/** Thread-page data fetcher: refs from Constellation, hydrated page replies,
 *  plus pagination + scroll-to-reply helpers. Optimistic mutations are in
 *  Thread.tsx and update the same query caches via setQueryData. */

import { useEffect } from "react";
import { useSearchParams } from "react-router-dom";
import { useSuspenseQuery } from "@tanstack/react-query";
import { threadPageQuery, threadRefsQuery } from "../lib/queries";
import { parseAtUri } from "../lib/util";
import {
  REPLIES_PER_PAGE,
  clampPage,
  pageForRkey,
  pageForReply,
  rkeyFromHash,
} from "../lib/replies";

export function useThreadReplies(threadUri: string) {
  const [params, setParams] = useSearchParams();

  const { data: refs } = useSuspenseQuery(threadRefsQuery(threadUri));
  const totalPages = Math.max(1, Math.ceil(refs.length / REPLIES_PER_PAGE));

  // --- Page derived from URL, clamped to the available range ---

  const requestedPage = parseInt(params.get("page") ?? "1", 10);
  const replyParam = params.get("reply");
  const hashRkey = rkeyFromHash();
  const initialPage =
    pageForRkey(refs, hashRkey) ??
    pageForReply(refs, replyParam) ??
    requestedPage;
  const page = clampPage(initialPage, refs.length);

  const pageStart = (page - 1) * REPLIES_PER_PAGE;
  const pageRefs = refs.slice(pageStart, pageStart + REPLIES_PER_PAGE);

  const { data: pageData } = useSuspenseQuery(
    threadPageQuery(threadUri, page, pageRefs),
  );
  const { replies, parentReplies } = pageData;

  // --- Keep URL in sync when the derived page differs from what's in it ---

  useEffect(() => {
    const fromUrl = parseInt(params.get("page") ?? "1", 10);
    if (fromUrl === page) return;
    setParams((prev) => writePageParam(prev, page), { replace: true });
    // eslint-disable-next-line react-hooks/exhaustive-deps -- params identity churns
  }, [page]);

  // --- Navigation helpers ---

  function setPage(next: number) {
    const clamped = clampPage(next, refs.length);
    setParams((prev) => writePageParam(prev, clamped));
  }

  function scrollToReply(uri: string) {
    const { rkey } = parseAtUri(uri);
    const onScreen = document.getElementById(`reply-${rkey}`);
    if (onScreen) {
      onScreen.scrollIntoView({ behavior: "smooth" });
      return;
    }
    const targetPage = pageForRkey(refs, rkey);
    if (targetPage === null) return;
    setParams((prev) => {
      const next = writePageParam(prev, targetPage);
      next.set("reply", uri);
      return next;
    });
  }

  return {
    page,
    setPage,
    totalPages,
    refs,
    replies,
    parentReplies,
    scrollToReply,
  };
}

function writePageParam(prev: URLSearchParams, page: number) {
  const next = new URLSearchParams(prev);
  if (page === 1) next.delete("page");
  else next.set("page", String(page));
  next.delete("reply");
  return next;
}