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#!/usr/bin/env -S node
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 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
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")
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