feat: add tab switcher for change to json diff view in CR (#10179)

Updates the strategy change component used in change requests to have a
"tab"-like functionality, where you can switch between "Change" (the
rendered strategy) and "View diff" (the JSON diff). This is a tab
switcher, so you navigate it with arrow keys if on a keyboard, and I've
set selection to follow focus for now. This is my preference as it saves
you extra space/enter taps, but we can remove it later if we want.

Most of the changes in this PR is wrapping the existing strategy change
components/sections in tab panels and tab context providers.

Later changes in this project will remove the existing "view diff" hover
link in favor of this view.

There is some work to do on the design front (in terms of spacing,
borders, etc), but this covers the core functionality.

The pre-existing strategy change component has been moved into the
"LegacyStrategyChange" file with no changes beyond a deprecation
comment. The existing tests now test the new component instead with no
breakage. (I anticipate breaking when we remove the view diff link,
though)



Change with strategy variants:
<img width="991" alt="image"
src="https://github.com/user-attachments/assets/ac28912f-5b08-4a9c-96da-81bfd0b2e68e"
/>

<img width="1005" alt="image"
src="https://github.com/user-attachments/assets/4addaacc-101c-46cb-888f-95dc3b1cac25"
/>


## Edge case: deleted strat with no reference strategy

There is a case in the code where "reference strategy" can be undefined
for a deleted strategy. It is defined as follows:

```ts
    const referenceStrategy =
        changeRequestState === 'Applied'
            ? change.payload.snapshot
            : currentStrategy;

```

I've decided to still show the "(no changes)" json diff in that setting,
so that the tabs actually affect something. I don't know how often this
happens, though: probably not anymore unless your CR is _ancient_, as we
introduced the snapshot quite a while ago, and `currentStrategy`
shouldn't really be undefined here, I should think.

Deleted strategy with no reference strategy:

Change:
<img width="1013" alt="image"
src="https://github.com/user-attachments/assets/352eaec9-c0ef-4d5a-b765-11304daf4474"
/>

Diff:
<img width="1029" alt="image"
src="https://github.com/user-attachments/assets/e69c81a6-1ef7-47ff-853a-9fb900b26303"
/>

frontend/src/component/changeRequest/ChangeRequest/Changes/Change/FeatureChange.tsx

@@ -8,13 +8,15 @@ import { objectId } from 'utils/objectId';
 import { ConditionallyRender } from 'component/common/ConditionallyRender/ConditionallyRender';
 import { Alert, Box, styled } from '@mui/material';
 import { ToggleStatusChange } from './ToggleStatusChange.tsx';
-import { StrategyChange } from './StrategyChange.tsx';
+import { LegacyStrategyChange } from './LegacyStrategyChange.tsx';
 import { VariantPatch } from './VariantPatch/VariantPatch.tsx';
 import { EnvironmentStrategyExecutionOrder } from './EnvironmentStrategyExecutionOrder/EnvironmentStrategyExecutionOrder.tsx';
 import { ArchiveFeatureChange } from './ArchiveFeatureChange.tsx';
 import { DependencyChange } from './DependencyChange.tsx';
 import { Link } from 'react-router-dom';
 import { ReleasePlanChange } from './ReleasePlanChange.tsx';
+import { StrategyChange } from './StrategyChange.tsx';
+import { useUiFlag } from 'hooks/useUiFlag.ts';
 
 const StyledSingleChangeBox = styled(Box, {
     shouldForwardProp: (prop: string) => !prop.startsWith('$'),
@@ -87,6 +89,11 @@ export const FeatureChange: FC<{
         ? feature.changes.length + 1
         : feature.changes.length;
 
