Add ability to listen to group of affix settings (#37679)

Currently we have the ability to listen for setting changes to two group
affix settings. However, it is possible that we might have the need to
listen to more than two. This commit adds a method that allows consumer
to listen to a list of affix settings for changes.

server/src/main/java/org/elasticsearch/common/settings/AbstractScopedSettings.java

@@ -296,6 +296,54 @@ public abstract class AbstractScopedSettings {
         });
     }
 
+    /**
+     * Adds a affix settings consumer that accepts the settings for a group of settings. The consumer is only
+     * notified if at least one of the settings change.
+     * <p>
+     * Note: Only settings registered in {@link SettingsModule} can be changed dynamically.
+     * </p>
+     */
+    public synchronized void addAffixGroupUpdateConsumer(List<Setting.AffixSetting<?>> settings, BiConsumer<String, Settings> consumer) {
+        List<SettingUpdater> affixUpdaters = new ArrayList<>(settings.size());
+        for (Setting.AffixSetting<?> setting : settings) {
+            ensureSettingIsRegistered(setting);
+            affixUpdaters.add(setting.newAffixUpdater((a,b)-> {}, logger, (a,b)-> {}));
+        }
+
+        addSettingsUpdater(new SettingUpdater<Map<String, Settings>>() {
+
+            @Override
+            public boolean hasChanged(Settings current, Settings previous) {
+                return affixUpdaters.stream().anyMatch(au -> au.hasChanged(current, previous));
+            }
+
+            @Override
+            public Map<String, Settings> getValue(Settings current, Settings previous) {
+                Set<String> namespaces = new HashSet<>();
+                for (Setting.AffixSetting<?> setting : settings) {
+                    SettingUpdater affixUpdaterA = setting.newAffixUpdater((k, v) -> namespaces.add(k), logger, (a, b) ->{});
+                    affixUpdaterA.apply(current, previous);
+                }
+                Map<String, Settings> namespaceToSettings = new HashMap<>(namespaces.size());
+                for (String namespace : namespaces) {
+                    Set<String> concreteSettings = new HashSet<>(settings.size());
+                    for (Setting.AffixSetting<?> setting : settings) {
+                        concreteSettings.add(setting.getConcreteSettingForNamespace(namespace).getKey());
+                    }
+                    namespaceToSettings.put(namespace, current.filter(concreteSettings::contains));
+                }
+                return namespaceToSettings;
+            }
+
+            @Override
+            public void apply(Map<String, Settings> values, Settings current, Settings previous) {
+                for (Map.Entry<String, Settings> entry : values.entrySet()) {
+                    consumer.accept(entry.getKey(), entry.getValue());
+                }
+            }
+        });
+    }
+
     private void ensureSettingIsRegistered(Setting.AffixSetting<?> setting) {
         final Setting<?> registeredSetting = this.complexMatchers.get(setting.getKey());
         if (setting != registeredSetting) {

server/src/test/java/org/elasticsearch/common/settings/ScopedSettingsTests.java

@@ -316,6 +316,91 @@ public class ScopedSettingsTests extends ESTestCase {
         assertEquals(0, results.size());
     }
 
