Simplify negated feature toggle constraint

app/constraints/feature_toggle_constraint.rb

@@ -3,11 +3,16 @@
 require "open_food_network/feature_toggle"
 
 class FeatureToggleConstraint
-  def initialize(feature_name)
+  def initialize(feature_name, negate: false)
     @feature = feature_name
+    @negate = negate
   end
 
   def matches?(request)
+    enabled?(request) ^ @negate
+  end
+
+  def enabled?(request)
     OpenFoodNetwork::FeatureToggle.enabled?(@feature, current_user(request))
   end
 

config/routes.rb

@@ -97,7 +97,7 @@ Openfoodnetwork::Application.routes.draw do
   end
 
    # When the split_checkout feature is disabled for the current user, use the legacy checkout
-  constraints ->(request) { OpenFoodNetwork::FeatureToggle.disabled? :split_checkout, request.env['warden']&.user } do
+  constraints FeatureToggleConstraint.new(:split_checkout, negate: true) do
     get '/checkout', to: 'checkout#edit'
     put '/checkout', to: 'checkout#update', as: :update_checkout
     get '/checkout/:state', to: 'checkout#edit', as: :checkout_state

spec/constraints/feature_toggle_constraint_spec.rb

@@ -0,0 +1,28 @@
+# frozen_string_literal: true
+
+require 'spec_helper'
+
+describe FeatureToggleConstraint do
+  subject { described_class.new("baking") }
+  let(:request) { double(env: env) }
+  let(:env) { {} }
+
+  it "constraints an unknown feature" do
+    expect(subject.matches?(request)).to eq false
+  end
+
+  it "allows an activated feature" do
+    Flipper.enable("baking")
+
+    expect(subject.matches?(request)).to eq true
+  end
+
+  it "negates results" do
+    subject = described_class.new("baking", negate: true)
+
+    expect(subject.matches?(request)).to eq true
+
+    Flipper.enable("baking")
+    expect(subject.matches?(request)).to eq false
+  end
+end