+    const useDiffableChangeComponent = useUiFlag('crDiffView');
+    const StrategyChangeComponent = useDiffableChangeComponent
+        ? StrategyChange
+        : LegacyStrategyChange;
+
     return (
         <StyledSingleChangeBox
             key={objectId(change)}
@@ -166,7 +173,7 @@ export const FeatureChange: FC<{
                 {change.action === 'addStrategy' ||
                 change.action === 'deleteStrategy' ||
                 change.action === 'updateStrategy' ? (
-                    <StrategyChange
+                    <StrategyChangeComponent
                         actions={actions}
                         change={change}
                         featureName={feature.name}

frontend/src/component/changeRequest/ChangeRequest/Changes/Change/LegacyStrategyChange.tsx

@@ -0,0 +1,357 @@
+import type React from 'react';
+import type { FC, ReactNode } from 'react';
+import { Box, styled, Tooltip, Typography } from '@mui/material';
+import BlockIcon from '@mui/icons-material/Block';
+import TrackChangesIcon from '@mui/icons-material/TrackChanges';
+import {
+    StrategyDiff,
+    StrategyTooltipLink,
+} from '../../StrategyTooltipLink/StrategyTooltipLink.tsx';
+import { StrategyExecution } from 'component/feature/FeatureView/FeatureOverview/FeatureOverviewEnvironments/FeatureOverviewEnvironment/EnvironmentAccordionBody/StrategyDraggableItem/StrategyItem/StrategyExecution/StrategyExecution';
+import type {
+    ChangeRequestState,
+    IChangeRequestAddStrategy,
+    IChangeRequestDeleteStrategy,
+    IChangeRequestUpdateStrategy,
+} from 'component/changeRequest/changeRequest.types';
+import { useCurrentStrategy } from './hooks/useCurrentStrategy.ts';
+import { Badge } from 'component/common/Badge/Badge';
+import { ConditionallyRender } from 'component/common/ConditionallyRender/ConditionallyRender';
+import { flexRow } from 'themes/themeStyles';
+import { EnvironmentVariantsTable } from 'component/feature/FeatureView/FeatureVariants/FeatureEnvironmentVariants/EnvironmentVariantsCard/EnvironmentVariantsTable/EnvironmentVariantsTable';
+import { ChangeOverwriteWarning } from './ChangeOverwriteWarning/ChangeOverwriteWarning.tsx';
+import type { IFeatureStrategy } from 'interfaces/strategy';
+
+export const ChangeItemWrapper = styled(Box)({
+    display: 'flex',
+    justifyContent: 'space-between',
+    alignItems: 'center',
+});
+
+const ChangeItemCreateEditDeleteWrapper = styled(Box)(({ theme }) => ({
+    display: 'grid',
+    gridTemplateColumns: 'auto auto',
+    justifyContent: 'space-between',
+    gap: theme.spacing(1),
+    alignItems: 'center',
+    marginBottom: theme.spacing(2),
+    width: '100%',
+}));
+
+const ChangeItemInfo: FC<{ children?: React.ReactNode }> = styled(Box)(
+    ({ theme }) => ({
+        display: 'grid',
+        gridTemplateColumns: '150px auto',
+        gridAutoFlow: 'column',
+        alignItems: 'center',
+        flexGrow: 1,
+        gap: theme.spacing(1),
+    }),
+);
+
+const StyledBox: FC<{ children?: React.ReactNode }> = styled(Box)(
+    ({ theme }) => ({
+        marginTop: theme.spacing(2),
+    }),
+);
+
+const StyledTypography: FC<{ children?: React.ReactNode }> = styled(Typography)(
+    ({ theme }) => ({
+        margin: `${theme.spacing(1)} 0`,
+    }),
+);
+
+const DisabledEnabledState: FC<{ show?: boolean; disabled: boolean }> = ({
+    show = true,
+    disabled,
+}) => {
+    if (!show) {
+        return null;
+    }
+
+    if (disabled) {
+        return (
+            <Tooltip
+                title='This strategy will not be taken into account when evaluating feature flag.'
+                arrow
+                sx={{ cursor: 'pointer' }}
+            >
+                <Badge color='disabled' icon={<BlockIcon />}>
+                    Disabled
+                </Badge>
+            </Tooltip>
+        );
+    }
+
+    return (
+        <Tooltip
+            title='This was disabled before and with this change it will be taken into account when evaluating feature flag.'
+            arrow
+            sx={{ cursor: 'pointer' }}
+        >
+            <Badge color='success' icon={<TrackChangesIcon />}>
+                Enabled
+            </Badge>
+        </Tooltip>
+    );
+};
+
+const EditHeader: FC<{
+    wasDisabled?: boolean;
+    willBeDisabled?: boolean;
+}> = ({ wasDisabled = false, willBeDisabled = false }) => {
+    if (wasDisabled && willBeDisabled) {
+        return (
