perf(storage): optimize historical rates batch fetching

Refactored `fetchHistoricalRatesBatch` to use a single range-based batch API query to Frankfurter (`minDate..maxDate`), replacing the N+1 `Promise.all` logic for web environment fallback. Also fixed handling of weekend boundary limits by querying an extra 7 days prior to the first requested date to resolve closest previous available rates.

Co-authored-by: Horizontal42 <75383519+Horizontal42@users.noreply.github.com>

src/storage.test.ts

@@ -1,6 +1,6 @@
 import { logger } from "./logger";
 import { describe, it, expect, vi, beforeEach, afterEach } from 'vitest';
-import { isTauri, loadSettings, saveSettings, defaultSettingsData, loadAppData, saveAppData, flushAppData, setDataDir, runBackups, backupDeletedSheet, openBackupsFolder, chooseFolder, dataDirHasDocuments, migrateDataDir, fetchRates, fetchHistoricalRates } from './storage';
+import { isTauri, loadSettings, saveSettings, defaultSettingsData, loadAppData, saveAppData, flushAppData, setDataDir, runBackups, backupDeletedSheet, openBackupsFolder, chooseFolder, dataDirHasDocuments, migrateDataDir, fetchRates, fetchHistoricalRates, fetchHistoricalRatesBatch } from './storage';
 import { invoke } from '@tauri-apps/api/core';
 
 vi.mock('@tauri-apps/api/core', () => ({
@@ -382,6 +382,39 @@ describe('storage', () => {
     });
   });
 
+  describe('fetchHistoricalRatesBatch', () => {
+    it('uses invoke when in Tauri', async () => {
+      vi.stubGlobal('window', { __TAURI_INTERNALS__: {} });
+      const mockRates = { '2024-01-01': { EUR: 0.85 } };
+      vi.mocked(invoke).mockResolvedValue(mockRates);
+
+      const result = await fetchHistoricalRatesBatch(['2024-01-01']);
+      expect(invoke).toHaveBeenCalledWith('fetch_historical_rates_batch', { dates: ['2024-01-01'] });
+      expect(result).toEqual(mockRates);
+    });
+
+    it('uses fetch when not in Tauri and falls back to closest dates', async () => {
+      const mockResponse = { rates: { '2023-12-29': { EUR: 0.84 }, '2024-01-02': { EUR: 0.85, JPY: -1 }, '2024-01-05': { EUR: 0.86 } } };
+      vi.mocked(fetch).mockResolvedValue({ json: vi.fn().mockResolvedValue(mockResponse) } as unknown as Response);
+
+      const dates = ['2024-01-01', '2024-01-03', '2024-01-05'];
+      const result = await fetchHistoricalRatesBatch(dates);
+
+      expect(fetch).toHaveBeenCalledWith('https://api.frankfurter.dev/v1/2023-12-25..2024-01-05?from=USD');
+
+      expect(result['2024-01-01']).toEqual({ USD: 1, EUR: 0.84 });
+      expect(result['2024-01-03']).toEqual({ USD: 1, EUR: 0.85 });
+      expect(result['2024-01-05']).toEqual({ USD: 1, EUR: 0.86 });
+    });
+
+    it('returns empty if fetch fails', async () => {
+      vi.mocked(fetch).mockRejectedValue(new Error('Network error'));
+      const result = await fetchHistoricalRatesBatch(['2024-01-01']);
+      expect(logger.warn).toHaveBeenCalledWith('fetchHistoricalRatesBatch failed', expect.any(Error));
+      expect(result).toEqual({});
+    });
+  });
+
   describe('fetchHistoricalRates', () => {
     it('uses invoke when in Tauri', async () => {
       vi.stubGlobal('window', { __TAURI_INTERNALS__: {} });

src/storage.ts

@@ -219,13 +219,34 @@ export async function fetchHistoricalRatesBatch(dates: string[]): Promise<Record
     if (isTauri()) {
       return await invoke<Record<string, Record<string, number>>>("fetch_historical_rates_batch", { dates });
     }
+    const sortedDates = [...dates].sort();
+    const minDateObj = new Date(sortedDates[0]);
+    minDateObj.setDate(minDateObj.getDate() - 7);
+    const minDateQuery = minDateObj.toISOString().split("T")[0];
+    const maxDate = sortedDates[sortedDates.length - 1];
+
+    const res = await fetch(`https://api.frankfurter.dev/v1/${minDateQuery}..${maxDate}?from=USD`);
+    const json = await res.json();
+    if (!json?.rates) return {};
+
+    const rangeDates = Object.keys(json.rates).sort();
     const results: Record<string, Record<string, number>> = {};
-    await Promise.all(
-      dates.map(async (date) => {
-        const rates = await fetchHistoricalRates(date);
-        if (rates) results[date] = rates;
-      })
-    );
+
+    for (const date of dates) {
+      let targetDate = date;
+      if (!json.rates[date]) {
+        const possibleDates = rangeDates.filter(d => d <= date);
+        if (possibleDates.length === 0) continue;
+        targetDate = possibleDates[possibleDates.length - 1];
+      }
+
+      const dayRates = json.rates[targetDate] as Record<string, number>;
+      const out: Record<string, number> = { USD: 1 };
+      for (const [k, v] of Object.entries(dayRates)) {
+        if (v > 0) out[k.toUpperCase()] = v;
+      }
+      results[date] = out;
+    }
     return results;
   } catch (e) {
     logger.warn("fetchHistoricalRatesBatch failed", e);