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Scroll only if the user is at the bottom of the container and remove visible bottom gap from chat messages stack
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apps/web/src/components/chat-messages.tsx
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apps/web/src/components/chat-messages.tsx
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import { useEffect, useRef } from "react";
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import { useEffect, useLayoutEffect, useRef } from "react";
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import type { ChatMessage as ChatMessageType } from "#/lib/types";
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import { ChatMessage } from "./chat-message";
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import { Stack } from "./layout";
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messages: ChatMessageType[];
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}
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const SCROLL_THRESHOLD_PX = 2;
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function getDistanceFromBottom(container: HTMLDivElement) {
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return container.scrollHeight - container.scrollTop - container.clientHeight;
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}
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function scrollToBottom(container: HTMLDivElement) {
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container.scrollTo({
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top: container.scrollHeight,
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behavior: "instant",
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});
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}
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export function ChatMessages({ messages }: ChatMessageProps) {
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const endRef = useRef<HTMLDivElement>(null);
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const containerRef = useRef<HTMLDivElement>(null);
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const hasInitializedScrollRef = useRef(false);
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const shouldStickToBottomRef = useRef(true);
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const previousMessagesRef = useRef(messages);
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useEffect(() => {
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if (messages.length === 0) return;
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endRef.current?.scrollIntoView({ block: "end", behavior: "instant" });
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const container = containerRef.current;
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if (!container) return;
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function updateShouldStickToBottom() {
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shouldStickToBottomRef.current =
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getDistanceFromBottom(container) <= SCROLL_THRESHOLD_PX;
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}
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updateShouldStickToBottom();
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container.addEventListener("scroll", updateShouldStickToBottom);
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return () => {
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container.removeEventListener("scroll", updateShouldStickToBottom);
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};
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}, []);
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useLayoutEffect(() => {
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const container = containerRef.current;
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if (!container || messages.length === 0) return;
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const previousMessages = previousMessagesRef.current;
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const previousLastMessage = previousMessages.at(-1);
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const lastMessage = messages.at(-1);
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const messageWasAppended = messages.length > previousMessages.length;
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const shouldForceScroll =
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!hasInitializedScrollRef.current ||
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(messageWasAppended &&
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(lastMessage?.role === "user" ||
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(previousLastMessage?.role === "user" &&
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lastMessage?.role === "assistant")));
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if (!hasInitializedScrollRef.current) {
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hasInitializedScrollRef.current = true;
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}
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if (shouldForceScroll || shouldStickToBottomRef.current) {
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scrollToBottom(container);
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shouldStickToBottomRef.current = true;
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}
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previousMessagesRef.current = messages;
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}, [messages]);
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return (
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<Stack className="no-scrollbar flex-1 overflow-y-auto">
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<Stack ref={containerRef} className="no-scrollbar flex-1 overflow-y-auto">
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{messages.map((message) => (
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<ChatMessage
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key={message.id}
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text={message.text}
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/>
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))}
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<div ref={endRef} />
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</Stack>
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);
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}