[ResponseOps][MaintenanceWindow] Update schedule duration API response to be same as request (elastic#238389)

## Summary

Fixes elastic#234019

This PR returns schedule duration in the API response same as request,
to avoid issue in terraform

<img width="685" height="791" alt="Screenshot 2025-10-10 at 12 34 14"
src="https://github.com/user-attachments/assets/2d52bd7d-9680-4b67-83e6-d10d89341fc7"
/>


### Checklist

Check the PR satisfies following conditions. 

Reviewers should verify this PR satisfies this list as well.

- [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
- [ ] Review the [backport
guidelines](https://docs.google.com/document/d/1VyN5k91e5OVumlc0Gb9RPa3h1ewuPE705nRtioPiTvY/edit?usp=sharing)
and apply applicable `backport:*` labels.

Author: js-jankisalvi

x-pack/platform/plugins/shared/alerting/common/routes/schedule/index.ts

@@ -17,3 +17,5 @@ export {
 export { transformCustomScheduleToRRule as transformCustomScheduleToRRuleV1 } from './transforms/custom_to_rrule/v1';
 export { transformRRuleToCustomSchedule as transformRRuleToCustomScheduleV1 } from './transforms/rrule_to_custom/v1';
 export type { ScheduleRequest as ScheduleRequestV1 } from './types/v1';
+
+export { getDurationInMilliseconds } from './transforms/custom_to_rrule/util';

x-pack/platform/plugins/shared/alerting/common/routes/schedule/transforms/custom_to_rrule/util.ts

@@ -0,0 +1,17 @@
+/*
+ * Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
+ * or more contributor license agreements. Licensed under the Elastic License
+ * 2.0; you may not use this file except in compliance with the Elastic License
+ * 2.0.
+ */
+
+import moment from 'moment-timezone';
+import { DURATION_REGEX } from '../../constants';
+
+export const getDurationInMilliseconds = (duration: string): number => {
+  const [, durationNumber, durationUnit] = duration.match(DURATION_REGEX) ?? [];
+
+  return moment
+    .duration(durationNumber, durationUnit as moment.unitOfTime.DurationConstructor)
+    .asMilliseconds();
+};

x-pack/platform/plugins/shared/alerting/common/routes/schedule/transforms/custom_to_rrule/v1.ts

@@ -5,11 +5,11 @@
  * 2.0.
  */
 
-import moment from 'moment-timezone';
 import { Frequency } from '@kbn/rrule';
 import type { RRuleRequestV1 } from '../../../r_rule';
 import type { ScheduleRequest } from '../../types/v1';
-import { DEFAULT_TIMEZONE, DURATION_REGEX, INTERVAL_FREQUENCY_REGEXP } from '../../constants';
+import { DEFAULT_TIMEZONE, INTERVAL_FREQUENCY_REGEXP } from '../../constants';
+import { getDurationInMilliseconds } from './util';
 
 const transformEveryToFrequency = (frequency?: string) => {
   switch (frequency) {
@@ -26,14 +26,6 @@ const transformEveryToFrequency = (frequency?: string) => {
   }
 };
 
-const getDurationInMilliseconds = (duration: string): number => {
-  const [, durationNumber, durationUnit] = duration.match(DURATION_REGEX) ?? [];
-
-  return moment
-    .duration(durationNumber, durationUnit as moment.unitOfTime.DurationConstructor)
-    .asMilliseconds();
-};
-
 export const transformCustomScheduleToRRule = (
   schedule: ScheduleRequest
 ): {

x-pack/platform/plugins/shared/alerting/server/routes/maintenance_window/apis/external/create/create_maintenance_window_route.test.ts

@@ -28,6 +28,7 @@ const mockMaintenanceWindow = {
   eventEndTime: new Date().toISOString(),
   status: MaintenanceWindowStatus.Running,
   id: 'test-id',
+  duration: 864000000,
 } as MaintenanceWindow;
 
 const createParams = {
@@ -124,7 +125,7 @@ describe('createMaintenanceWindowRoute', () => {
         id: 'test-id',
         schedule: {
           custom: {
-            duration: '60m',
+            duration: '10d',
             recurring: {
               occurrences: 2,
             },
@@ -140,6 +141,28 @@ describe('createMaintenanceWindowRoute', () => {
     });
   });
 
+  test('throws error if request duration does not match response duration', async () => {
+    const licenseState = licenseStateMock.create();
+    const router = httpServiceMock.createRouter();
+
+    createMaintenanceWindowRoute(router, licenseState);
+
+    maintenanceWindowClient.create.mockResolvedValueOnce({
+      ...mockMaintenanceWindow, // it has 60m duration
+      duration: 3600000,
+    } as MaintenanceWindow);
+
+    const [, handler] = router.post.mock.calls[0];
+    const [context, req, res] = mockHandlerArguments(
+      { maintenanceWindowClient },
+      { body: createParams }
+    );
+
+    await expect(handler(context, req, res)).rejects.toMatchInlineSnapshot(
+      `[Error: Request duration does not match response duration.]`
+    );
+  });
+
   test('ensures the license allows for creating maintenance windows', async () => {
     const licenseState = licenseStateMock.create();
     const router = httpServiceMock.createRouter();

x-pack/platform/plugins/shared/alerting/server/routes/maintenance_window/apis/external/create/create_maintenance_window_route.ts

@@ -18,6 +18,7 @@ import type {
 } from '../../../../../../common/routes/maintenance_window/external/apis/create';
 import { createMaintenanceWindowRequestBodySchemaV1 } from '../../../../../../common/routes/maintenance_window/external/apis/create';
 import { maintenanceWindowResponseSchemaV1 } from '../../../../../../common/routes/maintenance_window/external/response';
+import { getDurationInMilliseconds } from '../../../../../../common/routes/schedule';
 import { transformInternalMaintenanceWindowToExternalV1 } from '../common/transforms';
 import { transformCreateBodyV1 } from './transform_create_body';
 
