make april fools cycle through

website/common/script/content/constants/april_fools.js

@@ -1,6 +1,21 @@
 import eggs from '../eggs';
 
-export default function makeSubstitutionMap (swappedPotion) {
+const SWAPS = [
+  'Veggie',
+  'Dessert',
+  'VirtualPet',
+  'TeaShop',
+  'Fungi',
+  'Cryptid',
+];
+
+export function getMatchingSwap () {
+  const year = new Date().getFullYear();
+  const diff = year - 2020;
+  return SWAPS[diff % SWAPS.length];
+}
+
+export function makeSubstitutionMap (swappedPotion) {
   const substitutions = {
     pets: {
       'Pet-Wolf-': `Pet-Wolf-${swappedPotion}`,

website/common/script/content/constants/events.js

@@ -1,6 +1,6 @@
 /* eslint-disable key-spacing */
 import moment from 'moment';
-import makeSubstitutionMap from './april_fools';
+import { getMatchingSwap, makeSubstitutionMap} from './april_fools';
 
 // gem block: number of gems
 const gemsPromo = {
@@ -54,7 +54,7 @@ export const REPEATING_EVENTS = {
   aprilFools: {
     start: new Date('1970-04-01T04:00-04:00'),
     end: new Date('1970-04-02T03:59-04:00'),
-    spriteSubstitutions: makeSubstitutionMap('Cryptid'),
+    spriteSubstitutions: makeSubstitutionMap(getMatchingSwap()),
   },
   aprilFoolsResale: {
     start: new Date('1970-04-03T04:00-04:00'),