Make messages a little more clever

common/src/main/java/com/fogcomputing/SensorData.java

@@ -2,15 +2,17 @@ package com.fogcomputing;
 
 
 import java.io.Serializable;
+import java.sql.Timestamp;
 
 public record SensorData(
 		int temperature,
-		int usage
+		int usage,
+		Timestamp dateTime
 )
 		implements Serializable
 {
-	public SensorData(String temperature, String usage) {
-		this(Integer.parseInt(temperature), Integer.parseInt(usage));
+	public SensorData(String temperature, String usage, Timestamp dateTime) {
+		this(Integer.parseInt(temperature), Integer.parseInt(usage), dateTime);
 	}
 
 	@Override

common/src/main/java/com/fogcomputing/SensorDataAggregation.java

@@ -5,12 +5,18 @@ import java.sql.Timestamp;
 public record SensorDataAggregation(
 		int averageTemperature,
 		int averageUsage,
-		Timestamp timestamp
+		Timestamp first,
+		Timestamp last
 )
 		implements Message
 {
 	@Override
 	public String toString() {
-		return "SensorDataAggregation %s [averageTemperature=%d, averageUsage=%d]".formatted(timestamp, averageTemperature, averageUsage);
+		return "SensorDataAggregation [%s - %s] [averageTemperature=%d, averageUsage=%d]".formatted(
+				TimestampFormatter.timeOnly(first),
+				TimestampFormatter.timeOnly(last),
+				averageTemperature,
+				averageUsage
+		);
 	}
 }

common/src/main/java/com/fogcomputing/SensorDataBatch.java

@@ -6,16 +6,37 @@ import java.util.List;
 public record SensorDataBatch(
 		List<SensorData> sensorData,
 		int size,
-		Timestamp timestamp
+		Timestamp first,
+		Timestamp last
+
 )
-		implements Message {
-	public SensorDataBatch(List<SensorData> sensorData, Timestamp timestamp) {
-		this(sensorData, sensorData.size(), timestamp);
+		implements Message
+{
+	public static SensorDataBatch of(List<SensorData> sensorData) {
+
+		Timestamp first;
+		Timestamp last;
+		if (sensorData.isEmpty()) {
+			Timestamp now = new Timestamp(System.currentTimeMillis());
+			first = now;
+			last = now;
+		}
+		else {
+			first = sensorData.get(0).dateTime();
+			last = sensorData.get(sensorData.size() - 1).dateTime();
+		}
+
+		return new SensorDataBatch(sensorData, sensorData.size(), first, last);
 	}
 
 	@Override
 	public String toString() {
-		return "SensorDataBatch: size = %s, data[Temp,Usage] = %s, timestamp = %s".formatted(size, sensorData, timestamp);
+		return "SensorDataBatch: size = %s, time range = [%s-%s] data[Temp,Usage] = %s".formatted(
+				size,
+				TimestampFormatter.timeOnly(first),
+				TimestampFormatter.timeOnly(last),
+				sensorData
+		);
 	}
 
 	public SensorDataAggregation aggregate() {
@@ -29,6 +50,6 @@ public record SensorDataBatch(
 										.average()
 										.orElse(0);
 
-		return new SensorDataAggregation((int) averageTemperature, (int) averageUsage, timestamp);
+		return new SensorDataAggregation((int) averageTemperature, (int) averageUsage, first, last);
 	}
 }

common/src/main/java/com/fogcomputing/TimestampFormatter.java

+package com.fogcomputing;
+
+import java.sql.Timestamp;
+import java.time.ZoneOffset;
+import java.time.format.DateTimeFormatter;
+
+public class TimestampFormatter {
+
+	public static String timeOnly(Timestamp timestamp) {
+		return timestamp.toInstant()
+						.atOffset(ZoneOffset.UTC )
+						.format(DateTimeFormatter.ofPattern("HH:mm:ss" ));
+	}
+
+}

edge/src/main/java/com/fogcomputing/MessageSender.java

 package com.fogcomputing;
 
 import java.io.IOException;
-import java.sql.Timestamp;
 import java.util.ArrayList;
 import java.util.List;
 import java.util.concurrent.ConcurrentLinkedQueue;
@@ -9,7 +8,7 @@ import java.util.concurrent.TimeUnit;
 
 public class MessageSender implements Runnable {
 
-	private static final int DEFAULT_BATCH_SIZE = 15; // we send every 15 seconds, sensor data is written/collected every second
+	private static final int BATCH_SIZE = 15; // we send every 15 seconds, sensor data is written/collected every second
 
 	private final ConcurrentLinkedQueue<SensorData> messageBuffer;
 	private final Client client;
@@ -23,18 +22,22 @@ public class MessageSender implements Runnable {
 	public void run() {
 		while (!Thread.currentThread().isInterrupted()) {
 
-			List<SensorData> batch = new ArrayList<>(DEFAULT_BATCH_SIZE);
-			while (messageBuffer.peek() != null) {
+			List<SensorData> batch = new ArrayList<>(BATCH_SIZE);
+			while (batch.size() < BATCH_SIZE && messageBuffer.peek() != null) {
 				SensorData sensorData = messageBuffer.poll();
 				batch.add(sensorData);
 			}
 
-			Timestamp currentDateTime = new Timestamp(System.currentTimeMillis());
-			SensorDataBatch sensorDataBatch = new SensorDataBatch(batch, currentDateTime);
+			// send 1-x batches until buffer is empty, than sleep for 15 seconds
+			// this results in sending a batch of 15 SensorData every 15 seconds if server is working properly
+			if (batch.isEmpty()) {
+				ThreadUtils.sleep(15, TimeUnit.SECONDS);
+				continue;
+			}
+
+			SensorDataBatch sensorDataBatch = SensorDataBatch.of(batch);
 			byte[] response = client.trySend(sensorDataBatch);
 			handleResponse(response);
-
-			ThreadUtils.sleep(15, TimeUnit.SECONDS);
 		}
 	}
 

edge/src/main/java/com/fogcomputing/SensorDataCollector.java

 package com.fogcomputing;
 
+import java.sql.Timestamp;
 import java.util.concurrent.ConcurrentLinkedQueue;
 
 import lombok.RequiredArgsConstructor;
@@ -26,7 +27,8 @@ public class SensorDataCollector implements Runnable {
 				// we do sync read of both sensors
 				String usageData = usageSub.recvStr().substring(USAGE_TOPIC.length() + 1);
 				String temperatureData = temperatureSub.recvStr().substring(TEMPERATURE_TOPIC.length() + 1);
-				messageBuffer.offer(new SensorData(usageData, temperatureData));
+				Timestamp dateTime = new Timestamp(System.currentTimeMillis());
+				messageBuffer.offer(new SensorData(usageData, temperatureData, dateTime));
 			}
 		}
 	}