From 8aef480037b82a8082f5b871886efef7f1b3d23c Mon Sep 17 00:00:00 2001
From: Jakob Stechow <jakob.stechow@pm.me>
Date: Mon, 18 Nov 2024 00:06:53 +0100
Subject: [PATCH] fix: utc times in scheduler (#136)

---
 backend/src/utils/date.ts | 66 +++++++++++++++++++++------------------
 1 file changed, 35 insertions(+), 31 deletions(-)

diff --git a/backend/src/utils/date.ts b/backend/src/utils/date.ts
index ad11caf..ac5e0fc 100644
--- a/backend/src/utils/date.ts
+++ b/backend/src/utils/date.ts
@@ -2,56 +2,47 @@ import { DefaultPostgresInterval } from './interval';
 
 // TODO: this will only work for UTC+2, overall we need to add a local time zone in the recurring task group and do all the stuff dynamic.
 export function getStartOfInterval(interval: DefaultPostgresInterval): Date {
-  //HOTFIX: This seems very hacky. We should think of something more elegant to handle this in the future, also consider the case when
+  // HOTFIX: This seems very hacky. We should think of something more elegant to handle this in the future, also consider the case when
   //  assignment scheduler runs during the changing days of DST.
-  // Function to check if the current date is in the DST period (from last Sunday in March to last Sunday in October)
-  const isDSTPeriod = (date: Date) => {
-    const year = date.getFullYear();
-    const lastSundayInMarch = new Date(year, 2, 31); // Start from March 31
-    lastSundayInMarch.setDate(
-      lastSundayInMarch.getDate() - lastSundayInMarch.getDay(),
-    ); // Find the last Sunday in March
-    const lastSundayInOctober = new Date(year, 9, 31); // Start from October 31
-    lastSundayInOctober.setDate(
-      lastSundayInOctober.getDate() - lastSundayInOctober.getDay(),
-    ); // Find the last Sunday in October
-    return date >= lastSundayInMarch && date < lastSundayInOctober;
-  };
-
   // Determine target hour based on whether it's DST period
-  const targetHour = isDSTPeriod(new Date()) ? 22 : 23; // 22:00 during DST, 23:00 afterward
+  const targetHour = getIsDSTPeroid(new Date()) ? 22 : 23; // 22:00 during DST, 23:00 afterward
 
   switch (interval) {
     // Go back to previous day at the calculated target hour
     case '1 day': {
       const todayTargetTime = new Date();
-      todayTargetTime.setHours(targetHour, 0, 0, 0); // Set to target hour (22 or 23 based on DST)
+      todayTargetTime.setUTCHours(targetHour, 0, 0, 0); // Set to target hour (22 or 23 based on DST)
 
       // Go back to previous day
-      return new Date(todayTargetTime.setDate(todayTargetTime.getDate() - 1));
+      return new Date(
+        todayTargetTime.setUTCDate(todayTargetTime.getUTCDate() - 1),
+      );
     }
 
     // Go back to previous Sunday at the calculated target hour
     case '7 days': {
       const now = new Date();
       const todayTargetTime = new Date(now);
-      todayTargetTime.setHours(targetHour, 0, 0, 0); // Set to target hour (22 or 23 based on DST)
+      todayTargetTime.setUTCHours(targetHour, 0, 0, 0); // Set to target hour (22 or 23 based on DST)
 
-      if (now.getDay() === 0 && now.getTime() >= todayTargetTime.getTime()) {
+      if (now.getUTCDay() === 0 && now.getTime() >= todayTargetTime.getTime()) {
         // If it's Sunday and past target hour, return today at the target hour
         return todayTargetTime;
       } else {
         // Otherwise, find the previous Sunday at target hour
         const previousSundayTargetTime = new Date(todayTargetTime);
-        const daysSinceSunday = (now.getDay() + 7) % 7;
-        previousSundayTargetTime.setDate(
-          previousSundayTargetTime.getDate() - daysSinceSunday,
+        const daysSinceSunday = (now.getUTCDay() + 7) % 7;
+        previousSundayTargetTime.setUTCDate(
+          previousSundayTargetTime.getUTCDate() - daysSinceSunday,
         );
 
-        if (now.getDay() === 0 && now.getTime() < todayTargetTime.getTime()) {
+        if (
+          now.getUTCDay() === 0 &&
+          now.getTime() < todayTargetTime.getTime()
+        ) {
           // If it's Sunday but before target hour, go back to the previous Sunday
-          previousSundayTargetTime.setDate(
-            previousSundayTargetTime.getDate() - 7,
+          previousSundayTargetTime.setUTCDate(
+            previousSundayTargetTime.getUTCDate() - 7,
           );
         }
 
@@ -64,15 +55,15 @@ export function getStartOfInterval(interval: DefaultPostgresInterval): Date {
     case '1 mon':
       const now = new Date();
       const firstDayOfCurrentMonth = new Date(
-        now.getFullYear(),
-        now.getMonth(),
+        now.getUTCFullYear(),
+        now.getUTCMonth(),
         1,
       );
       const dayBeforeFirstDayOfCurrentMonth = new Date(firstDayOfCurrentMonth);
-      dayBeforeFirstDayOfCurrentMonth.setDate(
-        dayBeforeFirstDayOfCurrentMonth.getDate() - 1,
+      dayBeforeFirstDayOfCurrentMonth.setUTCDate(
+        dayBeforeFirstDayOfCurrentMonth.getUTCDate() - 1,
       );
-      dayBeforeFirstDayOfCurrentMonth.setHours(targetHour, 0, 0, 0); // Set to target hour (22 or 23 based on DST)
+      dayBeforeFirstDayOfCurrentMonth.setUTCHours(targetHour, 0, 0, 0); // Set to target hour (22 or 23 based on DST)
       return dayBeforeFirstDayOfCurrentMonth;
   }
 }
@@ -82,3 +73,16 @@ export function addDays(date: Date, days: number) {
   newDate.setUTCDate(date.getUTCDate() + days);
   return newDate;
 }
+
+export function getIsDSTPeroid(date: Date) {
+  const year = date.getFullYear();
+  const lastSundayInMarch = new Date(year, 2, 31);
+  lastSundayInMarch.setUTCDate(
+    lastSundayInMarch.getDate() - lastSundayInMarch.getDay(),
+  );
+  const lastSundayInOctober = new Date(year, 9, 31);
+  lastSundayInOctober.setUTCDate(
+    lastSundayInOctober.getDate() - lastSundayInOctober.getDay(),
+  );
+  return date >= lastSundayInMarch && date < lastSundayInOctober;
+}