@@ -65,6 +66,7 @@ export const createMaintenanceWindowRoute = (
         licenseState.ensureLicenseForMaintenanceWindow();
 
         const body: CreateMaintenanceWindowRequestBodyV1 = req.body;
+        const customSchedule = body.schedule.custom;
 
         const maintenanceWindowClient = (await context.alerting).getMaintenanceWindowClient();
 
@@ -74,9 +76,24 @@ export const createMaintenanceWindowRoute = (
 
         const response: CreateMaintenanceWindowResponseV1 =
           transformInternalMaintenanceWindowToExternalV1(maintenanceWindow);
+        // Return request duration in response when both are same otherwise throw an error
+        const requestDurationInMilliseconds = getDurationInMilliseconds(customSchedule.duration);
+
+        const responseDurationInMilliseconds = getDurationInMilliseconds(
+          response.schedule.custom.duration
+        );
+
+        if (requestDurationInMilliseconds !== responseDurationInMilliseconds) {
+          throw new Error('Request duration does not match response duration.');
+        }
 
         return res.ok({
-          body: response,
+          body: {
+            ...response,
+            schedule: {
+              custom: { ...response.schedule.custom, duration: customSchedule.duration },
+            },
+          },
         });
       })
     )

x-pack/platform/plugins/shared/alerting/server/routes/maintenance_window/apis/external/update/update_maintenance_window_route.test.ts

@@ -30,6 +30,7 @@ const mockMaintenanceWindow = {
   eventStartTime: new Date().toISOString(),
   eventEndTime: new Date().toISOString(),
   status: MaintenanceWindowStatus.Running,
+  duration: 864000000,
   id: 'test-id',
 } as MaintenanceWindow;
 
@@ -132,7 +133,7 @@ describe('updateMaintenanceWindowRoute', () => {
         id: 'test-id',
         schedule: {
           custom: {
-            duration: '60m',
+            duration: '10d',
             recurring: {
               occurrences: 2,
             },
@@ -148,6 +149,30 @@ describe('updateMaintenanceWindowRoute', () => {
     });
   });
 
+  test('throws error if request duration does not match response duration', async () => {
+    const licenseState = licenseStateMock.create();
+    const router = httpServiceMock.createRouter();
+
+    updateMaintenanceWindowRoute(router, licenseState);
+
+    maintenanceWindowClient.update.mockResolvedValueOnce({
+      ...getMockMaintenanceWindow(), // it has 60m duration
+      eventStartTime: new Date().toISOString(),
+      eventEndTime: new Date().toISOString(),
+      status: MaintenanceWindowStatus.Running,
+      id: 'test-id',
+    });
+    const [, handler] = router.patch.mock.calls[0];
+    const [context, req, res] = mockHandlerArguments(
+      { maintenanceWindowClient },
+      { params: updateRequestParams, body: updateRequestBody }
+    );
+
+    await expect(handler(context, req, res)).rejects.toMatchInlineSnapshot(
+      `[Error: Request duration does not match response duration.]`
+    );
+  });
+
   test('ensures the license allows for creating maintenance windows', async () => {
     const licenseState = licenseStateMock.create();
     const router = httpServiceMock.createRouter();

x-pack/platform/plugins/shared/alerting/server/routes/maintenance_window/apis/external/update/update_maintenance_window_route.ts

@@ -23,6 +23,7 @@ import {
 } from '../../../../../../common/routes/maintenance_window/external/apis/update';
 import { maintenanceWindowResponseSchemaV1 } from '../../../../../../common/routes/maintenance_window/external/response';
 import { transformInternalMaintenanceWindowToExternalV1 } from '../common/transforms';
+import { getDurationInMilliseconds } from '../../../../../../common/routes/schedule';
 
 import { transformUpdateBodyV1 } from './transform_update_body';
 
@@ -79,6 +80,7 @@ export const updateMaintenanceWindowRoute = (
 
         const body: UpdateMaintenanceWindowRequestBodyV1 = req.body;
         const params: UpdateMaintenanceWindowRequestParamsV1 = req.params;
+        const customSchedule = body?.schedule?.custom;
 
         const maintenanceWindowClient = (await context.alerting).getMaintenanceWindowClient();
 
@@ -90,8 +92,38 @@ export const updateMaintenanceWindowRoute = (
         const response: UpdateMaintenanceWindowResponseV1 =
           transformInternalMaintenanceWindowToExternalV1(maintenanceWindow);
 
+        // Return request duration in response when both are same otherwise throw an error
+        const requestDurationInMilliseconds = customSchedule?.duration
+          ? getDurationInMilliseconds(customSchedule.duration)
+          : undefined;
+
+        const responseDurationInMilliseconds = getDurationInMilliseconds(
+          response.schedule.custom.duration
+        );
+
+        if (
+          requestDurationInMilliseconds &&
+          requestDurationInMilliseconds !== responseDurationInMilliseconds
+        ) {
+          throw new Error('Request duration does not match response duration.');
+        }
+
+        const responseDuration = customSchedule?.duration
+          ? customSchedule.duration
+          : response.schedule.custom.duration;
+
         return res.ok({
-          body: response,
+          body: {
+            ...response,
+            schedule: {
+              custom: {
+                ...response.schedule.custom,
+                ...{
+                  duration: responseDuration,
+                },
+              },
+            },
+          },
         });
       })
     )