// (captures SOLID material, robust for open shells) OR unreachable by exterior flood-fill
/// (captures fully ENCLOSED air cavities). The union errs in the safe direction — solid or enclosed
/// both count as concealment; open regions (seat surface, under a thin table) read as exposed.
///
/// Bake and query (<see cref="ContainsWorld"/>) share the SAME mesh-local space, so
/// position/rotation/scale are handled uniformly.
/// </summary>
[DisallowMultipleComponent]
public class ConcealmentVolume : MonoBehaviour
{
    public enum BakeMethod { WindingNumberOrFloodFill, WindingNumberOnly, FloodFillOnly }

    [Header("Bake settings")]
    [Min(2)]
    [Tooltip("Voxels along the longest local-bounds axis. Higher = sharper & bigger bake. ~32 is a good start.")]
    [SerializeField] private int resolution = 32;

    [Tooltip("Source mesh. Auto = MeshCollider.sharedMesh, else MeshFilter.sharedMesh on this object.")]
    [SerializeField] private Mesh sourceMesh;

    [SerializeField] private BakeMethod method = BakeMethod.WindingNumberOrFloodFill;

    [Header("Debug")]
    [SerializeField] private bool drawBakedGizmos;
    [SerializeField] private Color gizmoColor = new Color(0.2f, 0.6f, 1f, 0.35f);

    // --- Baked data (local space) ---
    [SerializeField, HideInInspector] private Vector3 origin;   // local min corner of the grid
    [SerializeField, HideInInspector] private float voxelSize;
    [SerializeField, HideInInspector] private int nx, ny, nz;
    [SerializeField, HideInInspector] private uint[] bits;      // packed inside-flags, idx = ix + nx*(iy + ny*iz)
    [SerializeField, HideInInspector] private int insideCount;

    public bool HasBake => bits != null && bits.Length > 0 && nx > 0;

    private static readonly List<ConcealmentVolume> Active = new List<ConcealmentVolume>();
    public static IReadOnlyList<ConcealmentVolume> All => Active;

    private void OnEnable() { if (!Active.Contains(this)) Active.Add(this); }
    private void OnDisable() { Active.Remove(this); }

    /// <summary>World-space AABB of the baked grid (for broadphase rejection).</summary>
    public Bounds WorldBounds
    {
        get
        {
            Vector3 mn = origin;
            Vector3 mx = origin + new Vector3(nx * voxelSize, ny * voxelSize, nz * voxelSize);
            var local = new Bounds();
            local.SetMinMax(mn, mx);
            return GeometryUtil.TransformBounds(transform.localToWorldMatrix, local);
        }
    }

    /// <summary>O(1) test: is the world point inside a baked-as-solid/enclosed voxel?</summary>
    public bool ContainsWorld(Vector3 world)
    {
        if (!HasBake) return false;
        Vector3 lp = transform.InverseTransformPoint(world);
        int ix = Mathf.FloorToInt((lp.x - origin.x) / voxelSize);
        if (ix < 0 || ix >= nx) return false;
        int iy = Mathf.FloorToInt((lp.y - origin.y) / voxelSize);
        if (iy < 0 || iy >= ny) return false;
        int iz = Mathf.FloorToInt((lp.z - origin.z) / voxelSize);
        if (iz < 0 || iz >= nz) return false;
        int idx = ix + nx * (iy + ny * iz);
        return (bits[idx >> 5] & (1u << (idx & 31))) != 0;
    }

#if UNITY_EDITOR
    [ContextMenu("Bake Concealment Volume")]
    public void Bake()
    {
        Mesh mesh = sourceMesh;
        if (!mesh)
        {
            var mc = GetComponent<MeshCollider>();
            if (mc) mesh = mc.sharedMesh;
        }
        if (!mesh)
        {
            var mf = GetComponent<MeshFilter>();
            if (mf) mesh = mf.sharedMesh;
        }
        if (!mesh) { Debug.LogError($"[ConcealmentVolume] {name}: no source mesh.", this); return; }

        Vector3[] verts = mesh.vertices;
        int[] tris = mesh.triangles;
        if (verts.Length == 0 || tris.Length < 3) { Debug.LogError($"[ConcealmentVolume] {name}: empty mesh.", this); return; }

