[data.search] Clean up code around ES preference usage (#204076)

## Summary

While refreshing my memory on how we are using the Elasticsearch
`preference` parameter, I noticed we had a method `getEsPreference` that
was exported but not used. We then had an additional method
`getPreference` that was being used to actually set the parameter. I
consolidated these into one place and moved the tests so that we can
utilize it when ES|QL supports this parameter.

### Checklist

- [x] [Unit or functional
tests](https://www.elastic.co/guide/en/kibana/master/development-tests.html)
were updated or added to match the most common scenarios

---------

Co-authored-by: Marco Vettorello <[email protected]>
(cherry picked from commit df3665f)

src/plugins/data/common/search/search_source/fetch/get_search_params.test.ts

@@ -9,7 +9,7 @@
 
 import { UI_SETTINGS } from '../../../constants';
 import { GetConfigFn } from '../../../types';
-import { getSearchParams, getSearchParamsFromRequest } from './get_search_params';
+import { getSearchParamsFromRequest, getEsPreference } from './get_search_params';
 import { createStubDataView } from '@kbn/data-views-plugin/common/data_views/data_view.stub';
 
 function getConfigStub(config: any = {}): GetConfigFn {
@@ -18,11 +18,11 @@ function getConfigStub(config: any = {}): GetConfigFn {
 
 describe('getSearchParams', () => {
   test('includes custom preference', () => {
-    const config = getConfigStub({
+    const getConfig = getConfigStub({
       [UI_SETTINGS.COURIER_SET_REQUEST_PREFERENCE]: 'custom',
       [UI_SETTINGS.COURIER_CUSTOM_REQUEST_PREFERENCE]: 'aaa',
     });
-    const searchParams = getSearchParams(config);
+    const searchParams = getSearchParamsFromRequest({ index: 'abc', body: {} }, { getConfig });
     expect(searchParams.preference).toBe('aaa');
   });
 
@@ -94,4 +94,39 @@ describe('getSearchParams', () => {
     );
     expect(searchParams).not.toHaveProperty('expand_wildcards', 'all');
   });
+
+  describe('getEsPreference', () => {
+    const mockConfigGet = jest.fn();
+
+    beforeEach(() => {
+      mockConfigGet.mockClear();
+    });
+
+    test('returns the session ID if set to sessionId', () => {
+      mockConfigGet.mockImplementation((key: string) => {
+        if (key === UI_SETTINGS.COURIER_SET_REQUEST_PREFERENCE) return 'sessionId';
+        if (key === UI_SETTINGS.COURIER_CUSTOM_REQUEST_PREFERENCE) return 'foobar';
+      });
+      const preference = getEsPreference(mockConfigGet, 'my_session_id');
+      expect(preference).toBe('my_session_id');
+    });
+
+    test('returns the custom preference if set to custom', () => {
+      mockConfigGet.mockImplementation((key: string) => {
+        if (key === UI_SETTINGS.COURIER_SET_REQUEST_PREFERENCE) return 'custom';
+        if (key === UI_SETTINGS.COURIER_CUSTOM_REQUEST_PREFERENCE) return 'foobar';
+      });
+      const preference = getEsPreference(mockConfigGet);
+      expect(preference).toBe('foobar');
+    });
+
+    test('returns undefined if set to none', () => {
+      mockConfigGet.mockImplementation((key: string) => {
+        if (key === UI_SETTINGS.COURIER_SET_REQUEST_PREFERENCE) return 'none';
+        if (key === UI_SETTINGS.COURIER_CUSTOM_REQUEST_PREFERENCE) return 'foobar';
+      });
+      const preference = getEsPreference(mockConfigGet);
+      expect(preference).toBe(undefined);
+    });
+  });
 });

src/plugins/data/common/search/search_source/fetch/get_search_params.ts

@@ -12,20 +12,16 @@ import { UI_SETTINGS } from '../../../constants';
 import { GetConfigFn } from '../../../types';
 import type { SearchRequest } from './types';
 
-const sessionId = Date.now();
+const defaultSessionId = `${Date.now()}`;
 
-export function getSearchParams(getConfig: GetConfigFn) {
-  return {
-    preference: getPreference(getConfig),
-  };
-}
-
-export function getPreference(getConfig: GetConfigFn) {
-  const setRequestPreference = getConfig(UI_SETTINGS.COURIER_SET_REQUEST_PREFERENCE);
-  if (setRequestPreference === 'sessionId') return sessionId;
-  return setRequestPreference === 'custom'
-    ? getConfig(UI_SETTINGS.COURIER_CUSTOM_REQUEST_PREFERENCE)
-    : undefined;
+export function getEsPreference(
+  getConfigFn: GetConfigFn,
+  sessionId = defaultSessionId
+): SearchRequest['preference'] {
+  const setPreference = getConfigFn<string>(UI_SETTINGS.COURIER_SET_REQUEST_PREFERENCE);
+  if (setPreference === 'sessionId') return sessionId;
+  const customPreference = getConfigFn<string>(UI_SETTINGS.COURIER_CUSTOM_REQUEST_PREFERENCE);
+  return setPreference === 'custom' ? customPreference : undefined;
 }
 
 /** @public */
@@ -36,7 +32,7 @@ export function getSearchParamsFromRequest(
   dependencies: { getConfig: GetConfigFn }
 ): ISearchRequestParams {
   const { getConfig } = dependencies;
-  const searchParams = getSearchParams(getConfig);
+  const searchParams = { preference: getEsPreference(getConfig) };
   // eslint-disable-next-line @typescript-eslint/naming-convention
   const { track_total_hits, ...body } = searchRequest.body;
   const dataView = typeof searchRequest.index !== 'string' ? searchRequest.index : undefined;

src/plugins/data/common/search/search_source/fetch/index.ts

@@ -7,6 +7,6 @@
  * License v3.0 only", or the "Server Side Public License, v 1".
  */
 
-export { getSearchParams, getSearchParamsFromRequest, getPreference } from './get_search_params';
+export { getSearchParamsFromRequest, getEsPreference } from './get_search_params';
 export { RequestFailure } from './request_error';
 export * from './types';

src/plugins/data/public/search/index.ts

@@ -48,7 +48,6 @@ export {
   SEARCH_SESSIONS_MANAGEMENT_ID,
   waitUntilNextSessionCompletes$,
 } from './session';
-export { getEsPreference } from './es_search';
 
 export type { SearchInterceptorDeps } from './search_interceptor';
 export { SearchInterceptor } from './search_interceptor';