Fix minute.round with non-integer TZ offsets

.changeset/ninety-cycles-hug.md

@@ -0,0 +1,5 @@
+---
+'chronoshift': patch
+---
+
+Fix minute.round with non-integer TZ offsets

src/duration/duration.spec.ts

@@ -264,6 +264,31 @@ describe('Duration', () => {
       );
     });
 
+    it('works for PT20M with Asia/Kolkata (UTC+5:30)', () => {
+      const pt20m = new Duration('PT20M');
+      const kolkata = Timezone.fromJS('Asia/Kolkata');
+
+      // 12:00 UTC = 17:30 IST → floor to 17:20 IST = 11:50 UTC
+      expect(pt20m.floor(new Date('2025-11-27T12:00:00Z'), kolkata)).toEqual(
+        new Date('2025-11-27T11:50:00.000Z'),
+      );
+
+      // 12:25 UTC = 17:55 IST → floor to 17:40 IST = 12:10 UTC
+      expect(pt20m.floor(new Date('2025-11-27T12:25:00Z'), kolkata)).toEqual(
+        new Date('2025-11-27T12:10:00.000Z'),
+      );
+    });
+
+    it('works for PT5M with Asia/Kolkata (UTC+5:30)', () => {
+      const pt5m = new Duration('PT5M');
+      const kolkata = Timezone.fromJS('Asia/Kolkata');
+
+      // 12:02 UTC = 17:32 IST → floor to 17:30 IST = 12:00 UTC
+      expect(pt5m.floor(new Date('2025-11-27T12:02:00Z'), kolkata)).toEqual(
+        new Date('2025-11-27T12:00:00.000Z'),
+      );
+    });
+
     it('works for P2H', () => {
       const pt2h = new Duration('PT2H');
       expect(pt2h.floor(new Date('2013-09-29T03:02:03.456-07:00'), TZ_LA)).toEqual(

src/floor-shift-ceil/floor-shift-ceil.spec.ts

@@ -204,4 +204,27 @@ describe('floor/shift/ceil', () => {
       year.shift(new Date('2010-01-01T00:00:00-08:00'), tz, 1),
     );
   });
+
+  it('rounds minutes with non-integer timezone offsets', () => {
+    const kolkata = Timezone.fromJS('Asia/Kolkata');
+    const kathmandu = Timezone.fromJS('Asia/Kathmandu');
+
+    // Asia/Kolkata (UTC+5:30) with 20 minute boundary
+    expect(shifters.minute.round(new Date('2025-11-27T12:00:00Z'), 20, kolkata)).toEqual(
+      new Date('2025-11-27T11:50:00.000Z'),
+    );
+    expect(shifters.minute.round(new Date('2025-11-27T12:25:00Z'), 20, kolkata)).toEqual(
+      new Date('2025-11-27T12:10:00.000Z'),
+    );
+
+    // Asia/Kolkata (UTC+5:30) with 5 minute boundary
+    expect(shifters.minute.round(new Date('2025-11-27T12:02:00Z'), 5, kolkata)).toEqual(
+      new Date('2025-11-27T12:00:00.000Z'),
+    );
+
+    // Asia/Kathmandu (UTC+5:45) with 20 minute boundary
+    expect(shifters.minute.round(new Date('2025-11-27T12:00:00Z'), 20, kathmandu)).toEqual(
+      new Date('2025-11-27T11:55:00.000Z'),
+    );
+  });
 });

src/floor-shift-ceil/floor-shift-ceil.ts

@@ -79,6 +79,13 @@ export const second = timeShifterFiller({
   },
 });
 
+// Movement by minute is tz independent because in every timezone a minute is 60 seconds
+function minuteMove(dt: Date, _tz: Timezone, step: number) {
+  dt = new Date(dt.valueOf());
+  dt.setUTCMinutes(dt.getUTCMinutes() + step);
+  return dt;
+}
+
 export const minute = timeShifterFiller({
   canonicalLength: 60000,
   siblings: 60,
@@ -88,10 +95,16 @@ export const minute = timeShifterFiller({
     dt.setUTCSeconds(0, 0);
     return dt;
   },
-  round: (dt, roundTo, _tz) => {
-    const cur = dt.getUTCMinutes();
-    const adj = floorTo(cur, roundTo);
-    if (cur !== adj) dt.setUTCMinutes(adj);
+  round: (dt, roundTo, tz) => {
+    if (tz.isUTC()) {
+      const cur = dt.getUTCMinutes();
+      const adj = floorTo(cur, roundTo);
+      if (cur !== adj) dt.setUTCMinutes(adj);
+    } else {
+      const cur = fromDate(dt, tz.toString()).minute;
+      const adj = floorTo(cur, roundTo);
+      if (cur !== adj) return minuteMove(dt, tz, adj - cur);
+    }
     return dt;
   },
   shift: (dt, _tz, step) => {