module EloRatingSystem

# File lib/elo_rating_system.rb, line 15
def self.elo(old, exp, score, k_factor = 32)
  # @note Calculate the new Elo rating for a player.
  #
  # @param old      [Integer] The previous Elo rating.
  # @param exp      [Float]   The expected score for this match.
  # @param score    [Float]   The actual score for this match.
  # @param k_factor [Integer] The k-factor for Elo (default: 32).
  old + k_factor * (score - exp)
end

# File lib/elo_rating_system.rb, line 7
def self.expected(player_a, player_b)
  # @note Calculate expected score of A in a match against B.
  #
  # @param player_a [Integer] Elo rating for player a.
  # @param player_b [Integer] Elo rating for player b.
  1 / (1 + 10**((player_b - player_a.to_f) / 400))
end