using System;
using System.Collections;
using System.Collections.Generic;
using LibMMD.Model;
using UnityEngine;

namespace LibMMD.Unity3D
{
    // Converts PMX vertex-type morphs into Unity BlendShape frames at load time, so morph
    // playback can drive SkinnedMeshRenderer.SetBlendShapeWeight instead of rewriting
    // Mesh.vertices every frame. Bone/UV/material morphs are untouched (handled elsewhere /
    // unimplemented, same as before this change).
    internal static class MorphBlendShapeBuilder
    {
        internal static IEnumerator BuildIncremental(Mesh mesh, MmdModel model,
            List<int> vertexIndexList, MmdModelOptions options, Action<int[]> completed)
        {
            var vertexCount = vertexIndexList?.Count ?? model.Vertices.Length;
            var globalToLocal = vertexIndexList != null ? BuildReverseMap(vertexIndexList) : null;
            var blendShapeIndex = new int[model.Morphs.Length];
            Array.Fill(blendShapeIndex, -1);
            var deltaVertices = new Vector3[vertexCount];
            var slice = new MmdLoadTimeSlicer(options);

            for (var morphIndex = 0; morphIndex < model.Morphs.Length; morphIndex++)
            {
                var morph = model.Morphs[morphIndex];
                if (morph.Type != Morph.MorphType.MorphTypeVertex) continue;

                Array.Clear(deltaVertices, 0, deltaVertices.Length);
                var affectsThisMesh = false;
                foreach (var morphData in morph.MorphDatas)
                {
                    var data = (Morph.VertexMorph)morphData;
                    int localIndex;
                    if (globalToLocal == null) localIndex = data.VertexIndex;
                    else if (!globalToLocal.TryGetValue(data.VertexIndex, out localIndex)) continue;
                    deltaVertices[localIndex] += data.Offset;
                    affectsThisMesh = true;
                    if (slice.ShouldYield()) yield return null;
                }

                if (!affectsThisMesh) continue;
                mesh.AddBlendShapeFrame(morph.Name, 100f, (Vector3[])deltaVertices.Clone(), null, null);
                blendShapeIndex[morphIndex] = mesh.blendShapeCount - 1;
                if (slice.ShouldYield()) yield return null;
            }
            completed(blendShapeIndex);
        }

        private static Dictionary<int, int> BuildReverseMap(List<int> vertexIndexList)
        {
            var map = new Dictionary<int, int>(vertexIndexList.Count);
            for (var i = 0; i < vertexIndexList.Count; ++i)
            {
                map[vertexIndexList[i]] = i;
            }
            return map;
        }
    }
}