allows Alerts to recover gracefully from Executor errors

x-pack/legacy/plugins/alerting/server/lib/result_type.ts

@@ -0,0 +1,54 @@
+/*
+ * 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.
+ */
+
+export interface Ok<T> {
+  tag: 'ok';
+  value: T;
+}
+
+export interface Err<E> {
+  tag: 'err';
+  error: E;
+}
+export type Result<T, E> = Ok<T> | Err<E>;
+
+export function asOk<T>(value: T): Ok<T> {
+  return {
+    tag: 'ok',
+    value,
+  };
+}
+
+export function asErr<T>(error: T): Err<T> {
+  return {
+    tag: 'err',
+    error,
+  };
+}
+
+export function isOk<T, E>(result: Result<T, E>): result is Ok<T> {
+  return result.tag === 'ok';
+}
+
+export function isErr<T, E>(result: Result<T, E>): result is Err<E> {
+  return !isOk(result);
+}
+
+export async function promiseResult<T, E>(future: Promise<T>): Promise<Result<T, E>> {
+  try {
+    return asOk(await future);
+  } catch (e) {
+    return asErr(e);
+  }
+}
+
+export function map<T, E, Resolution>(
+  result: Result<T, E>,
+  onOk: (value: T) => Resolution,
+  onErr: (error: E) => Resolution
+): Resolution {
+  return isOk(result) ? onOk(result.value) : onErr(result.error);
+}