effects.js

import { fetchStatus } from "@lib/fetch";
import { userApi } from "@feature/users/api";
import { actions } from "./symbiotes";
import * as selectors from "./selectors";

/*
  userApi.fetchUser() should throw an Error, if server returned object with error
*/

/*
  Store of users, should be mapping of userId -> User
  Example: users: { 1: { id: 1, username: 'foo' } }

  For usernames we can have another mapping for username -> userId
  Example: usernames: { 'foo': 1 }

  actions.setUser(user) should set users[user.id] = user
  also it should set usernames[user.username] = user.id
*/

/*
  const getUsers = createSelector(
    getRootOfUsers,
    (root) => root.users
  )

  To select user by id, use selector with props
  const getUserById = createSelector(
    [getUsers, (state, props) => props.userId],
    (users, userId) => users[userId]
  )
  getUserById(getState(), { userId: 1 })


  To select by username
  const getUserByUsername = createSelectors(
    [
      getUsers,
      getUsernames,
      (state, props) => props.username,
    ],
    (users, usernames, username) => usernames[username] && users[usernames[username]]
  )
  getUserByUsername(getState(), { username: 'foo' })
*/

/**
 * Fetch is just a loading from the API
 */
const fetchUser = (username) => (dispatch) =>
  dispatch(userApi.fetchUser(username))
    .then((user) => ({ lastUpdate: Date.now(), ...user }))

/**
 * Load is a fetch and set to the store
 */
const loadUser = (username) => async (dispatch) => {
  const user = dispatch(fetchUser(username))
  dispatch(actions.setUser(user));
  return user
}

const TIMEOUT_TO_UPDATE_USER = 3000 // ms
const isUserNeedUpdate = (user) => Date.now() - user.lastUpdate > TIMEOUT_TO_UPDATE_USER;

export const loadOrUpdateUser = (username) => async (dispatch, getState) => {
  dispatch(actions.setFetchStatus(fetchStatus.loading));
  dispatch(actions.resetError());

  let user = getUserByUsername(getState(), { username });
  
  const isUserShouldBeLoaded = !user || isUserNeedUpdate(user)

  if (isUserShouldBeLoaded) {
    try {
      user = await dispatch(fetchUser(username));
      dispatch(actions.setFetchStatus(fetchStatus.finished));
    }
    catch (error) {
      dispatch(actions.setError(error.message));
      dispatch(actions.setFetchStatus(fetchStatus.failed));
    }
  }

  dispatch(actions.setCurrentUser(user));
};