import fs from "node:fs";

/** 与 multer 白名单一致：仅 PNG / JPEG / WebP（RIFF…WEBP） */
export const IMAGE_MAGIC_MISMATCH_MESSAGE = "文件内容与真实格式不符，请上传 PNG、JPEG 或 WebP 图片";

function matchesAllowedRasterMagic(head: Uint8Array): boolean {
  if (head.length < 12) {
    return false;
  }
  // JPEG
  if (head[0] === 0xff && head[1] === 0xd8 && head[2] === 0xff) {
    return true;
  }
  // PNG
  if (
    head[0] === 0x89
    && head[1] === 0x50
    && head[2] === 0x4e
    && head[3] === 0x47
    && head[4] === 0x0d
    && head[5] === 0x0a
    && head[6] === 0x1a
    && head[7] === 0x0a
  ) {
    return true;
  }
  // WebP (RIFF .... WEBP)
  if (
    head[0] === 0x52
    && head[1] === 0x49
    && head[2] === 0x46
    && head[3] === 0x46
    && head[8] === 0x57
    && head[9] === 0x45
    && head[10] === 0x42
    && head[11] === 0x50
  ) {
    return true;
  }
  return false;
}

/** 读取文件头并校验魔数（不依赖客户端 Content-Type） */
export function assertDiskFileIsAllowedRasterImage(filePath: string): void {
  const fd = fs.openSync(filePath, "r");
  try {
    const buf = Buffer.alloc(12);
    const n = fs.readSync(fd, buf, 0, 12, 0);
    if (n < 12 || !matchesAllowedRasterMagic(buf)) {
      throw new Error(IMAGE_MAGIC_MISMATCH_MESSAGE);
    }
  } finally {
    fs.closeSync(fd);
  }
}