import { useEffect, useState } from 'react';
import { getFallbackSession, onSessionPersisted, Session } from './sessions';

/**
 * [Gitea #105] Desktop, step 1: mirror the login tokens into the OS keychain.
 *
 * The session is still read from localStorage exactly as before; this only
 * keeps a copy in the keychain (Windows Credential Manager) and checks it by
 * reading it back, so real installs prove the keychain works before step 2
 * switches reads over to it. Nothing here can log anyone out: every failure
 * just records a status for Settings.
 *
 * Writes are serialized (a token rotation right after login must not race
 * the login's write) and time out, so a hung credential store can't pile up.
 * When there's no session the keychain entry is cleared, which also covers a
 * logout whose page reload beat the clear.
 */

export type KeychainTokens = {
  userId: string;
  deviceId: string;
  accessToken: string;
  refreshToken?: string;
};

export type KeychainMirrorStatus =
  | { state: 'idle' }
  | { state: 'unsupported' }
  | { state: 'ok' }
  | { state: 'cleared' }
  | { state: 'error'; error: string };

export type KeychainInvoke = (cmd: string, args?: Record<string, unknown>) => Promise<unknown>;

export const KEYCHAIN_TIMEOUT_MS = 5000;

export const tokensOf = (session: Session): KeychainTokens => ({
  userId: session.userId,
  deviceId: session.deviceId,
  accessToken: session.accessToken,
  ...(session.refreshToken ? { refreshToken: session.refreshToken } : {}),
});

export const sameTokens = (a: unknown, b: KeychainTokens): boolean => {
  if (!a || typeof a !== 'object') return false;
  const t = a as Partial<KeychainTokens>;
  return (
    t.userId === b.userId &&
    t.deviceId === b.deviceId &&
    t.accessToken === b.accessToken &&
    (t.refreshToken ?? undefined) === (b.refreshToken ?? undefined)
  );
};

const withTimeout = <T>(p: Promise<T>, ms: number): Promise<T> =>
  new Promise<T>((resolve, reject) => {
    const timer = setTimeout(() => reject(new Error('keychain timed out')), ms);
    p.then(
      (v) => {
        clearTimeout(timer);
        resolve(v);
      },
      (e) => {
        clearTimeout(timer);
        reject(e);
      },
    );
  });

const errorText = (e: unknown): string =>
  (e instanceof Error ? e.message : String(e)).slice(0, 200);

/**
 * Bring the keychain in line with `session` (null = no session). Reads first
 * and only writes when the stored copy differs, then verifies by reading back.
 */
export const syncKeychain = async (
  invoke: KeychainInvoke,
  session: Session | null,
  timeoutMs = KEYCHAIN_TIMEOUT_MS,
): Promise<KeychainMirrorStatus> => {
  // A desktop build without the commands (older than this feature) rejects
  // the call: that is "not supported", not an error to show the user.
  let supported: unknown;
  try {
    supported = await withTimeout(invoke('secure_session_supported'), timeoutMs);
  } catch {
    supported = false;
  }
  if (supported !== true) return { state: 'unsupported' };
  try {
    if (!session) {
      await withTimeout(invoke('secure_session_clear'), timeoutMs);
      return { state: 'cleared' };
    }
    const tokens = tokensOf(session);
    const stored = await withTimeout(invoke('secure_session_get'), timeoutMs);
    if (sameTokens(stored, tokens)) return { state: 'ok' };
    await withTimeout(invoke('secure_session_set', { tokens }), timeoutMs);
    const back = await withTimeout(invoke('secure_session_get'), timeoutMs);
    if (!sameTokens(back, tokens)) return { state: 'error', error: 'read-back did not match' };
    return { state: 'ok' };
  } catch (e) {
    return { state: 'error', error: errorText(e) };
  }
};

let status: KeychainMirrorStatus = { state: 'idle' };
const statusListeners = new Set<(s: KeychainMirrorStatus) => void>();
const setStatus = (next: KeychainMirrorStatus): void => {
  status = next;
  statusListeners.forEach((cb) => cb(next));
};

export const getKeychainMirrorStatus = (): KeychainMirrorStatus => status;

let started = false;

/** Start mirroring (desktop only; call once at boot). */
export const startKeychainMirror = (invoke: KeychainInvoke | undefined): void => {
  if (!invoke || started) return;
  started = true;
  let chain: Promise<unknown> = Promise.resolve();
  const enqueue = (session: Session | null) => {
    chain = chain.then(async () => setStatus(await syncKeychain(invoke, session)));
  };
  enqueue(getFallbackSession() ?? null);
  onSessionPersisted((session) => enqueue(session));
};

export const useKeychainMirrorStatus = (): KeychainMirrorStatus => {
  const [value, setValue] = useState(status);
  useEffect(() => {
    setValue(status);
    statusListeners.add(setValue);
    return () => {
      statusListeners.delete(setValue);
    };
  }, []);
  return value;
};