feat: add authoritative rating outcome scoring

server/domain/rating.go

@@ -30,6 +30,33 @@ type Opponent struct {
 	Score    float64
 }
 
+type MatchOutcome struct {
+	Team0Score int
+	Team1Score int
+	Overtime   bool
+	Abandoners map[string]bool
+}
+
+func ScoreForPlayer(outcome MatchOutcome, playerID string, team int) (float64, error) {
+	if playerID == "" || (team != 0 && team != 1) || outcome.Team0Score < 0 || outcome.Team1Score < 0 {
+		return 0, fmt.Errorf("invalid match outcome")
+	}
+	if outcome.Abandoners[playerID] {
+		return 0, nil
+	}
+	if outcome.Team0Score == outcome.Team1Score {
+		return 0.5, nil
+	}
+	winner := 0
+	if outcome.Team1Score > outcome.Team0Score {
+		winner = 1
+	}
+	if team == winner {
+		return 1, nil
+	}
+	return 0, nil
+}
+
 type RankedProfile struct {
 	Rating
 	RankedGames   int