Simplify leaderboard rows and defer disruptive refreshes

src/lib/leaderboard-updates.ts

@@ -0,0 +1,27 @@
+import type { LeaderboardResponse } from './leaderboard.js';
+
+export const leaderboardPageSize = 25;
+
+/** Keep a viewed ranking stable until the reader chooses to apply new results. */
+export function createLeaderboardUpdates(scope: string, current: LeaderboardResponse) {
+    let pending: LeaderboardResponse | null = null;
+    return {
+        reset(nextScope: string, report: LeaderboardResponse) {
+            scope = nextScope;
+            current = report;
+            pending = null;
+        },
+        receive(requestScope: string, report: LeaderboardResponse, inspecting: boolean) {
+            if (requestScope !== scope) return null;
+            if (JSON.stringify(current) === JSON.stringify(report)) pending = null;
+            else if (inspecting || pending) pending = report;
+            else current = report;
+            return { current, pending };
+        },
+        apply() {
+            if (pending) current = pending;
+            pending = null;
+            return current;
+        }
+    };
+}