Contestant 2: ID is a nice custom string

app/models/repository.rb

@@ -15,6 +15,7 @@ class Repository < ApplicationRecord
   validates :local_path, presence: true
 
   before_destroy :ensure_destroy_possible
+  before_create :set_unique_id
 
   class << self
 
@@ -42,6 +43,16 @@ def change_mirroring!(mirroring_enabled)
 
   private
 
+  def set_unique_id
+    self.unique_id = generate_unique_id if (custom? && !unique_id)
+  end
+
+  def generate_unique_id
+    last_repo = Repository.where(custom: true).order('length(unique_id), unique_id asc').last
+    return 'c1' unless last_repo
+    'c' + (last_repo.unique_id.gsub(/\D/, '').to_i + 1).to_s
+  end
+
   def ensure_destroy_possible
     throw(:abort) unless custom?
   end

app/services/repository_service.rb

@@ -21,12 +21,6 @@ def create_repository!(product, url, attributes, custom: false)
       attach_product!(product, repository) unless product.nil?
     end
 
-    # FIXME: this is a hack to add some not nice ID value
-    if custom
-      repository.unique_id = "hack#{repository.id}"
-      repository.save!
-    end
-
     repository
   end
 

spec/factories/repositories.rb

@@ -19,6 +19,7 @@
 
     trait :custom do
       custom true
+      unique_id nil
     end
 
     trait :with_products do

spec/models/repository_spec.rb

@@ -55,4 +55,20 @@
     it(:handles_subpath) { expect(Repository.make_local_path('http://localhost.com/foo/bar')).to eq('/foo/bar') }
     it(:handles_subpath_trailing_slash) { expect(Repository.make_local_path('http://localhost.com/foo/bar/')).to eq('/foo/bar/') }
   end
+
+  describe '#set_unique_id' do
+    let(:repo1) { create :repository, :custom, external_url: 'http://example.com/test1/' }
+    let(:repo2) { create :repository, :custom, external_url: 'http://example.com/test2/' }
+    let(:repo3) { create :repository, :custom, external_url: 'http://example.com/test3/' }
+
+    before do
+      repo1
+      repo2.destroy
+      repo3
+    end
+
+    it('first repo has correct id') { expect(repo1.unique_id).to eq('c1') }
+    it('second repo has correct id') { expect(repo2.unique_id).to eq('c2') }
+    it('third repo has correct id after deletion of the second repo') { expect(repo3.unique_id).to eq('c2') }
+  end
 end