require 'naught'

module ActiveNull
  class NullModelBuilder
    attr_reader :model, :overrides

    def initialize(model, overrides)
      @model = model
      @overrides = overrides
    end

    def build
      model = self.model
      null = Naught.build do |config|
        config.impersonate model

        model.reflect_on_all_associations.each do |relation|
          klass = begin
            if relation.options[:polymorphic]
              model.polymorphic_null_defaults[relation.name].constantize
            else
              relation.klass
            end
          rescue
            nil
          end
          next unless klass
          if relation.collection?
            define_method(relation.name) { klass.none }
          else
            define_method(relation.name) do
              return unless klass.respond_to? :null
              klass.null
            end
          end
        end

        model.column_defaults.each do |field, default|
          define_method(field.to_sym) { default }
        end

        def nil?
          true
        end

        def present?
          false
        end

        def blank?
          true
        end

        def to_json
          '{}'
        end

        if Object.const_defined? 'Draper'
          def decorate(options = {})
            decorator_class.decorate(self, options)
          end

          def decorator_class
            self.class.decorator_class
          end

          def decorator_class?
            self.class.decorator_class?
          end

          def applied_decorators
            []
          end

          def decorated_with?(decorator_class)
            false
          end

          def decorated?
            false
          end
        end
      end
      null.send(:include, Draper::Decoratable) if Object.const_defined? 'Draper'
      null.send(:include, overrides) if overrides
      set_null_model null
    end

    def name
      base_name = model.name.split('::').last
      "Null#{base_name}"
    end

    def full_name
      return name if module_parent == Object
      "#{module_parent_name}::#{name}"
    end

    def set_null_model(null)
      module_parent.const_set name, null
    end

    private

    def module_parent
      @module_parent ||= model.try(:module_parent) || model.parent
    end

    def module_parent_name
      @module_parent_name ||= model.try(:module_parent_name) || model.parent.name
    end
  end
end