Full refactor of codebase

src/services/elo.go

@@ -0,0 +1,136 @@
+// File elo implements a practical Elo rating update for head-to-head sports
+// such as table soccer. This variant has:
+//   - No home/away asymmetry
+//   - Margin of victory (MoV) factor using a robust bounded form
+//   - Simple burn-in: higher K for the first N games
+//   - No draws (inputs must produce a clear winner)
+//   - Rating floor
+//   - Per-match delta cap
+//   - No time weighting and no explicit uncertainty modeling
+
+package services
+
+import (
+	"errors"
+	"math"
+
+	"github.com/ascyii/qrank/src/repository"
+	"github.com/ascyii/qrank/src/utils"
+)
+
+var eloCfg = struct {
+	Mu0              float64
+	Scale            float64 // KNew applies to players during burn-in (first BurnInGames matches).
+	KNew             float64
+	KStd             float64
+	BurnInGames      int
+	RatingFloor      float64
+	MaxPerMatchDelta float64
+	MaxGoals         int
+}{
+	Mu0:              1500,
+	Scale:            400,
+	KNew:             48,
+	KStd:             24,
+	BurnInGames:      20,
+	RatingFloor:      500,
+	MaxPerMatchDelta: 60,
+	MaxGoals:         10,
+}
+
+type Team struct {
+	Players       []*repository.GameUser
+	Score         int
+	AverageRating float64
+}
+
+func NewTeam(players []*repository.GameUser, score int) *Team {
+	var t1s float64 = 0
+	for _, player := range players {
+		t1s += float64(player.User.Elo)
+
+	}
+	t1a := t1s / float64(len(players))
+
+	return &Team{Players: players, Score: score, AverageRating: t1a}
+}
+
+func GetNewElo(t1, t2 *Team) error {
+	// Update the teams
+	if t2.Score < 0 || t1.Score < 0 || t2.Score > eloCfg.MaxGoals || t1.Score > eloCfg.MaxGoals {
+		return errors.New("goals out of allowed range")
+	}
+	if t2.Score == t1.Score {
+		return errors.New("draws are not supported by this variant")
+	}
+
+	// Expected score (Bradley–Terry with logistic base-10)
+	teams := []*Team{t1, t2}
+	for i, t := range teams {
+		otherTeam := teams[1-i]
+		for i, p := range t.Players {
+			newRating, err := CalculateRating(p.User.Elo, otherTeam.AverageRating, t.Score, otherTeam.Score, p.User.GameCount)
+			if err != nil {
+				return err
+			}
+			t.Players[i].User.Elo = utils.RoundFloat(newRating, 1)
+		}
+	}
+
+	return nil
+}
+
+func CalculateRating(rA, rB float64, goalsA, goalsB, gamesA int) (newrA float64, err error) {
+	// Observed score (no draws)
+	var sA float64
+	if goalsA > goalsB {
+		sA = 1.0
+	} else {
+		sA = 0.0
+	}
+
+	// Margin of victory factor with clamped goal difference
+	diff := goalsA - goalsB
+	if diff < 0 {
+		diff = -diff
+	}
+	if diff < 1 {
+		diff = 1
+	}
+	if diff > eloCfg.MaxGoals {
+		diff = eloCfg.MaxGoals
+	}
+
+	// Raw delta before caps
+	eA := expected(eloCfg.Scale, rA, rB)
+	mov := movFactor(rA, rB, diff)
+
+	var Keff float64
+	if gamesA <= eloCfg.BurnInGames {
+		Keff = eloCfg.KNew
+	} else {
+		Keff = eloCfg.KStd
+	}
+
+	delta := Keff * mov * (sA - eA)
+
+	// Apply symmetric per-match cap
+	if delta > eloCfg.MaxPerMatchDelta {
+		delta = eloCfg.MaxPerMatchDelta
+	} else if delta < -eloCfg.MaxPerMatchDelta {
+		delta = -eloCfg.MaxPerMatchDelta
+	}
+
+	return rA + delta, nil
+}
+
+// expected returns the win probability for player A against B
+func expected(scale, rA, rB float64) float64 {
+	return 1.0 / (1.0 + math.Pow(10.0, -(rA-rB)/scale))
+}
+
+// movFactor returns a bounded margin-of-victory multiplier.
+func movFactor(rA, rB float64, diff int) float64 {
+	fd := float64(diff)
+	return math.Log(fd+1.0) * 2.2 / (math.Abs(rA-rB)*0.001 + 2.2)
+}