+            <Typography color='action.disabled'>Editing strategy:</Typography>
+        );
+    }
+
+    if (!wasDisabled && willBeDisabled) {
+        return <Typography color='error.dark'>Editing strategy:</Typography>;
+    }
+
+    if (wasDisabled && !willBeDisabled) {
+        return <Typography color='success.dark'>Editing strategy:</Typography>;
+    }
+
+    return <Typography>Editing strategy:</Typography>;
+};
+
+const hasDiff = (object: unknown, objectToCompare: unknown) =>
+    JSON.stringify(object) !== JSON.stringify(objectToCompare);
+
+const DeleteStrategy: FC<{
+    change: IChangeRequestDeleteStrategy;
+    changeRequestState: ChangeRequestState;
+    currentStrategy: IFeatureStrategy | undefined;
+    actions?: ReactNode;
+}> = ({ change, changeRequestState, currentStrategy, actions }) => {
+    const name =
+        changeRequestState === 'Applied'
+            ? change.payload?.snapshot?.name
+            : currentStrategy?.name;
+    const title =
+        changeRequestState === 'Applied'
+            ? change.payload?.snapshot?.title
+            : currentStrategy?.title;
+    const referenceStrategy =
+        changeRequestState === 'Applied'
+            ? change.payload.snapshot
+            : currentStrategy;
+
+    return (
+        <>
+            <ChangeItemCreateEditDeleteWrapper className='delete-strategy-information-wrapper'>
+                <ChangeItemInfo>
+                    <Typography
+                        sx={(theme) => ({
+                            color: theme.palette.error.main,
+                        })}
+                    >
+                        - Deleting strategy:
+                    </Typography>
+                    <StrategyTooltipLink name={name || ''} title={title}>
+                        <StrategyDiff
+                            change={change}
+                            currentStrategy={referenceStrategy}
+                        />
+                    </StrategyTooltipLink>
+                </ChangeItemInfo>
+                <div>{actions}</div>
+            </ChangeItemCreateEditDeleteWrapper>
+            {referenceStrategy && (
+                <StrategyExecution strategy={referenceStrategy} />
+            )}
+        </>
+    );
+};
+
+const UpdateStrategy: FC<{
+    change: IChangeRequestUpdateStrategy;
+    changeRequestState: ChangeRequestState;
+    currentStrategy: IFeatureStrategy | undefined;
+    actions?: ReactNode;
+}> = ({ change, changeRequestState, currentStrategy, actions }) => {
+    const previousTitle =
+        changeRequestState === 'Applied'
+            ? change.payload.snapshot?.title
+            : currentStrategy?.title;
+    const referenceStrategy =
+        changeRequestState === 'Applied'
+            ? change.payload.snapshot
+            : currentStrategy;
+    const hasVariantDiff = hasDiff(
+        referenceStrategy?.variants || [],
+        change.payload.variants || [],
+    );
+
+    return (
+        <>
+            <ChangeOverwriteWarning
+                data={{
+                    current: currentStrategy,
+                    change,
+                    changeType: 'strategy',
+                }}
+                changeRequestState={changeRequestState}
+            />
+            <ChangeItemCreateEditDeleteWrapper>
+                <ChangeItemInfo>
+                    <EditHeader
+                        wasDisabled={currentStrategy?.disabled}
+                        willBeDisabled={change.payload?.disabled}
+                    />
+                    <StrategyTooltipLink
+                        name={change.payload.name}
+                        title={change.payload.title}
+                        previousTitle={previousTitle}
+                    >
+                        <StrategyDiff
+                            change={change}
+                            currentStrategy={referenceStrategy}
+                        />
+                    </StrategyTooltipLink>
+                </ChangeItemInfo>
+                <div>{actions}</div>
+            </ChangeItemCreateEditDeleteWrapper>
+            <ConditionallyRender
+                condition={
+                    change.payload?.disabled !== currentStrategy?.disabled
+                }
+                show={
+                    <Typography
+                        sx={{
+                            marginTop: (theme) => theme.spacing(2),
+                            marginBottom: (theme) => theme.spacing(2),
