Flesh out Calculator behaviour

This adds the functionality to the calculator required to map per line
item taxes coming from the TaxJar API to the taxes required for each
line item in an order.

The calculator does not yet support shipping taxes.

1 files changed, 40 insertions, 8 deletions

diff --git a/lib/super_good/solidus_taxjar/tax_calculator.rb b/lib/super_good/solidus_taxjar/tax_calculator.rb
index e2a398e..e498da0 100644
--- a/lib/super_good/solidus_taxjar/tax_calculator.rb
+++ b/lib/super_good/solidus_taxjar/tax_calculator.rb
@@ -1,28 +1,60 @@
 module SuperGood
   module SolidusTaxJar
     class TaxCalculator
-      def initialize(order)
+      def self.default_api
+        ::SuperGood::SolidusTaxJar::API.new
+      end
+
+      def initialize(order, api: self.class.default_api)
         @order = order
+        @api = api
       end
 
       def calculate
+        return no_tax if order.tax_address.empty?
+        return no_tax unless taxjar_breakdown
+
         Spree::Tax::OrderTax.new(
           order_id: order.id,
-          line_item_taxes: line_item_rates,
-          shipment_taxes: shipment_rates
+          line_item_taxes: line_item_taxes,
+          shipment_taxes: []
         )
       end
 
       private
 
-      attr_reader :order
+      attr_reader :order, :api
+
+      def line_item_taxes
+        taxjar_breakdown.line_items.map do |line_item|
+          Spree::Tax::ItemTax.new(
+            item_id: line_item.id.to_i,
+            label: "Sales Tax",
+            tax_rate: tax_rate,
+            amount: line_item.tax_collectable,
+            included_in_price: false
+          )
+        end
+      end
+
+      def taxjar_breakdown
+        @taxjar_breakdown ||= taxjar_tax.breakdown
+      end
+
+      def taxjar_tax
+        @taxjar_taxes ||= api.tax_for(order)
+      end
 
-      def line_item_rates
-        []
+      def no_tax
+        Spree::Tax::OrderTax.new(
+          order_id: order.id,
+          line_item_taxes: [],
+          shipment_taxes: []
+        )
       end
 
-      def shipment_rates
-        []
+      def tax_rate
+        Spree::TaxRate.find_by(name: "Sales Tax")
       end
     end
   end