Add product quantity to DFC export

engines/dfc_provider/app/services/dfc_builder.rb

@@ -22,7 +22,8 @@ class DfcBuilder
     )
 
     DataFoodConsortium::Connector::SuppliedProduct.new(
-      id, name: variant.name, description: variant.description
+      id, name: variant.name, description: variant.description,
+          quantity: QuantitativeValueBuilder.quantity(variant),
     )
   end
 

engines/dfc_provider/app/services/quantitative_value_builder.rb

@@ -0,0 +1,29 @@
+# frozen_string_literal: true
+
+# Describes the quantity contained in a product, for example:
+#
+# - 1 piece of apple, usually meaning the whole fruit
+# - 2 litres of milk, for example in a big bottle or pouch
+# - 750 grams of bread, for example a loaf
+#
+# The DFC also supports specific units like loafs and cans but we don't have
+# standardised data within OFN to map to these types.
+class QuantitativeValueBuilder < DfcBuilder
+  def self.quantity(variant)
+    DataFoodConsortium::Connector::QuantitativeValue.new(
+      unit: unit(variant),
+      value: variant.unit_value,
+    )
+  end
+
+  def self.unit(variant)
+    case variant.product.variant_unit
+    when "volume"
+      DfcLoader.connector.MEASURES.UNIT.QUANTITYUNIT.LITRE
+    when "weight"
+      DfcLoader.connector.MEASURES.UNIT.QUANTITYUNIT.GRAM
+    else
+      DfcLoader.connector.MEASURES.UNIT.QUANTITYUNIT.PIECE
+    end
+  end
+end

engines/dfc_provider/spec/services/quantitative_value_builder_spec.rb

@@ -0,0 +1,46 @@
+# frozen_string_literal: true
+
+require DfcProvider::Engine.root.join("spec/spec_helper")
+
+describe QuantitativeValueBuilder do
+  subject(:builder) { described_class }
+  let(:variant) { build(:variant, product: product) }
+  let(:product) { build(:product, name: "Apple") }
+
+  describe ".quantity" do
+    it "recognises items" do
+      product.variant_unit = "item"
+      variant.unit_value = 1
+      quantity = builder.quantity(variant)
+
+      expect(quantity.value).to eq 1.0
+      expect(quantity.unit.semanticId).to eq "dfc-m:Piece"
+    end
+
+    it "recognises volume" do
+      product.variant_unit = "volume"
+      variant.unit_value = 2
+      quantity = builder.quantity(variant)
+
+      expect(quantity.value).to eq 2.0
+      expect(quantity.unit.semanticId).to eq "dfc-m:Litre"
+    end
+
+    it "recognises weight" do
+      product.variant_unit = "weight"
+      variant.unit_value = 1000 # 1kg
+      quantity = builder.quantity(variant)
+
+      expect(quantity.value).to eq 1000.0
+      expect(quantity.unit.semanticId).to eq "dfc-m:Gram"
+    end
+
+    it "falls back to items" do
+      product.variant_unit = nil
+      quantity = builder.quantity(variant)
+
+      expect(quantity.value).to eq 1.0
+      expect(quantity.unit.semanticId).to eq "dfc-m:Piece"
+    end
+  end
+end

engines/dfc_provider/spec/services/supplied_product_builder_spec.rb

@@ -0,0 +1,26 @@
+# frozen_string_literal: true
+
+require DfcProvider::Engine.root.join("spec/spec_helper")
+
+describe DfcBuilder do
+  let(:variant) {
+    build(:variant, id: 5).tap { |v| v.product.supplier_id = 7 }
+  }
+
+  describe ".supplied_product" do
+    it "assigns a semantic id" do
+      product = DfcBuilder.supplied_product(variant)
+
+      expect(product.semanticId).to eq(
+        "http://test.host/api/dfc-v1.6/enterprises/7/supplied_products/5"
+      )
+    end
+
+    it "assigns a quantity" do
+      product = DfcBuilder.supplied_product(variant)
+
+      expect(product.quantity.value).to eq 1.0
+      expect(product.quantity.unit.semanticId).to eq "dfc-m:Gram"
+    end
+  end
+end