refactor: split useReports into per-domain hooks + URL-bookmarked period (#70)

- New useReportsPeriod hook reads/writes period via ?from=&to=&period= URL params,
  default civil year, pure resolver exported for tests
- New per-domain hooks: useHighlights, useTrends, useCompare, useCategoryZoom
  (stubs wired to useReportsPeriod, to be fleshed out in #71-#74)
- Rewire legacy useReports to consume useReportsPeriod; keep backward-compat
  state shape (period/customDateFrom/customDateTo) so /reports tabs keep working
- Mark useReports @deprecated pending removal in #76
- Tests: 7 new cases covering resolveReportsPeriod defaults, bookmarks,
  invalid inputs, preset resolution

Fixes #70

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/hooks/useCategoryZoom.ts

@@ -0,0 +1,53 @@
+import { useReducer, useCallback } from "react";
+import { useReportsPeriod } from "./useReportsPeriod";
+
+interface State {
+  zoomedCategoryId: number | null;
+  rollupChildren: boolean;
+  isLoading: boolean;
+  error: string | null;
+}
+
+type Action =
+  | { type: "SET_CATEGORY"; payload: number | null }
+  | { type: "TOGGLE_ROLLUP"; payload: boolean }
+  | { type: "SET_LOADING"; payload: boolean }
+  | { type: "SET_ERROR"; payload: string };
+
+const initialState: State = {
+  zoomedCategoryId: null,
+  rollupChildren: true,
+  isLoading: false,
+  error: null,
+};
+
+function reducer(state: State, action: Action): State {
+  switch (action.type) {
+    case "SET_CATEGORY":
+      return { ...state, zoomedCategoryId: action.payload };
+    case "TOGGLE_ROLLUP":
+      return { ...state, rollupChildren: action.payload };
+    case "SET_LOADING":
+      return { ...state, isLoading: action.payload };
+    case "SET_ERROR":
+      return { ...state, error: action.payload, isLoading: false };
+    default:
+      return state;
+  }
+}
+
+export function useCategoryZoom() {
+  const { from, to } = useReportsPeriod();
+  const [state, dispatch] = useReducer(reducer, initialState);
+
+  const setCategory = useCallback((id: number | null) => {
+    dispatch({ type: "SET_CATEGORY", payload: id });
+  }, []);
+
+  const setRollupChildren = useCallback((flag: boolean) => {
+    dispatch({ type: "TOGGLE_ROLLUP", payload: flag });
+  }, []);
+
+  // Real fetch lives in Issue #74 (getCategoryZoom with recursive CTE).
+  return { ...state, setCategory, setRollupChildren, from, to };
+}

src/hooks/useCompare.ts

@@ -0,0 +1,46 @@
+import { useReducer, useCallback } from "react";
+import { useReportsPeriod } from "./useReportsPeriod";
+
+export type CompareMode = "mom" | "yoy" | "budget";
+
+interface State {
+  mode: CompareMode;
+  isLoading: boolean;
+  error: string | null;
+}
+
+type Action =
+  | { type: "SET_MODE"; payload: CompareMode }
+  | { type: "SET_LOADING"; payload: boolean }
+  | { type: "SET_ERROR"; payload: string };
+
+const initialState: State = {
+  mode: "mom",
+  isLoading: false,
+  error: null,
+};
+
+function reducer(state: State, action: Action): State {
+  switch (action.type) {
+    case "SET_MODE":
+      return { ...state, mode: action.payload };
+    case "SET_LOADING":
+      return { ...state, isLoading: action.payload };
+    case "SET_ERROR":
+      return { ...state, error: action.payload, isLoading: false };
+    default:
+      return state;
+  }
+}
+
+export function useCompare() {
+  const { from, to } = useReportsPeriod();
+  const [state, dispatch] = useReducer(reducer, initialState);
+
+  const setMode = useCallback((m: CompareMode) => {
+    dispatch({ type: "SET_MODE", payload: m });
+  }, []);
+
+  // Issue #73 will fetch via reportService.getCompareMonthOverMonth / ...YearOverYear
+  return { ...state, setMode, from, to };
+}

