require 'uuidtools'
require 'active_support/concern'
require_relative 'uuidify_exception'

# Mixin to add uuids to an active record model.
module Uuidify::UuidifyConcern
  extend ActiveSupport::Concern
  
  included do
    before_destroy :destroy_uuid
  end

  module ClassMethods
    # .find_by_uuid.  Used lookup so we know it's not rails magic.
    def lookup_uuid(uuid)
      uuid = Uuidify::Uuid.where(:model_uuid => uuid.raw, :model_name => self.to_s).first
      uuid ? find(uuid.model_id) : nil
    end

    # Delete entries where we don't have a model that can be instantiated anymore.
    def garbage_collect_uuids
      Uuidify::Uuid.where(:model_name => self.to_s).find_each do |uuid|
        if !where(:id => uuid.model_id).first
          uuid.destroy
        end
      end
    end
  end

  # Return a UUID, creating it if needed.
  def uuid
    abort_if_unsaved!

    model_name = self.class.to_s
    model_id = self.id

    uuid = Uuidify::Uuid.where(:model_name => model_name, :model_id => model_id).first

    if uuid.nil?
      new_uuid = UUIDTools::UUID.timestamp_create.raw
      uuid = Uuidify::Uuid.create(:model_name => model_name, :model_id => self.id, :model_uuid => new_uuid)
      uuid.save!
    end
    
    UUIDTools::UUID.parse_raw(uuid.model_uuid)
  end

  # Assign a UUID that came from an external source.
  def uuid= new_uuid
    abort_if_unsaved!
    Uuidify::Uuid.where(:model_name => self.class.to_s, :model_id => self.id).first_or_create!.update_column(:model_uuid, new_uuid.raw)
  end
  
  private

  def abort_if_unsaved!
    if self.id.nil?
      raise Uuidify::UuidifyException, "This model hasn't been persisted yet and Uuidify doesn't want to implicitly do that.  Won't create uuid"
    end
  end

  def destroy_uuid
    model_name = self.class.to_s
    model_id = self.id
    uuid = Uuidify::Uuid.where(:model_name => model_name, :model_id => model_id).first
    uuid.destroy if uuid
  end
end