/**
 * Errors the API reports to clients: an HTTP status, a stable machine-readable `code` and a
 * message ready to show. Clients branch on the code, never on the wording of the message.
 *
 *   400 bad_request         the request itself is wrong (missing or malformed parameters)
 *   404 unknown_endpoint    no such API address: the server is older than the client
 *   404 document_not_found  the document left the catalog
 *   404 group_not_found     the document has no such group
 *   413 file_too_large      an import over 10 MB
 *   422 unreadable_file     an import that is not a readable Word table
 *   429 too_many_requests   the client sends too much; Retry-After says when to come back
 *   429 busy                the server is parsing other imports
 *   502 source_unavailable  the university catalog did not answer
 *   502 source_invalid      the catalog answered, but its folders or tables are not recognised
 *   503 not_ready           /api/ready only: the server is still loading the catalog or its index
 *   504 source_timeout      the university catalog answered too slowly
 *   500 internal            a fault of the server itself
 */
export class ApiError extends Error {
  constructor(status, code, message) {
    super(message);
    this.status = status;
    this.code = code;
  }
}

export const apiError = (status, code, message) => new ApiError(status, code, message);

const SOURCE_DOWN = "Каталог университета сейчас не отвечает. Попробуйте позже.";
const SOURCE_SLOW = "Каталог университета отвечает слишком долго. Попробуйте позже.";

/**
 * A failed download from the university as an API error: fetch aborted on the time limit is a
 * timeout, any other failure (no connection, an HTTP error, a redirect) means the source is unavailable.
 */
export function sourceError(error) {
  if (error instanceof ApiError) return error;
  const timedOut = error?.name === "TimeoutError" || error?.name === "AbortError";
  return timedOut
    ? new ApiError(504, "source_timeout", SOURCE_SLOW)
    : new ApiError(502, "source_unavailable", SOURCE_DOWN);
}

/** Status, code and message for any error that reached the error handler. */
export function describe(error) {
  if (error instanceof ApiError)
    return { status: error.status, code: error.code, message: error.message };
  if (error?.code === "LIMIT_FILE_SIZE")
    return {
      status: 413,
      code: "file_too_large",
      message: "Файл больше 10 МБ. Выберите документ меньшего размера.",
    };
  return {
    status: 500,
    code: "internal",
    message: "Не удалось загрузить расписание. Проверьте подключение и попробуйте ещё раз.",
  };
}