src/hooks/useHighlights.ts

@@ -0,0 +1,64 @@
+import { useReducer, useEffect, useRef, useCallback } from "react";
+import { useReportsPeriod } from "./useReportsPeriod";
+
+// Stub highlights shape — to be fleshed out in Issue #71.
+export interface HighlightsData {
+  netBalanceCurrent: number;
+  netBalanceYtd: number;
+}
+
+interface State {
+  data: HighlightsData | null;
+  isLoading: boolean;
+  error: string | null;
+}
+
+type Action =
+  | { type: "SET_LOADING"; payload: boolean }
+  | { type: "SET_DATA"; payload: HighlightsData }
+  | { type: "SET_ERROR"; payload: string };
+
+const initialState: State = {
+  data: null,
+  isLoading: false,
+  error: null,
+};
+
+function reducer(state: State, action: Action): State {
+  switch (action.type) {
+    case "SET_LOADING":
+      return { ...state, isLoading: action.payload };
+    case "SET_DATA":
+      return { ...state, data: action.payload, isLoading: false, error: null };
+    case "SET_ERROR":
+      return { ...state, error: action.payload, isLoading: false };
+    default:
+      return state;
+  }
+}
+
+export function useHighlights() {
+  const { from, to } = useReportsPeriod();
+  const [state, dispatch] = useReducer(reducer, initialState);
+  const fetchIdRef = useRef(0);
+
+  const fetch = useCallback(async () => {
+    const id = ++fetchIdRef.current;
+    dispatch({ type: "SET_LOADING", payload: true });
+    try {
+      // Real implementation in Issue #71 will call reportService.getHighlights
+      const stub: HighlightsData = { netBalanceCurrent: 0, netBalanceYtd: 0 };
+      if (id !== fetchIdRef.current) return;
+      dispatch({ type: "SET_DATA", payload: stub });
+    } catch (e) {
+      if (id !== fetchIdRef.current) return;
+      dispatch({ type: "SET_ERROR", payload: e instanceof Error ? e.message : String(e) });
+    }
+  }, []);
+
+  useEffect(() => {
+    fetch();
+  }, [fetch, from, to]);
+
+  return { ...state, from, to };
+}

src/hooks/useReports.ts

@@ -1,7 +1,13 @@
+/**
+ * @deprecated — legacy monolithic reports hook. Kept during the refonte
+ * (Issues #70 → #76) so the pre-existing 4 tabs on `/reports` keep working
+ * while the new per-domain hooks (useHighlights / useTrends / useCompare /
+ * useCategoryZoom) are wired up. Will be removed in Issue #76 once every
+ * report migrates to its own route.
+ */
 import { useReducer, useCallback, useEffect, useRef } from "react";
 import type {
   ReportTab,
-  DashboardPeriod,
   MonthlyTrendItem,
   CategoryBreakdownItem,
   CategoryOverTimeData,
@@ -10,15 +16,12 @@ import type {
 import { getMonthlyTrends, getCategoryOverTime } from "../services/reportService";
 import { getExpensesByCategory } from "../services/dashboardService";
 import { getBudgetVsActualData } from "../services/budgetService";
-import { computeDateRange } from "../utils/dateRange";
+import { useReportsPeriod } from "./useReportsPeriod";
 
 export type CategoryTypeFilter = "expense" | "income" | "transfer" | null;
 
 interface ReportsState {
   tab: ReportTab;
-  period: DashboardPeriod;
-  customDateFrom: string;
-  customDateTo: string;
   sourceId: number | null;
   categoryType: CategoryTypeFilter;
   monthlyTrends: MonthlyTrendItem[];
@@ -33,7 +36,6 @@ interface ReportsState {
 
 type ReportsAction =
   | { type: "SET_TAB"; payload: ReportTab }
-  | { type: "SET_PERIOD"; payload: DashboardPeriod }
   | { type: "SET_LOADING"; payload: boolean }
   | { type: "SET_ERROR"; payload: string | null }
   | { type: "SET_MONTHLY_TRENDS"; payload: MonthlyTrendItem[] }
@@ -41,19 +43,13 @@ type ReportsAction =
   | { type: "SET_CATEGORY_OVER_TIME"; payload: CategoryOverTimeData }
   | { type: "SET_BUDGET_MONTH"; payload: { year: number; month: number } }
   | { type: "SET_BUDGET_VS_ACTUAL"; payload: BudgetVsActualRow[] }
-  | { type: "SET_CUSTOM_DATES"; payload: { dateFrom: string; dateTo: string } }
   | { type: "SET_SOURCE_ID"; payload: number | null }
   | { type: "SET_CATEGORY_TYPE"; payload: CategoryTypeFilter };
 
