removed compound throttler in favour of an alert throttler

We don't really need a generic compound throttler. Instead we now have an `AlertThrottler` that can be configured with optional `AckThrottler` and `PeriodThrottler`.

The logic of what throttler is applied first has therefore moved from the `Alert` to the `AlertThrottler` (back to its natural place)

Original commit: elastic/x-pack-elasticsearch@b81e467c97

src/main/java/org/elasticsearch/alerts/Alert.java

@@ -12,7 +12,7 @@ import org.elasticsearch.alerts.payload.PayloadRegistry;
 import org.elasticsearch.alerts.scheduler.schedule.Schedule;
 import org.elasticsearch.alerts.scheduler.schedule.ScheduleRegistry;
 import org.elasticsearch.alerts.throttle.AckThrottler;
-import org.elasticsearch.alerts.throttle.CompoundThrottler;
+import org.elasticsearch.alerts.throttle.AlertThrottler;
 import org.elasticsearch.alerts.throttle.PeriodThrottler;
 import org.elasticsearch.alerts.throttle.Throttler;
 import org.elasticsearch.alerts.trigger.Trigger;
@@ -65,14 +65,9 @@ public class Alert implements ToXContent {
         this.metadata = metadata;
         this.payload = payload != null ? payload : Payload.NOOP;
 
-        CompoundThrottler.Builder builder = CompoundThrottler.builder();
+        PeriodThrottler periodThrottler = throttlePeriod != null ? new PeriodThrottler(throttlePeriod) : null;
-        if (ackable) {
+        AckThrottler ackThrottler = ackable ? new AckThrottler() : null;
-            builder.add(new AckThrottler());
+        throttler = new AlertThrottler(periodThrottler, ackThrottler);
-        }
-        if (throttlePeriod != null) {
-            builder.add(new PeriodThrottler(throttlePeriod));
-        }
-        throttler = builder.build();
     }
 
     public String name() {

src/main/java/org/elasticsearch/alerts/throttle/AlertThrottler.java

@@ -0,0 +1,41 @@
+/*
+ * Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
+ * or more contributor license agreements. Licensed under the Elastic License;
+ * you may not use this file except in compliance with the Elastic License.
+ */
+package org.elasticsearch.alerts.throttle;
+
+import org.elasticsearch.alerts.Alert;
+import org.elasticsearch.alerts.trigger.Trigger;
+
+/**
+ *
+ */
+public class AlertThrottler implements Throttler {
+
+    private final PeriodThrottler periodThrottler;
+    private final AckThrottler ackThrottler;
+
+    public AlertThrottler(PeriodThrottler periodThrottler, AckThrottler ackThrottler) {
+        this.periodThrottler = periodThrottler;
+        this.ackThrottler = ackThrottler;
+    }
+
+    @Override
+    public Result throttle(Alert alert, Trigger.Result result) {
+        Result throttleResult = Result.NO;
+        if (periodThrottler != null) {
+            throttleResult = periodThrottler.throttle(alert, result);
+            if (throttleResult.throttle()) {
+                return throttleResult;
+            }
+        }
+        if (ackThrottler != null) {
+            throttleResult = ackThrottler.throttle(alert, result);
+            if (throttleResult.throttle()) {
+                return throttleResult;
+            }
+        }
+        return throttleResult;
+    }
+}

src/main/java/org/elasticsearch/alerts/throttle/CompoundThrottler.java

@@ -1,57 +0,0 @@
-/*
- * Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
- * or more contributor license agreements. Licensed under the Elastic License;
- * you may not use this file except in compliance with the Elastic License.
- */
-package org.elasticsearch.alerts.throttle;
-
-import org.elasticsearch.alerts.Alert;
-import org.elasticsearch.alerts.trigger.Trigger;
-import org.elasticsearch.common.collect.ImmutableList;
-
-import java.util.List;
-
-/**
- *
- */
-public class CompoundThrottler implements Throttler {
-
-    private final List<Throttler> throttlers;
-
-    public CompoundThrottler(List<Throttler> throttlers) {
-        this.throttlers = throttlers;
-    }
-
-    @Override
-    public Result throttle(Alert alert, Trigger.Result result) {
-        for (Throttler throttler : throttlers) {
-            Result rslt = throttler.throttle(alert, result);
-            if (rslt.throttle()) {
-                return rslt;
-            }
-        }
-        return Result.NO;
-    }
-
-    public static Builder builder() {
-        return new Builder();
-    }
-
-    public static class Builder {
-
-        private final ImmutableList.Builder<Throttler> throttlers = ImmutableList.builder();
-
-        private Builder() {
-        }
-
-        public Builder add(Throttler throttler) {
-            throttlers.add(throttler);
-            return this;
-        }
-
-        public Throttler build() {
-            ImmutableList<Throttler> list = throttlers.build();
-            return list.isEmpty() ? Throttler.NO_THROTTLE : new CompoundThrottler(list);
-        }
-    }
-}