Start making builders more configurable

A user may or may not use all builders. This gets us closer to making
this configurable from a settings file. (But not quite.)

lib/lifer/brain.rb

@@ -14,8 +14,13 @@ def init(root: Dir.pwd)
   def build!
     brainwash!
 
-    [Lifer::Builder::HTML].each do |builder|
-      builder.execute root: root
+    # FIXME:
+    # Make the list of builders configurable via settings.
+    #
+    builders = [:html, :rss]
+
+    builders.each do |builder|
+      Lifer::Builder.find(builder).execute root: root
     end
   end
 

lib/lifer/builder.rb

@@ -1,4 +1,22 @@
-module Lifer::Builder
+class Lifer::Builder
+  class << self
+    def find(name)
+      result = descendants.detect { |descendant| descendant.name == name }
+
+      raise StandardError, "no builder with name \"%s\"" % name if result.nil?
+      result
+    end
+
+    def name
+      super.split("::").last.downcase.to_sym
+    end
+
+    private
+
+    def descendants
+      ObjectSpace.each_object(Class).select { |klass| klass < self }
+    end
+  end
 end
 
 require_relative "builder/html"

lib/lifer/builder/html.rb

@@ -1,6 +1,6 @@
 require "fileutils"
 
-class Lifer::Builder::HTML
+class Lifer::Builder::HTML < Lifer::Builder
   class << self
     def execute(root:)
       Dir.chdir Lifer.output_directory do

lib/lifer/builder/rss.rb

@@ -4,7 +4,7 @@
 #
 #   https://www.rssboard.org/rss-specification
 #
-class Lifer::Builder::RSS
+class Lifer::Builder::RSS < Lifer::Builder
   DEFAULT_FEED_FILENAME = "feed.xml"
 
   class << self

spec/lifer/brain_spec.rb

@@ -11,6 +11,9 @@
       allow(Lifer::Builder::HTML)
         .to receive(:execute)
         .and_return(instance_double Lifer::Builder::HTML)
+      allow(Lifer::Builder::RSS)
+        .to receive(:execute)
+        .and_return(instance_double Lifer::Builder::RSS)
     end
 
     it "cleans up any existing output directory" do
@@ -33,10 +36,12 @@
 
     it "executes a build" do
       allow(Lifer::Builder::HTML).to receive(:execute).with(root: root)
+      allow(Lifer::Builder::RSS).to receive(:execute).with(root: root)
 
       subject
 
       expect(Lifer::Builder::HTML).to have_received(:execute).with(root: root)
+      expect(Lifer::Builder::RSS).to have_received(:execute).with(root: root)
     end
   end
 

spec/lifer/builder/html_spec.rb

@@ -97,4 +97,10 @@
       end
     end
   end
+
+  describe ".name" do
+    subject { described_class.name }
+
+    it { is_expected.to eq :html }
+  end
 end

spec/lifer/builder/rss_spec.rb

@@ -42,5 +42,10 @@
       end
     end
   end
-end
 
+  describe ".name" do
+    subject { described_class.name }
+
+    it { is_expected.to eq :rss }
+  end
+end

spec/lifer/builder_spec.rb

@@ -0,0 +1,28 @@
+require "spec_helper"
+
+RSpec.describe Lifer::Builder do
+  describe ".find" do
+    subject { described_class.find name }
+
+    context "when a builder with the given name exists" do
+      let(:name) { :html }
+
+      it { is_expected.to eq Lifer::Builder::HTML }
+    end
+
+    context "when a builder with the given name does not exist" do
+      let(:name) { :doesntexist }
+
+      it "raises an error" do
+        expect { subject }
+          .to raise_error StandardError, "no builder with name \"doesntexist\""
+      end
+    end
+  end
+
+  describe ".name" do
+    subject { described_class.name }
+
+    it { is_expected.to eq :builder }
+  end
+end