firefox/browser/extensions/newtab/content-src/lib/init-store.mjs

/* This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this file,
 * You can obtain one at http://mozilla.org/MPL/2.0/. */

/* eslint-env mozilla/remote-page */

import {
  actionCreators as ac,
  actionTypes as at,
  actionUtils as au,
} from "../../common/Actions.mjs";
// We disable import checking here as redux is installed via the npm packages
// at the newtab level, rather than in the top-level package.json.
// eslint-disable-next-line import/no-unresolved
import { applyMiddleware, combineReducers, createStore } from "redux";

export const MERGE_STORE_ACTION = "NEW_TAB_INITIAL_STATE";
export const OUTGOING_MESSAGE_NAME = "ActivityStream:ContentToMain";
export const INCOMING_MESSAGE_NAME = "ActivityStream:MainToContent";

/**
 * A higher-order function which returns a reducer that, on MERGE_STORE action,
 * will return the action.data object merged into the previous state.
 *
 * For all other actions, it merely calls mainReducer.
 *
 * Because we want this to merge the entire state object, it's written as a
 * higher order function which takes the main reducer (itself often a call to
 * combineReducers) as a parameter.
 *
 * @param  {function} mainReducer reducer to call if action != MERGE_STORE_ACTION
 * @return {function}             a reducer that, on MERGE_STORE_ACTION action,
 *                                will return the action.data object merged
 *                                into the previous state, and the result
 *                                of calling mainReducer otherwise.
 */
function mergeStateReducer(mainReducer) {
  return (prevState, action) => {
    if (action.type === MERGE_STORE_ACTION) {
      return { ...prevState, ...action.data };
    }

    return mainReducer(prevState, action);
  };
}

/**
 * messageMiddleware - Middleware that looks for SentToMain type actions, and sends them if necessary
 */
const messageMiddleware = () => next => action => {
  const skipLocal = action.meta && action.meta.skipLocal;
  if (au.isSendToMain(action)) {
    RPMSendAsyncMessage(OUTGOING_MESSAGE_NAME, action);
  }
  if (!skipLocal) {
    next(action);
  }
};

export const rehydrationMiddleware = ({ getState }) => {
  // NB: The parameter here is MiddlewareAPI which looks like a Store and shares
  // the same getState, so attached properties are accessible from the store.
  getState.didRehydrate = false;
  getState.didRequestInitialState = false;
  return next => action => {
    if (getState.didRehydrate || window.__FROM_STARTUP_CACHE__) {
      // Startup messages can be safely ignored by the about:home document
      // stored in the startup cache.
      if (
        window.__FROM_STARTUP_CACHE__ &&
        action.meta &&
        action.meta.isStartup
      ) {
        return null;
      }
      return next(action);
    }

    const isMergeStoreAction = action.type === MERGE_STORE_ACTION;
    const isRehydrationRequest = action.type === at.NEW_TAB_STATE_REQUEST;

    if (isRehydrationRequest) {
      getState.didRequestInitialState = true;
      return next(action);
    }

    if (isMergeStoreAction) {
      getState.didRehydrate = true;
      return next(action);
    }

    // If init happened after our request was made, we need to re-request
    if (getState.didRequestInitialState && action.type === at.INIT) {
      return next(ac.AlsoToMain({ type: at.NEW_TAB_STATE_REQUEST }));
    }

    if (
      au.isBroadcastToContent(action) ||
      au.isSendToOneContent(action) ||
      au.isSendToPreloaded(action)
    ) {
      // Note that actions received before didRehydrate will not be dispatched
      // because this could negatively affect preloading and the the state
      // will be replaced by rehydration anyway.
      return null;
    }

    return next(action);
  };
};

/**
 * initStore - Create a store and listen for incoming actions
 *
 * @param  {object} reducers An object containing Redux reducers
 * @param  {object} intialState (optional) The initial state of the store, if desired
 * @return {object}          A redux store
 */
export function initStore(reducers, initialState) {
  const store = createStore(
    mergeStateReducer(combineReducers(reducers)),
    initialState,
    globalThis.RPMAddMessageListener &&
      applyMiddleware(rehydrationMiddleware, messageMiddleware)
  );

  if (globalThis.RPMAddMessageListener) {
    globalThis.RPMAddMessageListener(INCOMING_MESSAGE_NAME, msg => {
      try {
        store.dispatch(msg.data);
      } catch (ex) {
        console.error("Content msg:", msg, "Dispatch error: ", ex);
        dump(
          `Content msg: ${JSON.stringify(msg)}\nDispatch error: ${ex}\n${
            ex.stack
          }`
        );
      }
    });
  }

  return store;
}