fix: use stable sorting algorithm for leaderboard

Author: Picoseconds

src/moomoo/Game.ts

@@ -3,7 +3,7 @@ import WebSocket from "ws";
 import Client from "./Client";
 import Player from "./Player";
 import * as lowDb from 'lowdb';
-import { randomPos, chunk } from "./util";
+import { randomPos, chunk, stableSort } from "./util";
 import msgpack from "msgpack-lite";
 import GameState from "./GameState";
 import * as Physics from "./Physics";
@@ -313,7 +313,11 @@ export default class Game {
 
     let leaderboardUpdate: (string | number)[] = [];
 
-    for (let player of this.state.players.sort((a, b) => a.points - b.points).reverse().slice(0, 10)) {
+    for (let player of stableSort(this.state.players, (a, b) => {
+      if (a.points > b.points) return -1;
+      if (a.points < b.points) return 1;
+      return 0;
+    }).reverse().slice(0, 10)) {
       leaderboardUpdate = leaderboardUpdate.concat([player.id, player.name, player.points]);
     }
 

src/moomoo/util.ts

@@ -33,4 +33,34 @@ function chunk<T>(arr: T[], len: number) {
   return chunks;
 }
 
-export { SkinColor, eucDistance, randomPos, chunk };
+interface Comparator<T> {
+  (a: T, b: T): number
+}
+
+interface Array<T> {
+  stableSort(cmp?: Comparator<T>): Array<T>;
+}
+
+let defaultCmp: Comparator<any> = (a, b) => {
+  if (a < b) return -1;
+  if (a > b) return 1;
+  return 0;
+}
+
+function stableSort<T>(array: T[], cmp: Comparator<T> = defaultCmp): T[] {
+  let stabilized = array.map((el, index) => <[T, number]>[el, index]);
+  let stableCmp: Comparator<[T, number]> = (a, b) => {
+    let order = cmp(a[0], b[0]);
+    if (order != 0) return order;
+    return a[1] - b[1];
+  }
+
+  stabilized.sort(stableCmp);
+  for (let i = 0; i < array.length; i++) {
+    array[i] = stabilized[i][0];
+  }
+
+  return array;
+}
+
+export { SkinColor, eucDistance, randomPos, chunk, stableSort };