[One Discover][Security Solution] Replace the use of Ecsflat with fieldsMetadata (#225105)

## Summary

As per
[comments](https://github.com/elastic/kibana/pull/204756#discussion_r2162038673)
by @davismcphee , this PR removes the usage of `EcsFlat` and replaces it
with `fieldsMetadata`.

src/platform/packages/shared/kbn-discover-utils/src/field_constants.ts

@@ -16,6 +16,7 @@ export const ERROR_MESSAGE_FIELD = 'error.message';
 export const EVENT_ORIGINAL_FIELD = 'event.original';
 export const EVENT_OUTCOME_FIELD = 'event.outcome';
 export const INDEX_FIELD = '_index';
+export const EVENT_CATEGORY_FIELD = 'event.category';
 
 // Trace fields
 export const TRACE_ID_FIELD = 'trace.id';

src/platform/plugins/shared/discover/public/context_awareness/profile_providers/security/components/alert_event_overview.test.tsx

@@ -12,7 +12,6 @@ import { fireEvent, render, screen } from '@testing-library/react';
 import { AlertEventOverview } from './alert_event_overview';
 import type { DataTableRecord } from '@kbn/discover-utils';
 import { dataViewMock } from '@kbn/discover-utils/src/__mocks__';
-import { EcsFlat } from '@elastic/ecs';
 import { useDiscoverServices } from '../../../../hooks/use_discover_services';
 import { encode } from '@kbn/rison';
 import { URLSearchParams } from 'url';
@@ -27,6 +26,19 @@ const mockDiscoverServices = {
   application: {
     getUrlForApp: mockGetUrlForApp,
   },
+  fieldsMetadata: {
+    useFieldsMetadata: jest.fn().mockReturnValue({
+      fieldsMetadata: {
+        'event.category': {
+          allowed_values: [
+            { name: 'process', description: 'Process events' },
+            { name: 'network', description: 'Network events' },
+          ],
+        },
+      },
+      loading: false,
+    }),
+  },
 };
 
 const mockRow = {
@@ -36,6 +48,7 @@ const mockRow = {
   _id: 'test-id',
   '@timestamp': '2021-08-02T14:00:00.000Z',
   'kibana.alert.url': 'test-url',
+  'event.category': 'process',
 };
 
 const mockHit = {
@@ -87,10 +100,7 @@ describe('AlertEventOverview', () => {
 
       render(<AlertEventOverview hit={localMockHit} dataView={mockDataView} />);
 
-      expect(screen.getByTestId('expandableContent-About')).toHaveTextContent(
-        EcsFlat['event.category'].allowed_values.find((i) => i.name === 'process')
-          ?.description as string
-      );
+      expect(screen.getByTestId('expandableContent-About')).toHaveTextContent('Process events');
     });
 
     test('should display timeline redirect url correctly', () => {
@@ -142,5 +152,73 @@ describe('AlertEventOverview', () => {
         `test-timeline-url?${searchParams}`
       );
     });
+
+    describe('ECS Description', () => {
+      test('should give ECS description for event.category field', () => {
+        render(<AlertEventOverview hit={mockHit} dataView={mockDataView} />);
+        expect(screen.getByTestId('about')).toHaveTextContent('Process events');
+      });
+      test('should give placeholder ECS description when fieldsMetadata is not available', () => {
+        (useDiscoverServices as jest.Mock).mockReturnValue({
+          ...mockDiscoverServices,
+          fieldsMetadata: {
+            useFieldsMetadata: jest.fn().mockReturnValue({
+              fieldsMetadata: undefined,
+              loading: false,
+            }),
+          },
+        });
+
+        render(<AlertEventOverview hit={mockHit} dataView={mockDataView} />);
+        expect(screen.getByTestId('about')).toHaveTextContent(
+          "This field doesn't have a description because it's not part of ECS."
+        );
+      });
+
+      test('should give placeholder ECS description when event.category field is not present in fieldMetada', () => {
+        (useDiscoverServices as jest.Mock).mockReturnValue({
+          ...mockDiscoverServices,
+          fieldsMetadata: {
+            useFieldsMetadata: jest.fn().mockReturnValue({
+              fieldsMetadata: {},
+              loading: false,
+            }),
+          },
+        });
+
+        render(<AlertEventOverview hit={mockHit} dataView={mockDataView} />);
+        expect(screen.getByTestId('about')).toHaveTextContent(
+          "This field doesn't have a description because it's not part of ECS."
+        );
+      });
+
+      test('should give placeholder ECS description when event.category field is not present in hit', () => {
+        const localMockHit = {
+          flattened: {
+            ...mockRow,
+            'event.category': undefined,
+          },
+        } as unknown as DataTableRecord;
+
+        render(<AlertEventOverview hit={localMockHit} dataView={mockDataView} />);
+        expect(screen.getByTestId('about')).toHaveTextContent(
+          "This field doesn't have a description because it's not part of ECS."
+        );
+      });
+
+      test('should give placeholder ECS when event.category fields has a value that is not in allowed values', () => {
+        const localMockHit = {
+          flattened: {
+            ...mockRow,
+            'event.category': 'unknown',
+          },
+        } as unknown as DataTableRecord;
+
+        render(<AlertEventOverview hit={localMockHit} dataView={mockDataView} />);
+        expect(screen.getByTestId('about')).toHaveTextContent(
+          "This field doesn't have a description because it's not part of ECS."
+        );
+      });
+    });
   });
 });

src/platform/plugins/shared/discover/public/context_awareness/profile_providers/security/components/alert_event_overview.tsx

