add PolicyCommandFactory

Signed-off-by: Stefan Maute <stefan.maute@bosch-si.com>

services/concierge/cache/src/main/java/org/eclipse/ditto/services/concierge/cache/PolicyCommandFactory.java

@@ -0,0 +1,56 @@
+/*
+ * Copyright (c) 2017-2018 Bosch Software Innovations GmbH.
+ *
+ * All rights reserved. This program and the accompanying materials
+ * are made available under the terms of the Eclipse Public License v2.0
+ * which accompanies this distribution, and is available at
+ * https://www.eclipse.org/org/documents/epl-2.0/index.php
+ *
+ * SPDX-License-Identifier: EPL-2.0
+ */
+package org.eclipse.ditto.services.concierge.cache;
+
+import java.util.UUID;
+
+import org.eclipse.ditto.model.base.headers.DittoHeaders;
+import org.eclipse.ditto.services.models.policies.commands.sudo.SudoRetrievePolicy;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+import org.slf4j.MDC;
+
+/**
+ * Creates commands to access the Policies service.
+ */
+final class PolicyCommandFactory {
+
+    private static final Logger LOGGER = LoggerFactory.getLogger(PolicyCommandFactory.class);
+
+    private PolicyCommandFactory() {
+        throw new AssertionError();
+    }
+
+    /**
+     * Creates a sudo command for retrieving a policy.
+     *
+     * @param policyId the policyId.
+     * @return the created command.
+     */
+    static SudoRetrievePolicy sudoRetrievePolicy(final String policyId) {
+        return SudoRetrievePolicy.of(policyId,
+                DittoHeaders.newBuilder().correlationId(getCorrelationId(policyId)).build());
+    }
+
+    private static String getCorrelationId(final String policyId) {
+        String correlationId = MDC.get("x-correlation-id");
+        if (null == correlationId) {
+            correlationId = UUID.randomUUID().toString();
+            LOGGER.debug("Found no correlation-id for SudoRetrievePolicy on Policy <{}>. Using new correlation-id: {}",
+                    policyId, correlationId);
+            return correlationId;
+        } else {
+            LOGGER.debug("Found correlation-id [{}] in MDC for SudoRetrievePolicy on Policy <{}>. ", correlationId, policyId);
+            return correlationId;
+        }
+    }
+
+}