Add licence ack messages for Inference

Author: davidkyle

x-pack/plugin/core/src/main/java/org/elasticsearch/license/XPackLicenseState.java

@@ -85,6 +85,7 @@ public class XPackLicenseState {
                 "Existing follower indices will continue to replicate data" }
         );
         messages.put(XPackField.REDACT_PROCESSOR, new String[] { "Executing a redact processor in an ingest pipeline will fail." });
+        messages.put(XPackField.INFERENCE, new String[] { "The Inference API is disabled" });
         EXPIRATION_MESSAGES = Collections.unmodifiableMap(messages);
     }
 
@@ -107,6 +108,7 @@ public class XPackLicenseState {
         messages.put(XPackField.ENTERPRISE_SEARCH, XPackLicenseState::enterpriseSearchAcknowledgementMessages);
         messages.put(XPackField.REDACT_PROCESSOR, XPackLicenseState::redactProcessorAcknowledgementMessages);
         messages.put(XPackField.ESQL, XPackLicenseState::esqlAcknowledgementMessages);
+        messages.put(XPackField.INFERENCE, XPackLicenseState::inferenceApiAcknowledgementMessages);
         ACKNOWLEDGMENT_MESSAGES = Collections.unmodifiableMap(messages);
     }
 
@@ -264,6 +266,26 @@ private static String[] esqlAcknowledgementMessages(OperationMode currentMode, O
         return Strings.EMPTY_ARRAY;
     }
 
+    private static String[] inferenceApiAcknowledgementMessages(OperationMode currentMode, OperationMode newMode) {
+        /*
+         * Provide an acknowledgement warning to customers that downgrade from Trial or Enterprise to a lower
+         * license level (Basic, Standard, Gold or Premium) that they will no longer be able to use the Inference API
+         */
+        switch (newMode) {
+            case TRIAL:
+            case ENTERPRISE:
+                break;
+            default:
+                switch (currentMode) {
+                    case TRIAL:
+                    case ENTERPRISE:
+                        return new String[] { "The Inference API will be disabled" };
+                }
+                break;
+        }
+        return Strings.EMPTY_ARRAY;
+    }
+
     private static String[] machineLearningAcknowledgementMessages(OperationMode currentMode, OperationMode newMode) {
         switch (newMode) {
             case BASIC:

x-pack/plugin/core/src/test/java/org/elasticsearch/license/XPackLicenseStateTests.java

@@ -13,6 +13,7 @@
 import org.elasticsearch.xpack.core.XPackField;
 
 import java.util.Arrays;
+import java.util.EnumSet;
 import java.util.List;
 import java.util.Map;
 import java.util.Set;
@@ -160,6 +161,31 @@ public void testEsqlAckTrialOrEnterpriseToNotTrialOrEnterprise() {
         }
     }
 
+    public void testInferenceAckMessageTrialOrEnterpriseToNotTrialOrEnterprise() {
+        var notTrialOrEnterprise = EnumSet.allOf(License.OperationMode.class);
+        notTrialOrEnterprise.remove(TRIAL);
+        notTrialOrEnterprise.remove(ENTERPRISE);
+        for (OperationMode to : notTrialOrEnterprise) {
+            assertAckMessages(XPackField.INFERENCE, randomFrom(TRIAL, ENTERPRISE), to, Set.of("The Inference API will be disabled"));
+        }
+    }
+
+    public void testInferenceAckMessageToTrialOrEnterprise() {
+        var fromAll = EnumSet.allOf(License.OperationMode.class);
+        for (OperationMode from : fromAll) {
+            assertAckMessages(XPackField.ESQL, from, randomFrom(TRIAL, ENTERPRISE), 0);
+        }
+    }
+
+    public void testInferenceAckMessageUnlicensedToUnlicensed() {
+        var notTrialOrEnterprise = EnumSet.allOf(License.OperationMode.class);
+        notTrialOrEnterprise.remove(TRIAL);
+        notTrialOrEnterprise.remove(ENTERPRISE);
+        for (OperationMode to : notTrialOrEnterprise) {
+            assertAckMessages(XPackField.INFERENCE, randomFrom(notTrialOrEnterprise), to, 0);
+        }
+    }
+
     public void testExpiredLicense() {
         // use standard feature which would normally be allowed at all license levels
         LicensedFeature feature = LicensedFeature.momentary("family", "enterpriseFeature", STANDARD);