+                            ...flexRow,
+                            gap: (theme) => theme.spacing(1),
+                        }}
+                    >
+                        This strategy will be{' '}
+                        <DisabledEnabledState
+                            disabled={change.payload?.disabled || false}
+                        />
+                    </Typography>
+                }
+            />
+            <StrategyExecution strategy={change.payload} />
+            {hasVariantDiff ? (
+                <StyledBox>
+                    {change.payload.variants?.length ? (
+                        <>
+                            <StyledTypography>
+                                {currentStrategy?.variants?.length
+                                    ? 'Updating strategy variants to:'
+                                    : 'Adding strategy variants:'}
+                            </StyledTypography>
+                            <EnvironmentVariantsTable
+                                variants={change.payload.variants || []}
+                            />
+                        </>
+                    ) : (
+                        <StyledTypography>
+                            Removed all strategy variants.
+                        </StyledTypography>
+                    )}
+                </StyledBox>
+            ) : null}
+        </>
+    );
+};
+
+const AddStrategy: FC<{
+    change: IChangeRequestAddStrategy;
+    actions?: ReactNode;
+}> = ({ change, actions }) => (
+    <>
+        <ChangeItemCreateEditDeleteWrapper>
+            <ChangeItemInfo>
+                <Typography
+                    color={
+                        change.payload?.disabled
+                            ? 'action.disabled'
+                            : 'success.dark'
+                    }
+                >
+                    + Adding strategy:
+                </Typography>
+                <StrategyTooltipLink
+                    name={change.payload.name}
+                    title={change.payload.title}
+                >
+                    <StrategyDiff change={change} currentStrategy={undefined} />
+                </StrategyTooltipLink>
+                <div>
+                    <DisabledEnabledState
+                        disabled
+                        show={change.payload?.disabled === true}
+                    />
+                </div>
+            </ChangeItemInfo>
+            <div>{actions}</div>
+        </ChangeItemCreateEditDeleteWrapper>
+        <StrategyExecution strategy={change.payload} />
+        {change.payload.variants?.length ? (
+            <StyledBox>
+                <StyledTypography>Adding strategy variants:</StyledTypography>
+                <EnvironmentVariantsTable
+                    variants={change.payload.variants || []}
+                />
+            </StyledBox>
+        ) : null}
+    </>
+);
+
+/**
+ * Deprecated: use StrategyChange instead. Remove file with flag crDiffView
+ * @deprecated
+ */
+export const LegacyStrategyChange: FC<{
+    actions?: ReactNode;
+    change:
+        | IChangeRequestAddStrategy
+        | IChangeRequestDeleteStrategy
+        | IChangeRequestUpdateStrategy;
+    environmentName: string;
+    featureName: string;
+    projectId: string;
+    changeRequestState: ChangeRequestState;
+}> = ({
+    actions,
+    change,
+    featureName,
+    environmentName,
+    projectId,
+    changeRequestState,
+}) => {
+    const currentStrategy = useCurrentStrategy(
+        change,
+        projectId,
+        featureName,
+        environmentName,
+    );
+
+    return (
+        <>
+            {change.action === 'addStrategy' && (
+                <AddStrategy change={change} actions={actions} />
+            )}
+            {change.action === 'deleteStrategy' && (
+                <DeleteStrategy
+                    change={change}
+                    changeRequestState={changeRequestState}
+                    currentStrategy={currentStrategy}
+                    actions={actions}
+                />
+            )}
+            {change.action === 'updateStrategy' && (
+                <UpdateStrategy
+                    change={change}
+                    changeRequestState={changeRequestState}
+                    currentStrategy={currentStrategy}
+                    actions={actions}
+                />
+            )}
+        </>
+    );
+};

