Add Promotable#current_lane_discounts

When we refactor the promotion system to use in-memory
adjustments/discounts to store discounts, we need to be able to ask
which discounts are in the current promotion lane. This allows that.

Author: mamhoff

promotions/app/models/concerns/solidus_promotions/discounted_amount.rb

@@ -9,6 +9,12 @@ def discounted_amount
       amount + previous_lane_discounts.sum(&:amount)
     end
 
+    def current_lane_discounts
+      raise NotCalculatingPromotions unless PromotionLane.current
+
+      discounts_by_lanes([PromotionLane.current])
+    end
+
     private
 
     # Returns discount objects added by promotion in lanes that come before the current lane.

promotions/app/models/solidus_promotions/not_calculating_promotions.rb

@@ -0,0 +1,6 @@
+# frozen_string_literal: true
+
+module SolidusPromotions
+  class NotCalculatingPromotions < StandardError
+  end
+end

promotions/spec/models/spree/line_item_spec.rb

@@ -91,4 +91,46 @@
       it { is_expected.to eq(26) }
     end
   end
+
+  describe "#current_lane_discounts" do
+    let(:order) { Spree::Order.new }
+    let(:tax_rate) { create(:tax_rate) }
+    let(:pre_lane_promotion) { create(:solidus_promotion, :with_adjustable_benefit, lane: :pre) }
+    let(:post_lane_promotion) { create(:solidus_promotion, :with_adjustable_benefit, lane: :post) }
+    let(:line_item) { Spree::LineItem.new(adjustments:, order:, price: 14, quantity: 2) }
+    let(:adjustments) { [tax_adjustment, pre_lane_adjustment, post_lane_adjustment] }
+    let(:tax_adjustment) { Spree::Adjustment.new(source: tax_rate, amount: 2) }
+    let(:pre_lane_adjustment) { Spree::Adjustment.new(source: pre_lane_promotion.benefits.first, amount: -3) }
+    let(:post_lane_adjustment) { Spree::Adjustment.new(source: post_lane_promotion.benefits.first, amount: -2) }
+
+    subject { line_item.current_lane_discounts }
+
+    it "raises an exception when there is no current lane" do
+      expect { subject }.to raise_exception(SolidusPromotions::NotCalculatingPromotions)
+    end
+
+    context "when in pre lane" do
+      before do
+        allow(SolidusPromotions::PromotionLane).to receive(:current) { "pre" }
+      end
+
+      it { is_expected.to contain_exactly(pre_lane_adjustment) }
+    end
+
+    context "when in default lane" do
+      before do
+        allow(SolidusPromotions::PromotionLane).to receive(:current) { "default" }
+      end
+
+      it { is_expected.to be_empty }
+    end
+
+    context "when in post lane" do
+      before do
+        allow(SolidusPromotions::PromotionLane).to receive(:current) { "post" }
+      end
+
+      it { is_expected.to contain_exactly(post_lane_adjustment) }
+    end
+  end
 end

promotions/spec/models/spree/shipment_spec.rb

@@ -70,4 +70,46 @@
       it { is_expected.to eq(12) }
     end
   end
+
+  describe "#current_lane_discounts" do
+    let(:order) { Spree::Order.new }
+    let(:tax_rate) { create(:tax_rate) }
+    let(:pre_lane_promotion) { create(:solidus_promotion, :with_adjustable_benefit, lane: :pre) }
+    let(:post_lane_promotion) { create(:solidus_promotion, :with_adjustable_benefit, lane: :post) }
+    let(:shipment) { Spree::Shipment.new(adjustments:, order:, cost: 14) }
+    let(:adjustments) { [tax_adjustment, pre_lane_adjustment, post_lane_adjustment] }
+    let(:tax_adjustment) { Spree::Adjustment.new(source: tax_rate, amount: 2) }
+    let(:pre_lane_adjustment) { Spree::Adjustment.new(source: pre_lane_promotion.benefits.first, amount: -3) }
+    let(:post_lane_adjustment) { Spree::Adjustment.new(source: post_lane_promotion.benefits.first, amount: -2) }
+
+    subject { shipment.current_lane_discounts }
+
+    it "raises an exception when there is no current lane" do
+      expect { subject }.to raise_exception(SolidusPromotions::NotCalculatingPromotions)
+    end
+
+    context "when in pre lane" do
+      before do
+        allow(SolidusPromotions::PromotionLane).to receive(:current) { "pre" }
+      end
+
+      it { is_expected.to contain_exactly(pre_lane_adjustment) }
+    end
+
+    context "when in default lane" do
+      before do
+        allow(SolidusPromotions::PromotionLane).to receive(:current) { "default" }
+      end
+
+      it { is_expected.to be_empty }
+    end
+
+    context "when in post lane" do
+      before do
+        allow(SolidusPromotions::PromotionLane).to receive(:current) { "post" }
+      end
+
+      it { is_expected.to contain_exactly(post_lane_adjustment) }
+    end
+  end
 end

promotions/spec/models/spree/shipping_rate_spec.rb

@@ -108,4 +108,45 @@
       it { is_expected.to eq(12) }
     end
   end
+
+  describe "#current_lane_discounts" do
+    let(:order) { Spree::Order.new }
+    let(:pre_lane_promotion) { create(:solidus_promotion, :with_adjustable_benefit, lane: :pre) }
+    let(:post_lane_promotion) { create(:solidus_promotion, :with_adjustable_benefit, lane: :post) }
+    let(:shipment) { Spree::Shipment.new(order:) }
+    let(:shipping_rate) { Spree::ShippingRate.new(discounts:, shipment:, amount: 14) }
+    let(:discounts) { [pre_lane_discount, post_lane_discount] }
+    let(:pre_lane_discount) { SolidusPromotions::ShippingRateDiscount.new(benefit: pre_lane_promotion.benefits.first, amount: -3) }
+    let(:post_lane_discount) { SolidusPromotions::ShippingRateDiscount.new(benefit: post_lane_promotion.benefits.first, amount: -2) }
+
+    subject { shipping_rate.current_lane_discounts }
+
+    it "raises an exception when there is no current lane" do
+      expect { subject }.to raise_exception(SolidusPromotions::NotCalculatingPromotions)
+    end
+
+    context "when in pre lane" do
+      before do
+        allow(SolidusPromotions::PromotionLane).to receive(:current) { "pre" }
+      end
+
+      it { is_expected.to contain_exactly(pre_lane_discount) }
+    end
+
+    context "when in default lane" do
+      before do
+        allow(SolidusPromotions::PromotionLane).to receive(:current) { "default" }
+      end
+
+      it { is_expected.to be_empty }
+    end
+
+    context "when in post lane" do
+      before do
+        allow(SolidusPromotions::PromotionLane).to receive(:current) { "post" }
+      end
+
+      it { is_expected.to contain_exactly(post_lane_discount) }
+    end
+  end
 end