From 2815a85e6ee4d6beda33039a5f4204dc5f546f84 Mon Sep 17 00:00:00 2001
From: sinnercode228 <sinnercode228@users.noreply.github.com>
Date: Wed, 21 Oct 2026 14:20:51 +0700
Subject: [PATCH] Align hour buckets to the site time zone

bucketStart() only used the timeZone for day buckets; the hour case
floored in UTC, so hourly timeseries on a half-offset zone (Asia/Kolkata,
Asia/Tehran) were 30 minutes off the local clock and the range snapping in
query.ts resolve() was off by the same amount. Align the hour case the way
startOfDay already does. Minute buckets stay UTC-floored because every zone
offset is a whole number of minutes.

Fixes #6
---
 packages/core/src/time.ts       | 12 ++++++++++--
 packages/core/test/time.test.ts | 21 +++++++++++++++++++++
 2 files changed, 31 insertions(+), 2 deletions(-)

diff --git a/packages/core/src/time.ts b/packages/core/src/time.ts
index 6ffde07..ce449a1 100644
--- a/packages/core/src/time.ts
+++ b/packages/core/src/time.ts
@@ -66,9 +66,17 @@ export function startOfDay(ts: number, timeZone = 'UTC'): number {
 export function bucketStart(ts: number, granularity: Granularity, timeZone = 'UTC'): number {
   switch (granularity) {
     case 'minute':
+      // Every zone offset is a whole number of minutes, so UTC and local
+      // minute boundaries always coincide.
       return Math.floor(ts / MINUTE) * MINUTE;
-    case 'hour':
-      return Math.floor(ts / HOUR) * HOUR;
+    case 'hour': {
+      // Align to the local hour, like startOfDay does for the day: half-offset
+      // zones (e.g. Asia/Kolkata) start their hours at :30 past the UTC hour.
+      const offset = tzOffsetMinutes(ts, timeZone) * MINUTE;
+      const localHour = Math.floor((ts + offset) / HOUR) * HOUR;
+      const offsetAtHour = tzOffsetMinutes(localHour - offset, timeZone) * MINUTE;
+      return localHour - offsetAtHour;
+    }
     case 'day':
       return startOfDay(ts, timeZone);
   }
diff --git a/packages/core/test/time.test.ts b/packages/core/test/time.test.ts
index f6ea8c4..0fbdb37 100644
--- a/packages/core/test/time.test.ts
+++ b/packages/core/test/time.test.ts
@@ -20,6 +20,27 @@ describe('time buckets', () => {
     expect(bucketStart(ts, 'hour')).toBe(at('2026-05-10T13:00:00Z'));
   });
 
+  it('aligns hour buckets to a half-offset zone', () => {
+    // 13:47 UTC is 19:17 in Kolkata (+5:30); the local hour starts at 19:00 IST = 13:30 UTC.
+    const ts = at('2026-05-10T13:47:31.500Z');
+    expect(bucketStart(ts, 'hour', 'Asia/Kolkata')).toBe(at('2026-05-10T13:30:00Z'));
+    // Minute buckets are unaffected: every zone offset is a whole number of minutes.
+    expect(bucketStart(ts, 'minute', 'Asia/Kolkata')).toBe(at('2026-05-10T13:47:00Z'));
+    expect(bucketsBetween(ts, ts + 2 * HOUR, 'hour', 'Asia/Kolkata')).toEqual([
+      at('2026-05-10T13:30:00Z'),
+      at('2026-05-10T14:30:00Z'),
+      at('2026-05-10T15:30:00Z'),
+    ]);
+  });
+
+  it('keeps hour buckets an hour apart across a whole-hour DST change', () => {
+    const tz = 'America/New_York';
+    // The fall-back hour (EDT -> EST) still steps by one real hour per local hour.
+    const b = bucketStart(at('2026-11-01T05:30:00Z'), 'hour', tz);
+    expect(b).toBe(at('2026-11-01T05:00:00Z'));
+    expect(nextBucket(b, 'hour', tz) - b).toBe(HOUR);
+  });
+
   it('computes local midnight for fixed-offset zones', () => {
     expect(tzOffsetMinutes(at('2026-05-10T12:00:00Z'), 'Europe/Moscow')).toBe(180);
     expect(startOfDay(at('2026-05-10T22:30:00Z'), 'Europe/Moscow')).toBe(