From 28507224dccde5bc9c646a7f2fcc994359cff551 Mon Sep 17 00:00:00 2001
From: "paseo-bot[bot]" <266920839+paseo-bot[bot]@users.noreply.github.com>
Date: Fri, 25 Sep 2026 00:54:41 +0200
Subject: [PATCH] Show the date for a message from today's weekday last week
 (#5341)

A reply sent last Friday at 12:02 PM, read on Friday at 11:47 AM, was
labelled "Friday 12:02 PM" because the weekday window counted 24-hour
periods, and that reply was just under seven of them old. Count calendar
days instead, so the weekday form covers only the previous six days and
today's weekday a week back shows its date.

Closes #5225

Co-authored-by: paseo-bot[bot] <266920839+paseo-bot[bot]@users.noreply.github.com>
---
 packages/app/src/utils/time.test.ts | 11 +++++++++++
 packages/app/src/utils/time.ts      | 25 +++++++++++++------------
 2 files changed, 24 insertions(+), 12 deletions(-)

diff --git a/packages/app/src/utils/time.test.ts b/packages/app/src/utils/time.test.ts
index f979797b55..292fffbf6d 100644
--- a/packages/app/src/utils/time.test.ts
+++ b/packages/app/src/utils/time.test.ts
@@ -108,6 +108,17 @@ describe("formatMessageTimestamp", () => {
     expect(formatted).toMatch(/10:12 PM|22:12/);
   });
 
+  it("shows the full date for last week's same weekday, even under seven days ago", () => {
+    // 2026-09-18 is a Friday. The reply is 6 days 23h45m old and lands on today's weekday,
+    // so a weekday label would read as today.
+    const now = new Date(2026, 8, 25, 11, 47);
+    const date = new Date(2026, 8, 18, 12, 2);
+    const formatted = formatMessageTimestamp(date, now);
+    expect(formatted).toMatch(/Sep|September/);
+    expect(formatted).toMatch(/18/);
+    expect(formatted).not.toMatch(/Friday/);
+  });
+
   it("includes full date for older timestamps", () => {
     const now = new Date(2026, 4, 14, 17, 30);
     const date = new Date(2026, 3, 1, 9, 5);
diff --git a/packages/app/src/utils/time.ts b/packages/app/src/utils/time.ts
index f91487dfb5..8fa94e8926 100644
--- a/packages/app/src/utils/time.ts
+++ b/packages/app/src/utils/time.ts
@@ -91,12 +91,14 @@ export function formatCompactTimeAgo(date: Date, now: Date = new Date()): string
   return describeCompactTimeAgo(date, now).label;
 }
 
-function isSameLocalDay(a: Date, b: Date): boolean {
-  return (
-    a.getFullYear() === b.getFullYear() &&
-    a.getMonth() === b.getMonth() &&
-    a.getDate() === b.getDate()
-  );
+/**
+ * How many local midnights lie between two instants: 0 for the same day, 1 for yesterday.
+ * Counted on the calendar rather than in elapsed time, so six days and 23 hours ago on
+ * today's weekday is 7, and rounded so a DST day of 23 or 25 hours still counts as one.
+ */
+function localCalendarDaysBetween(earlier: Date, later: Date): number {
+  const startOfDay = (d: Date) => new Date(d.getFullYear(), d.getMonth(), d.getDate());
+  return Math.round((startOfDay(later).getTime() - startOfDay(earlier).getTime()) / DAY_MS);
 }
 
 // Cached Intl formatter. Explicitly carrying `hourCycle` from the resolved
@@ -120,19 +122,18 @@ function getTimeFormatter(): Intl.DateTimeFormat {
 /**
  * Format a chat-message timestamp for hover-revealed UI.
  * - Same day: "10:11 PM" or "22:11" depending on user preference
- * - Within ~6 days: "Wednesday 10:11 PM"
- * - Older: "14 May 2026, 10:11 PM"
+ * - The previous 6 calendar days: "Wednesday 10:11 PM"
+ * - Older, including today's weekday last week: "14 May 2026, 10:11 PM"
  */
 export function formatMessageTimestamp(date: Date, now: Date = new Date()): string {
   const time = getTimeFormatter().format(date);
+  const daysAgo = localCalendarDaysBetween(date, now);
 
-  if (isSameLocalDay(date, now)) {
+  if (daysAgo === 0) {
     return time;
   }
 
-  const diffMs = now.getTime() - date.getTime();
-  const diffDays = Math.floor(diffMs / (1000 * 60 * 60 * 24));
-  if (diffDays >= 0 && diffDays < 7) {
+  if (daysAgo > 0 && daysAgo < 7) {
     const weekday = date.toLocaleDateString(undefined, { weekday: "long" });
     return `${weekday} ${time}`;
   }