Don't error when deleting supplier/group with already existing deleted name (closes foodcoops/foodsoft#197)

app/models/concerns/mark_as_deleted_with_name.rb

@@ -0,0 +1,25 @@
+module MarkAsDeletedWithName
+  extend ActiveSupport::Concern
+
+  def mark_as_deleted
+    # get maximum length of name
+    max_length = 100000
+    if lenval = self.class.validators_on(:name).detect { |v| v.is_a?(ActiveModel::Validations::LengthValidator) }
+      max_length = lenval.options[:maximum]
+    end
+    # find unique deleted name
+    # (would have been nice to use retry, but there is no general duplicate-entry exception)
+    n = ''
+    begin
+      append = ' \u2020' + n
+      deleted_name = name.truncate(max_length-append.length, omission: '') + append
+      if n.blank?
+        n = 'A'
+      else
+        n.succ!
+      end
+    end while self.class.where(name: deleted_name).exists?
+    # mark as deleted
+    update_columns deleted_at: Time.now, name: deleted_name
+  end
+end