 const now = new Date();
-const todayStr = `${now.getFullYear()}-${String(now.getMonth() + 1).padStart(2, "0")}-${String(now.getDate()).padStart(2, "0")}`;
-const monthStartStr = `${now.getFullYear()}-${String(now.getMonth() + 1).padStart(2, "0")}-01`;
 
 const initialState: ReportsState = {
   tab: "trends",
-  period: "6months",
-  customDateFrom: monthStartStr,
-  customDateTo: todayStr,
   sourceId: null,
   categoryType: "expense",
   monthlyTrends: [],
@@ -70,8 +66,6 @@ function reducer(state: ReportsState, action: ReportsAction): ReportsState {
   switch (action.type) {
     case "SET_TAB":
       return { ...state, tab: action.payload };
-    case "SET_PERIOD":
-      return { ...state, period: action.payload };
     case "SET_LOADING":
       return { ...state, isLoading: action.payload };
     case "SET_ERROR":
@@ -86,8 +80,6 @@ function reducer(state: ReportsState, action: ReportsAction): ReportsState {
       return { ...state, budgetYear: action.payload.year, budgetMonth: action.payload.month };
     case "SET_BUDGET_VS_ACTUAL":
       return { ...state, budgetVsActual: action.payload, isLoading: false };
-    case "SET_CUSTOM_DATES":
-      return { ...state, period: "custom" as DashboardPeriod, customDateFrom: action.payload.dateFrom, customDateTo: action.payload.dateTo };
     case "SET_SOURCE_ID":
       return { ...state, sourceId: action.payload };
     case "SET_CATEGORY_TYPE":
@@ -97,83 +89,84 @@ function reducer(state: ReportsState, action: ReportsAction): ReportsState {
   }
 }
 
+/** @deprecated — see module-level comment. */
 export function useReports() {
-  const [state, dispatch] = useReducer(reducer, initialState);
+  const { from, to, period, setPeriod, setCustomDates } = useReportsPeriod();
+  const [innerState, dispatch] = useReducer(reducer, initialState);
   const fetchIdRef = useRef(0);
 
-  const fetchData = useCallback(async (
-    tab: ReportTab,
-    period: DashboardPeriod,
-    budgetYear: number,
-    budgetMonth: number,
-    customFrom?: string,
-    customTo?: string,
-    srcId?: number | null,
-    catType?: CategoryTypeFilter,
-  ) => {
-    const fetchId = ++fetchIdRef.current;
-    dispatch({ type: "SET_LOADING", payload: true });
-    dispatch({ type: "SET_ERROR", payload: null });
+  const fetchData = useCallback(
+    async (
+      tab: ReportTab,
+      dateFrom: string,
+      dateTo: string,
+      budgetYear: number,
+      budgetMonth: number,
+      srcId: number | null,
+      catType: CategoryTypeFilter,
+    ) => {
+      const fetchId = ++fetchIdRef.current;
+      dispatch({ type: "SET_LOADING", payload: true });
+      dispatch({ type: "SET_ERROR", payload: null });
 
