- valid siren on create file

app/validators/siret_format_validator.rb

@@ -0,0 +1,21 @@
+class SiretFormatValidator < ActiveModel::EachValidator
+  def validate_each(record,attribute,value)
+    unless value =~ /^\d{14}$/
+      record.errors.add(attribute, :format)
+    end
+    unless value!= nil && (luhn_checksum(value) % 10 == 0)
+      record.errors.add(attribute, :checksum)
+    end
+  end
+
+  private
+  def luhn_checksum(value)
+    accum = 0
+    value.reverse.each_char.map(&:to_i).each_with_index do |digit, index|
+      t = index.even? ? digit : digit * 2
+      t = t - 9 if t >= 10
+      accum += t
+    end
+    accum
+  end
+end