Add tax_reverse_charge_mode to Spree::TaxCategory and update related specs

Introduce the `tax_reverse_charge_mode` enum to the `Spree::TaxCategory` model,
with values `disabled`, `loose`, and `strict`. The change includes a migration to add the `tax_reverse_charge_mode`
column to the `spree_tax_categories` table, with a default value of `0` (disabled).
Additionally, the English locale file has been updated to include translations for the new enum values.

The `tax_reverse_charge_mode` enum allows for more granular control over tax applicability
based on the reverse charge status of an address. This enhancement improves the flexibility
and accuracy of tax calculations by enabling different tax handling modes.

Author: JustShah

core/app/models/spree/tax_category.rb

@@ -10,6 +10,12 @@ class TaxCategory < Spree::Base
       self.tax_rate_tax_categories = []
     end
 
+    enum :tax_reverse_charge_mode, {
+      disabled: 0,
+      loose: 1,
+      strict: 2
+    }, prefix: true
+
     validates :name, presence: true
     validates_uniqueness_of :name, case_sensitive: true, unless: :deleted_at
 

core/config/locales/en.yml

@@ -392,6 +392,7 @@ en:
         is_default: Default
         name: Name
         tax_code: Tax Code
+        tax_reverse_charge_mode: Tax Reverse Charge Mode
       spree/tax_rate:
         amount: Rate
         expires_at: Expiration Date
@@ -2273,6 +2274,10 @@ en:
     tax_rate_amount_explanation: When using the "Default Tax" calculator, the amount is treated as a decimal amount to aid in calculations. (i.e. If the tax rate is 5% then enter 0.05) If using the "Flat Fee" calculator, the amount is used for the static fee.
     tax_rate_level: Tax Rate Level
     tax_rates: Tax Rates
+    tax_reverse_charge_modes:
+      disabled: Disabled
+      loose: Loose
+      strict: Strict
     taxon: Taxon
     taxon_attachment_removal_error: There was an error removing the attachment
     taxon_edit: Edit Taxon

core/db/migrate/20250226052907_add_tax_reverse_charge_mode_to_spree_tax_categories.rb

@@ -0,0 +1,8 @@
+# frozen_string_literal: true
+
+class AddTaxReverseChargeModeToSpreeTaxCategories < ActiveRecord::Migration[7.0]
+  def change
+    add_column :spree_tax_categories, :tax_reverse_charge_mode, :integer, default: 0, null: false,
+               comment: "Enum values: 0 = disabled, 1 = loose, 2 = strict"
+  end
+end

core/spec/models/spree/tax_category_spec.rb

@@ -47,4 +47,34 @@
       end
     end
   end
+
+  describe 'enum tax_reverse_charge_mode' do
+    it 'defines the expected enum values' do
+      expect(Spree::TaxCategory.tax_reverse_charge_modes).to eq({
+        'disabled' => 0,
+        'loose' => 1,
+        'strict' => 2
+      })
+    end
+
+    it 'allows valid values' do
+      tax_category = build(:tax_category)
+      # Updates the tax_reverse_charge_mode to "strict"
+      expect(tax_category).to be_valid
+      tax_category.tax_reverse_charge_mode_strict!
+
+      # Updates the tax_reverse_charge_mode to "loose"
+      expect(tax_category).to be_valid
+      tax_category.tax_reverse_charge_mode_loose!
+      expect(tax_category).to be_valid
+
+      # Updates the tax_reverse_charge_mode to "disabled"
+      tax_category.tax_reverse_charge_mode_disabled!
+      expect(tax_category).to be_valid
+    end
+
+    it 'raises an error for invalid values' do
+      expect { Spree::TaxCategory.new(tax_reverse_charge_mode: :invalid_status) }.to raise_error(ArgumentError)
+    end
+  end
 end