import { useCallback, useMemo, useRef, useState } from "react";
import useSWR from "swr";
import useSWRInfinite from "swr/infinite";
import type { AgentApiClient, AgentChatSessionSummary, AgentSessionPage } from "@/features/agent";
import { useWorkbenchSessionResources } from "./workbench-session-resources";

const TTL = 60_000;

export function useAgentHistory(client: AgentApiClient, scope: string) {
  const resources = useWorkbenchSessionResources();
  const [topicFilter, setTopicFilter] = useState<{ scope: string; id?: string }>({ scope });
  const topicId = topicFilter.scope === scope ? topicFilter.id : undefined;
  const setTopicId = useCallback((id: string | undefined) => setTopicFilter({ scope, id }), [scope]);
  const [query, setQuery] = useState("");
  const [open, setOpen] = useState(false);
  const [enabled, setEnabled] = useState(false);
  const [pendingUpdateKey, setPendingUpdateKey] = useState<string | null>(null);
  const viewKey = JSON.stringify([scope, query, topicId]);
  const view = useRef({ scope, query, topicId });
  view.current = { scope, query, topicId };
  const staged = useRef<{ key: string; page: AgentSessionPage } | null>(null);
  const [orderVersion, setOrderVersion] = useState(0);
  const key = useCallback((q: string, cursor?: string | null, topic?: string) => JSON.stringify(["history", scope, q, cursor ?? null, topic ?? null]), [scope]);
  const fetchPage = useCallback((q: string, cursor?: string | null, force = false, topic?: string) => resources.cache.load(key(q, cursor, topic),
    () => client.listSessionPage({ q, topicId: topic, includeCollaboration: true, cursor: cursor ?? undefined, signal: AbortSignal.timeout(15_000) }), TTL, { force }), [client, key, resources]);
  const recent = useSWR(["agent-recent-sessions", scope], () => fetchPage(""), {
    revalidateOnFocus: false, shouldRetryOnError: false,
  });
  const pages = useSWRInfinite<AgentSessionPage>(
    (_index, previous: AgentSessionPage | null) => !enabled || (previous && !previous.hasMore) ? null
      : ["agent-history-page", scope, query, previous?.nextCursor ?? null, topicId ?? null],
    ([, , q, cursor, topic]: [string, string, string, string | null, string | null]) => fetchPage(q, cursor, false, topic ?? undefined),
    { revalidateOnFocus: false, revalidateFirstPage: false, shouldRetryOnError: false, persistSize: false },
  );
  const sessions = useMemo(() => [...new Map((pages.data ?? (query || topicId ? [] : recent.data ? [recent.data] : []))
    .flatMap((page) => page.sessions).map((session) => [session.id, session])).values()], [pages.data, query, recent.data, topicId]);
  const refresh = useCallback(async () => {
    const page = staged.current?.key === viewKey ? staged.current.page : await fetchPage(query, null, true, topicId);
    if (view.current.scope !== scope || view.current.query !== query || view.current.topicId !== topicId) return;
    staged.current = null;
    await pages.mutate([page], { revalidate: false });
    await pages.setSize(1);
    if (!query && !topicId) await recent.mutate(page, { revalidate: false });
    setPendingUpdateKey(null);
    setOrderVersion((version) => version + 1);
  }, [fetchPage, pages, query, recent, scope, topicId, viewKey]);
  const ensure = useCallback(async () => {
    setOpen(true);
    setEnabled(true);
    const stale = (resources.cache.peek(key(query, null, topicId))?.expiresAt ?? 0) <= Date.now();
    const page = await fetchPage(query, null, false, topicId);
    if (view.current.scope !== scope || view.current.query !== query || view.current.topicId !== topicId) return;
    // Opening a window never invalidates a fresh page or hides existing content.
    if (!pages.data?.length) await pages.mutate([page], { revalidate: false });
    else if (stale) { staged.current = { key: viewKey, page }; setPendingUpdateKey(viewKey); }
    if (!query && !topicId) await recent.mutate(page, { revalidate: false });
  }, [fetchPage, key, pages, query, recent, resources, scope, topicId, viewKey]);
  const update = useCallback(async (change: (sessions: AgentChatSessionSummary[]) => AgentChatSessionSummary[]) => {
    resources.cache.updateMatching<AgentSessionPage>((cacheKey) => {
      if (!cacheKey.startsWith('["history",')) return false;
      const value = JSON.parse(cacheKey) as unknown[];
      return value[0] === "history" && value[1] === scope;
    }, (page) => ({ ...page, sessions: change(page.sessions) }));
    const recentPage = resources.cache.peek<AgentSessionPage>(key(""))?.value;
    if (recentPage) {
      const next = { ...recentPage, sessions: change(recentPage.sessions) };
      resources.cache.set(key(""), next, TTL);
      if (view.current.scope === scope) await recent.mutate(next, { revalidate: false });
    }
    if (view.current.scope !== scope || view.current.query !== query || view.current.topicId !== topicId) return;
    await pages.mutate((current) => current?.map((page) => ({ ...page, sessions: change(page.sessions) })), { revalidate: false });
    // Search and later pages can now have different membership/order. Retain what is being read.
    setPendingUpdateKey(viewKey);
  }, [key, pages, query, recent, resources, scope, topicId, viewKey]);
  return {
    topicId, setTopicId, sessions, recentSessions: recent.data?.sessions ?? [], query, setQuery,
    loading: (open ? pages.isLoading : recent.isLoading), error: pages.error ?? recent.error,
    loadingMore: pages.isValidating, hasMore: pages.data?.at(-1)?.hasMore ?? recent.data?.hasMore ?? false,
    loadMore: () => pages.setSize(pages.size + 1), refresh, ensure, update,
    pendingUpdate: pendingUpdateKey === viewKey, isOpen: open, orderVersion, close: () => setOpen(false),
  };
}