Calculate Elo ratings.

Primarily for use with future matchmaking system to provide better games for
everyone.

Show top 5 players of each game on the game pages.

1 files changed, 58 insertions, 0 deletions

diff --git a/tools/elo.js b/tools/elo.js
new file mode 100644
index 0000000..95ca58b
--- /dev/null
+++ b/tools/elo.js
@@ -0,0 +1,58 @@
+#!/usr/bin/env -S node
+
+const sqlite3 = require("better-sqlite3")
+
+const db = new sqlite3("db")
+
+const SQL_SELECT_GAMES = db.prepare("select * from games where status>1 and user_count=player_count and player_count>1 order by xtime")
+const SQL_SELECT_RATING = db.prepare("select * from player_rating_view where game_id=?")
+const SQL_INSERT_RATING = db.prepare("insert or replace into ratings (title_id,user_id,rating,count,last) values (?,?,?,?,?)")
+
+function elo_k(n) {
+	return n < 10 ? 60 : 30
+}
+
+function elo_ev(a, players) {
+	// Generalized formula for multiple players.
+	// https://arxiv.org/pdf/2104.05422.pdf
+	let sum = 0
+	for (let p of players)
+		sum += Math.pow(10, p.rating / 400)
+	return Math.pow(10, a.rating / 400) / sum
+}
+
+function elo_change(a, players, s) {
+	return Math.round(elo_k(a.count) * (s - elo_ev(a, players)))
+}
+
+function update_elo_ratings(game) {
+	let players = SQL_SELECT_RATING.all(game.game_id)
+	if (game.player_count !== players.length)
+		return
+
+	let winner = null
+	for (let p of players)
+		if (p.role === game.result)
+			winner = p
+
+	if (winner) {
+		for (let p of players) {
+			if (p === winner)
+				p.change = elo_change(p, players, 1)
+			else
+				p.change = elo_change(p, players, 0)
+		}
+	} else {
+		for (let p of players)
+			p.change = elo_change(p, players, 1 / game.player_count)
+	}
+
+	for (let p of players)
+		SQL_INSERT_RATING.run(game.title_id, p.user_id, p.rating + p.change, p.count+1, game.xtime)
+}
+
+db.exec("begin transaction")
+db.exec("delete from ratings")
+for (let game of SQL_SELECT_GAMES.all())
+	update_elo_ratings(game)
+db.exec("commit")