+    public void testAffixGroupUpdateConsumer() {
+        String prefix = randomAlphaOfLength(3) + "foo.";
+        String intSuffix = randomAlphaOfLength(3);
+        String listSuffix = randomAlphaOfLength(4);
+        Setting.AffixSetting<Integer> intSetting = Setting.affixKeySetting(prefix, intSuffix,
+            (k) ->  Setting.intSetting(k, 1, Property.Dynamic, Property.NodeScope));
+        Setting.AffixSetting<List<Integer>> listSetting = Setting.affixKeySetting(prefix, listSuffix,
+            (k) -> Setting.listSetting(k, Arrays.asList("1"), Integer::parseInt, Property.Dynamic, Property.NodeScope));
+        AbstractScopedSettings service = new ClusterSettings(Settings.EMPTY,new HashSet<>(Arrays.asList(intSetting, listSetting)));
+        Map<String, Settings> results = new HashMap<>();
+        Function<String, String> listBuilder = g -> (prefix + g + "." + listSuffix);
+        Function<String, String> intBuilder = g -> (prefix + g + "." + intSuffix);
+        String group1 = randomAlphaOfLength(3);
+        String group2 = randomAlphaOfLength(4);
+        String group3 = randomAlphaOfLength(5);
+        BiConsumer<String, Settings> listConsumer = results::put;
+
+        service.addAffixGroupUpdateConsumer(Arrays.asList(intSetting, listSetting), listConsumer);
+        assertEquals(0, results.size());
+        service.applySettings(Settings.builder()
+            .put(intBuilder.apply(group1), 2)
+            .put(intBuilder.apply(group2), 7)
+            .putList(listBuilder.apply(group1), "16", "17")
+            .putList(listBuilder.apply(group2), "18", "19", "20")
+            .build());
+        Settings groupOneSettings = results.get(group1);
+        Settings groupTwoSettings = results.get(group2);
+        assertEquals(2, intSetting.getConcreteSettingForNamespace(group1).get(groupOneSettings).intValue());
+        assertEquals(7, intSetting.getConcreteSettingForNamespace(group2).get(groupTwoSettings).intValue());
+        assertEquals(Arrays.asList(16, 17), listSetting.getConcreteSettingForNamespace(group1).get(groupOneSettings));
+        assertEquals(Arrays.asList(18, 19, 20), listSetting.getConcreteSettingForNamespace(group2).get(groupTwoSettings));
+        assertEquals(2, groupOneSettings.size());
+        assertEquals(2, groupTwoSettings.size());
+        assertEquals(2, results.size());
+
+        results.clear();
+
+        service.applySettings(Settings.builder()
+            .put(intBuilder.apply(group1), 2)
+            .put(intBuilder.apply(group2), 7)
+            .putList(listBuilder.apply(group1), "16", "17")
+            .putNull(listBuilder.apply(group2)) // removed
+            .build());
+
+        assertNull(group1 + " wasn't changed", results.get(group1));
+        groupTwoSettings = results.get(group2);
+        assertEquals(7, intSetting.getConcreteSettingForNamespace(group2).get(groupTwoSettings).intValue());
+        assertEquals(Arrays.asList(1), listSetting.getConcreteSettingForNamespace(group2).get(groupTwoSettings));
+        assertEquals(1, results.size());
+        assertEquals(2, groupTwoSettings.size());
+        results.clear();
+
+        service.applySettings(Settings.builder()
+            .put(intBuilder.apply(group1), 2)
+            .put(intBuilder.apply(group2), 7)
+            .putList(listBuilder.apply(group1), "16", "17")
+            .putList(listBuilder.apply(group3), "5", "6") // added
+            .build());
+        assertNull(group1 + " wasn't changed", results.get(group1));
+        assertNull(group2 + " wasn't changed", results.get(group2));
+
+        Settings groupThreeSettings = results.get(group3);
+        assertEquals(1, intSetting.getConcreteSettingForNamespace(group3).get(groupThreeSettings).intValue());
+        assertEquals(Arrays.asList(5, 6), listSetting.getConcreteSettingForNamespace(group3).get(groupThreeSettings));
+        assertEquals(1, results.size());
+        assertEquals(1, groupThreeSettings.size());
+        results.clear();
+
+        service.applySettings(Settings.builder()
+            .put(intBuilder.apply(group1), 4) // modified
+            .put(intBuilder.apply(group2), 7)
+            .putList(listBuilder.apply(group1), "16", "17")
+            .putList(listBuilder.apply(group3), "5", "6")
+            .build());
+        assertNull(group2 + " wasn't changed", results.get(group2));
+        assertNull(group3 + " wasn't changed", results.get(group3));
+
+        groupOneSettings = results.get(group1);
+        assertEquals(4, intSetting.getConcreteSettingForNamespace(group1).get(groupOneSettings).intValue());
+        assertEquals(Arrays.asList(16, 17), listSetting.getConcreteSettingForNamespace(group1).get(groupOneSettings));
+        assertEquals(1, results.size());
+        assertEquals(2, groupOneSettings.size());
+        results.clear();
+    }
+
     public void testAddConsumerAffix() {
         Setting.AffixSetting<Integer> intSetting = Setting.affixKeySetting("foo.", "bar",
             (k) ->  Setting.intSetting(k, 1, Property.Dynamic, Property.NodeScope));