LibreChat/client/src/components/Chat/Messages/MessagesView.tsx

import { useLayoutEffect, useState, useRef, useCallback } from 'react';
import type { ReactNode } from 'react';
import type { TMessage } from 'librechat-data-provider';
import ScrollToBottom from '~/components/Messages/ScrollToBottom';
import { CSSTransition } from 'react-transition-group';
import { useChatContext } from '~/Providers';
import MultiMessage from './MultiMessage';
import { useScrollToRef } from '~/hooks';

export default function MessagesView({
  messagesTree: _messagesTree,
  Header,
}: {
  messagesTree?: TMessage[] | null;
  Header?: ReactNode;
}) {
  const scrollableRef = useRef<HTMLDivElement | null>(null);
  const messagesEndRef = useRef<HTMLDivElement | null>(null);
  const [showScrollButton, setShowScrollButton] = useState(false);
  const [currentEditId, setCurrentEditId] = useState<number | string | null>(-1);
  const { conversation, showPopover, setAbortScroll } = useChatContext();
  const { conversationId } = conversation ?? {};

  // TODO: screenshot target ref
  // const { screenshotTargetRef } = useScreenshot();

  const checkIfAtBottom = useCallback(() => {
    if (!scrollableRef.current) {
      return;
    }

    const { scrollTop, scrollHeight, clientHeight } = scrollableRef.current;
    const diff = Math.abs(scrollHeight - scrollTop);
    const percent = Math.abs(clientHeight - diff) / clientHeight;
    const hasScrollbar = scrollHeight > clientHeight && percent >= 0.15;
    setShowScrollButton(hasScrollbar);
  }, [scrollableRef]);

  useLayoutEffect(() => {
    const timeoutId = setTimeout(() => {
      checkIfAtBottom();
    }, 650);

    // Add a listener on the window object
    window.addEventListener('scroll', checkIfAtBottom);

    return () => {
      clearTimeout(timeoutId);
      window.removeEventListener('scroll', checkIfAtBottom);
    };
  }, [_messagesTree, checkIfAtBottom]);

  let timeoutId: ReturnType<typeof setTimeout> | undefined;
  const debouncedHandleScroll = () => {
    clearTimeout(timeoutId);
    timeoutId = setTimeout(checkIfAtBottom, 100);
  };

  const scrollCallback = () => setShowScrollButton(false);
  const { scrollToRef: scrollToBottom, handleSmoothToRef } = useScrollToRef({
    targetRef: messagesEndRef,
    callback: scrollCallback,
    smoothCallback: () => {
      scrollCallback();
      setAbortScroll(false);
    },
  });

  return (
    <div
      className="flex-1 overflow-y-auto pt-0"
      ref={scrollableRef}
      onScroll={debouncedHandleScroll}
    >
      <div className="dark:gpt-dark-gray h-full">
        <div>
          <div className="flex flex-col pb-9 text-sm dark:bg-transparent">
            {(_messagesTree && _messagesTree?.length == 0) || _messagesTree === null ? (
              <div className="flex w-full items-center justify-center gap-1 bg-gray-50 p-3 text-sm text-gray-500 dark:border-gray-900/50 dark:bg-gray-800 dark:text-gray-300">
                Nothing found
              </div>
            ) : (
              <>
                {Header && Header}
                <MultiMessage
                  key={conversationId} // avoid internal state mixture
                  messageId={conversationId ?? null}
                  messagesTree={_messagesTree}
                  scrollToBottom={scrollToBottom}
                  setCurrentEditId={setCurrentEditId}
                  currentEditId={currentEditId ?? null}
                />
                <CSSTransition
                  in={showScrollButton}
                  timeout={400}
                  classNames="scroll-down"
                  unmountOnExit={false}
                  // appear
                >
                  {() =>
                    showScrollButton &&
                    !showPopover && <ScrollToBottom scrollHandler={handleSmoothToRef} />
                  }
                </CSSTransition>
              </>
            )}
            <div
              className="dark:gpt-dark-gray group h-0 w-full flex-shrink-0 dark:border-gray-900/50"
              ref={messagesEndRef}
            />
          </div>
        </div>
      </div>
    </div>
  );
}