refactor ui with ring buffer and display most recent

examples/companion_radio/ui-new/UITask.cpp

@@ -458,15 +458,17 @@ class MsgPreviewScreen : public UIScreen {
   };
   #define MAX_UNREAD_MSGS   32
   int num_unread;
+  int head = MAX_UNREAD_MSGS - 1; // index of latest unread message
   MsgEntry unread[MAX_UNREAD_MSGS];
 
 public:
   MsgPreviewScreen(UITask* task, mesh::RTCClock* rtc) : _task(task), _rtc(rtc) { num_unread = 0; }
 
   void addPreview(uint8_t path_len, const char* from_name, const char* msg) {
-    if (num_unread >= MAX_UNREAD_MSGS) return;  // full
+    head = (head + 1) % MAX_UNREAD_MSGS;
+    if (num_unread < MAX_UNREAD_MSGS) num_unread++;
 
-    auto p = &unread[num_unread++];
+    auto p = &unread[head];
     p->timestamp = _rtc->getCurrentTime();
     if (path_len == 0xFF) {
       sprintf(p->origin, "(D) %s:", from_name);
@@ -484,7 +486,7 @@ public:
     sprintf(tmp, "Unread: %d", num_unread);
     display.print(tmp);
 
-    auto p = &unread[0];
+    auto p = &unread[head];
 
     int secs = _rtc->getCurrentTime() - p->timestamp;
     if (secs < 60) {
@@ -520,14 +522,10 @@ public:
 
   bool handleInput(char c) override {
     if (c == KEY_NEXT || c == KEY_RIGHT) {
+      head = (head + MAX_UNREAD_MSGS - 1) % MAX_UNREAD_MSGS;
       num_unread--;
       if (num_unread == 0) {
         _task->gotoHomeScreen();
-      } else {
-        // delete first/curr item from unread queue
-        for (int i = 0; i < num_unread; i++) {
-          unread[i] = unread[i + 1];
-        }
       }
       return true;
     }