// Copyright 2017 The Draco Authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//      http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
//
using System;
using System.Collections;
using System.Collections.Generic;
using System.Runtime.InteropServices;
using UnityEngine;

public unsafe class DracoMeshLoader {
  // Must stay the order to be consistent with C++ interface.
  [StructLayout(LayoutKind.Sequential)] private struct DracoToUnityMesh {
    public int numFaces;
    public IntPtr indices;
    public int numVertices;
    public IntPtr position;
    // TODO(zhafang): Add other attributes.
    // public int numNormal;
    public float[] normal;
    // public int numColor;
    public float[] color;
    public float[] texcoord;
  }

  private struct DecodedMesh {
    public int[] faces;
    public Vector3[] vertices;
  }

  [DllImport("dracodec_unity")] private static extern int DecodeMeshForUnity(
      byte[] buffer, int length, DracoToUnityMesh **tmpMesh);

  static private int maxNumVerticesPerMesh = 60000;

  // Unity only support maximum 65534 vertices per mesh. So large meshes need
  // to be splitted.
  private void SplitMesh(DecodedMesh mesh, ref List<DecodedMesh> splittedMeshes) {
    List<int> facesLeft = new List<int>();
    for (int i = 0; i < mesh.faces.Length; ++i) {
      facesLeft.Add(mesh.faces[i]);
    }
    int numSubMeshes = 0;

    List<int> newCorners = new List<int>();
    Dictionary<int, int> indexToNewIndex = new Dictionary<int, int>();
    List<int> tmpLeftFaces = new List<int>();
    List<int> facesExtracted = new List<int>();
    List<Vector3> verticesExtracted = new List<Vector3>();

    while (facesLeft.Count > 0) {
      Debug.Log("Faces left: " + facesLeft.Count.ToString());
      numSubMeshes++;
      tmpLeftFaces.Clear();
      facesExtracted.Clear();
      verticesExtracted.Clear();

      int uniqueCornerId = 0;
      indexToNewIndex.Clear();
      for (int face = 0; face < facesLeft.Count / 3; ++face) {
        newCorners.Clear();
        // If all indices has appeared or there's still space for more vertices.
        for (int corner = 0; corner < 3; ++corner) {
          if (!indexToNewIndex.ContainsKey(facesLeft[face * 3 + corner])) {
            newCorners.Add(facesLeft[face * 3 + corner]);
          }
        }
        if (newCorners.Count + uniqueCornerId > maxNumVerticesPerMesh) {
          // Save face for the next sub-mesh.
          for (int corner = 0; corner < 3; ++corner) {
            tmpLeftFaces.Add(facesLeft[face * 3 + corner]);
          }
        } else {
          // Add new corners.
          for (int i = 0; i < newCorners.Count; ++i) {
            indexToNewIndex.Add(newCorners[i], uniqueCornerId);
            verticesExtracted.Add(mesh.vertices[newCorners[i]]);
            uniqueCornerId++;
          }
          // Add face to this sub-mesh.
          for (int corner = 0; corner < 3; ++corner) {
            facesExtracted.Add(
                indexToNewIndex[facesLeft[face * 3 + corner]]);
          }
        }
      }

      DecodedMesh subMesh = new DecodedMesh();
      subMesh.faces = facesExtracted.ToArray();
      subMesh.vertices = verticesExtracted.ToArray();
      splittedMeshes.Add(subMesh);

      facesLeft = tmpLeftFaces;
    }
  }

  private float ReadFloatFromIntPtr(IntPtr data, int offset) {
    byte[] byteArray = new byte[4];
    for (int j = 0; j < 4; ++j) {
      byteArray[j] = Marshal.ReadByte(data, offset + j);
    }
    return BitConverter.ToSingle(byteArray, 0);
  }

