gistfile1.rb

    def match! battle, winner, loser
      r_a = winner.rating
      r_b = loser.rating
      max = battle.max.to_i
      min = battle.min.to_i
      th = ( max - min ) / 2

      e_a = 1.0 / ( 1 + 10 ** ( (r_b - r_a) / 400 ))
      e_b = 1.0 / ( 1 + 10 ** ( (r_a - r_b) / 400 ))


      w_a = 1
      w_b = 0
      winner.won += 1
      loser.lost += 1
      
      k_a = r_a >= th ? 16 : 32
      k_b = r_b >= th ? 16 : 32

      r_a_new = ( r_a + k_a * ( w_a - e_a ) ).round
      r_b_new = ( r_b + k_b * ( w_b - e_b ) ).round

      winner.rating = r_a_new
      loser.rating = r_b_new

      winner.save!
      loser.save!

      battle.max = [max, r_a_new, r_b_new].max
      battle.min = [min, r_a_new, r_b_new].min
      battle.save!
    end