Add VPS-aware VPN IP allocation

src/main/java/com/litoralregas/vpnprovisioner/vps/WireGuardVpsService.java

@@ -0,0 +1,47 @@
+package com.litoralregas.vpnprovisioner.vps;
+
+import org.springframework.stereotype.Service;
+
+import java.util.HashSet;
+import java.util.Set;
+import java.util.regex.Matcher;
+import java.util.regex.Pattern;
+
+@Service
+public class WireGuardVpsService {
+
+    private static final Pattern VPN_IP_PATTERN =
+            Pattern.compile("\\b198\\.19\\.\\d{1,3}\\.\\d{1,3}\\b");
+
+    private final SshService sshService;
+
+    public WireGuardVpsService(SshService sshService) {
+        this.sshService = sshService;
+    }
+
+    public Set<String> findUsedVpnIps() {
+        SshCommandResult result = sshService.executeOnConfiguredVps(
+                "sudo wg show wg0 allowed-ips"
+        );
+
+        if (result.exitCode() != 0) {
+            throw new SshCommandException(
+                    "Failed to query WireGuard allowed IPs: " + result.stderr()
+            );
+        }
+
+        return parseVpnIps(result.stdout());
+    }
+
+    Set<String> parseVpnIps(String output) {
+        Set<String> ips = new HashSet<>();
+
+        Matcher matcher = VPN_IP_PATTERN.matcher(output);
+
+        while (matcher.find()) {
+            ips.add(matcher.group());
+        }
+
+        return ips;
+    }
+}