User Ability DSL

ability.rb

class User
  module Ability
    def self.included(klass)
      klass.instance_eval do
        def ability(role, abilities)
          send :define_method, role.to_sym do
            abilities
          end
        end
      end

      klass.class_eval do
        def has_ability?(ability)
          self.send(self.role.to_sym).include? ability
        end

        def abilities
          self.send(self.role.to_sym)
        end
      end
    end

    FAKE_METHOD = /can_(.+)\?/
    def method_missing(method, *args, &block)
      if method =~ FAKE_METHOD
        self.has_ability?(method[FAKE_METHOD, 1].to_sym)
      else
        super
      end
    end
  end
end

roles.rb

class User
  module Roles

    # Available roles, in descending order of authorization
    ROLES = [
      :viewer,
      :dev,
      :qa,
      :lead,
      :manager,
      :admin
    ]

    DEFAULT = ROLES.first

    def self.included(klass)
      ROLES.each do |role|
        klass.send :define_method, "make_#{role}".to_sym do
          update_attribute :role, role.to_s
        end

        klass.send :define_method, "#{role}?".to_sym do
          self.role.to_sym == role.to_sym
        end
      end
    end
  end
end

user.rb

class User
  include Roles
  include Ability
  
  ability :viewer, []
  ability :qa, [:reject, :accept, :start_test]
  ability :dev, [:start, :finish]
  ability :manager, [:review, :release, :commit, :backlog]
  ability :lead, [:commit, :backlog]
  ability :admin, [:reject, :accept, :start_test, :start, :finish, :review, :release, :commit, :backlog]
end