Counting the Days from the current_level?

There are 5 levels.

Each level has a certain amount of days in it that must pass before the habit can move up to the next level (as broken down by n_days):

      case n_days     
          when 0..9
            1
          when 10..24
            2
          when 25..44
            3  #Level 3
          when 45..69
            4
          when 70..99
            5
          else
            "Mastery"
         end
      end

How can we call the n_days from the present level in the habits index with something like <%= habit.current_level.n_days.count_off_from_zero_to_show %>?

For example, if we are specifically at 50 on level 3 it would show Day 5 in the habits index.

habit.rb

class Habit < ActiveRecord::Base
    belongs_to :user
    has_many :comments, as: :commentable
    has_many :levels
    serialize :committed, Array
    validates :date_started, presence: true
    before_save :current_level
    acts_as_taggable
    scope :private_submit, -> { where(private_submit: true) }
    scope :public_submit, -> { where(private_submit: false) }

attr_accessor :missed_one, :missed_two, :missed_three

    def save_with_current_level
        self.levels.build
        self.levels.build
        self.levels.build
        self.levels.build
        self.levels.build
        self.save
    end

    def self.committed_for_today
    today_name = Date::DAYNAMES[Date.today.wday].downcase
    ids = all.select { |h| h.committed.include? today_name }.map(&:id)
    where(id: ids)
  end 

    def current_level_strike
      levels[current_level - 1] # remember arrays indexes start at 0
    end

    def current_level
            return 0 unless date_started
            committed_wdays = committed.map { |day| Date::DAYNAMES.index(day.titleize) }
            n_days = ((date_started.to_date)..Date.today).count { |date| committed_wdays.include? date.wday } - self.missed_days

      case n_days     
          when 0..9
            1
          when 10..24
            2
          when 25..44
            3
          when 45..69
            4
          when 70..99
            5
          else
            "Mastery"
        end
    end
end

level.rb

class Level < ActiveRecord::Base
  belongs_to :habit
end

schema

create_table "habits", force: true do |t|
  t.integer  "missed_days",    default: 0
  t.text     "committed"
  t.integer  "days_lost",   default: 0
  t.datetime "date_started"
  t.string   "trigger"
  t.string   "target"
  t.string   "reward"
  t.boolean  "private_submit"
  t.integer  "user_id"
  t.datetime "created_at",                 null: false
  t.datetime "updated_at",                 null: false
  t.integer  "order"
end

add_index "habits", ["user_id", "created_at"], name: "index_habits_on_user_id_and_created_at"
add_index "habits", ["user_id"], name: "index_habits_on_user_id"

create_table "levels", force: true do |t|
  t.integer  "habit_id"
  t.integer  "days_lost",   default: 0
  t.integer  "missed_days",   default: 0
  t.integer  "current_level"
  t.datetime "created_at",                null: false
  t.datetime "updated_at",                null: false
end

add_index "levels", ["habit_id"], name: "index_levels_on_habit_id"

The Gist of it: http://ift.tt/1PISTF0