refactor habit compete

server/api/habits/[id]/complete.post.ts

@@ -8,6 +8,16 @@ interface CompletionResponse {
   updatedCoins: number;
 }
 
+/**
+ * Creates a Date object for the start of a given day in UTC.
+ * This is duplicated here as per the instruction not to create new shared utilities.
+ */
+function getStartOfDay(date: Date): Date {
+  const startOfDay = new Date(date);
+  startOfDay.setUTCHours(0, 0, 0, 0);
+  return startOfDay;
+}
+
 export default defineEventHandler(async (event): Promise<CompletionResponse> => {
   const userId = await getUserIdFromSession(event);
   const habitId = parseInt(event.context.params?.id || '', 10);
@@ -31,8 +41,7 @@ export default defineEventHandler(async (event): Promise<CompletionResponse> =>
   }
 
   // Normalize date to the beginning of the day for consistent checks
-  const startOfToday = new Date();
-  startOfToday.setUTCHours(0, 0, 0, 0);
+  const startOfToday = getStartOfDay(new Date()); // Correctly get a Date object
 
   const existingCompletion = await prisma.habitCompletion.findFirst({
     where: {