seeable.rb

# A mixin that makes a record "seeable" by users.
module Seeable
  def self.included(base)
    base.has_many :seeings, :as => :thing
  end

  # Note that user seeing this thing (now)
  # Returns true if the user has previously seen the object, and false otherwise
  # essentially the same as doing a seen_by? before noting the new seeing.
  def seen_by!(user)
    raise ArgumentError, 'A user object must be provided' if user.nil?
    unless seen_by? user
      Seeing.create(:user => user, :thing => self)
      return false
    end
    return true
  end

  # Has this thing been seen by user?
  def seen_by?(user)
    seeings.exists?(:user_id => user.id)
  end
end