Implement algorithmic generation of Docker image names given a programming language name.

lib/coursemology/polyglot/concrete_language/class_methods.rb

@@ -4,4 +4,26 @@
 # This is deliberately defined so that consumers of this library can inject methods into all
 # concrete languages' classes.
 module Coursemology::Polyglot::ConcreteLanguage::ClassMethods
+  # The default algorithm for translating a language to a corresponding Docker image name.
+  #
+  # This will:
+  #  1. Strip the +Coursemology::Polyglot::Language+ prefix.
+  #  2. Underscore the name.
+  #  3. Replace *n*Point*n* strings with dots (e.g. Python2Point7 to Python2.7).
+  #  4. Replace slashes with dashes.
+  def docker_image
+    # Remove the Coursemology::Polyglot::Language prefix
+    class_name = name
+    class_name = class_name.sub(/^Coursemology::Polyglot::Language::/, '')
+
+    # Use the underscored name
+    class_name = class_name.underscore
+
+    # Replace the "_point" string with a decimal
+    class_name.gsub!(/(?<=[\d])_point(?=[\d])/, '.')
+
+    # Replace slashes with dashes
+    class_name.tr!('/', '-')
+    class_name
+  end
 end

lib/coursemology/polyglot/language.rb

@@ -32,14 +32,15 @@ class Coursemology::Polyglot::Language
   # Concrete languages can be instantiated and used.
   #
   # @param [String] display_name The display name for the language
-  def self.concrete_language(display_name)
+  # @param [String] docker_image The Docker image to use for the given language. This defaults to
+  #   the string generated by +Coursemology::Polyglot::ConcreteLanguage.docker_image+.
+  def self.concrete_language(display_name, docker_image: nil)
     include Coursemology::Polyglot::ConcreteLanguage
     extend Coursemology::Polyglot::ConcreteLanguage::ClassMethods
 
     concrete_class_methods = Module.new do
-      define_method(:display_name) do
-        display_name
-      end
+      define_method(:display_name) { display_name }
+      define_method(:docker_image) { docker_image } if docker_image
     end
 
     extend concrete_class_methods

spec/coursemology/polyglot/concrete_language_spec.rb

@@ -0,0 +1,43 @@
+require 'spec_helper'
+
+RSpec.describe Coursemology::Polyglot::ConcreteLanguage do
+  class self::DummyLanguage < Coursemology::Polyglot::Language
+    concrete_language 'Dummy Concrete Language'
+  end
+
+  class self::DummyOverriddenNameLanguage < self::DummyLanguage
+    concrete_language 'Dummy Overridden Concrete Language'
+
+    def self.name
+      'Coursemology::Polyglot::Language::Dummy::OverriddenNameLanguage'.freeze
+    end
+  end
+
+  describe '.docker_image' do
+    it 'removes the Coursemology::Polyglot::Language prefix' do
+      expect(self.class::DummyOverriddenNameLanguage.docker_image).to \
+        start_with('dummy')
+    end
+
+    it 'preserves the nesting of namespaces' do
+      expect(self.class::DummyOverriddenNameLanguage.docker_image).to \
+        eq('dummy-overridden_name_language')
+    end
+
+    context 'when the name contains Point surrounded by numerals' do
+      class self::DummyLanguage1Point0 < self::DummyLanguage; end
+
+      it 'converts "Point" to dots' do
+        expect(self.class::DummyLanguage1Point0.docker_image).to end_with('dummy_language1.0')
+      end
+    end
+
+    context 'when the name contains Point but not surrounded by numerals' do
+      class self::DummyLanguagePoint < self::DummyLanguage; end
+
+      it 'preserves "Point"' do
+        expect(self.class::DummyLanguagePoint.docker_image).to end_with('dummy_language_point')
+      end
+    end
+  end
+end

spec/coursemology/polyglot/language_spec.rb

@@ -9,6 +9,11 @@ class self::DummyLanguage < self::AbstractLanguage
     concrete_language DISPLAY_NAME
   end
 
+  class self::DummyLanguageWithDockerImage < self::DummyLanguage
+    DOCKER_IMAGE = 'dummy-docker'
+    concrete_language 'Dummy Docker Image Language', docker_image: DOCKER_IMAGE
+  end
+
   describe '.concrete_language' do
     it 'sets the correct display name' do
       expect(self.class::DummyLanguage.display_name).to eq(self.class::DummyLanguage::DISPLAY_NAME)
@@ -23,6 +28,20 @@ class self::DummyLanguage < self::AbstractLanguage
       expect(self.class::DummyLanguage).to \
         be_a_kind_of(Coursemology::Polyglot::ConcreteLanguage::ClassMethods)
     end
+
+    context 'when an explicit Docker image name is specified' do
+      it 'returns the explicit image name' do
+        expect(self.class::DummyLanguageWithDockerImage.docker_image).to \
+          eq(self.class::DummyLanguageWithDockerImage::DOCKER_IMAGE)
+      end
+    end
+
+    context 'when no explicit Docker image is specified' do
+      it 'generates an image name' do
+        expect(self.class::DummyLanguage.docker_image).to \
+          eq('r_spec-example_groups-coursemology_polyglot_language-dummy_language')
+      end
+    end
   end
 
   describe '.concrete_languages' do