Validating user input for shopfront taxon order

app/models/enterprise.rb

@@ -56,6 +56,7 @@ class Enterprise < ActiveRecord::Base
   validates :address, presence: true, associated: true
   validates :email, presence: true
   validates_presence_of :owner
+  validate :shopfront_taxons
   validate :enforce_ownership_limit, if: lambda { owner_id_changed? && !owner_id.nil? }
   validates_length_of :description, :maximum => 255
 
@@ -341,4 +342,10 @@ class Enterprise < ActiveRecord::Base
       errors.add(:owner, "^#{owner.email} is not permitted to own any more enterprises (limit is #{owner.enterprise_limit}).")
     end
   end
+
+  def shopfront_taxons
+    unless preferred_shopfront_taxon_order =~ /\A((\d+,)*\d+)?\z/
+      errors.add(:shopfront_taxon_order, "must contain a list of taxons.")
+    end
+  end
 end

spec/models/enterprise_spec.rb

@@ -175,6 +175,41 @@ describe Enterprise do
         e = create(:enterprise, owner: nil)
         }.to raise_error ActiveRecord::RecordInvalid, "Validation failed: Owner can't be blank"
     end
+
+    describe "preferred_shopfront_taxon_order" do
+      it "empty strings are valid" do
+        enterprise = build(:enterprise, preferred_shopfront_taxon_order: "")
+        expect(enterprise).to be_valid
+      end
+
+      it "a single integer is valid" do
+        enterprise = build(:enterprise, preferred_shopfront_taxon_order: "11")
+        expect(enterprise).to be_valid
+      end
+
+      it "comma delimited integers are valid" do
+        enterprise = build(:enterprise, preferred_shopfront_taxon_order: "1,2,3")
+        expect(enterprise).to be_valid
+        enterprise = build(:enterprise, preferred_shopfront_taxon_order: "1,22,333")
+        expect(enterprise).to be_valid
+      end
+
+      it "commas at the beginning and end are disallowed" do
+        enterprise = build(:enterprise, preferred_shopfront_taxon_order: ",1,2,3")
+        expect(enterprise).to be_invalid
+        enterprise = build(:enterprise, preferred_shopfront_taxon_order: "1,2,3,")
+        expect(enterprise).to be_invalid
+      end
+
+      it "any other characters are invalid" do
+        enterprise = build(:enterprise, preferred_shopfront_taxon_order: "a1,2,3")
+        expect(enterprise).to be_invalid
+        enterprise = build(:enterprise, preferred_shopfront_taxon_order: ".1,2,3")
+        expect(enterprise).to be_invalid
+        enterprise = build(:enterprise, preferred_shopfront_taxon_order: " 1,2,3")
+        expect(enterprise).to be_invalid
+      end
+    end
   end
 
   describe "delegations" do