redux.js

/**
 * Redux-related helpers.
 */

import _ from 'lodash';

/**
 * Given any Flux Standard Action (FSA) with promise as the payload, it returns
 * a promise which resolves into the FSA result object.
 * @param {Object} action
 * @return Promise which resolves to the operation result.
 */
export function toFSA(action) {
  return action.payload.then(data => ({
    ...action,
    payload: data,
  }), error => ({
    ...action,
    payload: error,
    error: true,
  }));
}

/**
 * Given a mapping between reducer names and their promises, this function
 * waits till resolution of all promises and returns the mapping between
 * reducer names and the resolved reducers.
 * @param {Object} promises Object with promises of reducers.
 * @return Object with reducers.
 */
export function resolveReducers(promises) {
  return Promise.all(_.values(promises)).then((reducers) => {
    const map = {};
    _.keys(promises).forEach((key, index) => {
      map[key] = reducers[index];
    });
    return map;
  });
}

/**
 * Reduce multiple reducers into a single reducer from left to right.
 * Function-type reducers will be called directly with current state, and action
 * Object type reducers (eg: `{submissions: (state, action) => {}}`)
 *   will be called with the state's slice corresponding to object's key
 *   eg: `{submissions}` will be called with `submissions(state.submissions, action)`
 *
 * @params {function|Object} the reducers to be combined
 * @return function the unified reducer
 */
/* TODO: Can we simplify this function? */
export function combine(...reducers) {
  return (state, action) => {
    const nextState = {};
    const mergeState = Object.assign.bind(Object, nextState);

    reducers.forEach((reducer) => {
      if (typeof reducer === 'function') {
        return mergeState(reducer(state, action));
      }

      Object.keys(reducer).forEach((slice) => {
        mergeState({ [slice]: reducer[slice]((state || {})[slice], action) });
      });
      return undefined;
    });

    return nextState;
  };
}

/* We don't any `main` function in this module to export it by default. */
export default undefined;