ducks/conversations: Ensure metrics agree with in-memory messages

* ducks/conversations: Ensure metrics agree with in-memory messages
* Clean up logic cleaning up metrics

ts/state/ducks/conversations.ts

@@ -736,6 +736,21 @@ export function reducer(
 
     const lookup = fromPairs(messages.map(message => [message.id, message]));
 
+    let { newest, oldest } = metrics;
+
+    // If our metrics are a little out of date, we'll fix them up
+    if (messages.length > 0) {
+      const first = messages[0];
+      if (first && (!oldest || first.received_at < oldest.received_at)) {
+        oldest = pick(first, ['id', 'received_at']);
+      }
+
+      const last = messages[messages.length - 1];
+      if (last && (!newest || last.received_at > newest.received_at)) {
+        newest = pick(last, ['id', 'received_at']);
+      }
+    }
+
     return {
       ...state,
       selectedMessage: scrollToMessageId,
@@ -753,7 +768,11 @@ export function reducer(
             ? existingConversation.scrollToMessageCounter + 1
             : 0,
           messageIds,
-          metrics,
+          metrics: {
+            ...metrics,
+            newest,
+            oldest,
+          },
           resetCounter,
           heightChangeMessageIds: [],
         },