Show same cake day date independent of timezone (#2455)

* Show same cake day date independent of timezone

* Remove commented out assertions

src/shared/components/person/profile.tsx

@@ -24,7 +24,7 @@ import { canMod } from "@utils/roles";
 import type { QueryParams } from "@utils/types";
 import { RouteDataResponse } from "@utils/types";
 import classNames from "classnames";
-import { format, parseISO } from "date-fns";
+import { format } from "date-fns";
 import { NoOptionI18nKeys } from "i18next";
 import { Component, linkEvent } from "inferno";
 import { Link } from "inferno-router";
@@ -99,6 +99,7 @@ import { PersonListing } from "./person-listing";
 import { getHttpBaseInternal } from "../../utils/env";
 import { IRoutePropsWithFetch } from "../../routes";
 import { MediaUploads } from "../common/media-uploads";
+import { cakeDate } from "@utils/helpers";
 
 type ProfileData = RouteDataResponse<{
   personRes: GetPersonDetailsResponse;
@@ -695,7 +696,7 @@ export class Profile extends Component<ProfileRouteProps, ProfileState> {
                 <Icon icon="cake" />
                 <span className="ms-2">
                   {I18NextService.i18n.t("cake_day_title")}{" "}
-                  {format(parseISO(pv.person.published), "PPP")}
+                  {format(cakeDate(pv.person.published), "PPP")}
                 </span>
               </div>
               {!UserService.Instance.myUserInfo && (

src/shared/utils/helpers/index.ts

@@ -13,7 +13,7 @@ import getUnixTime from "./get-unix-time";
 import { groupBy } from "./group-by";
 import hostname from "./hostname";
 import hsl from "./hsl";
-import isCakeDay from "./is-cake-day";
+import isCakeDay, { cakeDate } from "./is-cake-day";
 import numToSI from "./num-to-si";
 import poll from "./poll";
 import randomStr from "./random-str";
@@ -27,6 +27,7 @@ import dedupByProperty from "./dedup-by-property";
 import getApubName from "./apub-name";
 
 export {
+  cakeDate,
   capitalizeFirstLetter,
   debounce,
   editListImmutable,

src/shared/utils/helpers/is-cake-day.ts

@@ -1,34 +1,18 @@
-import { parseISO, getYear, getDayOfYear, isLeapYear } from "date-fns";
+import { getYear, isSameDay, isSameYear, parse, setYear } from "date-fns";
 
-const leapDay = getDayOfYear(new Date(2024, 1, 29));
+// Returns a date in local time with the same year, month and day. Ignores the
+// source timezone. The goal is to show the same date in all timezones.
+export function cakeDate(published: string): Date {
+  return parse(published.substring(0, 10), "yyyy-MM-dd", new Date(0));
+}
 
 export default function isCakeDay(published: string): boolean {
-  const createDate = parseISO(published);
-  const createDateDayOfYear = getDayOfYear(createDate);
-  const isCreateDateLeapYear = isLeapYear(createDate);
-
+  const createDate = cakeDate(published);
   const currentDate = new Date();
-  let currentDateDayOfYear = getDayOfYear(currentDate);
-  const isCurrentDateLeapYear = isLeapYear(currentDate);
-
-  if (
-    isCreateDateLeapYear &&
-    !isCurrentDateLeapYear &&
-    currentDateDayOfYear >= leapDay
-  ) {
-    ++currentDateDayOfYear;
-  }
-
-  if (
-    !isCreateDateLeapYear &&
-    isCurrentDateLeapYear &&
-    createDateDayOfYear >= leapDay
-  ) {
-    --currentDateDayOfYear;
-  }
 
+  // The day-overflow of Date makes leap days become 03-01 in non leap years.
   return (
-    createDateDayOfYear === currentDateDayOfYear &&
-    getYear(createDate) !== getYear(currentDate)
+    isSameDay(currentDate, setYear(createDate, getYear(currentDate))) &&
+    !isSameYear(currentDate, createDate)
   );
 }