fix: prevent timezone conversion for non-sensitive date value (#146)

src/lib/utils/datetime/parse.test.ts

@@ -3,6 +3,8 @@ import { describe, it, expect } from 'vitest';
 
 import { mergeTimeWithDate } from './parse';
 
+import { toUtc } from '$lib/utils/datetime/helpers';
+
 describe('mergeTimeWithDate', () => {
   it('should merge date and time correctly for 24-hour format', () => {
     const result = mergeTimeWithDate('2023-10-10', '9:30', 'America/New_York');
@@ -80,6 +82,26 @@ describe('mergeTimeWithDate', () => {
     expect(result.getMinutes()).toBe(0);
   });
 
+  it('should merge date and time correctly for 18:59 in New York', () => {
+    const result = mergeTimeWithDate(
+      '2024-11-09T00:00:00.000Z',
+      '18:59',
+      'America/New_York',
+    );
+    expect(result).toBeInstanceOf(TZDate);
+    expect(result.getFullYear()).toBe(2024);
+    expect(result.getMonth() + 1).toBe(11);
+    expect(result.getDate()).toBe(9);
+    expect(result.getHours()).toBe(18);
+    expect(result.getMinutes()).toBe(59);
+  });
+
+  it('should throw an error for invalid date format', () => {
+    expect(() =>
+      mergeTimeWithDate('10-10-2023', '10:30', 'America/New_York'),
+    ).toThrow('Invalid ISO 8601 date time string: 10-10-2023');
+  });
+
   it('should throw an error for invalid time format', () => {
     expect(() =>
       mergeTimeWithDate('2023-10-10', '25:00', 'America/New_York'),

src/lib/utils/datetime/parse.ts

@@ -21,7 +21,7 @@ export const mergeTimeWithDate = (
   time: string,
   tzId: string,
 ): TZDate => {
-  const date = parseLocalISO(dateString, tzId);
+  const { year, month, day } = extractDateFromISO(dateString);
   const match = time.match(timePartsRegex);
   if (!match) {
     throw new Error('Invalid format');
@@ -44,7 +44,7 @@ export const mergeTimeWithDate = (
   }
 
   const result = parse(
-    `${date.getFullYear()}-${date.getMonth() + 1}-${date.getDate()} ${hours}:${minutes}`,
+    `${year}-${month}-${day} ${hours}:${minutes}`,
     'yyyy-M-d H:m',
     new Date(),
     { in: tz(tzId) },
@@ -83,6 +83,25 @@ export const dateValueFromISO = (iso: string) => {
   );
 };
 
+const ISO_DATE_REGEX = /(\d{4})-(\d{2})-(\d{2})/;
+const extractDateFromISO = (iso: string) => {
+  const match = iso.match(ISO_DATE_REGEX);
+  if (!match) {
+    throw new Error('Invalid ISO 8601 date time string: ' + iso);
+  }
+
+  const [, year, month, day] = match;
+  if (!year || !month || !day) {
+    throw new Error('Invalid ISO 8601 date time string: ' + iso);
+  }
+
+  return {
+    year: parseNumber(year, 1, 9999),
+    month: parseNumber(month, 1, 12),
+    day: parseNumber(day, 1, 31),
+  };
+};
+
 function parseNumber(value: string, min: number, max: number) {
   const val = Number(value);
   if (val < min || val > max) {