import { useCallback, useEffect, useRef, useState } from "react";
import { api, shortId, uploadAttachments } from "../api/client";
import { paths } from "../api/paths";
import type { DispatchBody, Task } from "../api/types";

export const TASK_PAGE_SIZE = 20;

// Task list, server-side paginated. The old hook fetched every task
// in the project and filtered client-side; at scale that made every
// 10 s refresh a full-table fetch and a full render. Now each fetch
// asks for one page (newest first) with the current filters, and the
// server returns total + status_counts for that filter set. tasks
// here is ONLY the current page; taskTotal / status counts are the
// project-wide / filtered totals from the server, never page-only
// numbers (DataCards must not present a page as the whole project).
// Page state lives in a ref as well as state, because refreshTasks
// is called from auto-refresh and from other hooks that must not
// reset the page, while filter/project changes reset it to page 1.
export function useTaskList() {
  const [tasks, setTasks] = useState<Task[]>([]);
  const [taskError, setTaskError] = useState("");
  const [statusFilter, setStatusFilter] = useState("");
  const [executorFilter, setExecutorFilter] = useState("");
  const [searchText, setSearchText] = useState("");
  const [page, setPageState] = useState(0);
  const [taskTotal, setTaskTotal] = useState(0);
  const [taskStatusCounts, setTaskStatusCounts] = useState<Record<string, number>>({});
  const pageRef = useRef(0);
  const filterRef = useRef({ status: "", executor: "", q: "" });
  filterRef.current = { status: statusFilter, executor: executorFilter, q: searchText };
  const lastProjectRef = useRef("");

  const refreshTasks = useCallback(async (pid?: string, currentPid?: string, pageOverride?: number) => {
    const id = pid !== undefined ? pid : currentPid;
    if (!id) { setTasks([]); setTaskTotal(0); setTaskStatusCounts({}); return; }
    lastProjectRef.current = id;
    const p = pageOverride !== undefined ? pageOverride : pageRef.current;
    const f = filterRef.current;
    try {
      const d = await api<{ tasks: Task[]; total?: number; status_counts?: Record<string, number> }>(
        paths.tasksPage(id, TASK_PAGE_SIZE, p * TASK_PAGE_SIZE, f.status, f.executor, f.q));
      setTasks(d.tasks || []);
      setTaskTotal(d.total ?? (d.tasks || []).length);
      setTaskStatusCounts(d.status_counts || {});
      setTaskError("");
    } catch (e: any) { setTaskError("加载失败：" + e.message); }
  }, []);

  const setPage = useCallback((p: number) => {
    const next = Math.max(0, p);
    pageRef.current = next;
    setPageState(next);
  }, []);

  const goToPage = useCallback((p: number) => {
    setPage(p);
    void refreshTasks(lastProjectRef.current || undefined, undefined, p);
  }, [refreshTasks, setPage]);

  // Filter changes refetch page 1 (debounced, so typing a search
  // query does not fire one request per keystroke). Project changes
  // do not fire this effect (filters are unchanged), so the store's
  // explicit refreshTasksFirstPage remains the only fetch there.
  useEffect(() => {
    if (!lastProjectRef.current) return;
    const t = setTimeout(() => { void refreshTasks(lastProjectRef.current, undefined, 0); }, 300);
    return () => clearTimeout(t);
    // eslint-disable-next-line react-hooks/exhaustive-deps
  }, [statusFilter, executorFilter, searchText]);

  // Filter/project changes reset to page 1: the old page may not
  // exist under the new filter, and staying on it would show an
  // empty page with a misleading "共 N 个" count.
  const setStatusFilterPage = useCallback((v: string) => { setStatusFilter(v); setPage(0); }, [setPage]);
  const setExecutorFilterPage = useCallback((v: string) => { setExecutorFilter(v); setPage(0); }, [setPage]);
  const setSearchTextPage = useCallback((v: string) => { setSearchText(v); setPage(0); }, [setPage]);
  const refreshTasksFirstPage = useCallback(async (pid?: string) => {
    setPage(0);
    await refreshTasks(pid, undefined, 0);
  }, [refreshTasks, setPage]);

  const totalPages = Math.max(1, Math.ceil(taskTotal / TASK_PAGE_SIZE));
  const taskCountText = taskTotal === 0
    ? "共 0 个任务"
    : "共 " + taskTotal + " 个任务，第 " + (page + 1) + " / " + totalPages + " 页";
  // Back-compat for the list section: it renders the current page
  // as-is (server already ordered newest first).
  const filteredTasks = tasks;

  const dispatch = useCallback(async (body: DispatchBody, atts: Array<{ path: string; file: File }>): Promise<string> => {
    const payload: DispatchBody = { ...body };
    if (atts.length) {
      payload.upload_id = await uploadAttachments(atts);
    }
    const t = await api<Task>(paths.tasksCreate, "POST", payload);
    return "任务已建：" + shortId(t.id);
  }, []);

  return {
    tasks, taskError, statusFilter, setStatusFilter: setStatusFilterPage,
    executorFilter, setExecutorFilter: setExecutorFilterPage,
    searchText, setSearchText: setSearchTextPage,
    filteredTasks, taskCountText, refreshTasks, refreshTasksFirstPage,
    page, totalPages, taskTotal, taskStatusCounts, goToPage, dispatch,
  };
}