fix: update isNew function to correctly determine if a post is new based on calendar days

Author: hrgui

src/components/app/blog/utils.test.ts

@@ -16,10 +16,16 @@ describe("isNew", () => {
     expect(isNew("not-a-date")).toBe(false);
   });
 
-  test("returns true when post date is exactly now", () => {
+  test("returns true when post date is earlier the same day", () => {
     vi.useFakeTimers();
     vi.setSystemTime(new Date("2026-03-27T12:00:00Z"));
-    expect(isNew("2026-03-27")).toBe(true);
+    expect(isNew("2026-03-27T10:00:00Z")).toBe(true);
+  });
+
+  test("returns true when post date is yesterday (calendar day)", () => {
+    vi.useFakeTimers();
+    vi.setSystemTime(new Date("2026-03-27T12:00:00Z"));
+    expect(isNew("2026-03-26")).toBe(true);
   });
 
   test("returns true when post date is 23 hours ago", () => {
@@ -28,10 +34,10 @@ describe("isNew", () => {
     expect(isNew("2026-03-26T13:00:00Z")).toBe(true);
   });
 
-  test("returns false when post date is more than 24 hours ago", () => {
+  test("returns false when post date is 2 or more calendar days ago", () => {
     vi.useFakeTimers();
     vi.setSystemTime(new Date("2026-03-27T12:00:00Z"));
-    expect(isNew("2026-03-26T11:59:59Z")).toBe(false);
+    expect(isNew("2026-03-25")).toBe(false);
   });
 
   test("returns false when post date is in the future", () => {

src/components/app/blog/utils.ts

@@ -2,8 +2,19 @@ export const isNew = (rawDate?: string) => {
   if (!rawDate) return false;
   const postDate = new Date(rawDate);
   if (Number.isNaN(postDate.getTime())) return false;
-  const diffMs = Date.now() - postDate.getTime();
-  return diffMs >= 0 && diffMs <= 24 * 60 * 60 * 1000;
+  const postDay = Date.UTC(
+    postDate.getUTCFullYear(),
+    postDate.getUTCMonth(),
+    postDate.getUTCDate()
+  );
+  const now = new Date();
+  const today = Date.UTC(
+    now.getUTCFullYear(),
+    now.getUTCMonth(),
+    now.getUTCDate()
+  );
+  const diffDays = (today - postDay) / (24 * 60 * 60 * 1000);
+  return diffDays >= 0 && diffDays <= 1;
 };
 
 export const toDisplayDate = (rawDate?: string) => {