module Statisticable
  extend ActiveSupport::Concern

  included do
    attr_reader :resource

    def initialize(resource)
      @resource = resource
    end

    def generate
      self.class.stats_methods.map { |stat_name| [stat_name, send(stat_name)] }.to_h
    end

    private

      def total_participants_with_gender
        participants.where.not(gender: nil).distinct.count
      end

      def total_male_participants
        participants.where(gender: "male").count
      end

      def total_female_participants
        participants.where(gender: "female").count
      end

      def total_unknown_gender_or_age
        participants.where("gender IS NULL OR date_of_birth is NULL").uniq.count
      end

      def male_percentage
        calculate_percentage(total_male_participants, total_participants_with_gender)
      end

      def female_percentage
        calculate_percentage(total_female_participants, total_participants_with_gender)
      end

      def age_groups
        groups = Hash.new(0)
        [[16, 19],
         [20, 24],
         [25, 29],
         [30, 34],
         [35, 39],
         [40, 44],
         [45, 49],
         [50, 54],
         [55, 59],
         [60, 64],
         [65, 69],
         [70, 74],
         [75, 79],
         [80, 84],
         [85, 89],
         [90, 140]].each do |start, finish|
          group_name = (finish == 140 ? "+ 90" : "#{start} - #{finish}")
          groups[group_name] = User.where(id: participants)
                                   .where("date_of_birth > ? AND date_of_birth < ?",
                                          finish.years.ago.beginning_of_year,
                                          start.years.ago.end_of_year).count
        end
        groups
      end

      def calculate_percentage(fraction, total)
        return 0.0 if total.zero?

        (fraction * 100.0 / total).round(3)
      end
  end

  class_methods do
    def stats_methods
      %i[total_participants total_male_participants
         total_female_participants total_unknown_gender_or_age
         male_percentage female_percentage age_groups]
    end

    def stats_cache(*method_names)
      method_names.each do |method_name|
        alias_method :"raw_#{method_name}", method_name

        define_method method_name do
          stats_cache(method_name) { send(:"raw_#{method_name}") }
        end
      end
    end
  end
end