        Bounds lb = mesh.bounds;
        float maxExtent = Mathf.Max(lb.size.x, Mathf.Max(lb.size.y, lb.size.z));
        if (maxExtent <= 1e-6f) { Debug.LogError($"[ConcealmentVolume] {name}: degenerate bounds.", this); return; }

        float vs = maxExtent / resolution;
        const int pad = 1; // empty shell so exterior flood always has a seed
        nx = Mathf.CeilToInt(lb.size.x / vs) + 2 * pad;
        ny = Mathf.CeilToInt(lb.size.y / vs) + 2 * pad;
        nz = Mathf.CeilToInt(lb.size.z / vs) + 2 * pad;
        voxelSize = vs;
        origin = lb.min - new Vector3(vs, vs, vs) * pad;

        int count = nx * ny * nz;
        bool[] wall = new bool[count];

        // --- 1) Rasterize triangles into wall voxels (barycentric supersampling, step = vs/2) ---
        for (int t = 0; t < tris.Length; t += 3)
        {
            Vector3 a = verts[tris[t]], b = verts[tris[t + 1]], c = verts[tris[t + 2]];
            float eMax = Mathf.Max((b - a).magnitude, (c - a).magnitude);
            int steps = Mathf.Max(1, Mathf.CeilToInt(eMax / (vs * 0.5f)));
            float inv = 1f / steps;
            for (int u = 0; u <= steps; u++)
            {
                for (int v = 0; v <= steps - u; v++)
                {
                    Vector3 p = a + (b - a) * (u * inv) + (c - a) * (v * inv);
                    int ix = Mathf.Clamp(Mathf.FloorToInt((p.x - origin.x) / vs), 0, nx - 1);
                    int iy = Mathf.Clamp(Mathf.FloorToInt((p.y - origin.y) / vs), 0, ny - 1);
                    int iz = Mathf.Clamp(Mathf.FloorToInt((p.z - origin.z) / vs), 0, nz - 1);
                    wall[ix + nx * (iy + ny * iz)] = true;
                }
            }
        }

        // --- 2) Exterior flood-fill (6-connected) through non-wall voxels ---
        bool[] outside = new bool[count];
        var stack = new Stack<int>(count / 4 + 16);
        for (int iz = 0; iz < nz; iz++)
            for (int iy = 0; iy < ny; iy++)
                for (int ix = 0; ix < nx; ix++)
                {
                    if (ix != 0 && ix != nx - 1 && iy != 0 && iy != ny - 1 && iz != 0 && iz != nz - 1) continue;
                    int idx = ix + nx * (iy + ny * iz);
                    if (!wall[idx] && !outside[idx]) { outside[idx] = true; stack.Push(idx); }
                }
        while (stack.Count > 0)
        {
            int idx = stack.Pop();
            int ix = idx % nx;
            int iy = (idx / nx) % ny;
            int iz = idx / (nx * ny);
            PushNeighbor(ix - 1, iy, iz, wall, outside, stack);
            PushNeighbor(ix + 1, iy, iz, wall, outside, stack);
            PushNeighbor(ix, iy - 1, iz, wall, outside, stack);
            PushNeighbor(ix, iy + 1, iz, wall, outside, stack);
            PushNeighbor(ix, iy, iz - 1, wall, outside, stack);
            PushNeighbor(ix, iy, iz + 1, wall, outside, stack);
        }

        // --- 3) Classify each voxel; pack into bits ---
        bits = new uint[(count + 31) >> 5];
        insideCount = 0;
        int floodOnly = 0, windingOnly = 0;
        bool useWinding = method != BakeMethod.FloodFillOnly;
        bool useFlood = method != BakeMethod.WindingNumberOnly;

        for (int iz = 0; iz < nz; iz++)
            for (int iy = 0; iy < ny; iy++)
                for (int ix = 0; ix < nx; ix++)
                {
                    int idx = ix + nx * (iy + ny * iz);
                    bool enclosed = useFlood && !outside[idx];
                    bool solid = false;
                    if (useWinding)
                        solid = WindingNumber(VoxelCenter(origin, ix, iy, iz, vs), verts, tris) > 0.5;
                    bool inside = enclosed || solid;
                    if (!inside) continue;
                    bits[idx >> 5] |= 1u << (idx & 31);
                    insideCount++;
                    if (enclosed && !solid) floodOnly++;
                    if (solid && !enclosed) windingOnly++;
                }

