/**
 * 只读 PMX 的**材质段**（布局与 PMX 2.0 规范 / mmd-parser 一致）。
 *
 * 为什么需要：Assimp 6.0.4 的 PMX 导入会把 MMD 的材质参数大量丢弃——
 * 实测 `【奥黛塔】_by_原神.zip`（39 个材质）里 PMX 有 36 个材质带
 * **不剔除背面（双面）**标志，而导出的 GLB 里 `doubleSided` 一个都没有：
 * 头发、裙摆、睫毛这类薄片会被单面剔除掉，看起来就是"颜色/贴图不对"。
 * 因此转换后按 PMX 原始参数把 GLB 材质补回来（见 `glb-materials.ts`）。
 *
 * 只读、尽力而为：任何越界/未知版本都返回 null，绝不让调用方失败。
 */

/** PMX 材质的关键参数（我们关心的子集） */
export interface PmxMaterialInfo {
  name: string;
  diffuse: [number, number, number, number];
  specular: [number, number, number];
  /** 镜面反射强度（MMD 的 specular power，常见的 0~100+） */
  shininess: number;
  ambient: [number, number, number];
  /** 原始 drawFlag：bit0 = 不剔除背面（双面） */
  flag: number;
  /** 是否双面渲染（drawFlag bit0） */
  doubleSided: boolean;
  /** 球面贴图（SPH/SPA）索引，-1 表示没有 */
  sphereTextureIndex: number;
  /** 球面贴图模式：0 关闭 / 1 乘算 / 2 加算 / 3 子贴图 */
  sphereMode: number;
  /** 0 = 使用 toonIndex 指定的贴图；1 = 使用共享 toon */
  toonFlag: number;
  toonIndex: number;
  /** 该材质覆盖的三角形数 */
  faceCount: number;
}

const PMX_MAGIC = 'PMX ';

class Cursor {
  private offset = 0;

  constructor(private readonly buffer: Buffer) {}

  get position(): number {
    return this.offset;
  }

  get remaining(): number {
    return this.buffer.length - this.offset;
  }

  u8(): number {
    const value = this.buffer.readUInt8(this.offset);
    this.offset += 1;
    return value;
  }

  i8(): number {
    const value = this.buffer.readInt8(this.offset);
    this.offset += 1;
    return value;
  }

  u16(): number {
    const value = this.buffer.readUInt16LE(this.offset);
    this.offset += 2;
    return value;
  }

  i32(): number {
    const value = this.buffer.readInt32LE(this.offset);
    this.offset += 4;
    return value;
  }

  u32(): number {
    const value = this.buffer.readUInt32LE(this.offset);
    this.offset += 4;
    return value;
  }

  f32(): number {
    const value = this.buffer.readFloatLE(this.offset);
    this.offset += 4;
    return value;
  }

  floats(count: number): number[] {
    const out: number[] = [];
    for (let i = 0; i < count; i += 1) out.push(this.f32());
    return out;
  }

  /** 按字节宽度读索引（PMX 允许 1 / 2 / 4 字节，**有符号**：-1 表示无） */
  index(size: number): number {
    if (size === 1) return this.i8();
    if (size === 2) {
      const value = this.buffer.readInt16LE(this.offset);
      this.offset += 2;
      return value;
    }
    return this.i32();
  }

  skip(bytes: number): void {
    this.offset += bytes;
  }

  /** PMX 文本：int32 字节长度 + 内容（UTF-16LE 或 UTF-8） */
  text(utf16: boolean): string {
    const length = this.i32();
    if (length < 0) throw new Error('PMX 文本长度非法');
    const raw = this.buffer.subarray(this.offset, this.offset + length);
    this.offset += length;
    return raw.toString(utf16 ? 'utf16le' : 'utf8');
  }
}

/**
 * 解析 PMX 的材质段；不是 PMX / 结构异常一律返回 null。
 * 会跳过顶点、面、贴图段，只为拿到材质参数，不做几何解析。
 */
export function parsePmxMaterials(buffer: Buffer): PmxMaterialInfo[] | null {
  try {
    if (buffer.length < 32 || buffer.toString('ascii', 0, 4) !== PMX_MAGIC) return null;
    const cursor = new Cursor(buffer);
    cursor.skip(4);
    cursor.f32(); // version
    const globalCount = cursor.u8();
    if (globalCount < 8) return null;
    const globals = [];
    for (let i = 0; i < globalCount; i += 1) globals.push(cursor.u8());
    const encoding = globals[0]; // 0 = UTF-16LE, 1 = UTF-8
    const additionalUvNum = globals[1];
    const vertexIndexSize = globals[2];
    const textureIndexSize = globals[3];
    const boneIndexSize = globals[5];
    const utf16 = encoding === 0;

    // 头部 4 段文本：name / nameEn / comment / commentEn
    for (let i = 0; i < 4; i += 1) cursor.text(utf16);

    // 顶点段：跳过
    const vertexCount = cursor.i32();
    if (vertexCount < 0) return null;
    for (let i = 0; i < vertexCount; i += 1) {
      cursor.skip(12 + 12 + 8 + additionalUvNum * 16);
      const type = cursor.u8();
      if (type === 0) cursor.skip(boneIndexSize);
      else if (type === 1) cursor.skip(boneIndexSize * 2 + 4);
      else if (type === 2) cursor.skip(boneIndexSize * 4 + 16);
      else if (type === 3) cursor.skip(boneIndexSize * 2 + 4 + 36);
      else if (type === 4) cursor.skip(boneIndexSize * 4 + 16); // QDEF（PMX 2.1）
      else return null;
      cursor.skip(4); // edge scale
      if (cursor.remaining <= 0) return null;
    }

    // 面段：索引个数 × 索引宽度
    const faceIndexCount = cursor.i32();
    if (faceIndexCount < 0) return null;
    cursor.skip(faceIndexCount * vertexIndexSize);

    // 贴图段：跳过
    const textureCount = cursor.i32();
    if (textureCount < 0) return null;
    for (let i = 0; i < textureCount; i += 1) cursor.text(utf16);

    // 材质段
    const materialCount = cursor.i32();
    if (materialCount < 0 || materialCount > 100_000) return null;
    const materials: PmxMaterialInfo[] = [];
    for (let i = 0; i < materialCount; i += 1) {
      const name = cursor.text(utf16);
      cursor.text(utf16); // englishName
      const diffuse = cursor.floats(4) as [number, number, number, number];
      const specular = cursor.floats(3) as [number, number, number];
      const shininess = cursor.f32();
      const ambient = cursor.floats(3) as [number, number, number];
      const flag = cursor.u8();
      cursor.skip(16 + 4); // edgeColor(4f) + edgeSize(1f)
      const textureIndex = cursor.index(textureIndexSize);
      const sphereTextureIndex = cursor.index(textureIndexSize);
      const sphereMode = cursor.u8();
      const toonFlag = cursor.u8();
      const toonIndex = toonFlag === 0 ? cursor.index(textureIndexSize) : cursor.i8();
      cursor.text(utf16); // comment
      const faceCount = Math.floor(cursor.u32() / 3);
      materials.push({
        name,
        diffuse,
        specular,
        shininess,
        ambient,
        flag,
        doubleSided: (flag & 0x01) !== 0,
        sphereTextureIndex,
        sphereMode,
        toonFlag,
        toonIndex,
        faceCount,
      });
    }
    return materials;
  } catch {
    return null;
  }
}