From 97d37fad0428fa89b496c3fcf7a3dc56b9086e37 Mon Sep 17 00:00:00 2001
From: camjac251 <camjac251@users.noreply.github.com>
Date: Mon, 20 Jul 2026 14:37:19 -0400
Subject: [PATCH] fix(ui): preserve local usage bucket dates

Daily usage buckets represent local calendar dates, but standard date parsing
interprets their ISO-like form as UTC and shifts them in non-UTC time zones.
Parse date-only buckets directly in local time so heatmap totals stay on the
reported day.
---
 packages/ui/src/lib/usage-activity.ts         | 18 +++++-
 packages/ui/test/unit/usage-activity.test.mjs | 60 ++++++++++++-------
 2 files changed, 55 insertions(+), 23 deletions(-)

diff --git a/packages/ui/src/lib/usage-activity.ts b/packages/ui/src/lib/usage-activity.ts
index bbaae29a..f2888f53 100644
--- a/packages/ui/src/lib/usage-activity.ts
+++ b/packages/ui/src/lib/usage-activity.ts
@@ -42,7 +42,7 @@ export function buildTokenActivity(series: UsageSeriesPoint[], options: TokenAct
   let observedEnd: Date | undefined;
 
   for (const point of series) {
-    const date = startOfLocalDay(new Date(point.bucket));
+    const date = startOfLocalDay(parseActivityDate(point.bucket));
     if (!isFiniteDate(date)) {
       continue;
     }
@@ -111,6 +111,22 @@ export function buildTokenActivity(series: UsageSeriesPoint[], options: TokenAct
   };
 }
 
+function parseActivityDate(bucket: string): Date {
+  const dateOnly = /^(\d{4})-(\d{1,2})-(\d{1,2})$/.exec(bucket.trim());
+  if (!dateOnly) {
+    return new Date(bucket);
+  }
+
+  const year = Number(dateOnly[1]);
+  const month = Number(dateOnly[2]);
+  const day = Number(dateOnly[3]);
+  const date = new Date(year, month - 1, day);
+  if (date.getFullYear() !== year || date.getMonth() !== month - 1 || date.getDate() !== day) {
+    return new Date(Number.NaN);
+  }
+  return date;
+}
+
 export function activityDateKey(date: Date): string {
   const year = date.getFullYear();
   const month = String(date.getMonth() + 1).padStart(2, "0");
diff --git a/packages/ui/test/unit/usage-activity.test.mjs b/packages/ui/test/unit/usage-activity.test.mjs
index 6b9da4e4..a006a3c3 100644
--- a/packages/ui/test/unit/usage-activity.test.mjs
+++ b/packages/ui/test/unit/usage-activity.test.mjs
@@ -3,32 +3,48 @@ import test from "node:test";
 import { buildTokenActivity, activityDateKey } from "@ccr/ui/lib/usage-activity.ts";
 
 test("buildTokenActivity summarizes observed token days and streaks", () => {
-  const summary = buildTokenActivity(
-    [
-      { bucket: "2026-06-02", totalTokens: 10 },
-      { bucket: "2026-06-03", totalTokens: 30 },
-      { bucket: "2026-06-04", totalTokens: 60 },
-      { bucket: "2026-06-05", totalTokens: -20 },
-      { bucket: "not-a-date", totalTokens: 999 }
-    ],
-    { minWeeks: 2 }
-  );
+  withTimezone("America/New_York", () => {
+    const summary = buildTokenActivity(
+      [
+        { bucket: "2026-06-02", totalTokens: 10 },
+        { bucket: "2026-06-03", totalTokens: 30 },
+        { bucket: "2026-06-04", totalTokens: 60 },
+        { bucket: "2026-06-05", totalTokens: -20 },
+        { bucket: "not-a-date", totalTokens: 999 }
+      ],
+      { minWeeks: 2 }
+    );
 
-  assert.equal(summary.totalTokens, 100);
-  assert.equal(summary.activeDays, 3);
-  assert.equal(summary.dayCount, 4);
-  assert.equal(summary.longestStreak, 3);
-  assert.equal(summary.maxTokens, 60);
-  assert.equal(summary.weekCount, 2);
-  assert.equal(summary.cells.length, 14);
+    assert.equal(summary.totalTokens, 100);
+    assert.equal(summary.activeDays, 3);
+    assert.equal(summary.dayCount, 4);
+    assert.equal(summary.longestStreak, 3);
+    assert.equal(summary.maxTokens, 60);
+    assert.equal(summary.weekCount, 2);
+    assert.equal(summary.cells.length, 14);
 
-  const cellsByDate = new Map(summary.cells.map((cell) => [cell.dateKey, cell]));
-  assert.equal(cellsByDate.get("2026-06-02")?.intensity, 1);
-  assert.equal(cellsByDate.get("2026-06-03")?.intensity, 3);
-  assert.equal(cellsByDate.get("2026-06-04")?.intensity, 4);
-  assert.equal(cellsByDate.get("2026-06-05")?.intensity, 0);
+    const cellsByDate = new Map(summary.cells.map((cell) => [cell.dateKey, cell]));
+    assert.equal(cellsByDate.get("2026-06-02")?.intensity, 1);
+    assert.equal(cellsByDate.get("2026-06-03")?.intensity, 3);
+    assert.equal(cellsByDate.get("2026-06-04")?.intensity, 4);
+    assert.equal(cellsByDate.get("2026-06-05")?.intensity, 0);
+  });
 });
 
 test("activityDateKey formats local calendar dates", () => {
   assert.equal(activityDateKey(new Date(2026, 0, 5, 14, 30)), "2026-01-05");
 });
+
+function withTimezone(timezone, run) {
+  const previousTimezone = process.env.TZ;
+  process.env.TZ = timezone;
+  try {
+    run();
+  } finally {
+    if (previousTimezone === undefined) {
+      delete process.env.TZ;
+    } else {
+      process.env.TZ = previousTimezone;
+    }
+  }
+}