Add a helper for build c3.js chart compatible data

spec/models/ahoy/data_source_spec.rb

@@ -0,0 +1,36 @@
+require 'rails_helper'
+
+describe Ahoy::DataSource do
+  describe '#build' do
+    before :each do
+      time_1 = DateTime.parse("2015-01-01")
+      time_2 = DateTime.parse("2015-01-02")
+      time_3 = DateTime.parse("2015-01-03")
+
+      create :ahoy_event, name: 'foo', time: time_1
+      create :ahoy_event, name: 'foo', time: time_1
+      create :ahoy_event, name: 'foo', time: time_2
+      create :ahoy_event, name: 'bar', time: time_1
+      create :ahoy_event, name: 'bar', time: time_3
+      create :ahoy_event, name: 'bar', time: time_3
+    end
+
+    it 'should work without data sources' do
+      ds = Ahoy::DataSource.new
+      expect(ds.build).to eq x: []
+    end
+
+    it 'should work with single data sources' do
+      ds = Ahoy::DataSource.new
+      ds.add 'foo', Ahoy::Event.where(name: 'foo').group_by_day(:time).count
+      expect(ds.build).to eq :x=>["2015-01-01", "2015-01-02"], "foo"=>[2, 1]
+    end
+
+    it 'should combine data sources' do
+      ds = Ahoy::DataSource.new
+      ds.add 'foo', Ahoy::Event.where(name: 'foo').group_by_day(:time).count
+      ds.add 'bar', Ahoy::Event.where(name: 'bar').group_by_day(:time).count
+      expect(ds.build).to eq :x=>["2015-01-01", "2015-01-02", "2015-01-03"], "foo"=>[2, 1, 0], "bar"=>[1, 0, 2]
+    end
+  end
+end