From 02ff2e3cb04221c5b6ea8805c750c59c408c0c03 Mon Sep 17 00:00:00 2001
From: Afonso Coutinho <afonso@omelhorsite.pt>
Date: Wed, 3 Jun 2026 05:37:39 +0100
Subject: [PATCH] fix: updating a calendar event ignores user timezone and
 shifts the time (#1695)

---
 src/tool_implementations.py            | 12 +++-
 tests/test_calendar_update_event_tz.py | 90 ++++++++++++++++++++++++++
 2 files changed, 100 insertions(+), 2 deletions(-)
 create mode 100644 tests/test_calendar_update_event_tz.py

diff --git a/src/tool_implementations.py b/src/tool_implementations.py
index 3413075..c7b2649 100644
--- a/src/tool_implementations.py
+++ b/src/tool_implementations.py
@@ -2422,9 +2422,17 @@ async def do_manage_calendar(content: str, owner: Optional[str] = None) -> Dict:
             if args.get("location") is not None:
                 ev.location = args["location"]
             if args.get("dtstart") is not None:
-                ev.dtstart = _parse_dt(args["dtstart"])
+                # Anchor naive/natural-language input to the USER's timezone and
+                # refresh is_utc, exactly like create_event. Parsing with the
+                # raw server-local _parse_dt here (and never touching is_utc)
+                # silently shifted an updated event by the user's UTC offset.
+                _eff_all_day = (
+                    args["all_day"] if args.get("all_day") is not None else ev.all_day
+                )
+                ev.dtstart, _su = _parse_event_dt(args["dtstart"])
+                ev.is_utc = bool(_su and not _eff_all_day)
             if args.get("dtend") is not None:
-                ev.dtend = _parse_dt(args["dtend"])
+                ev.dtend, _eu = _parse_event_dt(args["dtend"])
             if args.get("all_day") is not None:
                 ev.all_day = args["all_day"]
             # Tag/category + importance updates (any of these aliases).
diff --git a/tests/test_calendar_update_event_tz.py b/tests/test_calendar_update_event_tz.py
new file mode 100644
index 0000000..e4c22aa
--- /dev/null
+++ b/tests/test_calendar_update_event_tz.py
@@ -0,0 +1,90 @@
+"""update_event must anchor datetimes to the user tz, like create_event.
+
+create_event parses a naive/natural-language dtstart in the USER's
+timezone (parse_due_for_user -> stored naive-UTC, is_utc=True), but
+update_event parsed args["dtstart"] with the raw server-local _parse_dt
+and never refreshed is_utc. So updating an event to the same naive value
+it was created with silently shifted it by the user's UTC offset (9h for a
+Tokyo user) and left is_utc inconsistent. The do_manage_notes update path
+was already fixed for the analogous issue.
+"""
+import json
+import tempfile
+import uuid
+
+import pytest
+from sqlalchemy import create_engine
+from sqlalchemy.orm import sessionmaker
+from sqlalchemy.pool import NullPool
+
+import core.database as cdb
+from core.database import CalendarEvent
+
+_TMPDB = tempfile.NamedTemporaryFile(suffix=".db", delete=False)
+_ENGINE = create_engine(
+    f"sqlite:///{_TMPDB.name}",
+    connect_args={"check_same_thread": False},
+    poolclass=NullPool,
+)
+cdb.Base.metadata.create_all(_ENGINE)
+_TS = sessionmaker(bind=_ENGINE, autoflush=False, autocommit=False)
+
+
+@pytest.fixture(autouse=True)
+def _bind_temp_db(monkeypatch):
+    monkeypatch.setattr(cdb, "SessionLocal", _TS)
+    import routes.calendar_routes as cr
+    monkeypatch.setattr(cr, "SessionLocal", _TS, raising=False)
+    yield
+
+
+@pytest.fixture
+def tokyo_offset():
+    from routes.calendar_routes import set_user_tz_offset
+    set_user_tz_offset(540)  # Tokyo, UTC+9
+    try:
+        yield
+    finally:
+        set_user_tz_offset(None)
+
+
+async def test_update_event_dtstart_anchored_to_user_tz(tokyo_offset):
+    from src.tool_implementations import do_manage_calendar
+
+    owner = "tz-" + uuid.uuid4().hex[:6]
+    naive = "2026-06-10T14:00:00"  # 14:00 Tokyo == 05:00 UTC
+
+    created = await do_manage_calendar(json.dumps({
+        "action": "create_event",
+        "summary": "Standup",
+        "dtstart": naive,
+    }), owner=owner)
+    assert created.get("exit_code", 0) == 0, created
+    uid = created["uid"]
+
+    db = _TS()
+    try:
+        ev = db.query(CalendarEvent).filter(CalendarEvent.uid == uid).first()
+        created_dtstart, created_is_utc = ev.dtstart, ev.is_utc
+    finally:
+        db.close()
+
+    # Update the same event to the SAME naive wall-clock value.
+    updated = await do_manage_calendar(json.dumps({
+        "action": "update_event",
+        "uid": uid,
+        "dtstart": naive,
+    }), owner=owner)
+    assert updated.get("exit_code", 0) == 0, updated
+
+    db = _TS()
+    try:
+        ev = db.query(CalendarEvent).filter(CalendarEvent.uid == uid).first()
+        # Same input -> same stored moment and same is_utc flag as create.
+        assert ev.dtstart == created_dtstart
+        assert bool(ev.is_utc) == bool(created_is_utc)
+        # And concretely: 14:00 Tokyo is 05:00 UTC, stored naive-UTC.
+        assert ev.dtstart.hour == 5
+        assert bool(ev.is_utc) is True
+    finally:
+        db.close()