Added signal online indicator.

src/main/java/nl/andrewl/railsignalapi/model/Signal.java

@@ -2,6 +2,7 @@ package nl.andrewl.railsignalapi.model;
 
 import lombok.Getter;
 import lombok.NoArgsConstructor;
+import lombok.Setter;
 
 import javax.persistence.*;
 import java.util.Set;
@@ -23,6 +24,10 @@ public class Signal {
 	@OneToMany(mappedBy = "signal", orphanRemoval = true, cascade = CascadeType.ALL)
 	private Set<SignalBranchConnection> branchConnections;
 
+	@Column(nullable = false)
+	@Setter
+	private boolean online = false;
+
 	public Signal(RailSystem railSystem, String name, Set<SignalBranchConnection> branchConnections) {
 		this.railSystem = railSystem;
 		this.name = name;

src/main/java/nl/andrewl/railsignalapi/rest/dto/SignalResponse.java

@@ -9,7 +9,8 @@ import java.util.List;
 public record SignalResponse(
 		long id,
 		String name,
-		List<ConnectionData> branchConnections
+		List<ConnectionData> branchConnections,
+		boolean online
 ) {
 	public SignalResponse(Signal signal) {
 		this(
@@ -18,7 +19,8 @@ public record SignalResponse(
 				signal.getBranchConnections().stream()
 						.sorted(Comparator.comparing(SignalBranchConnection::getDirection))
 						.map(ConnectionData::new)
-						.toList()
+						.toList(),
+				signal.isOnline()
 		);
 	}
 

src/main/java/nl/andrewl/railsignalapi/service/SignalService.java

@@ -65,9 +65,15 @@ public class SignalService {
 	public void registerSignalWebSocketSession(Set<Long> signalIds, WebSocketSession session) {
 		this.signalWebSocketSessions.put(session, signalIds);
 		// Instantly send a data packet so that the signals are up-to-date.
+		RailSystem rs = null;
 		for (var signalId : signalIds) {
 			var signal = signalRepository.findById(signalId)
 					.orElseThrow(() -> new ResponseStatusException(HttpStatus.BAD_REQUEST, "Invalid signal id."));
+			if (rs == null) {
+				rs = signal.getRailSystem();
+			} else if (!rs.getId().equals(signal.getRailSystem().getId())) {
+				throw new ResponseStatusException(HttpStatus.BAD_REQUEST, "Cannot open signal websocket session for signals from different rail systems.");
+			}
 			for (var branchConnection : signal.getBranchConnections()) {
 				try {
 					session.sendMessage(new TextMessage(mapper.writeValueAsString(
@@ -80,11 +86,22 @@ public class SignalService {
 					e.printStackTrace();
 				}
 			}
+			signal.setOnline(true);
+			signalRepository.save(signal);
 		}
 	}
 
+	@Transactional
 	public void deregisterSignalWebSocketSession(WebSocketSession session) {
-		this.signalWebSocketSessions.remove(session);
+		var ids = this.signalWebSocketSessions.remove(session);
+		if (ids != null) {
+			for (var signalId : ids) {
+				signalRepository.findById(signalId).ifPresent(signal -> {
+					signal.setOnline(false);
+					signalRepository.save(signal);
+				});
+			}
+		}
 	}
 
 	public WebSocketSession getSignalWebSocketSession(long signalId) {