Add calculation for percentage voucher

It include calculation for order with taxes included in the price

app/models/voucher.rb

@@ -59,6 +59,9 @@ def create_adjustment(label, order)
   # We limit adjustment to the maximum amount needed to cover the order, ie if the voucher
   # covers more than the order.total we only need to create an adjustment covering the order.total
   def compute_amount(order)
-    -amount.clamp(0, order.total)
+    return -amount.clamp(0, order.total) if voucher_type == FLAT_RATE
+
+    percentage = amount / 100
+    -percentage * order.total
   end
 end

app/services/voucher_adjustments_service.rb

@@ -11,7 +11,9 @@ def self.calculate(order)
     adjustment = order.voucher_adjustments.first
 
     # Recalculate value
-    amount = adjustment.originator.compute_amount(order)
+    voucher = adjustment.originator
+    # TODO: see if we can remove this and do it in  handle_tax_excluded_from_price
+    amount = voucher.compute_amount(order)
 
     # It is quite possible to have an order with both tax included in and tax excluded from price.
     # We should be able to caculate the relevant amount apply the current calculation.
@@ -20,7 +22,7 @@ def self.calculate(order)
     if order.additional_tax_total.positive?
       handle_tax_excluded_from_price(order, amount)
     else
-      handle_tax_included_in_price(order, amount)
+      handle_tax_included_in_price(order, voucher)
     end
 
     # Move to closed state
@@ -55,9 +57,17 @@ def self.handle_tax_excluded_from_price(order, amount)
     )
   end
 
-  def self.handle_tax_included_in_price(order, amount)
-    voucher_rate = amount / order.total
-    included_tax = voucher_rate * order.included_tax_total
+  def self.handle_tax_included_in_price(order, voucher)
+    amount = voucher.compute_amount(order)
+
+    if voucher.voucher_type == Voucher::FLAT_RATE
+      # Flat rate tax calulation
+      voucher_rate = amount / order.total
+      included_tax = voucher_rate * order.included_tax_total
+    else
+      # Percentage rate tax calculation
+      included_tax = -voucher.amount / 100 * order.included_tax_total
+    end
 
     # Update Adjustment
     adjustment = order.voucher_adjustments.first

spec/models/voucher_spec.rb

@@ -34,20 +34,32 @@
   end
 
   describe '#compute_amount' do
-    subject { create(:voucher_flat_rate, code: 'new_code', enterprise: enterprise, amount: 10) }
-
     let(:order) { create(:order_with_totals) }
 
-    it 'returns -10' do
-      expect(subject.compute_amount(order).to_f).to eq(-10)
+    context "with flat rate voucher" do
+      subject { create(:voucher_flat_rate, code: 'new_code', enterprise: enterprise, amount: 10) }
+
+      it 'returns -amount' do
+        expect(subject.compute_amount(order).to_f).to eq(-10)
+      end
+
+      context 'when order total is smaller than voucher amount' do
+        it 'returns minus the order total' do
+          order.total = 6
+          order.save!
+
+          expect(subject.compute_amount(order).to_f).to eq(-6)
+        end
+      end
     end
 
-    context 'when order total is smaller than 10' do
-      it 'returns minus the order total' do
-        order.total = 6
-        order.save!
+    context "with percentage rate voucher" do
+      subject { create(:voucher_percentage, code: 'new_code', enterprise: enterprise, amount: 10) }
 
-        expect(subject.compute_amount(order).to_f).to eq(-6)
+      it 'returns calculated anount based on the percentage' do
+        # -0.1 (10%)  * $10 = $1
+        expected_amount = -0.1 * order.total
+        expect(subject.compute_amount(order).to_f).to eq(expected_amount.to_f)
       end
     end
   end