Simplify date util function using date-fns and make simple tests

apps/app/src/features/contribution-graph/utils/contribution-graph-utils.spec.ts

@@ -0,0 +1,90 @@
+import {
+  daysSinceLastUpdate,
+  getCurrentWeekStart,
+  getISOWeekId,
+} from './contribution-graph-utils';
+
+describe('Date Utility Functions (date-fns refactor)', () => {
+  describe('getISOWeekId', () => {
+    test('should return the correct ISO Week ID for a standard mid-year date (2025-W32)', () => {
+      // 2025-08-05 is a Tuesday in Week 32
+      const date = new Date('2025-08-05T12:00:00Z');
+      expect(getISOWeekId(date)).toBe('2025-W32');
+    });
+
+    test('should handle year boundary: Start of year 2025 (falls in Week 1 of 2025)', () => {
+      // 2025-01-01 is a Wednesday, falls in the first ISO week of 2025.
+      const date = new Date('2025-01-01T12:00:00Z');
+      expect(getISOWeekId(date)).toBe('2025-W01');
+    });
+
+    test('should handle year boundary: End of year 2024 (falls in Week 1 of 2025)', () => {
+      // 2024-12-31 is a Tuesday, falls in the first ISO week of 2025.
+      const date = new Date('2024-12-31T12:00:00Z');
+      expect(getISOWeekId(date)).toBe('2025-W01');
+    });
+
+    test('should handle year boundary: Start of year 2023 (falls in Week 52 of 2022)', () => {
+      // 2023-01-01 is a Sunday, which belongs to the last ISO week of 2022.
+      const date = new Date('2023-01-01T12:00:00Z');
+      expect(getISOWeekId(date)).toBe('2022-W52');
+    });
+  });
+
+  describe('daysSinceLastUpdate', () => {
+    test('should return 0 when lastUpdateDate equals currentDate', () => {
+      const date = new Date('2025-10-01T12:00:00Z');
+      expect(daysSinceLastUpdate(date, date)).toBe(0);
+    });
+
+    test('should return 3 if lastUpdateDate is 3 days in the future', () => {
+      const currentDate = new Date('2025-10-01T12:00:00Z');
+      const lastUpdateDate = new Date('2025-10-04T12:00:00Z');
+      // differenceInDays(lastUpdateDate, currentDate) -> 3
+      expect(daysSinceLastUpdate(lastUpdateDate, currentDate)).toBe(3);
+    });
+
+    test('should return 0 if lastUpdateDate is 3 days in the past (i.e., the update already occurred)', () => {
+      const currentDate = new Date('2025-10-04T12:00:00Z');
+      const lastUpdateDate = new Date('2025-10-01T12:00:00Z');
+      // differenceInDays(lastUpdateDate, currentDate) -> -3
+      // Math.max(0, -3) -> 0
+      expect(daysSinceLastUpdate(lastUpdateDate, currentDate)).toBe(0);
+    });
+
+    test('should return 0 regardless of time if lastUpdateDate is in the past', () => {
+      const currentDate = new Date('2025-10-02T01:00:00Z');
+      const lastUpdateDate = new Date('2025-10-01T23:00:00Z');
+      // differenceInDays ignores time, so lastUpdateDate (Oct 1) is before currentDate (Oct 2), resulting in -1
+      expect(daysSinceLastUpdate(lastUpdateDate, currentDate)).toBe(0);
+    });
+  });
+
+  describe('getCurrentWeekStart', () => {
+    // All expected outputs for startOfWeek are at 00:00:00, so we use T00:00:00Z
+    const expectedMonday = new Date('2025-09-29T00:00:00Z');
+
+    test('should return the Monday of the week for a mid-week date (Wednesday)', () => {
+      const wednesday = new Date('2025-10-01T12:00:00Z');
+      expect(getCurrentWeekStart(wednesday)).toEqual(expectedMonday);
+    });
+
+    test('should return the date itself if the input is a Monday', () => {
+      const monday = new Date('2025-09-29T12:00:00Z');
+      // The time will be reset to midnight (T00:00:00Z)
+      expect(getCurrentWeekStart(monday)).toEqual(expectedMonday);
+    });
+
+    test('should snap back to Monday for a Sunday', () => {
+      const sunday = new Date('2025-10-05T12:00:00Z');
+      expect(getCurrentWeekStart(sunday)).toEqual(expectedMonday);
+    });
+
+    test('should handle year boundary correctly (Monday, Jan 1st)', () => {
+      // 2024-01-01 is a Monday
+      const date = new Date('2024-01-01T12:00:00Z');
+      const expected = new Date('2024-01-01T00:00:00Z');
+      expect(getCurrentWeekStart(date)).toEqual(expected);
+    });
+  });
+});

apps/app/src/features/contribution-graph/utils/contribution-graph-utils.ts

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+import { differenceInDays, format, startOfWeek } from 'date-fns';
+
+/**
+ * Gets current week's ISO week ID, e.g 2025-W32
+ */
+export const getISOWeekId = (date: Date): string => {
+  return format(date, "RRRR-'W'II");
+};
+
+export const daysSinceLastUpdate = (
+    lastUpdateDate: Date,
+    currentDate: Date = new Date(),
+): number => {
+  const diffDays = differenceInDays(lastUpdateDate, currentDate);
+  return Math.max(0, diffDays);
+};
+
+export const getCurrentWeekStart = (date: Date = new Date()): Date => {
+  return startOfWeek(date, { weekStartsOn: 1 });
+};