accounts-frontend/src/components/accounts/reducer.js

import { ADD, REMOVE, ACTIVATE } from './actions';

/**
 * @typedef {AccountsState}
 * @property {Account} active
 * @property {Account[]} available
 */

/**
 * @param {AccountsState} state
 * @param {string} options.type
 * @param {object} options.payload
 *
 * @return {AccountsState}
 */
export default function accounts(
    state,
    {type, payload = {}}
) {
    switch (type) {
        case ADD:
            if (!payload || !payload.id || !payload.token || !payload.refreshToken) {
                throw new Error('Invalid or empty payload passed for accounts.add');
            }

            if (!state.available.some((account) => account.id === payload.id)) {
                state.available = state.available.concat(payload);
            }

            return state;

        case ACTIVATE:
            if (!payload || !payload.id || !payload.token || !payload.refreshToken) {
                throw new Error('Invalid or empty payload passed for accounts.add');
            }

            return {
                ...state,
                active: payload
            };

        case REMOVE:
            if (!payload || !payload.id) {
                throw new Error('Invalid or empty payload passed for accounts.remove');
            }

            return {
                ...state,
                available: state.available.filter((account) => account.id !== payload.id)
            };

        default:
            return {
                active: null,
                available: []
            };
    }
}