text: // @flow
  import isEqual from 'util/deep-equal';
  import { doPreferenceSet } from 'redux/actions/sync';
  
  const SHARED_PREFERENCE_VERSION = '0.1';
  let oldShared = {};
  
  export const buildSharedStateMiddleware = (
    actions: Array<string>,
    sharedStateFilters: {},
    sharedStateCb?: any => void
  ) => ({
    getState,
    dispatch,
  }: {
    getState: () => { user: any, settings: any },
    dispatch: any => void,
  }) => (next: ({}) => void) => (action: { type: string, data: any }) => {
    const currentState = getState();
  
    // We don't care if sync is disabled here, we always want to backup preferences to the wallet
    if (!actions.includes(action.type) || typeof action === 'function') {
      return next(action);
    }
  
    const actionResult = next(action);
    // Call `getState` after calling `next` to ensure the state has updated in response to the action
    const nextState: { user: any, settings: any } = getState();
    const syncEnabled =
      nextState.settings &&
      nextState.settings.clientSettings &&
      nextState.settings.clientSettings.enable_sync;
    const hasVerifiedEmail =
      nextState.user && nextState.user.user && nextState.user.user.has_verified_email;
    const preferenceKey = syncEnabled && hasVerifiedEmail ? 'shared' : 'local';
    const shared = {};
  
    Object.keys(sharedStateFilters).forEach(key => {
      const filter = sharedStateFilters[key];
      const { source, property, transform } = filter;
      let value = nextState[source][property];
      if (transform) {
        value = transform(value);
      }
  
      shared[key] = value;
    });
  
    if (!isEqual(oldShared, shared)) {
      // only update if the preference changed from last call in the same session
      oldShared = shared;
      dispatch(doPreferenceSet(preferenceKey, shared, SHARED_PREFERENCE_VERSION));
    }
  
    if (sharedStateCb) {
      // Pass dispatch to the callback to consumers can dispatch actions in response to preference set
      sharedStateCb({ dispatch, getState });
    }
  
    return actionResult;
  };
  