Reject invalid coupon discount

ecommerce/pricing/lib/pricing.rb

@@ -1,5 +1,6 @@
 require "infra"
 require_relative "pricing/discounts"
+require_relative "pricing/coupon_discount"
 require_relative "pricing/coupon"
 require_relative "pricing/commands"
 require_relative "pricing/events"

ecommerce/pricing/lib/pricing/coupon.rb

@@ -1,4 +1,5 @@
-require_relative 'events'
+require_relative "events"
+require_relative "coupon_discount"
 
 module Pricing
   class Coupon
@@ -10,22 +11,23 @@ def initialize(id)
       @id = id
     end
 
-    def register(name, code, discount)
+    def register(name, code, discount_raw)
       raise AlreadyRegistered if @registered
 
+      discount = discount_raw.is_a?(CouponDiscount) ? discount_raw : CouponDiscount.parse(discount_raw)
+
       apply CouponRegistered.new(
         data: {
           coupon_id: @id,
           name: name,
           code: code,
-          discount: discount
+          discount: discount.to_d
         }
       )
     end
 
-    on CouponRegistered do |event|
+    on CouponRegistered do |_event|
       @registered = true
     end
   end
 end
-

ecommerce/pricing/lib/pricing/coupon_discount.rb

@@ -0,0 +1,32 @@
+# frozen_string_literal: true
+
+require "bigdecimal"
+module Pricing
+  class CouponDiscount
+    UnacceptableRange = Class.new(StandardError)
+    Unparseable = Class.new(StandardError)
+
+    def self.parse(raw)
+      new(raw)
+    rescue ArgumentError
+      raise Unparseable, "Discount must be a number"
+    end
+
+    attr_reader :value
+
+    def initialize(raw)
+      @value = BigDecimal(raw.to_s).freeze
+
+      raise UnacceptableRange, "Discount must be greater than 0" if @value <= 0
+      raise UnacceptableRange, "Discount must be less than or equal to 100" if @value > 100
+    end
+
+    def to_d
+      value
+    end
+
+    def to_s
+      value.to_s("F")
+    end
+  end
+end

ecommerce/pricing/lib/pricing/offer.rb

@@ -92,12 +92,14 @@ def remove_free_product(order_id, product_id)
       )
     end
 
-    def use_coupon(coupon_id, discount)
+    def use_coupon(coupon_id, discount_raw)
+      discount = discount_raw.is_a?(CouponDiscount) ? discount_raw : CouponDiscount.parse(discount_raw)
+
       apply CouponUsed.new(
         data: {
           order_id: @id,
           coupon_id: coupon_id,
-          discount: discount
+          discount: discount.to_d
         }
       )
     end

ecommerce/pricing/test/coupon_discount_test.rb

@@ -0,0 +1,28 @@
+require_relative "test_helper"
+
+module Pricing
+  class CouponDiscountTest < Test
+    cover "Pricing::CouponDiscount*"
+
+    def test_rejects_zero
+      assert_raises(CouponDiscount::UnacceptableRange) { CouponDiscount.parse("0") }
+    end
+
+    def test_rejects_negative
+      assert_raises(CouponDiscount::UnacceptableRange) { CouponDiscount.parse("-0.01") }
+    end
+
+    def test_rejects_over_100
+      assert_raises(CouponDiscount::UnacceptableRange) { CouponDiscount.parse("100.01") }
+    end
+
+    def test_rejects_non_numeric
+      assert_raises(CouponDiscount::Unparseable) { CouponDiscount.parse("abc") }
+    end
+
+    def test_accepts_string_decimal
+      discount = CouponDiscount.parse("0.01")
+      assert_equal(BigDecimal("0.01"), discount.to_d)
+    end
+  end
+end

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

@@ -8,27 +8,35 @@ def new
   end
 
   def create
-    coupon_id = params[:coupon_id]
+    @coupon_id = params[:coupon_id].presence || SecureRandom.uuid
+
+    discount = Pricing::CouponDiscount.parse(params[:discount])
 
     ActiveRecord::Base.transaction do
-      create_coupon(coupon_id)
+      create_coupon(@coupon_id, discount)
     end
+  rescue Pricing::CouponDiscount::UnacceptableRange, Pricing::CouponDiscount::Unparseable
+    flash.now[:alert] = "Discount must be greater than 0 and less than or equal to 100"
+    render "new", status: :unprocessable_entity
   rescue Pricing::Coupon::AlreadyRegistered
-    flash[:notice] = "Coupon is already registered"
-    render "new"
+    flash.now[:alert] = "Coupon is already registered"
+    render "new", status: :unprocessable_entity
+  rescue Infra::Command::Invalid
+    flash.now[:alert] = "Invalid coupon data"
+    render "new", status: :unprocessable_entity
   else
     redirect_to coupons_path, notice: "Coupon was successfully created"
   end
 
   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.to_d
       )
     )
     command_bus.(
@@ -38,5 +46,4 @@ def create_coupon(coupon_id)
       )
     )
   end
-
-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)