-    try {
-      switch (tab) {
-        case "trends": {
-          const { dateFrom, dateTo } = computeDateRange(period, customFrom, customTo);
-          const data = await getMonthlyTrends(dateFrom, dateTo, srcId ?? undefined);
-          if (fetchId !== fetchIdRef.current) return;
-          dispatch({ type: "SET_MONTHLY_TRENDS", payload: data });
-          break;
-        }
-        case "byCategory": {
-          const { dateFrom, dateTo } = computeDateRange(period, customFrom, customTo);
-          const data = await getExpensesByCategory(dateFrom, dateTo, srcId ?? undefined);
-          if (fetchId !== fetchIdRef.current) return;
-          dispatch({ type: "SET_CATEGORY_SPENDING", payload: data });
-          break;
-        }
-        case "overTime": {
-          const { dateFrom, dateTo } = computeDateRange(period, customFrom, customTo);
-          const data = await getCategoryOverTime(dateFrom, dateTo, undefined, srcId ?? undefined, catType ?? undefined);
-          if (fetchId !== fetchIdRef.current) return;
-          dispatch({ type: "SET_CATEGORY_OVER_TIME", payload: data });
-          break;
-        }
-        case "budgetVsActual": {
-          const data = await getBudgetVsActualData(budgetYear, budgetMonth);
-          if (fetchId !== fetchIdRef.current) return;
-          dispatch({ type: "SET_BUDGET_VS_ACTUAL", payload: data });
-          break;
+      try {
+        switch (tab) {
+          case "trends": {
+            const data = await getMonthlyTrends(dateFrom, dateTo, srcId ?? undefined);
+            if (fetchId !== fetchIdRef.current) return;
+            dispatch({ type: "SET_MONTHLY_TRENDS", payload: data });
+            break;
+          }
+          case "byCategory": {
+            const data = await getExpensesByCategory(dateFrom, dateTo, srcId ?? undefined);
+            if (fetchId !== fetchIdRef.current) return;
+            dispatch({ type: "SET_CATEGORY_SPENDING", payload: data });
+            break;
+          }
+          case "overTime": {
+            const data = await getCategoryOverTime(dateFrom, dateTo, undefined, srcId ?? undefined, catType ?? undefined);
+            if (fetchId !== fetchIdRef.current) return;
+            dispatch({ type: "SET_CATEGORY_OVER_TIME", payload: data });
+            break;
+          }
+          case "budgetVsActual": {
+            const data = await getBudgetVsActualData(budgetYear, budgetMonth);
+            if (fetchId !== fetchIdRef.current) return;
+            dispatch({ type: "SET_BUDGET_VS_ACTUAL", payload: data });
+            break;
+          }
         }
+      } catch (e) {
+        if (fetchId !== fetchIdRef.current) return;
+        dispatch({
+          type: "SET_ERROR",
+          payload: e instanceof Error ? e.message : String(e),
+        });
       }
-    } catch (e) {
-      if (fetchId !== fetchIdRef.current) return;
-      dispatch({
-        type: "SET_ERROR",
-        payload: e instanceof Error ? e.message : String(e),
-      });
-    }
-  }, []);
+    },
+    [],
+  );
 
   useEffect(() => {
-    fetchData(state.tab, state.period, state.budgetYear, state.budgetMonth, state.customDateFrom, state.customDateTo, state.sourceId, state.categoryType);
-  }, [state.tab, state.period, state.budgetYear, state.budgetMonth, state.customDateFrom, state.customDateTo, state.sourceId, state.categoryType, fetchData]);
+    fetchData(
+      innerState.tab,
+      from,
+      to,
+      innerState.budgetYear,
+      innerState.budgetMonth,
+      innerState.sourceId,
+      innerState.categoryType,
+    );
+  }, [fetchData, innerState.tab, from, to, innerState.budgetYear, innerState.budgetMonth, innerState.sourceId, innerState.categoryType]);
 
   const setTab = useCallback((tab: ReportTab) => {
     dispatch({ type: "SET_TAB", payload: tab });
   }, []);
 
-  const setPeriod = useCallback((period: DashboardPeriod) => {
-    dispatch({ type: "SET_PERIOD", payload: period });
-  }, []);
-
   const setBudgetMonth = useCallback((year: number, month: number) => {
     dispatch({ type: "SET_BUDGET_MONTH", payload: { year, month } });
   }, []);
 
-  const setCustomDates = useCallback((dateFrom: string, dateTo: string) => {
-    dispatch({ type: "SET_CUSTOM_DATES", payload: { dateFrom, dateTo } });
-  }, []);
-
   const setSourceId = useCallback((id: number | null) => {
     dispatch({ type: "SET_SOURCE_ID", payload: id });
   }, []);
@@ -182,5 +175,12 @@ export function useReports() {
     dispatch({ type: "SET_CATEGORY_TYPE", payload: catType });
   }, []);
 
+  const state = {
+    ...innerState,
+    period,
+    customDateFrom: from,
+    customDateTo: to,
+  };
+
   return { state, setTab, setPeriod, setCustomDates, setBudgetMonth, setSourceId, setCategoryType };
 }

