feat: add SWR for data fetching with optimistic updates

frontend/hooks/useStats.js

@@ -0,0 +1,57 @@
+import useSWR from 'swr';
+import { getStats, getTrendStats, getCategoryStats } from '../lib/api';
+
+export function useStats(month) {
+  const key = month ? ['stats', month] : null;
+
+  const { data, error, isLoading, mutate } = useSWR(
+    key,
+    () => getStats(month),
+    {
+      revalidateOnFocus: false,
+    }
+  );
+
+  return {
+    stats: data || { income: 0, expense: 0, balance: 0 },
+    isLoading,
+    error,
+    mutate,
+  };
+}
+
+export function useTrendStats(period = 'month', month) {
+  const key = ['trend', period, month];
+
+  const { data, error, isLoading } = useSWR(
+    key,
+    () => getTrendStats(period, month),
+    {
+      revalidateOnFocus: false,
+    }
+  );
+
+  return {
+    trend: data || [],
+    isLoading,
+    error,
+  };
+}
+
+export function useCategoryStats(month, type = 'all') {
+  const key = ['categoryStats', month, type];
+
+  const { data, error, isLoading } = useSWR(
+    key,
+    () => getCategoryStats(month, type),
+    {
+      revalidateOnFocus: false,
+    }
+  );
+
+  return {
+    categories: data || [],
+    isLoading,
+    error,
+  };
+}