adds checkbox to reverse the vat on the admin product page

app/models/admin/products_decorator.rb

@@ -0,0 +1,27 @@
+Admin::ProductsHelper.module_eval do
+  # returns the price of the product to show for display purposes
+  def product_price(product_or_variant, options={})
+    options.assert_valid_keys(:format_as_currency, :show_vat_text)
+    options.reverse_merge! :format_as_currency => true, :show_vat_text => Spree::Config[:show_price_inc_vat]
+
+    amount = product_or_variant.price
+    amount += Calculator::Vat.calculate_tax_on(product_or_variant) if Spree::Config[:show_price_inc_vat]
+    options.delete(:format_as_currency) ? format_price(amount, options) : amount
+  end
+end
+
+Admin::ProductsController.class_eval do
+  before_filter :vat_fix , :only => :update
+
+  def vat_fix
+    return unless params[:price_includes_vat]
+    taxid = params[:product][:tax_category_id]
+    rate = TaxRate.find( taxid ) if taxid
+    rate = Calculator::Vat.default_rates.first unless rate
+    rate = TaxRate.first unless rate
+    price = params[:product][:price].to_f
+    price = price / (1 + rate.amount)
+    puts "Adjusted price by #{rate.amount} to #{price} (was #{params[:product][:price]})"
+    params[:product][:price] = price
+  end
+end

app/models/order_decorator.rb

@@ -42,15 +42,3 @@ def create_tax_charge!
     end
   end
 end
-
-Admin::ProductsHelper.module_eval do
-  # returns the price of the product to show for display purposes
-  def product_price(product_or_variant, options={})
-    options.assert_valid_keys(:format_as_currency, :show_vat_text)
-    options.reverse_merge! :format_as_currency => true, :show_vat_text => Spree::Config[:show_price_inc_vat]
-
-    amount = product_or_variant.price
-    amount += Calculator::Vat.calculate_tax_on(product_or_variant) if Spree::Config[:show_price_inc_vat]
-    options.delete(:format_as_currency) ? format_price(amount, options) : amount
-  end
-end

lib/spree_vat_fix.rb

@@ -14,6 +14,8 @@ def self.activate
 end
 class Hooks < Spree::ThemeSupport::HookListener
   insert_before :admin_product_form_right do 
-    "Price incl vat <%=product_price(@product)%>"
+    "<%=product_price(@product)%> Reverse <%= t('vat')%> 
+    <input type='checkbox' name='price_includes_vat' value='true' checked='true'/>     "
   end
 end
+