require_relative "rank_king/web"
require_relative "rank_king/models"
require_relative "rank_king/open_skill"

module RankKing
  OS = OpenSkill.new
  Match = Data.define(:a, :b)

  def self.find_match(axis:)
    items = axis.pool.items

    items.combination(2).sort_by {|combo|
      ratings = combo.map {|item| os_rating(axis:, item:) }
      Math.sqrt(
        [ratings, ratings.reverse]
          .map {|game| [game, OS.rate(game.map {[_1]}).flatten] }
          .sum {|pre,post| pre.zip(post).sum { (_1.sigma - _2.sigma)**2 }}
      )
    }.last
  end

  def self.rank(axis:, winner:, loser:)
    fail unless [winner, loser].all? { _1.pool == axis.pool }

    game = [winner, loser].map { os_rating(axis:, item: _1) }
    result = OS.rate(game.map { [_1] }).flatten

    DB.transaction do
      Ranking.create(axis:, winner:, loser:)
      Rating.update_or_create({axis:, item: winner}, result.fetch(0).to_h)
      Rating.update_or_create({axis:, item: loser}, result.fetch(1).to_h)
    end
  end

  private

  def self.os_rating(**filter)
    if result = Rating.where(**filter).first
      OS.rating(mu: result.mu, sigma: result.sigma)
    else
      OS.rating
    end
  end
end