src/hooks/useReportsPeriod.test.ts

@@ -0,0 +1,53 @@
+import { describe, it, expect } from "vitest";
+import { resolveReportsPeriod } from "./useReportsPeriod";
+
+describe("resolveReportsPeriod", () => {
+  const fixedToday = new Date("2026-04-14T12:00:00Z");
+
+  it("defaults to current civil year when no URL params are set", () => {
+    const result = resolveReportsPeriod(null, null, null, fixedToday);
+    expect(result.from).toBe("2026-01-01");
+    expect(result.to).toBe("2026-12-31");
+    expect(result.period).toBe("custom");
+  });
+
+  it("restores state from bookmarked from/to params", () => {
+    const result = resolveReportsPeriod("2025-03-01", "2025-06-30", null, fixedToday);
+    expect(result.from).toBe("2025-03-01");
+    expect(result.to).toBe("2025-06-30");
+    expect(result.period).toBe("custom");
+  });
+
+  it("keeps period=yearly alongside explicit from/to", () => {
+    const result = resolveReportsPeriod("2024-01-01", "2024-12-31", "year", fixedToday);
+    expect(result.period).toBe("year");
+  });
+
+  it("ignores malformed dates and falls back to the civil year", () => {
+    const result = resolveReportsPeriod("not-a-date", "also-not", null, fixedToday);
+    expect(result.from).toBe("2026-01-01");
+    expect(result.to).toBe("2026-12-31");
+    expect(result.period).toBe("custom");
+  });
+
+  it("resolves preset period values without from/to", () => {
+    const result = resolveReportsPeriod(null, null, "6months", fixedToday);
+    expect(result.period).toBe("6months");
+    expect(result.from).toBeTruthy();
+    expect(result.to).toBeTruthy();
+  });
+
+  it("rejects an invalid period string and falls back to civil year custom", () => {
+    const result = resolveReportsPeriod(null, null, "bogus", fixedToday);
+    expect(result.period).toBe("custom");
+    expect(result.from).toBe("2026-01-01");
+  });
+
+  it("treats `all` as a preset with empty range (service handles the clauses)", () => {
+    const result = resolveReportsPeriod(null, null, "all", fixedToday);
+    expect(result.period).toBe("all");
+    // Fallback civil year when computeDateRange returns empty
+    expect(result.from).toBe("2026-01-01");
+    expect(result.to).toBe("2026-12-31");
+  });
+});

src/hooks/useReportsPeriod.ts

@@ -0,0 +1,119 @@
+import { useCallback, useMemo } from "react";
+import { useSearchParams } from "react-router-dom";
+import type { DashboardPeriod } from "../shared/types";
+import { computeDateRange } from "../utils/dateRange";
+
+const VALID_PERIODS: readonly DashboardPeriod[] = [
+  "month",
+  "3months",
+  "6months",
+  "year",
+  "12months",
+  "all",
+  "custom",
+];
+
+function isValidPeriod(p: string | null): p is DashboardPeriod {
+  return p !== null && (VALID_PERIODS as readonly string[]).includes(p);
+}
+
+function isValidIsoDate(s: string | null): s is string {
+  return !!s && /^\d{4}-\d{2}-\d{2}$/.test(s);
+}
+
+function currentYearRange(today: Date = new Date()): { from: string; to: string } {
+  const year = today.getFullYear();
+  return { from: `${year}-01-01`, to: `${year}-12-31` };
+}
+
+/**
+ * Pure resolver used by the hook and unit tests. Exposed to keep the core
+ * logic hookless and testable without rendering a router.
+ */
+export function resolveReportsPeriod(
+  rawFrom: string | null,
+  rawTo: string | null,
+  rawPeriod: string | null,
+  today: Date = new Date(),
+): { from: string; to: string; period: DashboardPeriod } {
+  if (isValidIsoDate(rawFrom) && isValidIsoDate(rawTo)) {
+    const p = isValidPeriod(rawPeriod) ? rawPeriod : "custom";
+    return { from: rawFrom, to: rawTo, period: p };
+  }
+  if (isValidPeriod(rawPeriod) && rawPeriod !== "custom") {
+    const range = computeDateRange(rawPeriod);
+    const { from: defaultFrom, to: defaultTo } = currentYearRange(today);
+    return {
+      from: range.dateFrom ?? defaultFrom,
+      to: range.dateTo ?? defaultTo,
+      period: rawPeriod,
+    };
+  }
+  const { from, to } = currentYearRange(today);
+  return { from, to, period: "custom" };
+}
+
+export interface UseReportsPeriodResult {
+  from: string;
+  to: string;
+  period: DashboardPeriod;
+  setPeriod: (period: DashboardPeriod) => void;
+  setCustomDates: (from: string, to: string) => void;
+}
+
+/**
+ * Reads/writes the active reporting period via the URL query string so it is
+ * bookmarkable and shared across the four report sub-routes.
+ *
+ * Defaults to the current civil year (Jan 1 → Dec 31).
+ */
+export function useReportsPeriod(): UseReportsPeriodResult {
+  const [searchParams, setSearchParams] = useSearchParams();
+
+  const rawPeriod = searchParams.get("period");
+  const rawFrom = searchParams.get("from");
+  const rawTo = searchParams.get("to");
+
+  const { from, to, period } = useMemo(
+    () => resolveReportsPeriod(rawFrom, rawTo, rawPeriod),
+    [rawPeriod, rawFrom, rawTo],
+  );
+
+  const setPeriod = useCallback(
+    (next: DashboardPeriod) => {
+      setSearchParams(
+        (prev) => {
+          const params = new URLSearchParams(prev);
+          if (next === "custom") {
+            params.set("period", "custom");
+          } else {
+            params.set("period", next);
+            params.delete("from");
+            params.delete("to");
+          }
+          return params;
+        },
+        { replace: true },
+      );
+    },
+    [setSearchParams],
+  );
+
+  const setCustomDates = useCallback(
+    (nextFrom: string, nextTo: string) => {
+      setSearchParams(
+        (prev) => {
+          const params = new URLSearchParams(prev);
+          params.set("period", "custom");
+          params.set("from", nextFrom);
+          params.set("to", nextTo);
+          return params;
+        },
+        { replace: true },
+      );
+    },
+    [setSearchParams],
+  );
+
+  return { from, to, period, setPeriod, setCustomDates };
+}

