# frozen_string_literal: true

module Users
  module Digests
    class YearOverYearCalculator
      def initialize(user, year)
        @user = user
        @year = year.to_i
      end

      def call
        return {} unless previous_year_stats.exists?

        {
          'previous_year' => year - 1,
          'distance_change_percent' => calculate_distance_change_percent,
          'countries_change' => calculate_countries_change,
          'cities_change' => calculate_cities_change
        }.compact
      end

      private

      attr_reader :user, :year

      def previous_year_stats
        @previous_year_stats ||= user.stats.where(year: year - 1)
      end

      def current_year_stats
        @current_year_stats ||= user.stats.where(year: year)
      end

      def calculate_distance_change_percent
        prev_distance = previous_year_stats.sum(:distance)
        return nil if prev_distance.zero?

        curr_distance = current_year_stats.sum(:distance)
        ((curr_distance - prev_distance).to_f / prev_distance * 100).round
      end

      def calculate_countries_change
        prev_count = count_countries(previous_year_stats)
        curr_count = count_countries(current_year_stats)

        curr_count - prev_count
      end

      def calculate_cities_change
        prev_count = count_cities(previous_year_stats)
        curr_count = count_cities(current_year_stats)

        curr_count - prev_count
      end

      def count_countries(stats)
        stats.flat_map do |stat|
          toponyms = stat.toponyms
          next [] unless toponyms.is_a?(Array)

          toponyms.filter_map { |t| t['country'] if t.is_a?(Hash) && t['country'].present? }
        end.uniq.count
      end

      def count_cities(stats)
        stats.flat_map do |stat|
          toponyms = stat.toponyms
          next [] unless toponyms.is_a?(Array)

          toponyms.flat_map do |t|
            next [] unless t.is_a?(Hash) && t['cities'].is_a?(Array)

            t['cities'].filter_map { |c| c['city'] if c.is_a?(Hash) && c['city'].present? }
          end
        end.uniq.count
      end
    end
  end
end