impr: optimize getFirstDayOfWeek (@fehmer) (monkeytypegame#6457)

!nuf

Author: fehmer

frontend/src/ts/utils/date-and-time.ts

@@ -1,6 +1,6 @@
 import { roundTo2 } from "@monkeytype/util/numbers";
 import { Day } from "date-fns";
-import * as Locales from "date-fns/locale";
+
 /**
  * Converts seconds to a human-readable string representation of time.
  * @param sec The number of seconds to convert.
@@ -106,6 +106,115 @@ export function secondsToString(
   return ret.trim();
 }
 
+/*
+generated by
+import * as Locales from "date-fns/locale";
+const result = {};
+  for (const locale of Object.keys(Locales)) {
+    // @ts-ignore
+    const data = Locales[locale] as Locales.Locale;
+    result[locale] = (data.options?.weekStartsOn as number) % 7;
+  }
+  */
+
+const weekStartsOnFallback: Record<string, Day> = {
+  af: 0,
+  ar: 6,
+  arDZ: 0,
+  arEG: 0,
+  arMA: 1,
+  arSA: 0,
+  arTN: 1,
+  az: 1,
+  be: 1,
+  beTarask: 1,
+  bg: 1,
+  bn: 0,
+  bs: 1,
+  ca: 1,
+  ckb: 0,
+  cs: 1,
+  cy: 0,
+  da: 1,
+  de: 1,
+  deAT: 1,
+  el: 1,
+  enAU: 1,
+  enCA: 0,
+  enGB: 1,
+  enIE: 1,
+  enIN: 1,
+  enNZ: 1,
+  enUS: 0,
+  enZA: 0,
+  eo: 1,
+  es: 1,
+  et: 1,
+  eu: 1,
+  faIR: 6,
+  fi: 1,
+  fr: 1,
+  frCA: 0,
+  frCH: 1,
+  fy: 1,
+  gd: 0,
+  gl: 1,
+  gu: 1,
+  he: 0,
+  hi: 0,
+  hr: 1,
+  ht: 1,
+  hu: 1,
+  hy: 1,
+  id: 1,
+  is: 1,
+  it: 1,
+  itCH: 1,
+  ja: 0,
+  jaHira: 0,
+  ka: 1,
+  kk: 1,
+  km: 0,
+  kn: 1,
+  ko: 0,
+  lb: 1,
+  lt: 1,
+  lv: 1,
+  mk: 1,
+  mn: 1,
+  ms: 1,
+  mt: 1,
+  nb: 1,
+  nl: 1,
+  nlBE: 1,
+  nn: 1,
+  oc: 1,
+  pl: 1,
+  pt: 1,
+  ptBR: 0,
+  ro: 1,
+  ru: 1,
+  se: 1,
+  sk: 1,
+  sl: 1,
+  sq: 1,
+  sr: 1,
+  srLatn: 1,
+  sv: 1,
+  ta: 1,
+  te: 0,
+  th: 0,
+  tr: 1,
+  ug: 0,
+  uk: 1,
+  uz: 1,
+  uzCyrl: 1,
+  vi: 1,
+  zhCN: 1,
+  zhHK: 0,
+  zhTW: 1,
+};
+
 export function getFirstDayOfTheWeek(): Day {
   if (navigator.language === undefined || navigator.language === null) {
     return 0;
@@ -128,20 +237,16 @@ export function getFirstDayOfTheWeek(): Day {
     return (locale.getWeekInfo().firstDay as number) % 7;
   }
 
-  //use date-fns for browsers like firefox
-  // @ts-ignore
-  let dateFnsLocale = Locales[
-    navigator.language.replaceAll("-", "")
-  ] as Locales.Locale;
-
-  if (dateFnsLocale === undefined || dateFnsLocale === null) {
-    //retry with language only
-    // @ts-ignore
-    dateFnsLocale = Locales[navigator.language.split("-")[0]] as Locales.Locale;
+  //use fallback generated from date-fns for browsers like firefox
+  let fallback = weekStartsOnFallback[navigator.language.replaceAll("-", "")];
+  if (fallback !== undefined) {
+    return fallback;
   }
 
-  if (dateFnsLocale !== undefined && dateFnsLocale !== null) {
-    return ((dateFnsLocale.options?.weekStartsOn ?? 0) % 7) as Day;
+  //retry with language only
+  fallback = weekStartsOnFallback[navigator.language.split("-")[0] as string];
+  if (fallback !== undefined) {
+    return fallback;
   }
 
   return 0; //start on sunday