redux-reducer.js

import selectn from 'selectn';
import { union } from 'lodash';

/**
 * list of default fields for all of our lists
 * @type {{items: Array, isFetching: boolean, lastUpdated: null, didInvalidate: boolean, pagination: {}}}
 */
export const defaultFields = {
    items: [],
    isFetching: false,
    lastUpdated: null,
    didInvalidate: false,
    pagination: {}
};

/**
 * Helper function that allow to reduce boilerplate when creating initial states for reducers
 * @param {Array} entityNames - array of needed fields
 * @returns {Object} initial state for our reducer
 *
 * @example
 *
 * const initialState = createInitialState(['movies']);
 *
 * {
 *  entities: {},
 *  movies: {
 *   items: [],
 *   isFetching: false,
 *   lastUpdated: null,
 *   didInvalidate: null,
 *   pagination: {}
 *  }
 * }
 */

export const createInitialState = (entityNames = []) => {
    return Object.assign({entities: {}}, ...entityNames.map(name => ({
        [name]: defaultFields
    })));
};

export const createReducer = (initialState, handlers = { common: state => state }) => {
    if (!handlers.hasOwnProperty('common')) throw new Error('Expected an \`common\` method.');

    return (state = initialState, action) => {
        const newState = handlers.common(state, action);

        if (handlers.hasOwnProperty(action.type)) {
            return handlers[action.type](newState, action);
        }

        return newState;
    };
};

export const mergeIsFetching = (type, isFetching) => state => {
    return Object.assign({}, state, {
        [type]: Object.assign({}, state[type], {
            isFetching
        })
    });
};

export const mergeIntoBag = (entityName, type) => (state, action) => {
    const ids = selectn(`payload.result.${entityName}`, action) || [];
    const pagination = selectn('payload.result.meta.pagination', action) || {};

    return Object.assign({}, state, {
        [type]: Object.assign({}, state[type], {
            isFetching: false,
            items: union(state[type].items, ids),
            lastUpdated: Date.now(),
            pagination
        })
    });
};