Replace isRelativeDay with date-fns isYesterday (#8286)

* Fix isRelativeDay returning wrong result across month boundaries

isRelativeDay compared the target date's day-of-month against the raw
`getDate() + offsetInDays` value instead of the day after setDate()
normalizes it. On the 1st of a month that raw value is 0 (or negative),
so a date that really is "yesterday" (the last day of the previous month)
was never matched. This made the "Yesterday" grouping in the Upcoming
Episodes view fall back to a full date on the 1st of every month.

Compare against yesterday.getDate() after the setDate() adjustment so the
month/year rollover is respected. Add unit tests covering the same-month,
month-boundary and year-boundary cases for -1/0/+1 offsets.

* Replace isRelativeDay with date-fns isYesterday

Both call sites only ever asked for an offset of -1, so drop the custom
helper and use date-fns instead, per review feedback.

---------

Co-authored-by: Konstantin Ostrovskii <4070730+Grinv@users.noreply.github.com>

src/apps/legacy/controllers/shows/tvupcoming.js

@@ -1,3 +1,5 @@
+import { isYesterday } from 'date-fns';
+
 import cardBuilder from 'components/cardbuilder/cardBuilder';
 import { getBackdropShape } from 'components/cardbuilder/utils/shape';
 import imageLoader from 'components/images/imageLoader';
@@ -55,7 +57,7 @@ function renderUpcoming(elem, items) {
         if (item.PremiereDate) {
             try {
                 const premiereDate = datetime.parseISO8601Date(item.PremiereDate, true);
-                dateText = datetime.isRelativeDay(premiereDate, -1) ? globalize.translate('Yesterday') : datetime.toLocaleDateString(premiereDate, {
+                dateText = isYesterday(premiereDate) ? globalize.translate('Yesterday') : datetime.toLocaleDateString(premiereDate, {
                     weekday: 'long',
                     month: 'short',
                     day: 'numeric'

src/apps/modern/features/libraries/utils/upcomingEpisodes.ts

@@ -1,3 +1,5 @@
+import { isYesterday } from 'date-fns';
+
 import datetime from 'scripts/datetime';
 import globalize from 'lib/globalize';
 import type { ItemDto } from 'types/base/models/item-dto';
@@ -22,7 +24,7 @@ export function groupsUpcomingEpisodes(items: ItemDto[]) {
                     item.PremiereDate,
                     true
                 );
-                dateText = datetime.isRelativeDay(premiereDate, -1) ?
+                dateText = isYesterday(premiereDate) ?
                     globalize.translate('Yesterday') :
                     datetime.toLocaleDateString(premiereDate, {
                         weekday: 'long',

src/scripts/datetime.js

@@ -273,19 +273,6 @@ export function getDisplayTime(date) {
     return time;
 }
 
-export function isRelativeDay(date, offsetInDays) {
-    if (!date) {
-        throw new Error('date cannot be null');
-    }
-
-    const yesterday = new Date();
-    const day = yesterday.getDate() + offsetInDays;
-
-    yesterday.setDate(day); // automatically adjusts month/year appropriately
-
-    return date.getFullYear() === yesterday.getFullYear() && date.getMonth() === yesterday.getMonth() && date.getDate() === day;
-}
-
 export default {
     parseISO8601Date: parseISO8601Date,
     getDisplayRunningTime: getDisplayRunningTime,
@@ -293,7 +280,6 @@ export default {
     toLocaleDateString: toLocaleDateString,
     toLocaleString: toLocaleString,
     getDisplayTime: getDisplayTime,
-    isRelativeDay: isRelativeDay,
     toLocaleTimeString: toLocaleTimeString,
     supportsLocalization: function () {
         return toLocaleTimeStringSupportsLocales;