Merge pull request #170 from rapid7/task/issue-99-support-extending-t…

…he-convection-dsl

Fix #99 - Support extending the convection resource DSL

lib/convection/control/stack.rb

@@ -254,7 +254,7 @@ def diff
       #   template has any changes compared to the current template (in
       #   CloudFormation).
       def resource_changes?
-        ours = { 'Resources' => @template.resources.map(&:render) }
+        ours = { 'Resources' => @template.all_resources.map(&:render) }
         thiers = { 'Resources' => @current_template['Resources'] }
 
         ours.diff(thiers).any?

lib/convection/model/template.rb

@@ -24,6 +24,12 @@ def attach_resource(name, klass)
               resources[rname] = resource
             end
           end
+
+          def attach_resource_collection(name, klass)
+            define_method(name) do |rname, &block|
+              resource_collections[rname] = klass.new(rname, self, &block)
+            end
+          end
         end
       end
 
@@ -187,6 +193,7 @@ class Template
       attr_reader :parameters
       attr_reader :mappings
       attr_reader :conditions
+      attr_reader :resource_collections
       attr_reader :resources
       attr_reader :outputs
 
@@ -207,6 +214,7 @@ def initialize(stack = nil, &block)
         @mappings = Collection.new
         @conditions = Collection.new
         @resources = Collection.new
+        @resource_collections = Collection.new
         @outputs = Collection.new
         @metadata = Collection.new
       end
@@ -217,6 +225,11 @@ def clone(stack_)
 
       def execute
         instance_exec(&@definition)
+
+        resource_collections.each do |_, group|
+          group.run_definition
+          group.execute
+        end
       end
 
       def render(stack_ = nil)
@@ -231,12 +244,18 @@ def render(stack_ = nil)
           'Parameters' => parameters.map(&:render),
           'Mappings' => mappings.map(&:render),
           'Conditions' => conditions.map(&:render),
-          'Resources' => resources.map(&:render),
+          'Resources' => all_resources.map(&:render),
           'Outputs' => outputs.map(&:render),
           'Metadata' => metadata.map(&:render)
         }
       end
 
+      def all_resources
+        resource_collections.reduce(resources) do |result, (_name, resource_collection)|
+          result.merge(resource_collection.resources)
+        end
+      end
+
       def diff(other, stack_ = nil)
         render(stack_).diff(other).map { |diff| Diff.new(diff[0], *diff[1]) }
       end
@@ -353,5 +372,6 @@ def validate_bytesize(rendered_stack)
 require_relative 'template/resource'
 require_relative 'template/resource_property'
 require_relative 'template/resource_attribute'
+require_relative 'template/resource_collection'
 require_relative 'template/output'
 require_relative 'template/metadata'

lib/convection/model/template/resource_collection.rb

@@ -0,0 +1,48 @@
+require 'forwardable'
+require_relative './resource'
+require_relative '../mixin/conditional'
+
+module Convection
+  module Model
+    class Template
+      # A collection of different {Convection::Model::Template::Resource}s.
+      class ResourceCollection
+        extend Forwardable
+        include DSL::Helpers
+        include DSL::Template::Resource
+        include Mixin::Conditional
+
+        attr_reader :name
+        attr_reader :parent
+        attr_reader :template
+
+        def_delegator :@template, :stack
+
+        class << self
+          def attach_to_dsl(dsl_name)
+            DSL::Template::Resource.attach_resource_collection(dsl_name, self)
+          end
+        end
+
+        def initialize(name, parent, &definition)
+          @definition = definition
+          @name = name
+          @parent = parent
+          @template = parent.template
+        end
+
+        # @note This method is in place to be overriden by subclasses.
+        def execute
+        end
+
+        def run_definition
+          instance_exec(&@definition) if @definition
+        end
+
+        def resources
+          @resources ||= Convection::Model::Collection.new
+        end
+      end
+    end
+  end
+end

spec/convection/model/template/resource_collection_spec.rb

@@ -0,0 +1,63 @@
+require 'spec_helper'
+
+class Convection::Model::Template
+  describe ResourceCollection do
+    class WebService < Convection::Model::Template::ResourceCollection
+      attach_to_dsl(:web_service)
+
+      attribute :use_elastic_load_balancing
+
+      def execute
+        web_service = self # Expose this instance to nested template methods.
+
+        ec2_instance "#{name}WebService"
+
+        elb "#{name}LoadBalancer" do
+          tag 'Description', "Load balancer for the #{web_service.name} web service."
+        end if use_elastic_load_balancing
+      end
+    end
+
+    let(:use_elb_value) { nil }
+    let(:template) do
+      outer_scope = self
+      Convection.template do
+        description 'ResourceCollection Test Template'
+
+        # A lone resource for testing merging of resources and nested resources.
+        ec2_instance 'LoneResource1'
+
+        web_service 'ExampleDotOrg' do
+          use_elastic_load_balancing outer_scope.use_elb_value
+        end
+      end
+    end
+
+    subject do
+      template_json
+        .fetch('Resources')
+    end
+
+    context 'when the use_elastic_load_balancing attribute is set' do
+      let(:use_elb_value) { true }
+
+      it { is_expected.to have_key('LoneResource1') }
+      it { is_expected.to have_key('ExampleDotOrgWebService') }
+      it { is_expected.to have_key('ExampleDotOrgLoadBalancer') }
+    end
+
+    context 'when the use_elastic_load_balancing attribute is not set' do
+      let(:use_elb_value) { false }
+
+      it { is_expected.to have_key('LoneResource1') }
+      it { is_expected.to have_key('ExampleDotOrgWebService') }
+      it { is_expected.to_not have_key('ExampleDotOrgLoadBalancer') }
+    end
+
+    private
+
+    def template_json
+      JSON.parse(template.to_json)
+    end
+  end
+end