[feature] Only select the latest epoch when it is selected

#190

Now, selecting any epoch but the latest one causes the selection to
stay on it, despite any new epochs arriving.

Added a react key to each epoch, since the scroll-to effect doesn't
work in certain edge cases. Now, new epochs always scroll because they
always mount with a clean state.

src/day8/re_frame_10x/navigation/epochs/events.cljs

@@ -91,7 +91,8 @@
                                                       (remove (fn [trace]
                                                                 (or (when drop-reagent (metam/low-level-reagent-trace? trace))
                                                                     (when drop-re-frame (metam/low-level-re-frame-trace? trace)))))) all-traces)
-            match-ids (mapv first-match-id retained-matches)]
+            match-ids (mapv first-match-id retained-matches)
+            latest-selected? (-> db :epochs :selected-epoch-id #{(first-match-id (last previous-matches))})]
         {:db       (-> db
                        (assoc-in [:traces :all] retained-traces)
                        (update :epochs assoc
@@ -101,8 +102,11 @@
                                :parse-state parse-state
                                :sub-state new-sub-state
                                :subscription-info subscription-info)
-                       ;; Reset selected epoch to the head of the list if we got a new event in.
-                       (cond-> (seq new-matches) (assoc-in [:epochs :selected-epoch-id] (last match-ids))))
+                       ;; Select the latest event when it arrives, unless the user has selected an older one.
+                       (cond-> (and (seq new-matches)
+                                    (or latest-selected?
+                                        (not (seq previous-matches))))
+                         (assoc-in [:epochs :selected-epoch-id] (last match-ids))))
          :dispatch (when quiescent? [::quiescent])})
       ;; Else
       {:db db})))
@@ -191,4 +195,4 @@
   ::set-filter
   [(rf/path [:epochs :filter-str]) rf/trim-v]
   (fn [_ [filter-str]]
-    filter-str))
+    filter-str))