Ruby Model Relationships - Three way Relationship

I have an app that has 3 specific models; User, Country and City. The ideal relationship for each would be as follow:

User

• has_many :countries
• has_many :cities, through: :country

Country

• has_many :users
• has_many :cities

City

• has_many :users
• belongs_to :country

Most of those relationships are fairly straight forward, however, the User-to-City relationship is giving me a bit of a problem. I want to be able to assign a city to a user, as long as the user has been assigned to the country associated to the city. Right now I am not even able to assign a user a city, let alone institute the correct logic for the restriction.

So far what I have been able to read and search has led to the below. Please let me know if you need anything else. Any help is much appreciated!

User.rb

class User < ApplicationRecord

  before_save { self.email = email.downcase}
  #attr_accessible :username, :email
  validates_confirmation_of :password
  has_secure_password

  validates :username, presence: true, length: { maximum: 25 }, uniqueness: {case_sensitive: false}
  VALID_EMAIL_REGEX = /\A[\w+\-.]+@[a-z\d\-]+(\.[a-z\d\-]+)*\.[a-z]+\z/i
  validates :email, presence: true, length: { maximum: 255 }, format: { with: VALID_EMAIL_REGEX }
  validates :password, presence: true, confirmation: true, length: { minimum: 6 }
  validates :password_confirmation, presence: true

  has_many :trips
  has_many :visits, through: :trips
  has_many :countries, through: :trips
  has_many :cities, through: :visits

end

Country.rb

class Country < ApplicationRecord

  has_many :trips
  has_many :cities
  has_many :users, through: :trips

end

City.rb

class City < ApplicationRecord

  has_many :visits
  has_many :users, through: :visits
  belongs_to :country

end

Trip.rb

class Trip < ApplicationRecord

  belongs_to :country
  belongs_to :user
  has_many :visits
  has_many :cities, through: :visits

end

Visit.rb

class Visit < ApplicationRecord

  belongs_to :trip
  belongs_to :city
  has_one :country, through: :city
  has_one :user, through: :trip

end