An Epic that tallies time spent in workspaces

tally-workspace-usage.js

/**
 * Keep a running total of time spent on each workspace and, once the app is quit,
 * fire an action that updates the usage property in the store.
 */
const tallyWorkspaceUsageEpic = (action$, store, scheduler) => {
  return selectionChangedObservable(action$, store)
    .timeInterval(scheduler)
    .pairwise()
    .reduce(usagePayloadFromIntervals, {})
    .map((payload) => ({
      type: WORKSPACE.UPDATE_USAGE,
      payload
    }));
};

/**
 * An Observable that emits any time the selected workspace might change.
 */
function selectionChangedObservable(action$, store) {
  /**
   * We need to terminate the stream when the app is quit, otherwise reduce
   * won't kick in.
   */
  return action$.ofType(
    WORKSPACE.ADDED,
    WORKSPACE.REMOVED,
    WORKSPACE.SELECTION_CHANGED
  )
  .takeUntil(action$.ofType(APP.QUIT))
  .filter(() => getWorkspacesCount(store) > 1);
}

/**
 * An interval pair here represents a workspace changed event. Given a pair like:
 *
 * [ { value: 'Workspace 1', interval: 5000 } ],
 * [ { value: 'Workspace 2', interval: 10000 } ]
 *
 * The value from the first corresponds to the workspace that was selected, and
 * the interval from the second represents the amount of time it was selected for.
 */
function usagePayloadFromIntervals(payload, intervals) {
  const [ first, second ] = intervals;
  const existingTime = payload[first.value] || 0;
  payload[first.value] = existingTime + second.interval;
  return payload;
}