Have time.js use UTC-related getters/setters (#30857) (#30869)

Backport #30857 by kemzeb

Co-authored-by: Kemal Zebari <60799661+kemzeb@users.noreply.github.com>
Co-authored-by: Sam Fisher <fisher@3echelon.local>

4 files changed, 22 insertions, 17 deletions

diff --git a/web_src/js/components/RepoCodeFrequency.vue b/web_src/js/components/RepoCodeFrequency.vue
index adce431264..1d40d6d417 100644
--- a/web_src/js/components/RepoCodeFrequency.vue
+++ b/web_src/js/components/RepoCodeFrequency.vue
@@ -67,7 +67,7 @@ export default {
           const weekValues = Object.values(this.data);
           const start = weekValues[0].week;
           const end = firstStartDateAfterDate(new Date());
-          const startDays = startDaysBetween(new Date(start), new Date(end));
+          const startDays = startDaysBetween(start, end);
           this.data = fillEmptyStartDaysWithZeroes(startDays, this.data);
           this.errorText = '';
         } else {
diff --git a/web_src/js/components/RepoContributors.vue b/web_src/js/components/RepoContributors.vue
index 2347c41ae4..f7b05831e0 100644
--- a/web_src/js/components/RepoContributors.vue
+++ b/web_src/js/components/RepoContributors.vue
@@ -114,7 +114,7 @@ export default {
           const weekValues = Object.values(total.weeks);
           this.xAxisStart = weekValues[0].week;
           this.xAxisEnd = firstStartDateAfterDate(new Date());
-          const startDays = startDaysBetween(new Date(this.xAxisStart), new Date(this.xAxisEnd));
+          const startDays = startDaysBetween(this.xAxisStart, this.xAxisEnd);
           total.weeks = fillEmptyStartDaysWithZeroes(startDays, total.weeks);
           this.xAxisMin = this.xAxisStart;
           this.xAxisMax = this.xAxisEnd;
diff --git a/web_src/js/components/RepoRecentCommits.vue b/web_src/js/components/RepoRecentCommits.vue
index 502af533da..8759978e78 100644
--- a/web_src/js/components/RepoRecentCommits.vue
+++ b/web_src/js/components/RepoRecentCommits.vue
@@ -62,7 +62,7 @@ export default {
           const data = await response.json();
           const start = Object.values(data)[0].week;
           const end = firstStartDateAfterDate(new Date());
-          const startDays = startDaysBetween(new Date(start), new Date(end));
+          const startDays = startDaysBetween(start, end);
           this.data = fillEmptyStartDaysWithZeroes(startDays, data).slice(-52);
           this.errorText = '';
         } else {
diff --git a/web_src/js/utils/time.js b/web_src/js/utils/time.js
index 1848792c98..7c7eabd1a3 100644
--- a/web_src/js/utils/time.js
+++ b/web_src/js/utils/time.js
@@ -1,25 +1,30 @@
 import dayjs from 'dayjs';
+import utc from 'dayjs/plugin/utc.js';
 import {getCurrentLocale} from '../utils.js';
 
-// Returns an array of millisecond-timestamps of start-of-week days (Sundays)
+dayjs.extend(utc);
+
+/**
+ * Returns an array of millisecond-timestamps of start-of-week days (Sundays)
+ *
+ * @param startConfig The start date. Can take any type that `Date` accepts.
+ * @param endConfig The end date. Can take any type that `Date` accepts.
+ */
 export function startDaysBetween(startDate, endDate) {
+  const start = dayjs.utc(startDate);
+  const end = dayjs.utc(endDate);
+
+  let current = start;
+
   // Ensure the start date is a Sunday
-  while (startDate.getDay() !== 0) {
-    startDate.setDate(startDate.getDate() + 1);
+  while (current.day() !== 0) {
+    current = current.add(1, 'day');
   }
 
-  const start = dayjs(startDate);
-  const end = dayjs(endDate);
   const startDays = [];
-
-  let current = start;
   while (current.isBefore(end)) {
     startDays.push(current.valueOf());
-    // we are adding 7 * 24 hours instead of 1 week because we don't want
-    // date library to use local time zone to calculate 1 week from now.
-    // local time zone is problematic because of daylight saving time (dst)
-    // used on some countries
-    current = current.add(7 * 24, 'hour');
+    current = current.add(1, 'week');
   }
 
   return startDays;
@@ -29,10 +34,10 @@ export function firstStartDateAfterDate(inputDate) {
   if (!(inputDate instanceof Date)) {
     throw new Error('Invalid date');
   }
-  const dayOfWeek = inputDate.getDay();
+  const dayOfWeek = inputDate.getUTCDay();
   const daysUntilSunday = 7 - dayOfWeek;
   const resultDate = new Date(inputDate.getTime());
-  resultDate.setDate(resultDate.getDate() + daysUntilSunday);
+  resultDate.setUTCDate(resultDate.getUTCDate() + daysUntilSunday);
   return resultDate.valueOf();
 }