nextjs-rewrite (#5)

Reviewed-on: #5
Co-authored-by: David Gwilliam <dhgwilliam@gmail.com>
Co-committed-by: David Gwilliam <dhgwilliam@gmail.com>

src/lib/elo-utils.ts

@@ -0,0 +1,152 @@
+/**
+ * Elo Rating Utilities
+ * 
+ * Provides functions for calculating Elo ratings and changes
+ * Based on the standard Elo rating system
+ */
+
+/**
+ * Calculate the expected score for a player based on rating difference
+ * @param ratingA Player A's rating
+ * @param ratingB Player B's rating
+ * @returns Expected score (0-1) for Player A
+ */
+export function calculateExpectedScore(ratingA: number, ratingB: number): number {
+  const ratingDiff = ratingA - ratingB;
+  return 1 / (1 + Math.pow(10, -ratingDiff / 400));
+}
+
+/**
+ * Calculate Elo rating change for a single game
+ * @param rating Player's current rating
+ * @param opponentRating Opponent's rating
+ * @param actualScore Actual score (1 = win, 0.5 = draw, 0 = loss)
+ * @param kFactor K-factor (how much ratings change per game)
+ * @returns Elo rating change (positive or negative)
+ */
+export function calculateEloChange(
+  rating: number,
+  opponentRating: number,
+  actualScore: number,
+  kFactor: number = 32
+): number {
+  const expectedScore = calculateExpectedScore(rating, opponentRating);
+  return kFactor * (actualScore - expectedScore);
+}
+
+/**
+ * Calculate team Elo rating as average of individual ratings
+ * @param rating1 Rating of player 1
+ * @param rating2 Rating of player 2
+ * @returns Team rating
+ */
+export function calculateTeamElo(rating1: number, rating2: number): number {
+  return (rating1 + rating2) / 2;
+}
+
+/**
+ * Update player statistics after a match
+ * @param currentRating Current player rating
+ * @param currentGamesPlayed Current games played count
+ * @param currentWins Current wins count
+ * @param eloChange Elo rating change
+ * @param won Whether the player won
+ * @returns Updated statistics
+ */
+export function updatePlayerStats(
+  currentRating: number,
+  currentGamesPlayed: number,
+  currentWins: number,
+  eloChange: number,
+  won: boolean
+): {
+  newRating: number;
+  newGamesPlayed: number;
+  newWins: number;
+  newLosses: number;
+  winRate: number;
+} {
+  const newRating = currentRating + Math.round(eloChange);
+  const newGamesPlayed = currentGamesPlayed + 1;
+  const newWins = currentWins + (won ? 1 : 0);
+  const newLosses = newGamesPlayed - newWins;
+  const winRate = newGamesPlayed > 0 ? newWins / newGamesPlayed : 0;
+
+  return {
+    newRating,
+    newGamesPlayed,
+    newWins,
+    newLosses,
+    winRate,
+  };
+}
+
+/**
+ * Calculate new rating after a match
+ * @param currentRating Current rating
+ * @param opponentRating Opponent's rating
+ * @param won Whether the player won
+ * @param kFactor K-factor (default 32)
+ * @returns New rating
+ */
+export function calculateNewRating(
+  currentRating: number,
+  opponentRating: number,
+  won: boolean,
+  kFactor: number = 32
+): number {
+  const actualScore = won ? 1 : 0;
+  const eloChange = calculateEloChange(currentRating, opponentRating, actualScore, kFactor);
+  return Math.round(currentRating + eloChange);
+}
+
+/**
+ * Validate rating is within reasonable bounds
+ * @param rating Rating to validate
+ * @returns Whether the rating is valid
+ */
+export function isValidRating(rating: number): boolean {
+  return rating >= 100 && rating <= 3000;
+}
+
+/**
+ * Get rating tier name based on rating
+ * @param rating Player rating
+ * @returns Tier name
+ */
+export function getRatingTier(rating: number): string {
+  if (rating < 1100) return 'Beginner';
+  if (rating < 1300) return 'Novice';
+  if (rating < 1500) return 'Intermediate';
+  if (rating < 1700) return 'Advanced';
+  if (rating < 1900) return 'Expert';
+  if (rating < 2100) return 'Master';
+  return 'Grandmaster';
+}
+
+/**
+ * Calculate expected score for a team match
+ * @param team1Rating Average rating of team 1
+ * @param team2Rating Average rating of team 2
+ * @returns Expected score for team 1
+ */
+export function calculateExpectedTeamScore(team1Rating: number, team2Rating: number): number {
+  return calculateExpectedScore(team1Rating, team2Rating);
+}
+
+/**
+ * Calculate Elo change for team match
+ * @param team1Rating Average rating of team 1
+ * @param team2Rating Average rating of team 2
+ * @param team1Score Actual score for team 1 (1 = win, 0.5 = draw, 0 = loss)
+ * @param kFactor K-factor (default 32)
+ * @returns Elo change for team 1
+ */
+export function calculateTeamEloChange(
+  team1Rating: number,
+  team2Rating: number,
+  team1Score: number,
+  kFactor: number = 32
+): number {
+  return calculateEloChange(team1Rating, team2Rating, team1Score, kFactor);
+}