src/hooks/useTrends.ts

@@ -0,0 +1,81 @@
+import { useReducer, useEffect, useRef, useCallback } from "react";
+import type { MonthlyTrendItem, CategoryOverTimeData } from "../shared/types";
+import { getMonthlyTrends, getCategoryOverTime } from "../services/reportService";
+import { useReportsPeriod } from "./useReportsPeriod";
+
+export type TrendsSubView = "global" | "byCategory";
+
+interface State {
+  subView: TrendsSubView;
+  monthlyTrends: MonthlyTrendItem[];
+  categoryOverTime: CategoryOverTimeData;
+  isLoading: boolean;
+  error: string | null;
+}
+
+type Action =
+  | { type: "SET_SUBVIEW"; payload: TrendsSubView }
+  | { type: "SET_LOADING"; payload: boolean }
+  | { type: "SET_TRENDS"; payload: MonthlyTrendItem[] }
+  | { type: "SET_CATEGORY_OVER_TIME"; payload: CategoryOverTimeData }
+  | { type: "SET_ERROR"; payload: string };
+
+const initialState: State = {
+  subView: "global",
+  monthlyTrends: [],
+  categoryOverTime: { categories: [], data: [], colors: {}, categoryIds: {} },
+  isLoading: false,
+  error: null,
+};
+
+function reducer(state: State, action: Action): State {
+  switch (action.type) {
+    case "SET_SUBVIEW":
+      return { ...state, subView: action.payload };
+    case "SET_LOADING":
+      return { ...state, isLoading: action.payload };
+    case "SET_TRENDS":
+      return { ...state, monthlyTrends: action.payload, isLoading: false, error: null };
+    case "SET_CATEGORY_OVER_TIME":
+      return { ...state, categoryOverTime: action.payload, isLoading: false, error: null };
+    case "SET_ERROR":
+      return { ...state, error: action.payload, isLoading: false };
+    default:
+      return state;
+  }
+}
+
+export function useTrends() {
+  const { from, to } = useReportsPeriod();
+  const [state, dispatch] = useReducer(reducer, initialState);
+  const fetchIdRef = useRef(0);
+
+  const fetch = useCallback(async (subView: TrendsSubView, dateFrom: string, dateTo: string) => {
+    const id = ++fetchIdRef.current;
+    dispatch({ type: "SET_LOADING", payload: true });
+    try {
+      if (subView === "global") {
+        const data = await getMonthlyTrends(dateFrom, dateTo);
+        if (id !== fetchIdRef.current) return;
+        dispatch({ type: "SET_TRENDS", payload: data });
+      } else {
+        const data = await getCategoryOverTime(dateFrom, dateTo);
+        if (id !== fetchIdRef.current) return;
+        dispatch({ type: "SET_CATEGORY_OVER_TIME", payload: data });
+      }
+    } catch (e) {
+      if (id !== fetchIdRef.current) return;
+      dispatch({ type: "SET_ERROR", payload: e instanceof Error ? e.message : String(e) });
+    }
+  }, []);
+
+  useEffect(() => {
+    fetch(state.subView, from, to);
+  }, [fetch, state.subView, from, to]);
+
+  const setSubView = useCallback((sv: TrendsSubView) => {
+    dispatch({ type: "SET_SUBVIEW", payload: sv });
+  }, []);
+
+  return { ...state, setSubView, from, to };
+}