frontend/src/component/changeRequest/ChangeRequest/Changes/Change/StrategyChange.tsx

@@ -1,6 +1,14 @@
 import type React from 'react';
 import type { FC, ReactNode } from 'react';
-import { Box, styled, Tooltip, Typography } from '@mui/material';
+import {
+    Box,
+    Button,
+    type ButtonProps,
+    styled,
+    Tooltip,
+    Typography,
+} from '@mui/material';
+import { Tab, Tabs, TabsList, TabPanel } from '@mui/base';
 import BlockIcon from '@mui/icons-material/Block';
 import TrackChangesIcon from '@mui/icons-material/TrackChanges';
 import {
@@ -29,12 +37,10 @@ export const ChangeItemWrapper = styled(Box)({
 });
 
 const ChangeItemCreateEditDeleteWrapper = styled(Box)(({ theme }) => ({
-    display: 'grid',
-    gridTemplateColumns: 'auto auto',
+    display: 'flex',
     justifyContent: 'space-between',
     gap: theme.spacing(1),
     alignItems: 'center',
-    marginBottom: theme.spacing(2),
     width: '100%',
 }));
 
@@ -157,15 +163,63 @@ const DeleteStrategy: FC<{
                         />
                     </StrategyTooltipLink>
                 </ChangeItemInfo>
-                <div>{actions}</div>
+                {actions}
             </ChangeItemCreateEditDeleteWrapper>
-            {referenceStrategy && (
-                <StrategyExecution strategy={referenceStrategy} />
-            )}
+            <TabPanel>
+                {referenceStrategy && (
+                    <StrategyExecution strategy={referenceStrategy} />
+                )}
+            </TabPanel>
+            <TabPanel>
+                <StrategyDiff
+                    change={change}
+                    currentStrategy={referenceStrategy}
+                />
+            </TabPanel>
         </>
     );
 };
 
