module ActiveModel
  module Lint
    # == Active \Model \Lint \Tests
    #
    # You can test whether an object is compliant with the Active \Model API by
    # including <tt>ActiveModel::Lint::Tests</tt> in your TestCase. It will
    # include tests that tell you whether your object is fully compliant,
    # or if not, which aspects of the API are not implemented.
    #
    # Note an object is not required to implement all APIs in order to work
    # with Action Pack. This module only intends to provide guidance in case
    # you want all features out of the box.
    #
    # These tests do not attempt to determine the semantic correctness of the
    # returned values. For instance, you could implement <tt>valid?</tt> to
    # always return +true+, and the tests would pass. It is up to you to ensure
    # that the values are semantically meaningful.
    #
    # Objects you pass in are expected to return a compliant object from a call
    # to <tt>to_model</tt>. It is perfectly fine for <tt>to_model</tt> to return
    # +self+.
    module Tests

      # Passes if the object's model responds to <tt>to_key</tt> and if calling
      # this method returns +nil+ when the object is not persisted.
      # Fails otherwise.
      #
      # <tt>to_key</tt> returns an Enumerable of all (primary) key attributes
      # of the model, and is used to a generate unique DOM id for the object.
      def test_to_key
        assert model.respond_to?(:to_key), "The model should respond to to_key"
        def model.persisted?() false end
        assert model.to_key.nil?, "to_key should return nil when `persisted?` returns false"
      end

      # Passes if the object's model responds to <tt>to_param</tt> and if
      # calling this method returns +nil+ when the object is not persisted.
      # Fails otherwise.
      #
      # <tt>to_param</tt> is used to represent the object's key in URLs.
      # Implementers can decide to either raise an exception or provide a
      # default in case the record uses a composite primary key. There are no
      # tests for this behavior in lint because it doesn't make sense to force
      # any of the possible implementation strategies on the implementer.
      def test_to_param
        assert model.respond_to?(:to_param), "The model should respond to to_param"
        def model.to_key() [1] end
        def model.persisted?() false end
        assert model.to_param.nil?, "to_param should return nil when `persisted?` returns false"
      end

      # Passes if the object's model responds to <tt>to_partial_path</tt> and if
      # calling this method returns a string. Fails otherwise.
      #
      # <tt>to_partial_path</tt> is used for looking up partials. For example,
      # a BlogPost model might return "blog_posts/blog_post".
      def test_to_partial_path
        assert model.respond_to?(:to_partial_path), "The model should respond to to_partial_path"
        assert_kind_of String, model.to_partial_path
      end

      # Passes if the object's model responds to <tt>persisted?</tt> and if
      # calling this method returns either +true+ or +false+. Fails otherwise.
      #
      # <tt>persisted?</tt> is used when calculating the URL for an object.
      # If the object is not persisted, a form for that object, for instance,
      # will route to the create action. If it is persisted, a form for the
      # object will route to the update action.
      def test_persisted?
        assert model.respond_to?(:persisted?), "The model should respond to persisted?"
        assert_boolean model.persisted?, "persisted?"
      end

      # Passes if the object's model responds to <tt>model_name</tt> both as
      # an instance method and as a class method, and if calling this method
      # returns a string with some convenience methods: <tt>:human</tt>,
      # <tt>:singular</tt> and <tt>:plural</tt>.
      #
      # Check ActiveModel::Naming for more information.
      def test_model_naming
        assert model.class.respond_to?(:model_name), "The model class should respond to model_name"
        model_name = model.class.model_name
        assert model_name.respond_to?(:to_str)
        assert model_name.human.respond_to?(:to_str)
        assert model_name.singular.respond_to?(:to_str)
        assert model_name.plural.respond_to?(:to_str)

        assert model.respond_to?(:model_name), "The model instance should respond to model_name"
        assert_equal model.model_name, model.class.model_name
      end

      # Passes if the object's model responds to <tt>errors</tt> and if calling
      # <tt>[](attribute)</tt> on the result of this method returns an array.
      # Fails otherwise.
      #
      # <tt>errors[attribute]</tt> is used to retrieve the errors of a model
      # for a given attribute. If errors are present, the method should return
      # an array of strings that are the errors for the attribute in question.
      # If localization is used, the strings should be localized for the current
      # locale. If no error is present, the method should return an empty array.
      def test_errors_aref
        assert model.respond_to?(:errors), "The model should respond to errors"
        assert model.errors[:hello].is_a?(Array), "errors#[] should return an Array"
      end

      private
        def model
          assert @model.respond_to?(:to_model), "The object should respond to to_model"
          @model.to_model
        end

        def assert_boolean(result, name)
          assert result == true || result == false, "#{name} should be a boolean"
        end
    end
  end
end