@@ -9,7 +9,7 @@
 
 import React, { useMemo, useState } from 'react';
 import type { FC, PropsWithChildren } from 'react';
-import { getFieldValue } from '@kbn/discover-utils';
+import { fieldConstants, getFieldValue } from '@kbn/discover-utils';
 import type { DocViewerComponent } from '@kbn/unified-doc-viewer/src/services/types';
 import {
   EuiTitle,
@@ -19,6 +19,7 @@ import {
   EuiFlexGroup,
   EuiFlexItem,
   EuiText,
+  EuiSkeletonText,
 } from '@elastic/eui';
 import * as i18n from '../translations';
 import { getSecurityTimelineRedirectUrl } from '../utils';
@@ -62,12 +63,18 @@ export const ExpandableSection: FC<PropsWithChildren<{ title: string }>> = ({
 export const AlertEventOverview: DocViewerComponent = ({ hit }) => {
   const {
     application: { getUrlForApp },
+    fieldsMetadata,
   } = useDiscoverServices();
 
   const timelinesURL = getUrlForApp('securitySolutionUI', {
     path: 'alerts',
   });
 
+  const result = fieldsMetadata?.useFieldsMetadata({
+    attributes: ['allowed_values', 'name', 'flat_name'],
+    fieldNames: [fieldConstants.EVENT_CATEGORY_FIELD],
+  });
+
   const reason = useMemo(() => getFieldValue(hit, 'kibana.alert.reason') as string, [hit]);
   const description = useMemo(
     () => getFieldValue(hit, 'kibana.alert.rule.description') as string,
@@ -100,9 +107,18 @@ export const AlertEventOverview: DocViewerComponent = ({ hit }) => {
     >
       <EuiFlexItem>
         <ExpandableSection title={i18n.aboutSectionTitle}>
-          <EuiText size="s" data-test-subj="about">
-            {getEcsAllowedValueDescription(eventCategory)}
-          </EuiText>
+          {result?.loading ? (
+            <EuiSkeletonText
+              lines={2}
+              size={'s'}
+              isLoading={result?.loading}
+              contentAriaLabel={i18n.ecsDescriptionLoadingAriaLable}
+            />
+          ) : (
+            <EuiText size="s" data-test-subj="about">
+              {getEcsAllowedValueDescription(result?.fieldsMetadata, eventCategory)}
+            </EuiText>
+          )}
         </ExpandableSection>
       </EuiFlexItem>
       {description ? (

src/platform/plugins/shared/discover/public/context_awareness/profile_providers/security/translations.ts

@@ -54,3 +54,10 @@ export const reasonSectionTitle = i18n.translate(
     defaultMessage: 'Reason',
   }
 );
+
+export const ecsDescriptionLoadingAriaLable = i18n.translate(
+  'discover.profile.security.flyout.ecsDescriptionLoadingAriaLabel',
+  {
+    defaultMessage: 'Loading ECS description',
+  }
+);

src/platform/plugins/shared/discover/public/context_awareness/profile_providers/security/utils/ecs_description.ts

@@ -7,9 +7,8 @@
  * License v3.0 only", or the "Server Side Public License, v 1".
  */
 
-import { EcsFlat } from '@elastic/ecs';
+import type { UseFieldsMetadataHook } from '@kbn/fields-metadata-plugin/public/hooks/use_fields_metadata';
 import * as i18n from '../translations';
-export type EcsAllowedValue = (typeof EcsFlat)['event.category']['allowed_values'][0];
 
 /**
  * Helper function to return the description of an allowed value of the specified field
@@ -17,8 +16,11 @@ export type EcsAllowedValue = (typeof EcsFlat)['event.category']['allowed_values
  * @param value
  * @returns ecs description of the value
  */
-export const getEcsAllowedValueDescription = (value: string): string => {
-  const allowedValues: EcsAllowedValue[] = EcsFlat['event.category']?.allowed_values ?? [];
+export const getEcsAllowedValueDescription = (
+  fieldsMetadata: ReturnType<UseFieldsMetadataHook>['fieldsMetadata'] = {},
+  value: string
+): string => {
+  const allowedValues = fieldsMetadata['event.category']?.allowed_values ?? [];
   const result =
     allowedValues?.find((item) => item.name === value)?.description ?? i18n.noEcsDescriptionReason;
   return result;