Filter payment methods in Spree depending on the shipping name

filter_payment_methods.rb

# Filter payment methods in Spree depending on the shipping name,
# use the following snippet within your activation method to
# make it work:
#
# CheckoutsController.class_eval { include FilterPaymentMethods }
#
# The magic happens within the InstanceMethods module, change the
# regexp to fit your needs.
#
# Kai Krakow, http://github.com/kakra
# provided as-is

module FilterPaymentMethods

  def self.included(base)
    base.send :include, InstanceMethods
    base.instance_eval do
      alias_method_chain :load_available_payment_methods, :filter_by_shipping
    end
  end

  module InstanceMethods

    private

    def load_available_payment_methods_with_filter_by_shipping
      load_available_payment_methods_without_filter_by_shipping
      shipping_name = @checkout.try(:shipping_method).try(:name)
      if shipping_name.match /Nachnahme/
        @payment_methods.reject! {|pm| !pm.name.match /Nachnahme/ }
      else
        @payment_methods.reject! {|pm| pm.name.match /Nachnahme/ }
      end
      @payment_mentod = @payment_methods.first unless @payment_methods.include? @payment_method
    end

  end
end