        UnityEditor.Undo.RecordObject(this, "Bake Concealment Volume");
        UnityEditor.EditorUtility.SetDirty(this);
        if (!Application.isPlaying)
            UnityEditor.SceneManagement.EditorSceneManager.MarkSceneDirty(gameObject.scene);

        Debug.Log($"[ConcealmentVolume] {name}: baked {nx}x{ny}x{nz} (vs={vs:F3}) -> inside={insideCount}/{count} " +
                  $"(winding-only={windingOnly}, flood-only={floodOnly}), bits={bits.Length * 4}B", this);
    }

    [ContextMenu("Clear Bake")]
    public void ClearBake()
    {
        bits = null; nx = ny = nz = 0; insideCount = 0;
        UnityEditor.EditorUtility.SetDirty(this);
    }

    private void PushNeighbor(int ix, int iy, int iz, bool[] wall, bool[] outside, Stack<int> stack)
    {
        if (ix < 0 || ix >= nx || iy < 0 || iy >= ny || iz < 0 || iz >= nz) return;
        int idx = ix + nx * (iy + ny * iz);
        if (wall[idx] || outside[idx]) return;
        outside[idx] = true;
        stack.Push(idx);
    }

    /// <summary>Generalized winding number at p (mesh-local). ~1 inside a solid, ~0 outside; robust for open shells.</summary>
    private static double WindingNumber(Vector3 p, Vector3[] verts, int[] tris)
    {
        double sum = 0.0;
        double px = p.x, py = p.y, pz = p.z;
        for (int t = 0; t < tris.Length; t += 3)
        {
            Vector3 A = verts[tris[t]], B = verts[tris[t + 1]], C = verts[tris[t + 2]];
            double ax = A.x - px, ay = A.y - py, az = A.z - pz;
            double bx = B.x - px, by = B.y - py, bz = B.z - pz;
            double cx = C.x - px, cy = C.y - py, cz = C.z - pz;
            double la = System.Math.Sqrt(ax * ax + ay * ay + az * az);
            double lb = System.Math.Sqrt(bx * bx + by * by + bz * bz);
            double lc = System.Math.Sqrt(cx * cx + cy * cy + cz * cz);
            if (la < 1e-12 || lb < 1e-12 || lc < 1e-12) continue;
            // triple product a . (b x c)
            double crx = by * cz - bz * cy;
            double cry = bz * cx - bx * cz;
            double crz = bx * cy - by * cx;
            double numer = ax * crx + ay * cry + az * crz;
            double denom = la * lb * lc
                         + (ax * bx + ay * by + az * bz) * lc
                         + (bx * cx + by * cy + bz * cz) * la
                         + (cx * ax + cy * ay + cz * az) * lb;
            sum += System.Math.Atan2(numer, denom) * 2.0;
        }
        return sum / (4.0 * System.Math.PI);
    }

    /// <summary>Local-space center of grid voxel (ix, iy, iz).</summary>
    private static Vector3 VoxelCenter(Vector3 origin, int ix, int iy, int iz, float size)
        => new Vector3(origin.x + (ix + 0.5f) * size, origin.y + (iy + 0.5f) * size, origin.z + (iz + 0.5f) * size);

    private void OnDrawGizmosSelected()
    {
        if (!drawBakedGizmos || !HasBake) return;
        Gizmos.color = gizmoColor;
        Gizmos.matrix = transform.localToWorldMatrix;
        Vector3 cube = Vector3.one * (voxelSize * 0.9f);
        for (int iz = 0; iz < nz; iz++)
            for (int iy = 0; iy < ny; iy++)
                for (int ix = 0; ix < nx; ix++)
                {
                    int idx = ix + nx * (iy + ny * iz);
                    if ((bits[idx >> 5] & (1u << (idx & 31))) == 0) continue;
                    Gizmos.DrawCube(VoxelCenter(origin, ix, iy, iz, voxelSize), cube);
                }
    }
#endif
}