Add metadata to tax related voucher adjustment

In the scenario where you have tax excluded from price, when adding
a voucher to an order, we create 2 voucher adjusments. One of them
represent the tax part of the voucher, and has a label starting with
"Tax". To better differentiate them and allow a reliable way to
query it, we add a metadata entry.

app/models/spree/adjustment.rb

@@ -70,6 +70,9 @@ module Spree
     scope :credit, -> { where('amount < 0') }
     scope :return_authorization, -> { where(originator_type: "Spree::ReturnAuthorization") }
     scope :voucher, -> { where(originator_type: "Voucher") }
+    scope :voucher_tax, -> {
+      voucher.joins(:metadata).where(metadata: { fee_name: "Tax", fee_type: "Voucher" })
+    }
     scope :non_voucher, -> { where.not(originator_type: "Voucher") }
     scope :inclusive, -> { where(included: true) }
     scope :additional, -> { where(included: false) }

app/services/voucher_adjustments_service.rb

@@ -44,11 +44,9 @@ class VoucherAdjustmentsService
   end
 
   def voucher_excluded_tax
-    return 0.0 if @order.voucher_adjustments.empty?
+    return 0.0 if @order.voucher_adjustments.voucher_tax.empty?
 
-    return 0.0 if @order.voucher_adjustments.where("label LIKE 'Tax%'").empty?
-
-    @order.voucher_adjustments.where("label LIKE 'Tax%'").first.amount
+    @order.voucher_adjustments.voucher_tax.first.amount
   end
 
   private
@@ -86,6 +84,14 @@ class VoucherAdjustmentsService
     tax_adjustment = @order.adjustments.find_or_initialize_by(adjustment_attributes)
     tax_adjustment.amount = tax_amount
     tax_adjustment.save
+
+    # Add metada so we know which voucher adjustment is Tax related
+    AdjustmentMetadata.create(
+      adjustment: tax_adjustment,
+      enterprise: adjustment.originator.enterprise,
+      fee_name: "Tax",
+      fee_type: "Voucher"
+    )
   end
 
   def handle_tax_included_in_price(amount, voucher)

spec/services/voucher_adjustments_service_spec.rb

@@ -136,6 +136,12 @@ describe VoucherAdjustmentsService do
           # -0.058479532 * 11 = -0.64
           expect(tax_adjustment.amount.to_f).to eq(-0.64)
           expect(tax_adjustment.label).to match("Tax")
+
+          expect(tax_adjustment.metadata.enterprise_id).to eq(
+            tax_adjustment.originator.enterprise.id
+          )
+          expect(tax_adjustment.metadata.fee_name).to eq("Tax")
+          expect(tax_adjustment.metadata.fee_type).to eq("Voucher")
         end
 
         context "when re calculating" do
@@ -330,9 +336,9 @@ describe VoucherAdjustmentsService do
 
     it "returns the amount from the tax voucher adjustment" do
       voucher_adjustment = voucher.create_adjustment(voucher.code, order)
-      # Manually add voucher tax adjustment, so we don't have to do a big data setup to be able to
-      # use VoucherAdjustmentsService.update
-      order.adjustments.create!(
+      # Manually add voucher tax adjustment and metadata, so we don't have to do a big data setup
+      # to be able to use VoucherAdjustmentsService.update
+      tax_adjustment = order.adjustments.create!(
         originator: voucher_adjustment.originator,
         order: order,
         label: "Tax #{voucher_adjustment.label}",
@@ -342,6 +348,12 @@ describe VoucherAdjustmentsService do
         included_tax: 0,
         amount: 0.5
       )
+      AdjustmentMetadata.create(
+        adjustment: tax_adjustment,
+        enterprise: tax_adjustment.originator.enterprise,
+        fee_name: "Tax",
+        fee_type: "Voucher"
+      )
 
       expect(voucher_excluded_tax).to eq(0.5)
     end