import { $t } from '#/locales';

const OLE2_SIGNATURE = [208, 207, 17, 224, 161, 177, 26, 225];

const supportedExtensions = Object.freeze([
  'txt',
  'pdf',
  'docx',
  'md',
  'pptx',
  'xlsx',
  'csv',
]);
const supportedExtensionSet = new Set(supportedExtensions);
const supportedTypeLabel = supportedExtensions
  .map((extension) => extension.toUpperCase())
  .join('、');

function extensionOf(fileName: string) {
  const normalizedName = String(fileName || '')
    .trim()
    .toLowerCase();
  const dotIndex = normalizedName.lastIndexOf('.');
  return dotIndex === -1 ? '' : normalizedName.slice(dotIndex + 1);
}

function supports(fileName: string) {
  return supportedExtensionSet.has(extensionOf(fileName));
}

async function validateFiles(files: File[]) {
  for (const file of files) {
    const extension = extensionOf(file.name);
    if (!supportedExtensionSet.has(extension)) {
      throw new Error(
        $t('message.upload.unsupportedFileType', {
          fileName: file.name,
          types: supportedTypeLabel,
        }),
      );
    }
    if (extension !== 'xlsx') {
      continue;
    }
    const prefix = new Uint8Array(await file.slice(0, 8).arrayBuffer());
    if (hasZipSignature(prefix)) {
      continue;
    }
    const messageKey = startsWith(prefix, OLE2_SIGNATURE)
      ? 'message.upload.legacyExcelAsXlsx'
      : 'message.upload.invalidXlsx';
    throw new Error($t(messageKey, { fileName: file.name }));
  }
}

/**
 * 知识库导入与工作流文档解析共用的文件格式策略。
 */
export const DocumentParseFilePolicy = Object.freeze({
  accept: supportedExtensions.map((extension) => `.${extension}`).join(','),
  supportedExtensions,
  supportedTypeLabel,
  supports,
  validateFiles,
});

function hasZipSignature(prefix: Uint8Array) {
  return (
    prefix.length >= 4 &&
    prefix[0] === 80 &&
    prefix[1] === 75 &&
    ((prefix[2] === 3 && prefix[3] === 4) ||
      (prefix[2] === 5 && prefix[3] === 6) ||
      (prefix[2] === 7 && prefix[3] === 8))
  );
}

function startsWith(prefix: Uint8Array, signature: number[]) {
  return (
    prefix.length >= signature.length &&
    signature.every((value, index) => prefix[index] === value)
  );
}