CBS-Mobile-App/src/services/api/interceptors.ts

import type { AxiosError, AxiosInstance, AxiosResponse } from 'axios';

import type { CbsEnvelope } from '../../types/cbs';
import { sessionManager } from '../security/sessionManager';
import { secureStorage } from '../storage/secureStorage';
import { apiLogger } from './apiLogger';
import { CbsApiError, isCbsErrorCode, type FieldErrors } from './cbsErrors';
import { rememberServerTime } from './serverClock';

const unauthorizedHandlers = new Set<() => void>();

export const registerUnauthorizedHandler = (handler: () => void) => {
  unauthorizedHandlers.add(handler);

  return () => {
    unauthorizedHandlers.delete(handler);
  };
};

const looksLikeEnvelope = (value: unknown): value is CbsEnvelope<unknown> =>
  typeof value === 'object' && value !== null && 'success' in value;

/**
 * `VALIDATION_ERROR` is the one failure that also fills `data`, with a
 * field-to-message map. Anything else in there on a failure is not a field map.
 */
const readFieldErrors = (envelope: CbsEnvelope<unknown>): FieldErrors | undefined => {
  if (envelope.errorCode !== 'VALIDATION_ERROR') {
    return undefined;
  }

  const { data } = envelope;

  if (typeof data !== 'object' || data === null) {
    return undefined;
  }

  const entries = Object.entries(data as Record<string, unknown>).filter(
    (entry): entry is [string, string] => typeof entry[1] === 'string',
  );

  return entries.length > 0 ? Object.fromEntries(entries) : undefined;
};

/** The absolute URL a failed request was aimed at, for a dev-only diagnostic. */
const describeTarget = (error: AxiosError) => {
  const base = error.config?.baseURL ?? '';
  const path = error.config?.url ?? '';

  return `${base}${path}` || 'the server';
};

const envelopeToError = (status: number, envelope: CbsEnvelope<unknown>) =>
  new CbsApiError({
    status,
    code: isCbsErrorCode(envelope.errorCode) ? envelope.errorCode : 'UNKNOWN_ERROR',
    message: envelope.message || 'Unexpected service error',
    fieldErrors: readFieldErrors(envelope),
  });

/**
 * `SESSION_INVALID` means the token we hold is dead and every screen must drop
 * it. `INVALID_CREDENTIALS` shares the 401 but means a wrong MPIN on the
 * sign-in form — bouncing the user out of a screen they are not in yet would
 * be nonsense, so only the former trips the global handler.
 */
export const handleSessionLoss = async (error: CbsApiError) => {
  if (error.code !== 'SESSION_INVALID') {
    return;
  }

  await secureStorage.clearSession();
  sessionManager.clear();
  unauthorizedHandlers.forEach((handler) => handler());
};

export const attachInterceptors = (client: AxiosInstance) => {
  client.interceptors.request.use(async (config) => {
    const token = await secureStorage.getAccessToken();

    if (token) {
      const nextHeaders = (config.headers ?? {}) as Record<string, string>;
      nextHeaders.Authorization = `Bearer ${token}`;
      config.headers = nextHeaders as never;
    }

    // Logged here, at the end of the interceptor, so the curl shows the
    // headers the request will actually be sent with — the token itself as a
    // placeholder.
    apiLogger.request(config);

    return config;
  });

  client.interceptors.response.use(
    async (response: AxiosResponse) => {
      apiLogger.response(response);

      if (!looksLikeEnvelope(response.data)) {
        return response;
      }

      const envelope = response.data as CbsEnvelope<unknown>;

      // Branch on `success`, not on the HTTP status: a failure can arrive with
      // a 2xx, and treating it as a payload would hand callers `undefined`.
      if (!envelope.success) {
        const error = envelopeToError(response.status, envelope);
        apiLogger.failure(response, `envelope said success: false -> ${error.code}`);
        await handleSessionLoss(error);
        throw error;
      }

      // Any authenticated call refreshes the server's idle timer, so mirror
      // that locally — otherwise the app would sign the user out while the
      // session is still very much alive.
      if (response.config.headers?.Authorization) {
        sessionManager.touch();
      }

      // Unwrap so callers read the payload directly rather than the envelope.
      // The server's `timestamp` is kept aside for anything counting down to
      // a server expiry — see `serverClock`.
      const unwrapped = { ...response, data: envelope.data };
      rememberServerTime(unwrapped, envelope.timestamp);

      return unwrapped;
    },
    async (error: AxiosError) => {
      if (error instanceof CbsApiError) {
        return Promise.reject(error);
      }

      if (error.response) {
        apiLogger.failure(error.response, `HTTP error ${error.code ?? ''}`.trim());
      } else {
        apiLogger.networkFailure(error);
      }

      const status = Number(error.response?.status ?? 0);
      const body = error.response?.data;

      if (looksLikeEnvelope(body)) {
        const cbsError = envelopeToError(status, body);
        await handleSessionLoss(cbsError);

        return Promise.reject(cbsError);
      }

      if (error.code === 'ECONNABORTED' || error.code === 'ETIMEDOUT') {
        return Promise.reject(
          new CbsApiError({
            status: 0,
            code: 'REQUEST_TIMEOUT',
            message: 'The request timed out',
          }),
        );
      }

      // No response at all: nothing answered on the other end. The usual causes
      // are the backend not running, it being bound to 127.0.0.1 instead of
      // 0.0.0.0, the handset being on a different network from the host, a
      // firewall on the host port, or cleartext HTTP blocked in a release build.
      //
      // Naming the URL that failed matters more than it looks: without it this
      // is indistinguishable from a server-side fault, and the address the
      // phone needs is often not the one that works in the laptop's browser.
      if (!error.response) {
        return Promise.reject(
          new CbsApiError({
            status: 0,
            code: 'NETWORK_ERROR',
            message: __DEV__
              ? `Could not reach ${describeTarget(error)}. Check the backend is running and that this device can reach that address.`
              : error.message || 'Could not reach the server',
          }),
        );
      }

      return Promise.reject(
        new CbsApiError({
          status,
          code: 'UNKNOWN_ERROR',
          message: error.message || 'Unexpected service error',
        }),
      );
    },
  );
};