Log first message timestamp at startup

This gives an idea when reading the logs about the state of the loaded
data at startup.

coverage-sample.xml

@@ -0,0 +1,50 @@
+<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
+
+<!-- Reads AIS messages from two different sources. Connecting via TCP. Coverage
+	data is saved memory only (the default). -->
+<aisCoverageConfiguration>
+    <aisbus>
+        <transformer xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+                     xsi:type="sourceTypeSatTransformerConfiguration">
+            <gh_region>802</gh_region>
+            <gh_region>804</gh_region>
+            <gh_region>810</gh_region>
+            <source>CanAISShore</source>
+        </transformer>
+        <provider xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+                  xsi:type="tcpClientProviderConfiguration">
+            <hostPort>205.193.156.26:9001</hostPort>
+        </provider>
+
+        <consumer xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+                  xsi:type="distributerConsumerConfiguration">
+            <name>UNFILTERED</name>
+        </consumer>
+
+        <busQueueSize>10000</busQueueSize>
+    </aisbus>
+
+    <!--Sets the grid granularity; the latitude and longitude minimum degree -->
+    <latSize>0.0225225225</latSize>
+    <lonSize>0.0386812541</lonSize>
+
+    <databaseConfiguration>
+        <type>MongoDB</type>
+        <addr>localhost</addr>
+        <dbName>classB</dbName>
+        <port>27017</port>
+        <persistenceIntervalInMinutes>60</persistenceIntervalInMinutes>
+    </databaseConfiguration>
+
+    <!--<databaseConfiguration>-->
+    <!--<type>MemoryOnly</type>-->
+    <!--</databaseConfiguration>-->
+
+    <!-- Access the frontend via http://localhost:8090/coverage -->
+    <serverConfiguration>
+        <port>8090</port>
+        <webappPath>web</webappPath>
+        <contextPath>/coverage</contextPath>
+    </serverConfiguration>
+    <windowSize>1</windowSize>
+</aisCoverageConfiguration>

src/main/java/dk/dma/ais/coverage/AisCoverage.java

@@ -25,9 +25,11 @@
 import dk.dma.ais.coverage.web.WebServer;
 import dk.dma.ais.packet.AisPacket;
 import dk.dma.ais.reader.AisReader;
+import dk.dma.commons.util.DateTimeUtil;
 import net.jcip.annotations.GuardedBy;
 import net.jcip.annotations.ThreadSafe;
 import org.apache.commons.collections4.IterableUtils;
+import org.joda.time.PeriodType;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
@@ -106,6 +108,9 @@ private void loadCoverageDataFromDatabase() {
         }
         Instant end = Instant.now();
         LOG.info("Loading coverage data and converting to memory structure took [{}] ms", Duration.between(start, end).toMillis());
+        if (Helper.firstMessage != null) {
+            LOG.info("First message timestamp: {}. Window size should be: {}", Helper.firstMessage, DateTimeUtil.toInterval(Helper.firstMessage, new Date()).toPeriod(PeriodType.hours()).getHours());
+        }
     }
 
     private void adjustSystemEarliestMessageFromCell(Cell cell) {