/**
 * Gives components the session, and the functions that sign in, sign out and
 * make requests with its token.
 *
 * @module
 */

import { useCallback, useContext } from "react";

import { AuthContext } from "../../contexts/auth/AuthContext.ts";

import type { AuthResponse, SelfUser } from "../../../shared/user.ts";
import type { UserSettings } from "../../../shared/settings.ts";
import type { Session } from "../../utils/auth/storage.ts";
import { takeEarly } from "../../utils/shared/earlyFetch.ts";
import {
  forgetStoredSession,
  isTokenExpired,
  storeSession,
} from "../../utils/auth/storage.ts";

/**
 * Returned by {@link useAuth} to any component that needs the session. Its
 * functions are stable until the session's token changes.
 */
export interface UseAuthResult {
  user: SelfUser | null;
  /**
   * The user's settings, once `AuthProvider` has read them. `useSettings` is
   * the way to read and change them.
   */
  settings: UserSettings | null;
  token: string | null;
  /**
   * The token for file and thumbnail URLs, where it shows in the query string.
   * A session from before media tokens falls back to the session token until
   * AuthProvider fetches one.
   */
  mediaToken: string | null;
  /** Starts a session from a sign-in or sign-up response, in every tab. */
  login: (response: AuthResponse) => void;
  /**
   * Ends the session this render holds. A 401 can land after the session has
   * moved on to fresh tokens (a password change, here or in another tab), and
   * must not sign those out.
   */
  logout: () => void;
  /**
   * Merges `patch` into the session, in memory and in storage. The profile page
   * uses it for a new avatar or email, the password dialog for fresh tokens.
   */
  updateSession: (patch: Partial<Session>) => void;
  /**
   * Calls `fetch` with the session's token, and a JSON content type unless the
   * body is FormData. An expired token, or a 401, ends the session. An expired
   * token answers a 401 without calling the server.
   */
  authFetch: (input: RequestInfo, init?: RequestInit) => Promise<Response>;
  /**
   * Works like `authFetch` for a multipart upload that shows progress, as the
   * dump creation dialog's file upload does. It goes through XHR, since `fetch`
   * reports nothing until the whole body is sent. It still answers a
   * `Response`, so callers use `expectOk` as usual.
   *
   * `onProgress` receives a fraction from 0 to 1, or `null` once the body is
   * sent and the server is working, or when the length is unknown.
   */
  authUpload: (
    url: string,
    body: FormData,
    onProgress: (fraction: number | null) => void,
    method?: string,
  ) => Promise<Response>;
}

/**
 * Returns the session and the functions that act on it. It must be called
 * under `AuthProvider`.
 */
export function useAuth(): UseAuthResult {
  const { authResponse, setAuthResponse } = useContext(AuthContext);

  const login = useCallback((response: AuthResponse) => {
    setAuthResponse(response);
    storeSession(response);
  }, [setAuthResponse]);

  const sessionToken = authResponse?.token;
  const logout = useCallback(() => {
    setAuthResponse((prev) => prev?.token === sessionToken ? null : prev);
    forgetStoredSession(sessionToken);
  }, [setAuthResponse, sessionToken]);

  const updateSession = useCallback((patch: Partial<Session>) => {
    setAuthResponse((prev) => {
      if (!prev) return prev;
      const next = { ...prev, ...patch };
      storeSession(next);
      return next;
    });
  }, [setAuthResponse]);

  const authFetch = useCallback(async (
    input: RequestInfo,
    init: RequestInit = {},
  ) => {
    const token = authResponse?.token;

    if (token && isTokenExpired(token)) {
      logout();
      // Callers already handle a 401 from the server; this looks the same.
      return new Response(null, { status: 401 });
    }

    const isFormData = init.body instanceof FormData;

    // The page a visit lands on finds its first request already sent, as the
    // app booted (utils/shared/earlyFetch.ts).
    const early = typeof input === "string" &&
        (init.method ?? "GET") === "GET"
      ? takeEarly(input, token)
      : undefined;
    const res = await (early ?? fetch(input, {
      ...init,
      headers: {
        ...(init.headers ?? {}),
        ...(token ? { Authorization: `Bearer ${token}` } : {}),
        // The browser sets FormData's Content-Type, with its boundary.
        ...(isFormData ? {} : { "Content-Type": "application/json" }),
      },
    }));

    if (res.status === 401) {
      logout();
    }

    return res;
  }, [authResponse?.token, logout]);

  const authUpload = useCallback((
    url: string,
    body: FormData,
    onProgress: (fraction: number | null) => void,
    method = "POST",
  ): Promise<Response> => {
    const token = authResponse?.token;

    if (token && isTokenExpired(token)) {
      logout();
      return Promise.resolve(new Response(null, { status: 401 }));
    }

    return new Promise((resolve, reject) => {
      const xhr = new XMLHttpRequest();
      xhr.open(method, url);
      if (token) xhr.setRequestHeader("Authorization", `Bearer ${token}`);
      // The browser sets the Content-Type, with the multipart boundary.

      xhr.upload.addEventListener("progress", (e) => {
        onProgress(e.lengthComputable ? e.loaded / e.total : null);
      });
      xhr.upload.addEventListener("load", () => onProgress(null));

      xhr.addEventListener("load", () => {
        if (xhr.status === 401) logout();
        resolve(
          new Response(xhr.responseText, {
            status: xhr.status,
            statusText: xhr.statusText,
          }),
        );
      });
      // The error `fetch` throws on a network failure, so that
      // `friendlyFetchError` reports it the same way.
      xhr.addEventListener(
        "error",
        () => reject(new TypeError("Failed to fetch")),
      );
      xhr.addEventListener(
        "abort",
        () => reject(new TypeError("Failed to fetch")),
      );

      xhr.send(body);
    });
  }, [authResponse?.token, logout]);

  return {
    user: authResponse?.user ?? null,
    settings: authResponse?.settings ?? null,
    token: authResponse?.token ?? null,
    mediaToken: authResponse?.mediaToken ?? authResponse?.token ?? null,
    login,
    logout,
    updateSession,
    authFetch,
    authUpload,
  };
}

/**
 * Returned by {@link useRequiredAuth}. It is {@link UseAuthResult} with a user
 * that can't be null.
 */
export interface UseRequiredAuthResult extends UseAuthResult {
  user: SelfUser;
}

/**
 * Returns the session, for a page that `RestrictedLoggedIn` guards, such as
 * `DumpEdit`, so it needn't check for a user.
 *
 * @throws {Error} When no one is signed in, which means the route has no guard.
 */
export function useRequiredAuth(): UseRequiredAuthResult {
  const {
    user,
    settings,
    token,
    mediaToken,
    login,
    logout,
    updateSession,
    authFetch,
    authUpload,
  } = useAuth();

  if (!user) {
    throw new Error(
      "Invariant: useRequiredAuth called outside a protected route",
    );
  }
  return {
    user,
    settings,
    token,
    mediaToken,
    login,
    logout,
    updateSession,
    authFetch,
    authUpload,
  };
}