fix: use local timezone for date grouping instead of UTC

ben-vargas · ben-vargas · commit ea9ecc0dd31d · 2025-08-03T20:24:09.000-06:00
The date formatters were using UTC timezone which caused usage data to be grouped incorrectly. For example, usage at 20:00 local time would appear on the next day if the local timezone was behind UTC. This regression was introduced in PR #409 (commit f7c5251) which added explicit UTC timezone to the Intl.DateTimeFormat configuration. The fix removes the hardcoded 'timeZone: UTC' option, allowing the formatters to respect the system's local timezone or the TZ environment variable if set. Changes: - Remove 'timeZone: UTC' from dateFormatter - Remove 'timeZone: UTC' from datePartsFormatter - Update comment to reflect local timezone usage This ensures usage data is grouped by the user's local date boundaries rather than UTC date boundaries.
diff --git a/src/data-loader.ts b/src/data-loader.ts
@@ -517,10 +517,9 @@ function extractUniqueModels<T>(
 
 /**
  * Date formatter using Intl.DateTimeFormat for consistent formatting
- * Using UTC to avoid timezone issues
+ * Uses local timezone for proper date grouping
  */
 const dateFormatter = new Intl.DateTimeFormat('en-CA', {
-	timeZone: 'UTC',
 	year: 'numeric',
 	month: '2-digit',
 	day: '2-digit',
@@ -541,7 +540,6 @@ export function formatDate(dateStr: string): string {
  * Date parts formatter for extracting year, month, and day separately
  */
 const datePartsFormatter = new Intl.DateTimeFormat('en', {
-	timeZone: 'UTC',
 	year: 'numeric',
 	month: '2-digit',
 	day: '2-digit',
