Make Collector a singleton class

Rakefile

@@ -9,6 +9,6 @@ task :watchr do
 end
 
 task :environment do
-  require 'lib/metrics_collector'
+  require 'metrics_collector'
   require 'spec/sample_app'
 end

lib/metrics_collector.rb

@@ -1,6 +1,4 @@
-require 'set'
-
-require 'metrics_collector/metric'
 require 'metrics_collector/collector'
+require 'metrics_collector/metric'
 require 'metrics_collector/metric_snapshot'
 require 'metrics_collector/model_additions'

lib/metrics_collector/collector.rb

@@ -1,21 +1,28 @@
+require 'set'
+require 'singleton'
+
 module MetricsCollector
   class Collector
-    @@monitored_classes = Set.new
+    attr_reader :metrics
 
-    def self.monitor(klass)
-      @@monitored_classes << klass
+    def initialize
+      @metrics = Set.new
     end
 
-    def self.monitored_classes
-      @@monitored_classes
+    def monitor(metric)
+      @metrics << metric
     end
 
-    def self.clear
-      @@monitored_classes = Set.new
+    def clear
+      @metrics.clear
     end
 
-    def self.collect
-      monitored_classes.collect { |klass| klass.metrics.values }.flatten.collect { |metric| metric.snapshot}
+    def collect
+      metrics.collect { |metric| metric.snapshot }
     end
   end
+
+  class SingletonCollector < Collector
+    include Singleton
+  end
 end

lib/metrics_collector/metric_snapshot.rb

@@ -8,6 +8,10 @@ def initialize(name, value)
       self.value = value
     end
 
+    def to_s
+      "#{name}: #{value}"
+    end
+
   end
 end
 

lib/metrics_collector/model_additions.rb

@@ -1,15 +1,8 @@
 module MetricsCollector
   module ModelAdditions
     module ClassMethods
-      @@metrics = Hash.new
-
-      def metric(name, &block)
-        MetricsCollector::Collector.monitor(self)
-        @@metrics[name] = MetricsCollector::Metric.new(self, name, &block)
-      end
-
-      def metrics
-        @@metrics
+      def metric(name, collector = MetricsCollector::SingletonCollector.instance, &block)
+        collector.monitor(MetricsCollector::Metric.new(self, name, &block))
       end
     end
   end

lib/tasks/metrics_collector.rake

@@ -2,7 +2,8 @@ namespace :metrics_collector do
 
   desc "Collect all defined metrics"
   task :collect => [:environment] do
-    puts MetricsCollector::Collector.collect.inspect
+    snapshots = MetricsCollector::SingletonCollector.instance.collect
+    puts snapshots.collect(&:to_s)
   end
 
 end

spec/metrics_collector/collector_spec.rb

@@ -1,20 +1,50 @@
 require "spec_helper"
 
 describe MetricsCollector::Collector do
-  subject { MetricsCollector::Collector }
-
   before do
-    MetricsCollector::Collector.clear
+    @collector = MetricsCollector::Collector.new
+  end
+
+  subject { @collector }
+
+  it "adds metrics to monitor" do
+    metric = double("metric")
+    subject.monitor(metric)
+    subject.metrics.should include(metric)
+  end
+
+  it "only adds a single entry of each metric" do
+    metric = double("metric")
+    subject.monitor(metric)
+    subject.monitor(metric)
+    subject.metrics.size.should eq(1)
   end
 
-  it "adds classes to monitor" do
-    subject.monitor(Project)
-    subject.monitored_classes.should include(Project)
+  context "with a metric" do
+    before do
+      @metric = double("metric")
+      @collector.monitor(@metric)
+    end
+
+    it "clears all metrics" do
+      subject.clear
+      subject.metrics.should be_empty
+    end
+
+    it "collects metric snapshots" do
+      snapshot = double("snapshot")
+      @metric.should_receive(:snapshot).and_return(snapshot)
+      subject.collect.should include(snapshot)
+    end
+  end
+end
+
+describe MetricsCollector::SingletonCollector do
+  it "behaves like a singleton" do
+    MetricsCollector::SingletonCollector.instance.should be(MetricsCollector::SingletonCollector.instance)
   end
 
