import React, { useCallback, useEffect, useRef, useState } from "react";
import { Virtuoso } from "react-virtuoso";
import { renderMessage } from "./renderMessage";
import "./chat-message-list.styles.scss";

export default function ChatMessageListComponent({ messages }) {
  const virtuosoRef = useRef(null);
  const [atBottom, setAtBottom] = useState(true);
  const loadedImagesRef = useRef(0);

  const handleScrollStateChange = (isAtBottom) => {
    setAtBottom(isAtBottom);
  };

  const resetImageLoadState = () => {
    loadedImagesRef.current = 0;
  };

  const preloadImages = useCallback((imagePaths, onComplete) => {
    resetImageLoadState();

    if (imagePaths.length === 0) {
      onComplete();
      return;
    }

    imagePaths.forEach((url) => {
      const img = new Image();
      img.src = url;
      img.onload = img.onerror = () => {
        loadedImagesRef.current += 1;
        if (loadedImagesRef.current === imagePaths.length) {
          onComplete();
        }
      };
    });
  }, []);

  // Ensure all images are loaded on initial render
  useEffect(() => {
    const imagePaths = messages
      .filter((message) => message.image && message.image_path?.length > 0)
      .flatMap((message) => message.image_path);

    preloadImages(imagePaths, () => {
      if (virtuosoRef.current) {
        virtuosoRef.current.scrollToIndex({
          index: messages.length - 1,
          align: "end",
          behavior: "auto"
        });
      }
    });
  }, [messages, preloadImages]);

  // Handle scrolling when new messages are added
  useEffect(() => {
    if (!atBottom) return;

    const latestMessage = messages[messages.length - 1];
    const imagePaths = latestMessage?.image_path || [];

    preloadImages(imagePaths, () => {
      if (virtuosoRef.current) {
        virtuosoRef.current.scrollToIndex({
          index: messages.length - 1,
          align: "end",
          behavior: "smooth"
        });
      }
    });
  }, [messages, atBottom, preloadImages]);

  return (
    <div className="chat">
      <Virtuoso
        ref={virtuosoRef}
        data={messages}
        overscan={!!messages.reduce((acc, message) => acc + (message.image_path?.length || 0), 0) ? messages.length : 0}
        itemContent={(index) => renderMessage(messages, index)}
        followOutput={(isAtBottom) => handleScrollStateChange(isAtBottom)}
        initialTopMostItemIndex={messages.length - 1}
        style={{ height: "100%", width: "100%" }}
      />
    </div>
  );
}
