feat: support more user-friendly scrolling

Author: Sherlocksuper

app/components/chat.tsx

@@ -960,9 +960,29 @@ function _Chat() {
           (scrollRef.current.scrollTop + scrollRef.current.clientHeight),
       ) <= 1
     : false;
+  const isAttachWithTop = useCallback(() => {
+    // if user is typing, should scroll
+    if (!scrollRef.current) return false;
+    // get lastMessageId
+    const lastMessageId = session.messages[session.messages.length - 1]?.id;
+    if (!lastMessageId) return false;
+    const lastMessage = document.getElementById(lastMessageId);
+    if (!lastMessage) return false;
+
+    const topDistance =
+      lastMessage.getBoundingClientRect().top -
+      scrollRef.current.getBoundingClientRect().top;
+    // leave some space for user question
+    return topDistance < 100;
+  }, [session.messages, scrollRef]);
+
+  const isTyping = userInput !== "";
+
+  // if user is typing, should auto scroll to bottom
+  // if user is not typing, should auto scroll to bottom only if already at bottom
   const { setAutoScroll, scrollDomToBottom } = useScrollToBottom(
     scrollRef,
-    isScrolledToBottom,
+    (isScrolledToBottom || isAttachWithTop()) && !isTyping,
   );
   const [hitBottom, setHitBottom] = useState(true);
   const isMobileScreen = useMobileScreen();
@@ -1717,6 +1737,7 @@ function _Chat() {
                           ? styles["chat-message-user"]
                           : styles["chat-message"]
                       }
+                      id={message.id}
                     >
                       <div className={styles["chat-message-container"]}>
                         <div className={styles["chat-message-header"]}>