using System.Collections.Generic;
using UnityEngine;

/// <summary>Shared mesh/bounds/hierarchy helpers.</summary>
public static class GeometryUtil
{
    /// <summary>Depth-first hierarchy search by name; checks <paramref name="root"/> itself first.</summary>
    public static Transform FindDeep(Transform root, string name)
    {
        if (root.name == name) return root;
        for (int i = 0; i < root.childCount; i++)
        {
            var found = FindDeep(root.GetChild(i), name);
            if (found) return found;
        }
        return null;
    }

    /// <summary>Divides a world scale back out of a freshly baked mesh so it is true unit-scale local
    /// geometry (BakeMesh freezes the transform's lossyScale into the vertices). No-op at scale 1;
    /// <paramref name="scratch"/> is reused so nothing is allocated per bake.</summary>
    public static void RescaleToUnitScale(Mesh baked, Vector3 lossyScale, List<Vector3> scratch)
    {
        if (lossyScale.x == 1f && lossyScale.y == 1f && lossyScale.z == 1f) return;

        float ix = lossyScale.x != 0f ? 1f / lossyScale.x : 0f;
        float iy = lossyScale.y != 0f ? 1f / lossyScale.y : 0f;
        float iz = lossyScale.z != 0f ? 1f / lossyScale.z : 0f;
        baked.GetVertices(scratch);
        for (int i = 0; i < scratch.Count; i++)
        {
            Vector3 v = scratch[i];
            v.x *= ix; v.y *= iy; v.z *= iz;
            scratch[i] = v;
        }
        baked.SetVertices(scratch);
        baked.RecalculateBounds();
    }

    /// <summary>World AABB enclosing a local AABB after an affine transform (encapsulates the 8 transformed corners).</summary>
    public static Bounds TransformBounds(Matrix4x4 m, Bounds local)
    {
        Vector3 mn = local.min, mx = local.max;
        Vector3 c0 = m.MultiplyPoint3x4(mn);
        Bounds b = new Bounds(c0, Vector3.zero);
        b.Encapsulate(m.MultiplyPoint3x4(new Vector3(mx.x, mn.y, mn.z)));
        b.Encapsulate(m.MultiplyPoint3x4(new Vector3(mn.x, mx.y, mn.z)));
        b.Encapsulate(m.MultiplyPoint3x4(new Vector3(mn.x, mn.y, mx.z)));
        b.Encapsulate(m.MultiplyPoint3x4(new Vector3(mx.x, mx.y, mn.z)));
        b.Encapsulate(m.MultiplyPoint3x4(new Vector3(mx.x, mn.y, mx.z)));
        b.Encapsulate(m.MultiplyPoint3x4(new Vector3(mn.x, mx.y, mx.z)));
        b.Encapsulate(m.MultiplyPoint3x4(mx));
        return b;
    }
}