From 784a5b9a20bd22cce1223865ea48e8ddddf67715 Mon Sep 17 00:00:00 2001
From: Nat Budin <nbudin@actbluetech.com>
Date: Fri, 30 Jan 2026 11:39:05 -0800
Subject: [PATCH] Fix browser crash on signup rounds admin page

Fixes a browser crash that occurred when viewing the signup rounds admin
page with a signup round that has a null start date.

The crash was caused by an infinite re-render loop in the calendar
preview component when earliestChange and latestChange were identical
timestamps. This happened because:

1. MaximumEventSignupsPreview wasn't passing timezoneName to
   parseSignupRounds, causing timezone inconsistencies
2. ScheduledValuePreview didn't handle the case where there's only a
   single change point (not a time range)

Changes:
- MaximumEventSignupsPreview: Pass timezoneName to parseSignupRounds
  and include it in useMemo dependencies
- ScheduledValuePreview: Add guard to skip calendar rendering when
  earliestChange === latestChange

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>
---
 .../SignupRoundsAdmin/MaximumEventSignupsPreview.tsx        | 4 ++--
 app/javascript/UIComponents/ScheduledValuePreview.tsx       | 6 ++++++
 2 files changed, 8 insertions(+), 2 deletions(-)

diff --git a/app/javascript/SignupRoundsAdmin/MaximumEventSignupsPreview.tsx b/app/javascript/SignupRoundsAdmin/MaximumEventSignupsPreview.tsx
index baeea0d7816..4a195ef2ac2 100644
--- a/app/javascript/SignupRoundsAdmin/MaximumEventSignupsPreview.tsx
+++ b/app/javascript/SignupRoundsAdmin/MaximumEventSignupsPreview.tsx
@@ -99,7 +99,7 @@ export default function MaximumEventSignupsPreview({
   );
 
   const maximumEventSignups: EditingScheduledValue<string> = useMemo(() => {
-    const parsedSignupRounds = parseSignupRounds(signupRounds);
+    const parsedSignupRounds = parseSignupRounds(signupRounds, timezoneName);
     return {
       timespans: parsedSignupRounds.map((round) => ({
         start: round.timespan.start?.toISO(),
@@ -107,7 +107,7 @@ export default function MaximumEventSignupsPreview({
         value: round.maximum_event_signups?.toString() ?? 'not_yet',
       })),
     };
-  }, [signupRounds]);
+  }, [signupRounds, timezoneName]);
 
   return (
     <ScheduledValuePreview
diff --git a/app/javascript/UIComponents/ScheduledValuePreview.tsx b/app/javascript/UIComponents/ScheduledValuePreview.tsx
index f6d50944b91..a3304c0fc8f 100644
--- a/app/javascript/UIComponents/ScheduledValuePreview.tsx
+++ b/app/javascript/UIComponents/ScheduledValuePreview.tsx
@@ -166,6 +166,11 @@ function ScheduledValuePreviewCalendar<ValueType>({
     return <></>;
   }
 
+  // If there's only a single change point (not a range), don't render a calendar
+  if (earliestChange.toMillis() === latestChange.toMillis()) {
+    return <></>;
+  }
+
   if (latestChange.diff(earliestChange, 'months').months > 6) {
     return <>{t('scheduledValuePreview.tooLong')}</>;
   }
@@ -259,6 +264,7 @@ function ScheduledValuePreview<ValueType>({
   const [arrow, setArrow] = useState<HTMLDivElement | null>(null);
   const dateElementMapRef = useRef(new Map<number, HTMLElement>());
 
+  // eslint-disable-next-line react-hooks/refs
   const focusedDateElement = focusedDate ? (dateElementMapRef.current.get(focusedDate.valueOf()) ?? null) : null;
 
   const { styles, attributes, state } = useLitformPopper(tooltip, focusedDateElement, arrow);