FlexiRate: Allow calculating prices

This turned out to be rather complicated.

Author: mamhoff

promotions/app/models/solidus_promotions/calculators/flexi_rate.rb

@@ -51,8 +51,33 @@ class FlexiRate < Spree::Calculator
       #   line_item.quantity # => 5
       #   calculator.compute_line_item(line_item) # => 15.0 (10 + 5, limited to 2 items)
       def compute_line_item(line_item)
-        items_count = line_item.quantity
-        items_count = [items_count, preferred_max_items].min unless preferred_max_items.zero?
+        compute_for_quantity(line_item.quantity)
+      end
+
+      def compute_price(price, options = {})
+        order = options[:order]
+        desired_quantity = options[:quantity] || 0
+        return Spree::ZERO if desired_quantity.zero?
+
+        already_ordered_quantity = if order
+          order.line_items.detect do |line_item|
+            line_item.variant == price.variant
+          end&.quantity || 0
+        else
+          0
+        end
+        possible_discount = compute_for_quantity(already_ordered_quantity + desired_quantity)
+        existing_discount = compute_for_quantity(already_ordered_quantity)
+        round_to_currency(
+          (possible_discount - existing_discount) / desired_quantity,
+          price.currency
+        )
+      end
+
+      private
+
+      def compute_for_quantity(quantity)
+        items_count = preferred_max_items.zero? ? quantity : [quantity, preferred_max_items].min
 
         return Spree::ZERO if items_count.zero?
 

promotions/lib/solidus_promotions/configuration.rb

@@ -127,7 +127,8 @@ def shipment_conditions=(conditions)
       ],
       "SolidusPromotions::Benefits::AdvertisePrice" => [
         "SolidusPromotions::Calculators::Percent",
-        "SolidusPromotions::Calculators::FlatRate"
+        "SolidusPromotions::Calculators::FlatRate",
+        "SolidusPromotions::Calculators::FlexiRate"
       ]
     }
 

promotions/spec/models/solidus_promotions/calculators/flexi_rate_spec.rb

@@ -10,24 +10,20 @@
       preferred_max_items: max_items
     )
   end
-  let(:line_item) do
-    mock_model(
-      Spree::LineItem, quantity: quantity
-    )
-  end
+
   let(:first_item) { 0 }
   let(:additional_item) { 0 }
   let(:max_items) { 0 }
 
-  let(:line_item) do
-    mock_model(
-      Spree::LineItem, quantity: quantity
-    )
-  end
-
   it_behaves_like "a promotion calculator"
 
-  context "compute" do
+  context "compute_line_item" do
+    let(:line_item) do
+      mock_model(
+        Spree::LineItem, quantity: quantity
+      )
+    end
+
     subject { calculator.compute(line_item) }
 
     context "with all amounts 0" do
@@ -176,6 +172,183 @@
     end
   end
 
+  context "compute_price" do
+    let(:variant) { mock_model(Spree::Variant) }
+    let(:price) { mock_model(Spree::Price, amount: 12, variant: variant, currency: "USD") }
+    let(:order) { mock_model(Spree::Order, line_items: [line_item]) }
+    let(:line_item_quantity) { 0 }
+    let(:line_item) do
+      mock_model(
+        Spree::LineItem,
+        quantity: line_item_quantity,
+        variant: variant
+      )
+    end
+
+    subject { calculator.compute(price, { order: order, quantity: quantity }) }
+
+    context "with no order given" do
+      let(:order) { nil }
+
+      context "when first_item and additional_item have values" do
+        let(:first_item) { 1.13 }
+        let(:additional_item) { 2.11 }
+
+        context "with quantity 2" do
+          let(:quantity) { 2 }
+
+          it { is_expected.to eq(1.62) }
+        end
+      end
+    end
+
+    context "if nothing is in the cart" do
+      let(:line_item_quantity) { 0 }
+
+      context "when first_item and additional_items have values" do
+        let(:first_item) { 1.13 }
+        let(:additional_item) { 2.11 }
+
+        context "with quantity 0" do
+          let(:quantity) { 0 }
+
+          it { is_expected.to eq 0 }
+        end
+
+        context "with quantity 1" do
+          let(:quantity) { 1 }
+
+          it { is_expected.to eq 1.13 }
+        end
+
+        context "with quantity 2" do
+          let(:quantity) { 2 }
+
+          it { is_expected.to eq 1.62 }
+        end
+
+        context "with quantity 10" do
+          let(:quantity) { 3 }
+
+          it { is_expected.to eq 1.78 }
+        end
+
+        context "with quantity 10" do
+          let(:quantity) { 10 }
+
+          it { is_expected.to eq 2.01 }
+        end
+
+        context "with max_items 5" do
+          let(:max_items) { 5 }
+
+          context "with quantity 0" do
+            let(:quantity) { 0 }
+
+            it { is_expected.to eq 0 }
+          end
+
+          context "with quantity 1" do
+            let(:quantity) { 1 }
+
+            it { is_expected.to eq 1.13 }
+          end
+
+          context "with quantity 2" do
+            let(:quantity) { 2 }
+
+            it { is_expected.to eq 1.62 }
+          end
+
+          context "with quantity 5" do
+            let(:quantity) { 5 }
+
+            it { is_expected.to eq 1.91 }
+          end
+
+          context "with quantity 10" do
+            let(:quantity) { 10 }
+
+            it { is_expected.to eq 0.96 }
+          end
+        end
+      end
+    end
+
+    context "with items already in the cart" do
+      let(:line_item_quantity) { 2 }
+
+      context "when first_item and additional_items have values" do
+        let(:first_item) { 1.13 }
+        let(:additional_item) { 2.11 }
+
+        context "with quantity 0" do
+          let(:quantity) { 0 }
+
+          it { is_expected.to eq 0 }
+        end
+
+        context "with quantity 1" do
+          let(:quantity) { 1 }
+
+          it { is_expected.to eq 2.11 }
+        end
+
+        context "with quantity 2" do
+          let(:quantity) { 2 }
+
+          it { is_expected.to eq 2.11 }
+        end
+
+        context "with quantity 10" do
+          let(:quantity) { 3 }
+
+          it { is_expected.to eq 2.11 }
+        end
+
+        context "with quantity 10" do
+          let(:quantity) { 10 }
+
+          it { is_expected.to eq 2.11 }
+        end
+
+        context "with max_items 5" do
+          let(:max_items) { 5 }
+
+          context "with quantity 0" do
+            let(:quantity) { 0 }
+
+            it { is_expected.to eq 0 }
+          end
+
+          context "with quantity 1" do
+            let(:quantity) { 1 }
+
+            it { is_expected.to eq 2.11 }
+          end
+
+          context "with quantity 2" do
+            let(:quantity) { 2 }
+
+            it { is_expected.to eq 2.11 }
+          end
+
+          context "with quantity 5" do
+            let(:quantity) { 5 }
+
+            it { is_expected.to eq 1.27 }
+          end
+
+          context "with quantity 10" do
+            let(:quantity) { 10 }
+
+            it { is_expected.to eq 0.63 }
+          end
+        end
+      end
+    end
+  end
+
   it "allows creation of new object with all the attributes" do
     attributes = { preferred_first_item: 1, preferred_additional_item: 1, preferred_max_items: 1 }
     calculator = described_class.new(attributes)