Start services (#63720)

* feat: 🎸 add createStartServicesGetter() to /public  kibana_util

* test: 💍 add createStartServicesGetter() tests

src/plugins/kibana_utils/public/core/create_start_service_getter.test.ts

@@ -0,0 +1,78 @@
+/*
+ * Licensed to Elasticsearch B.V. under one or more contributor
+ * license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright
+ * ownership. Elasticsearch B.V. licenses this file to you under
+ * the Apache License, Version 2.0 (the "License"); you may
+ * not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+import { StartServicesAccessor } from '../../../../core/public';
+import { createStartServicesGetter } from './create_start_service_getter';
+import { Defer } from '../../common/defer';
+
+describe('createStartServicesGetter', () => {
+  test('throws if services are accessed before accessor resolves', async () => {
+    const future = new Defer<any>();
+    const accessor: StartServicesAccessor = async () => await future.promise;
+    const start = createStartServicesGetter(accessor);
+
+    await new Promise(r => setTimeout(r, 1));
+
+    expect(() => start()).toThrowErrorMatchingInlineSnapshot(
+      `"Trying to access start services before start."`
+    );
+  });
+
+  test('returns services after accessor resolves even if first time called before it resolved', async () => {
+    const future = new Defer<any>();
+    const core = {};
+    const plugins = {};
+    const self = {};
+    const accessor: StartServicesAccessor = async () => await future.promise;
+    const start = createStartServicesGetter(accessor);
+
+    await new Promise(r => setTimeout(r, 1));
+
+    expect(() => start()).toThrow();
+
+    await new Promise(r => setTimeout(r, 1));
+    future.resolve([core, plugins, self]);
+    await future.promise;
+
+    expect(start()).toEqual({
+      core,
+      plugins,
+      self,
+    });
+  });
+
+  test('returns services if called after accessor resolves', async () => {
+    const future = new Defer<any>();
+    const core = {};
+    const plugins = {};
+    const self = {};
+    const accessor: StartServicesAccessor = async () => await future.promise;
+    const start = createStartServicesGetter(accessor);
+
+    await new Promise(r => setTimeout(r, 1));
+    future.resolve([core, plugins, self]);
+    await future.promise;
+
+    expect(start()).toEqual({
+      core,
+      plugins,
+      self,
+    });
+  });
+});

src/plugins/kibana_utils/public/core/create_start_service_getter.ts

@@ -0,0 +1,56 @@
+/*
+ * Licensed to Elasticsearch B.V. under one or more contributor
+ * license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright
+ * ownership. Elasticsearch B.V. licenses this file to you under
+ * the Apache License, Version 2.0 (the "License"); you may
+ * not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+import { CoreStart, StartServicesAccessor } from '../../../../core/public';
+
+export interface StartServices<Plugins = unknown, OwnContract = unknown> {
+  plugins: Plugins;
+  self: OwnContract;
+  core: CoreStart;
+}
+
+export type StartServicesGetter<Plugins = unknown, OwnContract = unknown> = () => StartServices<
+  Plugins,
+  OwnContract
+>;
+
+export const createStartServicesGetter = <TPluginsStart extends object, TStart>(
+  accessor: StartServicesAccessor<TPluginsStart, TStart>
+): StartServicesGetter<TPluginsStart, TStart> => {
+  let services: StartServices<TPluginsStart, TStart> | undefined;
+
+  accessor().then(
+    ([core, plugins, self]) => {
+      services = {
+        core,
+        plugins,
+        self,
+      };
+    },
+    error => {
+      // eslint-disable-next-line no-console
+      console.error('Could not access start services.', error);
+    }
+  );
+
+  return () => {
+    if (!services) throw new Error('Trying to access start services before start.');
+    return services;
+  };
+};

src/plugins/kibana_utils/public/core/index.ts

@@ -18,3 +18,4 @@
  */
 
 export * from './create_kibana_utils_core';
+export * from './create_start_service_getter';