perf: improve top-20 leaderboard algorithm

src/main.rs

@@ -48,12 +48,14 @@ enum LeaderboardUpdateType {
 	Increment { loscore: u32 },
 }
 
-static CHANCE: f64 = 1.0 / 3.0;
+const CHANCE: f64 = 1.0 / 3.0;
 
 const PATH_HISCORES: &str = "hiscores.json";
 const PATH_LOSCORES: &str = "loscores.json";
 const PATH_PINGSCORES: &str = "pingscores.json";
 
+const MAX_LEADERBOARD: usize = 20;
+
 #[tokio::main]
 async fn main() {
 	fn read_file<T: for<'de> de::Deserialize<'de>>(file_path: &str) -> Arc<Mutex<T>> {
@@ -61,8 +63,17 @@ async fn main() {
 		Arc::new(Mutex::new(serde_json::from_str(&file_contents).unwrap()))
 	}
 
+	/// Makes the vector at `vec` one with a capacity of exactly [`MAX_LEADERBOARD`] if `vec` is
+	/// smaller or equal.
+	fn exact_leaderboard<T>(mut vec: impl DerefMut<Target = Vec<T>>) {
+		let mut old_vec = std::mem::replace(&mut *vec, Vec::with_capacity(MAX_LEADERBOARD));
+		old_vec.drain(..).for_each(|e| vec.push(e));
+	}
+
 	let hiscores: Arc<Mutex<Vec<Entry>>> = read_file(PATH_HISCORES);
+	exact_leaderboard(hiscores.lock().await);
 	let loscores: Arc<Mutex<Vec<Entry>>> = read_file(PATH_LOSCORES);
+	exact_leaderboard(loscores.lock().await);
 	let pingscores: Arc<Mutex<HashMap<String, (u64, u32)>>> = read_file(PATH_PINGSCORES);
 
 	let (tx, rx) = mpsc::channel::<LeaderboardUpdate>(1024);
@@ -129,22 +140,29 @@ async fn handle_hiscores(
 ) {
 	fn update_scoretable<G: Deref<Target = Vec<Entry>> + DerefMut>(
 		score_name: &str,
-		mut scoretable: G,
+		mut scoretable_lock: G,
 		name: &str,
 		score: u32,
 		file_path: &str,
 	) {
-		if scoretable.last().is_none_or(|e| score > e.score) {
+		let scoretable = &mut *scoretable_lock;
+
+		if let Some(index_to_insert_at) = scoretable.iter().position(|e| score > e.score) {
 			println!("New {score_name} {score} by {name}");
-			scoretable.push(Entry {
+			scoretable[index_to_insert_at..].rotate_right(1);
+			let push_out = std::mem::replace(
+				&mut scoretable[index_to_insert_at],
+				Entry {
 					score,
 					person: name.to_string(),
-			});
-			scoretable.sort();
-			scoretable.reverse();
-			scoretable.truncate(20);
-			let file_contents: String = serde_json::to_string(&*scoretable).unwrap();
-			drop(scoretable);
+				},
+			);
+			if scoretable.len() < MAX_LEADERBOARD {
+				scoretable.push(push_out);
+			}
+
+			let file_contents: String = serde_json::to_string(&*scoretable_lock).unwrap();
+			drop(scoretable_lock);
 			let mut file = fs::OpenOptions::new()
 				.write(true)
 				.truncate(true)
@@ -152,6 +170,12 @@ async fn handle_hiscores(
 				.unwrap();
 			file.write_all(file_contents.as_bytes()).unwrap();
 			file.flush().unwrap();
+		} else if scoretable.len() < MAX_LEADERBOARD {
+			println!("New {score_name} {score} by {name}");
+			scoretable.push(Entry {
+				score,
+				person: name.to_string(),
+			});
 		}
 	}