import sharp from 'sharp'

export const MAX_BRAND_IMAGE_BYTES = 5 * 1024 * 1024
export const MAX_BRAND_IMAGE_PIXELS = 4_194_304
export const MAX_BRAND_IMAGE_DIMENSION = 4096

export type ValidatedBrandImage = {
  extension: 'png' | 'jpg' | 'webp'
  contentType: 'image/png' | 'image/jpeg' | 'image/webp'
  width: number
  height: number
}

const FORMAT_DETAILS: Record<string, Pick<ValidatedBrandImage, 'extension' | 'contentType'>> = {
  png: { extension: 'png', contentType: 'image/png' },
  jpeg: { extension: 'jpg', contentType: 'image/jpeg' },
  webp: { extension: 'webp', contentType: 'image/webp' },
}

/**
 * 品牌图属于高可见度系统配置，不能只看 magic bytes。
 * 这里会真正解码整张图，阻止截断文件、伪造 MIME、动画和解压炸弹进入数据库。
 */
export async function validateBrandImage(
  buffer: Buffer,
  declaredContentType?: string | null,
): Promise<ValidatedBrandImage> {
  if (buffer.length <= 0 || buffer.length > MAX_BRAND_IMAGE_BYTES) {
    throw new Error('品牌图片必须是 5MB 以内的有效文件')
  }

  const image = sharp(buffer, {
    failOn: 'error',
    limitInputPixels: MAX_BRAND_IMAGE_PIXELS,
    animated: false,
  })
  const metadata = await image.metadata()
  const format = metadata.format ? FORMAT_DETAILS[metadata.format] : undefined
  const width = metadata.width || 0
  const height = metadata.height || 0

  if (!format) {
    throw new Error('品牌图片只支持 PNG、JPEG 或 WebP')
  }
  if (
    width < 1 ||
    height < 1 ||
    width > MAX_BRAND_IMAGE_DIMENSION ||
    height > MAX_BRAND_IMAGE_DIMENSION ||
    width * height > MAX_BRAND_IMAGE_PIXELS
  ) {
    throw new Error('品牌图片尺寸无效或像素过大')
  }
  if ((metadata.pages || 1) > 1) {
    throw new Error('品牌图片不支持动画格式')
  }

  const normalizedDeclaredType = String(declaredContentType || '')
    .split(';', 1)[0]
    .trim()
    .toLowerCase()
  if (normalizedDeclaredType && normalizedDeclaredType !== format.contentType) {
    throw new Error('品牌图片内容与声明格式不一致')
  }

  // metadata() 主要读取头信息；raw().toBuffer() 强制完整解码，截断图片会在这里失败。
  await image.clone().raw().toBuffer()

  return {
    ...format,
    width,
    height,
  }
}