export type User = { id: number; username: string };
export type Genre = { id: number; name: string };
export type ReadingStatus = "not_started" | "reading" | "finished";
export type Book = {
  id: number;
  title: string;
  author: string;
  genre: Genre;
  total_pages: number;
  current_page: number;
  status: ReadingStatus;
  created_at: string;
  updated_at: string;
};
export type Note = {
  id: number;
  book_id: number;
  body: string;
  created_at: string;
  updated_at: string;
};

export class ApiError extends Error {
  readonly status: number;
  readonly field?: string;

  constructor(status: number, message: string, field?: string) {
    super(message);
    this.status = status;
    this.field = field;
  }
}

let handleUnauthorized: () => void = () => {};
let authEpoch = 0;

// A 401 only means "signed out" for the session that sent the request; one started before
// a later login, logout or expiry must not end the session that replaced it.
export function startAuthEpoch() {
  authEpoch += 1;
}

export function setUnauthorizedHandler(handler: () => void) {
  handleUnauthorized = handler;
}

export async function api<T>(
  method: "GET" | "POST" | "PATCH" | "DELETE",
  path: string,
  body?: unknown,
): Promise<T> {
  const epoch = authEpoch;
  const response = await fetch(`/api${path}`, {
    method,
    credentials: "same-origin",
    headers: { "Content-Type": "application/json" },
    body: body === undefined ? undefined : JSON.stringify(body),
  });
  if (response.status === 204) return undefined as T;
  const data = await response.json().catch(() => null);
  if (!response.ok) {
    if (
      response.status === 401 &&
      !path.startsWith("/auth/") &&
      epoch === authEpoch
    ) {
      startAuthEpoch();
      handleUnauthorized();
    }
    throw new ApiError(
      response.status,
      data?.error ?? `Request failed with status ${response.status}`,
      data?.field,
    );
  }
  return data as T;
}

export function errorMessage(error: unknown): string {
  return error instanceof ApiError
    ? error.message
    : "Could not reach the server; check your connection and try again";
}