sluggable.rb

module Mongoid
  module Sluggable

    def self.included(klass)
      klass.field :slug, type: String, default: ""
      klass.before_validation :generate_slug
      klass.after_save :add_slug_history
      klass.validates :slug, presence: true
      klass.validate :slug_uniqueness
      klass.validate :slug_history_path
      klass.has_many :slug_histories, as: :sluggable
      klass.extend(ClassMethods)
    end

    def slug_uniqueness
      if slug_changed? && !embedded?
        unless slug_collisions.empty?
          errors.add(:slug, "(#{self.slug}) not unique")
        end
      end
    end

    def slug_history_path
      collisions = slug_history_collisions

      unless collisions.empty?
        errors.add(:slug, "(#{self.resource_uri}) exists as a source in a slug history")
      end
    end

    def slug_base
      self.name
    end

    def generate_slug
      self.slug = build_slug_name if slug.blank?
      self.slug = slug.split('/').map(&:parameterize).join('/')
      ind = 2
 
      until (slug_collisions + slug_history_collisions).empty?
        self.slug = self.build_slug_name(ind)
        ind += 1
      end
 
      return self.slug
    end

    def slug_history_collisions
      histories = SlugHistory.where(source: self.resource_uri).to_a
      histories.delete_if { |x| x.sluggable_id == self.id }
    end

    def build_slug_name(ind = nil)
      slug = File.join(*[self.slug_base].flatten.compact.map {|x| x.parameterize})
      slug += "-#{ind}" if ind
      return slug
    end

    def slug_collisions
      self.class.where(slug: /^#{self.slug}$/i) - [self]
    end

    def add_slug_history
      if self.slug_was && self.slug_changed?
        self.slug_histories.create(source: self.slug_was, destination: self.slug)
      end
    end

    # Full URI Methods
    def resource_uri(slug = self.slug)
      "/#{self.class.name.downcase}/#{self.slug}"
    end

    module ClassMethods

      def by_slug_or_id(slug)
        self.any_of({id: slug}, {slug: /^#{slug.to_s}/i})
      end

    end

  end
end