module ActionController
  module SerializationAssertions
    extend ActiveSupport::Concern

    included do
      setup :setup_subscriptions
      teardown :teardown_subscriptions
    end

    def setup_subscriptions
      @serializers = Hash.new(0)

      ActiveSupport::Notifications.subscribe("!serialize.active_model_serializers") do |name, start, finish, id, payload|
        serializer = payload[:serializer]
        @serializers[serializer] += 1
      end
    end

    def teardown_subscriptions
      ActiveSupport::Notifications.unsubscribe("!serialize.active_model_serializers")
    end

    def process(*args)
      @serializers = Hash.new(0)
      super
    end

    # Asserts that the request was rendered with the appropriate serializers.
    #
    #  # assert that the "PostSerializer" serializer was rendered
    #  assert_serializer "PostSerializer"
    #
    #  # assert that the "PostSerializer" serializer was rendered
    #  assert_serializer :post_serializer
    #
    #  # assert that the rendered serializer starts with "Post"
    #  assert_serializer %r{\APost.+\Z}
    #
    #  # assert that no serializer was rendered
    #  assert_serializer nil
    #
    def assert_serializer(options = {}, message = nil)
      # Force body to be read in case the template is being streamed.
      response.body

      case options
      when NilClass, Regexp, String, Symbol
        rendered = @serializers
        msg = message || "expecting <#{options.inspect}> but rendering with <#{rendered.keys}>"

        matches_serializer =
          case options
          when Symbol
            options = options.to_s.camelize
            rendered.any? do |serializer, count|
              serializer == options
            end
          when String
            !options.empty? && rendered.any? do |serializer, count|
              serializer == options
            end
          when Regexp
            rendered.any? do |serializer, count|
              serializer.match(options)
            end
          when NilClass
            rendered.blank?
          end
        assert matches_serializer, msg
      else
        raise ArgumentError, "assert_serializer only accepts a String, Symbol, Regexp, or nil"
      end
    end
  end
end