  // TODO(zhafang): Add back LoadFromURL.
  public int LoadMeshFromAsset(string assetName, ref List<Mesh> meshes) {
    TextAsset asset = Resources.Load(assetName, typeof(TextAsset)) as TextAsset;
    if (asset == null) {
      Debug.Log("Didn't load file!");
      return -1;
    }
    byte[] encodedData = asset.bytes;
    Debug.Log(encodedData.Length.ToString());
    if (encodedData.Length == 0) {
      Debug.Log("Didn't load encoded data!");
      return -1;
    }
    return DecodeMesh(encodedData, ref meshes);
  }

  public unsafe int DecodeMesh(byte[] data, ref List<Mesh> meshes) {
    DracoToUnityMesh *tmpMesh;
    if (DecodeMeshForUnity(data, data.Length, &tmpMesh) <= 0) {
      Debug.Log("Failed: Decoding error.");
      return -1;
    }

    Debug.Log("Num indices: " + tmpMesh -> numFaces.ToString());
    Debug.Log("Num vertices: " + tmpMesh -> numVertices.ToString());

    int numFaces = tmpMesh -> numFaces;
    int[] newTriangles = new int[tmpMesh -> numFaces * 3];
    for (int i = 0; i < tmpMesh -> numFaces; ++i) {
      newTriangles[i * 3] = Marshal.ReadInt32(tmpMesh -> indices, i * 3 * 4);
      newTriangles[i * 3 + 1] =
        Marshal.ReadInt32(tmpMesh -> indices, i * 3 * 4 + 4);
      newTriangles[i * 3 + 2] =
        Marshal.ReadInt32(tmpMesh -> indices, i * 3 * 4 + 8);
    }

    // For floating point numbers, there's no Marshal functions could directly
    // read from the unmanaged data.
    // TODO(zhafang): Find better way to read float numbers.
    Vector3[] newVertices = new Vector3[tmpMesh -> numVertices];
    int byteStridePerValue = 4;
    int numValuePerVertex = 3;
    int byteStridePerVertex = byteStridePerValue * numValuePerVertex;
    /*
     * TODO(zhafang): Change to:
     * float[] pos = new float[3];
     * for (int i = 0; i < tmpMesh -> numVertices; ++i) {
     *       Marshal.Copy(tmpMesh->position, pos, 3 * i, 3);
     *             for (int j = 0; j < 3; ++j) {
     *                        newVertices[i][j] = pos[j];
     *             }
     * }
     */
    for (int i = 0; i < tmpMesh -> numVertices; ++i) {
      for (int j = 0; j < 3; ++j) {
        newVertices[i][j] =
            ReadFloatFromIntPtr(
                tmpMesh -> position,
                i * byteStridePerVertex + byteStridePerValue * j);
      }
    }
    Marshal.FreeCoTaskMem(tmpMesh -> indices);
    Marshal.FreeCoTaskMem(tmpMesh -> position);
    Marshal.FreeCoTaskMem((IntPtr) tmpMesh);

    if (newVertices.Length > maxNumVerticesPerMesh) {
      // Unity only support maximum 65534 vertices per mesh. So large meshes
      // need to be splitted.
      DecodedMesh decodedMesh = new DecodedMesh();
      decodedMesh.vertices = newVertices;
      decodedMesh.faces = newTriangles;
      List<DecodedMesh> splittedMeshes = new List<DecodedMesh>();

      SplitMesh(decodedMesh, ref splittedMeshes);
      for (int i = 0; i < splittedMeshes.Count; ++i) {
        Mesh mesh = new Mesh();
        mesh.vertices = splittedMeshes[i].vertices;
        mesh.triangles = splittedMeshes[i].faces;

        mesh.RecalculateBounds();
        mesh.RecalculateNormals();
        meshes.Add(mesh);
      }
    } else {
      Mesh mesh = new Mesh();
      mesh.vertices = newVertices;
      mesh.triangles = newTriangles;

      mesh.RecalculateBounds();
      mesh.RecalculateNormals();
      meshes.Add(mesh);
    }
    // TODO(zhafang): Resize mesh to the a proper scale.

    return numFaces;
  }
}