Reject invalid coupon discount

ecommerce/pricing/test/coupons_test.rb

@@ -36,5 +36,19 @@ def test_100_is_ok
     def test_0_01_is_ok
       register_coupon(@uid, fake_name, @code, "0.01")
     end
+
+    def test_negative_discount_is_rejected
+      assert_raises(Infra::Command::Invalid) do
+        register_coupon(@uid, fake_name, @code, -0.01)
+      end
+    end
+
+    def test_negative_discount_string_is_rejected
+      assert_raises(Infra::Command::Invalid) do
+        register_coupon(@uid, fake_name, @code, "-150")
+      end
+    end
+
+
   end
 end

rails_application/app/controllers/coupons_controller.rb

@@ -8,10 +8,13 @@ def new
   end
 
   def create
-    coupon_id = params[:coupon_id]
+    @coupon_id = params[:coupon_id].presence || SecureRandom.uuid
+
+    discount = validated_discount(params[:discount])
+    return render_invalid_discount unless discount
 
     ActiveRecord::Base.transaction do
-      create_coupon(coupon_id)
+      create_coupon(@coupon_id, discount)
     end
   rescue Pricing::Coupon::AlreadyRegistered
     flash[:notice] = "Coupon is already registered"
@@ -22,13 +25,13 @@ def create
 
   private
 
-  def create_coupon(coupon_id)
+  def create_coupon(coupon_id,discount)
     command_bus.(
       Pricing::RegisterCoupon.new(
         coupon_id: coupon_id,
         name: params[:name],
         code: params[:code],
-        discount: params[:discount]
+        discount: discount
       )
     )
     command_bus.(
@@ -39,4 +42,20 @@ def create_coupon(coupon_id)
     )
   end
 
+  def validated_discount(raw)
+      return nil if raw.blank?
+
+      value = BigDecimal(raw.to_s)
+      return nil unless value > 0 && value <= 100
+
+      value
+  rescue ArgumentError
+      nil
+  end
+
+  def render_invalid_discount
+    flash.now[:alert] = "Discount must be greater than 0 and less than or equal to 100"
+    render "new", status: :unprocessable_entity
+  end
+
 end

rails_application/app/views/coupons/new.html.erb

@@ -18,15 +18,15 @@
   <label for="coupon" class="block font-bold">
     Name
   </label>
-  <%= text_field_tag :name, "", required: true, class: "mt-1 focus:ring-blue-500 focus:border-blue-500 block shadow-sm sm:text-sm border-gray-300 rounded-md" %>
+  <%= text_field_tag :name,  params[:name], required: true, class: "mt-1 focus:ring-blue-500 focus:border-blue-500 block shadow-sm sm:text-sm border-gray-300 rounded-md" %>
 
   <label for="coupon" class="block font-bold">
     Code
   </label>
-  <%= text_field_tag :code, "", required: true, class: "mt-1 focus:ring-blue-500 focus:border-blue-500 block shadow-sm sm:text-sm border-gray-300 rounded-md" %>
+  <%= text_field_tag :code,  params[:code], required: true, class: "mt-1 focus:ring-blue-500 focus:border-blue-500 block shadow-sm sm:text-sm border-gray-300 rounded-md" %>
 
   <label for="coupon" class="block font-bold">
     Discount
   </label>
-  <%= number_field_tag :discount, nil, min: 1, max: 100, step: 0.01, id: "discount", required: true, class: "mt-1 focus:ring-blue-500 focus:border-blue-500 block shadow-sm sm:text-sm border-gray-300 rounded-md" %>
+  <%= number_field_tag :discount,  params[:discount], min: 1, max: 100, step: 0.01, id: "discount", required: true, class: "mt-1 focus:ring-blue-500 focus:border-blue-500 block shadow-sm sm:text-sm border-gray-300 rounded-md" %>
 <% end %>

rails_application/test/integration/coupons_test.rb

@@ -23,6 +23,27 @@ def test_creation
     assert_select("td", "6.69")
   end
 
+  def test_creation_with_negative_discount_is_rejected
+    register_store("Test Store")
+
+    get "/coupons/new"
+    coupon_id = css_select("input[name='coupon_id']").first["value"]
+
+    post "/coupons", params: {
+      coupon_id: coupon_id,
+      name: "Bad Coupon",
+      code: "NEG",
+      discount: "-150"
+    }
+
+    assert_response :unprocessable_entity
+
+    get "/coupons"
+    assert_response :success
+    assert_select("td", text: "Bad Coupon", count: 0)
+    assert_select("td", text: "NEG", count: 0)
+  end
+
   private
 
   def register_coupon(name, code, discount)