Logout handled by reducers

[outoftime]

Removes the logOut() thunk action creator and handles all state transitions directly in reducers.

Flow looks like this:

Workspace component dispatches USER_LOGGED_OUT

projects reducer consumes USER_LOGGED_OUT

• Retains only current project (see below note on how it knows what the current project is)

ui reducer consumes USER_LOGGED_OUT

• Closes active submenu if it’s the projects list

user reducer consumes USER_LOGGED_OUT

• Sets user state to unauthenticated

We do introduce a new pattern to reducers, in order for the project reducer to be able to do the right thing.

When the user logs out, we want to clear all projects out of the list except for the current project. This requires the projects reducer to know what the current project is.

There are several ways to solve this problem without giving the projects
reducer access to the rest of the store:

1. Have the current project key passed in the action payload by the point of dispatch (e.g. from the Workspace component)
2. Use a thunk action creator that can introspect the current state and then add the current project key to a dispatched action payload
3. Duplicate the information in the currentProject subtree, also marking the object in projects as current
4. Don’t bother trimming the projects store–just enforce a rule that only the current project is visible using a selector

However, each of these approaches has significant disadvantages:

1. The fact that a reducer needs to know about the current project when consuming USER_LOGGED_OUT is an implementation detail of the store; the component that initially dispatches the action should not need to know this
2. Thunk action creators are considered harmful and are being removed from our code
3. It’s a very good idea to keep the Redux store fully normalized.
4. This approach would lead to an incoherent store state, and we’d have roughly the same problem when the user logs in.

Contra the author of this highly upvoted GitHub issue comment, I don’t think it’s an antipattern for reducers to have access to the entire store. In fact, this is the great strength of Redux—we’re able to model all state transitions based on a universally-agreed-upon answer to the question “what is the current state of the world?” The combineReducers approach to isolating the reducer logic for different parts of the subtree is a very useful tool for organizing code; it’s not a mandate to only organize code that way.

Further, options 1 and 2 above feel a bit ridiculous because, fundamentally, reducers do have access to the entire state. Why would we jump through hoops just to give the reducer information it already has access to?

So: establish a pattern that reducer modules may export a named reduceRoot function, which takes the entire state and performs reductions on it. The top-level root reducer will import this function and apply it to the state after running the isolated reducers using the reduce-reducers module.