Always require invoice VAT rate

Closes #1031

app/models/invoice.rb

@@ -28,16 +28,12 @@ class Invoice < ActiveRecord::Base
 
   validates :due_date, :currency, :seller_name,
             :seller_iban, :buyer_name, :items, presence: true
-  validates :vat_rate, numericality: { greater_than_or_equal_to: 0, less_than: 100 },
-            allow_nil: true
 
   before_create :set_invoice_number
-  before_create :apply_default_vat_rate, unless: :vat_rate?
   before_create :calculate_total, unless: :total?
   before_create :apply_default_buyer_vat_no, unless: :buyer_vat_no?
 
   attribute :vat_rate, ::Type::VATRate.new
-  attr_readonly :vat_rate
 
   def set_invoice_number
     last_no = Invoice.order(number: :desc).where('number IS NOT NULL').limit(1).pluck(:number).first
@@ -85,7 +81,6 @@ class Invoice < ActiveRecord::Base
   end
 
   def vat_amount
-    return 0 unless vat_rate
     subtotal * vat_rate / 100
   end
 
@@ -105,10 +100,6 @@ class Invoice < ActiveRecord::Base
 
   private
 
-  def apply_default_vat_rate
-    self.vat_rate = buyer.effective_vat_rate
-  end
-
   def apply_default_buyer_vat_no
     self.buyer_vat_no = buyer.vat_no
   end

app/models/invoice/vat_rate_calculator.rb

@@ -0,0 +1,19 @@
+class Invoice
+  class VatRateCalculator
+    attr_reader :registry
+    attr_reader :registrar
+
+    def initialize(registry: Registry.current, registrar:)
+      @registry = registry
+      @registrar = registrar
+    end
+
+    def calculate
+      if registrar.vat_liable_locally?(registry)
+        registry.vat_rate
+      else
+        registrar.vat_rate || 0
+      end
+    end
+  end
+end

app/models/registrar.rb

@@ -22,9 +22,9 @@ class Registrar < ActiveRecord::Base
   validates :reference_no, format: Billing::ReferenceNo::REGEXP
   validate :forbid_special_code
 
-  validates :vat_rate, presence: true, if: 'foreign_vat_payer? && vat_no.blank?'
-  validates :vat_rate, absence: true, if: :home_vat_payer?
-  validates :vat_rate, absence: true, if: 'foreign_vat_payer? && vat_no?'
+  validates :vat_rate, presence: true, if: 'vat_liable_in_foreign_country? && vat_no.blank?'
+  validates :vat_rate, absence: true, if: :vat_liable_locally?
+  validates :vat_rate, absence: true, if: 'vat_liable_in_foreign_country? && vat_no?'
   validates :vat_rate, numericality: { greater_than_or_equal_to: 0, less_than: 100 },
             allow_nil: true
 
@@ -52,7 +52,9 @@ class Registrar < ActiveRecord::Base
   end
 
   def issue_prepayment_invoice(amount, description = nil)
-    invoices.create(
+    vat_rate = ::Invoice::VatRateCalculator.new(registrar: self).calculate
+
+    invoices.create!(
       issue_date: Time.zone.today,
       due_date: (Time.zone.now + Setting.days_to_keep_invoices_active.days).to_date,
       description: description,
@@ -84,6 +86,7 @@ class Registrar < ActiveRecord::Base
       buyer_url: website,
       buyer_email: email,
       reference_no: reference_no,
+      vat_rate: vat_rate,
       items_attributes: [
         {
           description: 'prepayment',
@@ -146,12 +149,16 @@ class Registrar < ActiveRecord::Base
     end
   end
 
-  def effective_vat_rate
-    if home_vat_payer?
-      Registry.instance.vat_rate
-    else
-      vat_rate
-    end
+  def vat_country=(country)
+    self.address_country_code = country.alpha2
+  end
+
+  def vat_country
+    country
+  end
+
+  def vat_liable_locally?(registry = Registry.current)
+    vat_country == registry.vat_country
   end
 
   def notify(action)
@@ -169,11 +176,7 @@ class Registrar < ActiveRecord::Base
     errors.add(:code, :forbidden) if code == 'CID'
   end
 
-  def home_vat_payer?
-    country == Registry.instance.legal_address_country
+  def vat_liable_in_foreign_country?
+    !vat_liable_locally?
   end
-
-  def foreign_vat_payer?
-    !home_vat_payer?
-  end
-end
+end

app/models/registry.rb

@@ -1,11 +1,13 @@
 class Registry
-  include Singleton
+  include ActiveModel::Model
 
-  def vat_rate
-    Setting.registry_vat_prc.to_d * 100
-  end
+  attr_accessor :vat_rate
+  attr_accessor :vat_country
 
-  def legal_address_country
-    Country.new(Setting.registry_country_code)
+  def self.current
+    vat_rate = Setting.registry_vat_prc.to_d * 100
+    vat_country = Country.new(Setting.registry_country_code)
+
+    new(vat_rate: vat_rate, vat_country: vat_country)
   end
-end
+end