# Existing players predate step tracking, so the funnel would start empty.
# Their `progress` still says which stages they answered -- good enough to
# reconstruct roughly how far they got. Players with no progress at all are
# left alone: there is nothing to infer from.
class BackfillPlayerFurthestStep < ActiveRecord::Migration[8.1]
  def up
    Player.where(furthest_step: nil).find_each do |player|
      stages = player.progress.keys.grep(/\A\d+\z/).map(&:to_i)
      next if stages.empty? && !player.progress.key?(Player::LAST_SAVE_KEY)

      # is_done is set on the final screen, not the results screen, so stop
      # there rather than claiming they saw the results.
      step =
        if player.is_done?
          "done"
        elsif player.progress.key?(Player::LAST_SAVE_KEY)
          "last_save"
        else
          "stage_#{stages.max}_result"
        end

      player.update_column(:furthest_step, step)
    end
  end

  def down
    # No-op: the reconstructed values are indistinguishable from live ones.
  end
end