fix: use local time instead of JST

Author: ryoppippi

data-loader.test.ts

@@ -26,11 +26,10 @@ mock.module("node:os", () => ({
 }));
 
 describe("formatDate", () => {
-	test("formats UTC timestamp to JST date", () => {
-		// UTC midnight = JST 9 AM
+	test("formats UTC timestamp to local date", () => {
+		// Test with UTC timestamps - results depend on local timezone
 		expect(formatDate("2024-01-01T00:00:00Z")).toBe("2024-01-01");
-		// UTC 3 PM = JST midnight next day
-		expect(formatDate("2024-01-01T15:00:00Z")).toBe("2024-01-02");
+		expect(formatDate("2024-01-01T15:00:00Z")).toBe("2024-01-01");
 	});
 
 	test("handles various date formats", () => {

data-loader.ts

@@ -39,10 +39,9 @@ export type SessionUsage = v.InferOutput<typeof SessionUsageSchema>;
 
 export const formatDate = (dateStr: string): string => {
 	const date = new Date(dateStr);
-	const offsetDate = new Date(date.getTime() + 9 * 60 * 60 * 1000); // UTC+9 for JST
-	const year = offsetDate.getUTCFullYear();
-	const month = String(offsetDate.getUTCMonth() + 1).padStart(2, "0");
-	const day = String(offsetDate.getUTCDate()).padStart(2, "0");
+	const year = date.getFullYear();
+	const month = String(date.getMonth() + 1).padStart(2, "0");
+	const day = String(date.getDate()).padStart(2, "0");
 	return `${year}-${month}-${day}`;
 };