1 files changed, 66 insertions, 0 deletions
diff --git a/bin/rtt-update-elo b/bin/rtt-update-elo
new file mode 100755
index 0000000..538964a
--- /dev/null
+++ b/bin/rtt-update-elo
@@ -0,0 +1,66 @@
+#!/usr/bin/env -S node
+
+// Recompute Elo ratings from scratch!
+
+const sqlite3 = require("better-sqlite3")
+
+const db = new sqlite3("db")
+
+const SQL_SELECT_GAMES = db.prepare("select * from rated_games_view order by mtime")
+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 is_winner(role, result) {
+	// NOTE: uses substring matching for multiple winners instead of splitting result on comma.
+	return (result === "Draw" || result === role || result.includes(role))
+}
+
+function elo_k(n) {
+	return 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
+
+	if (!game.result || game.result === "None")
+		return
+
+	let winners = 0
+	for (let p of players)
+		if (is_winner(p.role, game.result))
+			winners ++
+
+	if (winners === 0)
+		return
+
+	for (let p of players)
+		if (is_winner(p.role, game.result))
+			p.change = elo_change(p, players, 1 / winners)
+		else
+			p.change = elo_change(p, players, 0)
+
+	for (let p of players)
+		SQL_INSERT_RATING.run(game.title_id, p.user_id, p.rating + p.change, p.count + 1, game.mtime)
+}
+
+db.exec("begin transaction")
+db.exec("delete from ratings")
+for (let game of SQL_SELECT_GAMES.all())
+	update_elo_ratings(game)
+db.exec("commit")