-  it "only adds a single entry of each class" do
-    subject.monitor(Project)
-    subject.monitor(Project)
-    subject.monitored_classes.size.should eq(1)
+  it "does not directly allow instanciation" do
+    lambda { MetricsCollector::SingletonCollector.new }.should raise_error(NoMethodError)
   end
 end

spec/metrics_collector/metric_snapshot_spec.rb

@@ -1,57 +1,23 @@
 require "spec_helper"
 
 describe MetricsCollector::MetricSnapshot do
-  before(:all) do
-    MetricsCollector::Collector.clear
 
-    Project.metrics.clear
-
-    class Project
-      @@count = 0
-
-      metric :counter do
-        @@count += 1
-      end
-
-      def self.reset
-        @@count = 0
-      end
-    end
+  before do
+    @snapshot = MetricsCollector::MetricSnapshot.new(:name, 1.0)
   end
 
-  context "with a class monitored" do
-    before(:each) do
-      Project.reset
-    end
-
-    context "collecting the metrics" do
-      let(:collection) { MetricsCollector::Collector.collect }
-      subject { collection }
-
-      it "has a collection of snapshots" do
-        subject.should_not be_empty
-      end
+  let(:snapshot) { @snapshot }
 
-      it "contains only one metric" do
-        subject.size.should == 1
-      end
-
-      context "with a metric" do
-        subject { collection.first }
-
-        it "contains a MetricSnapshot" do
-          subject.should be_a(MetricsCollector::MetricSnapshot)
-        end
+  it "has a name" do
+    snapshot.name.should eq(:name)
+  end
 
-        it "contains a snapshot for Project counter" do
-          subject.name.should eq(:counter)
-        end
+  it "has a value" do
+    snapshot.value.should eq(1.0)
+  end
 
-        it "contains a reading from Project counter" do
-          subject.value.should == 1
-        end
-      end
-    end
+  it "outputs as a formatted string" do
+    snapshot.to_s.should eq("name: 1.0")
   end
 
 end

spec/metrics_collector/metric_spec.rb

@@ -26,6 +26,7 @@
   end
 
   context "when taking a snapshot" do
+
     subject { metric.snapshot }
 
     it "creates a snapshot" do

spec/metrics_collector/model_additions_spec.rb

@@ -1,49 +1,21 @@
 require "spec_helper"
 
 describe MetricsCollector::ModelAdditions do
-  subject { Project }
-
   it "can define metrics on models" do
-    subject.should respond_to(:metric)
+    Project.should respond_to(:metric)
   end
 
-  context "with a metric defined" do
-    before do
-      subject.class_eval do
-        metric :count do
-          0.0
-        end
-      end
-    end
-
-    it "adds that metric to the metric list" do
-      subject.metrics.should_not be_empty
-    end
-
-    it "adds the class to Collector" do
-      MetricsCollector::Collector.monitored_classes.should include(Project)
-    end
-
-    it "saves the block as a metric instance" do
-      subject.metrics[:count].should be_kind_of(MetricsCollector::Metric)
-    end
-  end
+  context "when defining a metric" do
+    it "is added to the collector" do
+      collector = double("collector")
+      collector.should_receive(:monitor).with(an_instance_of(MetricsCollector::Metric))
 
-  context "with multiple metrics defined" do
-    before do
       Project.class_eval do
-        metric :count do
-          0.0
-        end
-
-        metric :usage do
+        metric(:count, collector) do
           0.0
         end
       end
-    end
 
-    it "contains multiple unique metrics" do
-      subject.metrics.size.should == 2
     end
   end
 end