Fetch more messages if oldest unread

- If we are fetching older messages for buddy, then keep fetching until
  oldest is not unread

src/api/messages.ts

@@ -205,6 +205,16 @@ const sortSentTime = (a: Message, b: Message) => {
   return a.sentTime < b.sentTime ? -1 : 1;
 };
 
+export const getIsOldestFetchedMessageUnread = (
+  fetchedBuddyMessages: Record<string, Message>,
+) => {
+  const sorted = Object.keys(fetchedBuddyMessages)
+    .map(msgId => fetchedBuddyMessages[msgId])
+    .sort(sortSentTime);
+
+  return !sorted[sorted.length - 1].isSeen;
+};
+
 export const extractMostRecentId = (messages: MessageMapping) => {
   const flattenedMessages = Object.keys(messages).reduce<
     Record<string, Message>

src/state/reducers/messages.ts

@@ -93,16 +93,32 @@ export const reducer: automaton.Reducer<State, actions.Action> = (
 
       const previousMsgId = messageApi.extractMostRecentId(nextMessages);
 
-      const [pollingParams, nextPollingParams] = messageApi.getNextParams(
+      const isFetchingOlderMessagesAndIsOldestFetchedUnread =
+        state.currentParams.type === 'OlderThan'
+          ? messageApi.getIsOldestFetchedMessageUnread(
+              newMessages[state.currentParams.buddyId],
+            )
+          : false;
+
+      const [first, rest] = messageApi.getNextParams(
         action.payload,
         state.pollingQueue,
         state.currentParams,
         previousMsgId,
       );
 
+      const { nextFetch, nextCurrent, nextQueue } =
+        isFetchingOlderMessagesAndIsOldestFetchedUnread
+          ? {
+              nextCurrent: state.currentParams,
+              nextFetch: state.currentParams,
+              nextQueue: [first, ...rest],
+            }
+          : { nextCurrent: first, nextFetch: first, nextQueue: rest };
+
       const nextCmd = withToken(
         flow(
-          messageApi.fetchMessages(pollingParams),
+          messageApi.fetchMessages(nextFetch),
           T.delay(config.messageFetchDelay),
         ),
         actions.make('messages/get/completed'),
@@ -113,8 +129,8 @@ export const reducer: automaton.Reducer<State, actions.Action> = (
           ...state,
           messages: RD.success(nextMessages),
           previousMsgId,
-          pollingQueue: nextPollingParams,
-          currentParams: pollingParams,
+          pollingQueue: nextQueue,
+          currentParams: nextCurrent,
         },
         nextCmd,
       );