# frozen_string_literal: true

module EuchreCamp
  module Services
    class EloCalculator
      # Standard Elo K-factor
      K_FACTOR = 32

      # Calculate Elo ratings for a 2v2 Euchre match
      #
      # @param player_ratings [Hash] player_id => current_rating
      # @param team_1_players [Array<Integer>] player IDs for team 1
      # @param team_2_players [Array<Integer>] player IDs for team 2
      # @param team_1_score [Integer] score for team 1
      # @param team_2_score [Integer] score for team 2
      # @return [Hash] player_id => { rating_before:, rating_after:, rating_change: }
      def self.calculate(player_ratings:, team_1_players:, team_2_players:, team_1_score:, team_2_score:)
        # Validate inputs
        raise ArgumentError, "Team 1 must have exactly 2 players" unless team_1_players.length == 2
        raise ArgumentError, "Team 2 must have exactly 2 players" unless team_2_players.length == 2

        # Determine winner (first to 10 points)
        team_1_wins = team_1_score >= 10
        team_2_wins = team_2_score >= 10

        unless team_1_wins || team_2_wins
          raise ArgumentError, "One team must reach 10 points to win"
        end

        if team_1_wins && team_2_wins
          raise ArgumentError, "Only one team can win (both reached 10 points)"
        end

        winner = team_1_wins ? :team_1 : :team_2

        # Calculate average ratings for each team
        team_1_avg = team_1_players.map { |id| player_ratings[id] }.sum / 2.0
        team_2_avg = team_2_players.map { |id| player_ratings[id] }.sum / 2.0

        # Calculate expected scores using Elo formula
        # E = 1 / (1 + 10^((R_opp - R_team) / 400))
        expected_team_1 = 1.0 / (1.0 + 10.0**((team_2_avg - team_1_avg) / 400.0))
        expected_team_2 = 1.0 / (1.0 + 10.0**((team_1_avg - team_2_avg) / 400.0))

        # Actual scores (1 for win, 0 for loss)
        actual_team_1 = team_1_wins ? 1.0 : 0.0
        actual_team_2 = team_2_wins ? 1.0 : 0.0

        # Calculate rating changes for each player
        results = {}

        # Team 1 players
        team_1_players.each do |player_id|
          old_rating = player_ratings[player_id]
          rating_change = K_FACTOR * (actual_team_1 - expected_team_1)
          new_rating = (old_rating + rating_change).round
          results[player_id] = {
            rating_before: old_rating,
            rating_after: new_rating,
            rating_change: rating_change.round
          }
        end

        # Team 2 players
        team_2_players.each do |player_id|
          old_rating = player_ratings[player_id]
          rating_change = K_FACTOR * (actual_team_2 - expected_team_2)
          new_rating = (old_rating + rating_change).round
          results[player_id] = {
            rating_before: old_rating,
            rating_after: new_rating,
            rating_change: rating_change.round
          }
        end

        results
      end
    end
  end
end