#434

frontend/src/lib/utils.ts

@@ -17,24 +17,26 @@ export const cn = (...inputs: ClassValue[]) => twMerge (clsx (...inputs))
 
 type DatePrecision = 'month' | 'day' | 'hour' | 'minute' | 'second' | null
 
-const dateFormatters = new Map<DatePrecision, Intl.DateTimeFormat> ()
-let ainuDateFormatter: Intl.DateTimeFormat | null = null
+const dateFormatters = new Map<string, Intl.DateTimeFormat> ()
+const ainuDateFormatters = new Map<string, Intl.DateTimeFormat> ()
 
 
 const formatDateString = (
     date: Date,
     unknown: DatePrecision,
     locale: LocaleCode,
+    timeZone = 'Asia/Tokyo',
 ): string => {
+  const key = `${timeZone}/${unknown}`
   if (Number.isNaN (date.getTime ()))
     return date.toString ()
   if (locale === 'ja')
   {
-    if (!dateFormatters.has (unknown))
+    if (!dateFormatters.has (key))
     {
-      dateFormatters.set (unknown, new Intl.DateTimeFormat ('ja-JP-u-ca-japanese', {
+      dateFormatters.set (key, new Intl.DateTimeFormat ('ja-JP-u-ca-japanese', {
 	  era: 'long', year: 'numeric',
-	  timeZone: 'Asia/Tokyo',
+	  timeZone,
 	  month: unknown === 'month' ? undefined : 'long',
 	  day: unknown != null && ['month', 'day'].includes (unknown) ? undefined : 'numeric',
 	  weekday: unknown != null && ['month', 'day'].includes (unknown) ? undefined : 'short',
@@ -42,14 +44,15 @@ const formatDateString = (
 	  minute: unknown == null || unknown === 'second' ? 'numeric' : undefined,
 	  second: unknown == null ? 'numeric' : undefined }))
     }
-    return dateFormatters.get (unknown)!.format (date)
+    return dateFormatters.get (key)!.format (date)
   }
-  ainuDateFormatter ??= new Intl.DateTimeFormat ('en-CA', {
+  if (!ainuDateFormatters.has (timeZone))
+    ainuDateFormatters.set (timeZone, new Intl.DateTimeFormat ('en-CA', {
       year: 'numeric', month: '2-digit', day: '2-digit',
-      timeZone: 'Asia/Tokyo',
+      timeZone,
       hour: '2-digit', minute: '2-digit', second: '2-digit',
-      hourCycle: 'h23' })
-  const parts = ainuDateFormatter.formatToParts (date)
+      hourCycle: 'h23' }))
+  const parts = ainuDateFormatters.get (timeZone)!.formatToParts (date)
   const part = (type: string) => parts.find (entry => entry.type === type)?.value ?? ''
   const omitDay = unknown != null && ['month', 'day'].includes (unknown)
   const dateParts = [part ('year'),
@@ -76,7 +79,8 @@ export const localisedDateString = (
     value: string | Date,
     locale: LocaleCode,
     unknown: DatePrecision = null,
-): string => dateString (value, unknown, locale)
+    timeZone?: string,
+): string => formatDateString (toDate (value), unknown, locale, timeZone)
 
 
 export const originalCreatedAtString = (