/**
 * ELO rating system utilities for Cloud Go
 */

const DEFAULT_RATING = 1200;
const K_FACTOR = 32; // Standard K-factor for chess-like games

/**
 * Calculate expected score for a player
 * @param playerRating - Player's current rating
 * @param opponentRating - Opponent's current rating
 * @returns Expected score (0-1)
 */
function calculateExpectedScore(playerRating: number, opponentRating: number): number {
  return 1 / (1 + Math.pow(10, (opponentRating - playerRating) / 400));
}

/**
 * Calculate new ELO rating after a game
 * @param currentRating - Player's current rating
 * @param opponentRating - Opponent's rating
 * @param actualScore - Actual game result (1 = win, 0.5 = draw, 0 = loss)
 * @returns New rating
 */
export function calculateNewRating(
  currentRating: number,
  opponentRating: number,
  actualScore: number
): number {
  const expectedScore = calculateExpectedScore(currentRating, opponentRating);
  const ratingChange = K_FACTOR * (actualScore - expectedScore);
  return Math.round(currentRating + ratingChange);
}

/**
 * Get the default rating for players without a profile
 */
export function getDefaultRating(): number {
  return DEFAULT_RATING;
}