chore: scroll-related UX adjustments in the Unleash AI chat (#8478)

https://linear.app/unleash/issue/2-2857/make-some-scroll-related-ux-adjustments-to-the-unleash-ai-chat

Introduces scroll-related UX enhancements to the Unleash AI chat,
providing a smoother and more refined user experience.

frontend/src/component/ai/AIChat.tsx

@@ -20,6 +20,10 @@ const AI_ERROR_MESSAGE = {
     content: `I'm sorry, I'm having trouble understanding you right now. I've reported the issue to the team. Please try again later.`,
 } as const;
 
+type ScrollOptions = ScrollIntoViewOptions & {
+    onlyIfAtEnd?: boolean;
+};
+
 const StyledAIIconContainer = styled('div')(({ theme }) => ({
     position: 'fixed',
     bottom: 20,
@@ -88,21 +92,43 @@ export const AIChat = () => {
 
     const [messages, setMessages] = useState<ChatMessage[]>([]);
 
+    const isAtEndRef = useRef(true);
     const chatEndRef = useRef<HTMLDivElement | null>(null);
 
-    const scrollToEnd = (options?: ScrollIntoViewOptions) => {
+    const scrollToEnd = (options?: ScrollOptions) => {
         if (chatEndRef.current) {
+            const shouldScroll = !options?.onlyIfAtEnd || isAtEndRef.current;
+
+            if (shouldScroll) {
                 chatEndRef.current.scrollIntoView(options);
             }
+        }
     };
 
     useEffect(() => {
-        scrollToEnd({ behavior: 'smooth' });
+        scrollToEnd();
-    }, [messages]);
+
+        const intersectionObserver = new IntersectionObserver(
+            ([entry]) => {
+                isAtEndRef.current = entry.isIntersecting;
+            },
+            { threshold: 1.0 },
+        );
+
+        if (chatEndRef.current) {
+            intersectionObserver.observe(chatEndRef.current);
+        }
+
+        return () => {
+            if (chatEndRef.current) {
+                intersectionObserver.unobserve(chatEndRef.current);
+            }
+        };
+    }, [open]);
 
     useEffect(() => {
-        scrollToEnd();
+        scrollToEnd({ behavior: 'smooth', onlyIfAtEnd: true });
-    }, [open]);
+    }, [messages]);
 
     const onSend = async (content: string) => {
         if (!content.trim() || loading) return;
@@ -153,7 +179,7 @@ export const AIChat = () => {
                 minSize={{ width: '270px', height: '200px' }}
                 maxSize={{ width: '90vw', height: '90vh' }}
                 defaultSize={{ width: '320px', height: '450px' }}
-                onResize={scrollToEnd}
+                onResize={() => scrollToEnd({ onlyIfAtEnd: true })}
             >
                 <StyledChat>
                     <AIChatHeader
@@ -176,7 +202,13 @@ export const AIChat = () => {
                         )}
                         <div ref={chatEndRef} />
                     </StyledChatContent>
-                    <AIChatInput onSend={onSend} loading={loading} />
+                    <AIChatInput
+                        onSend={onSend}
+                        loading={loading}
+                        onHeightChange={() =>
+                            scrollToEnd({ onlyIfAtEnd: true })
+                        }
+                    />
                 </StyledChat>
             </StyledResizable>
         </StyledAIChatContainer>

frontend/src/component/ai/AIChatInput.tsx

@@ -1,4 +1,4 @@
-import { useState } from 'react';
+import { useEffect, useRef, useState } from 'react';
 import {
     IconButton,
     InputAdornment,
@@ -32,11 +32,40 @@ const StyledIconButton = styled(IconButton)({
 export interface IAIChatInputProps {
     onSend: (message: string) => void;
     loading: boolean;
+    onHeightChange?: () => void;
 }
 
-export const AIChatInput = ({ onSend, loading }: IAIChatInputProps) => {
+export const AIChatInput = ({
+    onSend,
+    loading,
+    onHeightChange,
+}: IAIChatInputProps) => {
     const [message, setMessage] = useState('');
 
+    const inputContainerRef = useRef<HTMLDivElement | null>(null);
+    const previousHeightRef = useRef<number>(0);
+
+    useEffect(() => {
+        const resizeObserver = new ResizeObserver(([entry]) => {
+            const newHeight = entry.contentRect.height;
+
+            if (newHeight !== previousHeightRef.current) {
+                previousHeightRef.current = newHeight;
+                onHeightChange?.();
+            }
+        });
+
+        if (inputContainerRef.current) {
+            resizeObserver.observe(inputContainerRef.current);
+        }
+
+        return () => {
+            if (inputContainerRef.current) {
+                resizeObserver.unobserve(inputContainerRef.current);
+            }
+        };
+    }, [onHeightChange]);
+
     const send = () => {
         if (!message.trim() || loading) return;
         onSend(message);
@@ -44,7 +73,7 @@ export const AIChatInput = ({ onSend, loading }: IAIChatInputProps) => {
     };
 
     return (
-        <StyledAIChatInputContainer>
+        <StyledAIChatInputContainer ref={inputContainerRef}>
             <StyledAIChatInput
                 autoFocus
                 size='small'

frontend/src/setupTests.ts

@@ -9,10 +9,27 @@ class ResizeObserver {
     disconnect() {}
 }
 
+class IntersectionObserver {
+    root: any;
+    rootMargin: any;
+    thresholds: any;
+
+    observe() {}
+    unobserve() {}
+    disconnect() {}
+    takeRecords() {
+        return [];
+    }
+}
+
 if (!window.ResizeObserver) {
     window.ResizeObserver = ResizeObserver;
 }
 
+if (!window.IntersectionObserver) {
+    window.IntersectionObserver = IntersectionObserver;
+}
+
 process.env.TZ = 'UTC';
 
 const errorsToIgnore = [