# Computes the country leaderboard using a blended score that balances overall
# impact with per-employee efficiency, so bigger teams don't win on size alone.
#
# For each country:
#   tomatoes      = number of finished play sessions (players where is_done)
#   per_employee  = tomatoes / employee headcount   (nil if headcount unknown)
#   impact_index  = tomatoes     / max(tomatoes)     * 100
#   efficiency    = per_employee / max(per_employee) * 100
#   score         = impact_index * IMPACT_WEIGHT + efficiency * EFFICIENCY_WEIGHT
#
# Tune the balance here. The proposal's default is an even 50/50 split; raise
# EFFICIENCY_WEIGHT to lean more toward fairness across team sizes.
class LeaderboardScore
  IMPACT_WEIGHT     = 0.5
  EFFICIENCY_WEIGHT = 1.0 - IMPACT_WEIGHT

  def self.call
    new.call
  end

  def call
    rows = build_rows
    max_tomatoes = rows.map { |r| r[:tomatoes] }.max.to_f
    max_per_emp  = rows.filter_map { |r| r[:per_employee] }.max.to_f

    rows.map { |r| score_row(r, max_tomatoes, max_per_emp) }
        .sort_by { |r| [ -r[:score], r[:country_code] ] }
  end

  private

  # One row per known country, so the API always lists every country. Only
  # players that are done AND tagged with a known country contribute tomatoes;
  # countries with no finished players still appear, with 0 tomatoes / 0 score.
  def build_rows
    known      = I18n.t("countries").keys.map(&:to_s)
    counts     = Player.where(is_done: true, country: known).group(:country).count
    headcounts = self.class.headcounts

    known.map do |country|
      tomatoes     = counts[country].to_i
      employees    = headcounts[country].to_i
      per_employee = employees.positive? ? tomatoes.to_f / employees : nil
      { country: country, tomatoes: tomatoes, per_employee: per_employee }
    end
  end

  def score_row(row, max_tomatoes, max_per_emp)
    impact     = max_tomatoes.positive? ? row[:tomatoes] / max_tomatoes * 100 : 0.0
    efficiency = if row[:per_employee] && max_per_emp.positive?
      row[:per_employee] / max_per_emp * 100
    else
      # No headcount for this country: fall back to impact only rather than
      # penalising it with a zero efficiency score.
      impact
    end

    blended = impact * IMPACT_WEIGHT + efficiency * EFFICIENCY_WEIGHT

    {
      country_code: row[:country].to_s.upcase,
      score:        blended.round,
      tomatoes:     row[:tomatoes],
      per_employee: row[:per_employee]&.round(2)
    }
  end

  def self.headcounts
    @headcounts ||= YAML.safe_load_file(
      Rails.root.join("config", "country_headcounts.yml"),
      permitted_classes: [], aliases: false
    ) || {}
  end
end