feat(MultipleAlarmActionStrategy): add method to get flattened actions (#423)

---

_By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license_

Author: Eugene Cheung

API.md

@@ -7,6 +7,12 @@ export function multipleActions(...actions: IAlarmActionStrategy[]) {
   return new MultipleAlarmActionStrategy(actions);
 }
 
+export function isMultipleAlarmActionStrategy(
+  obj?: any
+): obj is MultipleAlarmActionStrategy {
+  return !!(obj && obj instanceof MultipleAlarmActionStrategy);
+}
+
 /**
  * Alarm action strategy that combines multiple actions in the same order as they were given.
  */
@@ -20,4 +26,26 @@ export class MultipleAlarmActionStrategy implements IAlarmActionStrategy {
   addAlarmActions(props: AlarmActionStrategyProps): void {
     this.actions.forEach((action) => action.addAlarmActions(props));
   }
+
+  /**
+   * Returns list of alarm actions where any nested instances of MultipleAlarmActionStrategy
+   * are flattened.
+   *
+   * @returns flattened list of alarm actions.
+   */
+  flattenedAlarmActions(): IAlarmActionStrategy[] {
+    return this._flattenedAlarmActions(...this.actions);
+  }
+
+  private _flattenedAlarmActions(
+    ...actions: IAlarmActionStrategy[]
+  ): IAlarmActionStrategy[] {
+    return actions.flatMap((action) => {
+      if (isMultipleAlarmActionStrategy(action)) {
+        return this._flattenedAlarmActions(action);
+      }
+
+      return [action];
+    });
+  }
 }

lib/common/alarm/action/MultipleAlarmActionStrategy.ts

@@ -3,7 +3,11 @@ import { Template } from "aws-cdk-lib/assertions";
 import { Alarm, Metric } from "aws-cdk-lib/aws-cloudwatch";
 import { Topic } from "aws-cdk-lib/aws-sns";
 
-import { multipleActions, SnsAlarmActionStrategy } from "../../../../lib";
+import {
+  isMultipleAlarmActionStrategy,
+  multipleActions,
+  SnsAlarmActionStrategy,
+} from "../../../../lib";
 
 test("snapshot test: multiple actions", () => {
   const stack = new Stack();
@@ -15,12 +19,24 @@ test("snapshot test: multiple actions", () => {
     threshold: 0,
     metric: new Metric({ namespace: "Dummy", metricName: "Dummy" }),
   });
-  const action = multipleActions(
-    new SnsAlarmActionStrategy({ onAlarmTopic: topic1 }),
-    new SnsAlarmActionStrategy({ onAlarmTopic: topic2 }),
-    new SnsAlarmActionStrategy({ onAlarmTopic: topic3 })
-  );
+
+  const action1 = new SnsAlarmActionStrategy({ onAlarmTopic: topic1 });
+  const action2 = new SnsAlarmActionStrategy({ onAlarmTopic: topic2 });
+  const action3 = new SnsAlarmActionStrategy({ onAlarmTopic: topic3 });
+
+  const action = multipleActions(action1, action2, action3);
   action.addAlarmActions({ alarm, action });
 
   expect(Template.fromStack(stack)).toMatchSnapshot();
+  expect(action.flattenedAlarmActions()).toEqual([action1, action2, action3]);
+});
+
+test("isMultipleAlarmActionStrategy", () => {
+  const stack = new Stack();
+  const topic1 = new Topic(stack, "DummyTopic1");
+  const snsAction = new SnsAlarmActionStrategy({ onAlarmTopic: topic1 });
+  const multipleAction = multipleActions(snsAction);
+
+  expect(isMultipleAlarmActionStrategy(multipleAction)).toBe(true);
+  expect(isMultipleAlarmActionStrategy(snsAction)).toBe(false);
 });