Add method ServiceUsageMetrics.get_date_range

Minimal implementation of `ServiceUsageMetrics.get_date_range`, with
a test.

services/dataservices-metrics/lib/service_usage_metrics.rb

@@ -39,6 +39,23 @@ module CartoDB
       total
     end
 
+    def get_date_range(service, metric, date_from, date_to)
+      check_valid_data(service, metric)
+
+      total = 0
+      values = {}
+      (date_from..date_to).each do |date|
+        year_month_key = date_year_month(date)
+        if values[year_month_key].nil?
+          key_prefix = @orgname.nil? ? user_key_prefix(service, metric, date) : org_key_prefix(service, metric, date)
+          values[year_month_key] = @redis.zrange(key_prefix, 0, -1, with_scores: true).to_h
+        end
+        total += values[year_month_key][date_day(date)]
+      end
+
+      total
+    end
+
     protected
 
     def check_valid_data(_service, _metric)

services/dataservices-metrics/spec/unit/service_usage_metrics_spec.rb

@@ -68,4 +68,23 @@ describe CartoDB::ServiceUsageMetrics do
       @usage_metrics.get(:dummy_service, :dummy_metric).should eq 0
     end
   end
+
+  describe :get_date_range do
+    before(:each) do
+      @redis_mock = MockRedis.new
+      @usage_metrics = CartoDB::ServiceUsageMetrics.new('rtorre', 'team', @redis_mock)
+      @usage_metrics.stubs(:check_valid_data)
+    end
+
+    it 'gets a sum of the zscores stored in a given date range' do
+      @redis_mock.zincrby('org:team:dummy_service:dummy_metric:201703', _amount=1, _day='20')
+      @redis_mock.zincrby('org:team:dummy_service:dummy_metric:201703', _amount=2, _day='21')
+      @redis_mock.zincrby('org:team:dummy_service:dummy_metric:201703', _amount=3, _day='22')
+
+      @usage_metrics.get_date_range('dummy_service',
+                                    'dummy_metric',
+                                    Date.new(2017, 03, 20),
+                                    Date.new(2017, 03, 22)).should eq 6
+    end
+  end
 end