Add support for skipping idle counters

This is the same issue as reported in iZettle#78. For some reason,
idle counters still get reported. It would be nice if we could
not send anything from the client during its idle period.

metrics-influxdb/src/main/java/com/izettle/metrics/influxdb/InfluxDbReporter.java

@@ -395,6 +395,9 @@ private void reportHistogram(String name, Histogram histogram, long now) {
     }
 
     private void reportCounter(String name, Counter counter, long now) {
+        if (canSkipMetric(name, counter)) {
+            return;
+        }
         Map<String, Object> fields = new HashMap<String, Object>();
         fields.put("count", counter.getCount());
 

metrics-influxdb/src/test/java/com/izettle/metrics/influxdb/InfluxDbReporterTest.java

@@ -26,9 +26,11 @@
 import java.util.SortedMap;
 import java.util.TreeMap;
 import java.util.concurrent.TimeUnit;
+
 import org.junit.Before;
 import org.junit.Test;
 import org.mockito.ArgumentCaptor;
+import org.mockito.ArgumentMatchers;
 import org.mockito.Mock;
 import org.mockito.Mockito;
 import org.mockito.MockitoAnnotations;
@@ -517,6 +519,28 @@ public void shouldSkipIdleMetrics() throws Exception {
         verify(influxDb, times(1)).appendPoints(Mockito.any(InfluxDbPoint.class));
     }
 
+    @Test
+    public void shouldSkipIdleCounters()  {
+        when(influxDb.hasSeriesData()).thenReturn(true);
+
+        final Counter counter = mock(Counter.class);
+        when(counter.getCount()).thenReturn(42L);
+
+        InfluxDbReporter skippingReporter = InfluxDbReporter
+                .forRegistry(registry)
+                .convertRatesTo(TimeUnit.SECONDS)
+                .convertDurationsTo(TimeUnit.MILLISECONDS)
+                .filter(MetricFilter.ALL)
+                .withTags(globalTags)
+                .skipIdleMetrics(true)
+                .build(influxDb);
+
+        skippingReporter.report(map(), map("question-of-life", counter), map(), map(), map());
+        skippingReporter.report(map(), map("question-of-life", counter), map(), map(), map());
+
+        verify(influxDb, times(1)).appendPoints(ArgumentMatchers.any(InfluxDbPoint.class));
+    }
+
     @Test
     public void shouldCatchExceptions() throws Exception {
         doThrow(ConnectException.class).when(influxDb).writeData();