+const ActionsContainer = styled('div')(({ theme }) => ({
+    display: 'flex',
+    gap: theme.spacing(1),
+    alignItems: 'center',
+}));
+
+const StyledTabList = styled(TabsList)(({ theme }) => ({
+    display: 'inline-flex',
+    flexDirection: 'row',
+    gap: theme.spacing(0.5),
+}));
+
+const StyledButton = styled(Button)(({ theme }) => ({
+    whiteSpace: 'nowrap',
+    color: theme.palette.text.secondary,
+    fontWeight: 'normal',
+    '&[aria-selected="true"]': {
+        fontWeight: 'bold',
+        color: theme.palette.primary.main,
+        background: theme.palette.background.elevation1,
+    },
+}));
+
+export const StyledTab = styled(({ children }: ButtonProps) => (
+    <Tab slots={{ root: StyledButton }}>{children}</Tab>
+))(({ theme }) => ({
+    position: 'absolute',
+    top: theme.spacing(-0.5),
+    left: theme.spacing(2),
+    transform: 'translateY(-50%)',
+    padding: theme.spacing(0.75, 1),
+    lineHeight: 1,
+    fontSize: theme.fontSizes.smallerBody,
+    color: theme.palette.text.primary,
+    background: theme.palette.background.application,
+    borderRadius: theme.shape.borderRadiusExtraLarge,
+    zIndex: theme.zIndex.fab,
+    textTransform: 'uppercase',
+}));
+
 const UpdateStrategy: FC<{
     change: IChangeRequestUpdateStrategy;
     changeRequestState: ChangeRequestState;
@@ -212,7 +266,7 @@ const UpdateStrategy: FC<{
                         />
                     </StrategyTooltipLink>
                 </ChangeItemInfo>
-                <div>{actions}</div>
+                {actions}
             </ChangeItemCreateEditDeleteWrapper>
             <ConditionallyRender
                 condition={
@@ -234,27 +288,36 @@ const UpdateStrategy: FC<{
                     </Typography>
                 }
             />
-            <StrategyExecution strategy={change.payload} />
-            {hasVariantDiff ? (
-                <StyledBox>
-                    {change.payload.variants?.length ? (
-                        <>
+
+            <TabPanel>
+                <StrategyExecution strategy={change.payload} />
+                {hasVariantDiff ? (
+                    <StyledBox>
+                        {change.payload.variants?.length ? (
+                            <>
+                                <StyledTypography>
+                                    {currentStrategy?.variants?.length
+                                        ? 'Updating strategy variants to:'
+                                        : 'Adding strategy variants:'}
+                                </StyledTypography>
+                                <EnvironmentVariantsTable
+                                    variants={change.payload.variants || []}
+                                />
+                            </>
+                        ) : (
                             <StyledTypography>
-                                {currentStrategy?.variants?.length
-                                    ? 'Updating strategy variants to:'
-                                    : 'Adding strategy variants:'}
+                                Removed all strategy variants.
                             </StyledTypography>
-                            <EnvironmentVariantsTable
-                                variants={change.payload.variants || []}
-                            />
-                        </>
-                    ) : (
-                        <StyledTypography>
-                            Removed all strategy variants.
-                        </StyledTypography>
-                    )}
-                </StyledBox>
-            ) : null}
+                        )}
+                    </StyledBox>
+                ) : null}
+            </TabPanel>
+            <TabPanel>
+                <StrategyDiff
+                    change={change}
+                    currentStrategy={referenceStrategy}
+                />
+            </TabPanel>
         </>
     );
 };
@@ -288,17 +351,24 @@ const AddStrategy: FC<{
                     />
                 </div>
             </ChangeItemInfo>
-            <div>{actions}</div>
+            {actions}
         </ChangeItemCreateEditDeleteWrapper>
-        <StrategyExecution strategy={change.payload} />
-        {change.payload.variants?.length ? (
-            <StyledBox>
-                <StyledTypography>Adding strategy variants:</StyledTypography>
-                <EnvironmentVariantsTable
-                    variants={change.payload.variants || []}
-                />
-            </StyledBox>
-        ) : null}
+        <TabPanel>
+            <StrategyExecution strategy={change.payload} />
+            {change.payload.variants?.length ? (
+                <StyledBox>
+                    <StyledTypography>
+                        Adding strategy variants:
+                    </StyledTypography>
+                    <EnvironmentVariantsTable
+                        variants={change.payload.variants || []}
+                    />
+                </StyledBox>
+            ) : null}
+        </TabPanel>
+        <TabPanel>
+            <StrategyDiff change={change} currentStrategy={undefined} />
+        </TabPanel>
     </>
 );
 
@@ -327,17 +397,31 @@ export const StrategyChange: FC<{
         environmentName,
     );
 
+    const Actions = (
+        <ActionsContainer>
+            <StyledTabList>
+                <StyledTab>Change</StyledTab>
+                <StyledTab>View diff</StyledTab>
+            </StyledTabList>
+            {actions}
+        </ActionsContainer>
+    );
+
     return (
-        <>
+        <Tabs
+            aria-label='View rendered change or JSON diff'
+            selectionFollowsFocus
+            defaultValue={0}
+        >
             {change.action === 'addStrategy' && (
-                <AddStrategy change={change} actions={actions} />
+                <AddStrategy change={change} actions={Actions} />
             )}
             {change.action === 'deleteStrategy' && (
                 <DeleteStrategy
                     change={change}
                     changeRequestState={changeRequestState}
                     currentStrategy={currentStrategy}
-                    actions={actions}
+                    actions={Actions}
                 />
             )}
             {change.action === 'updateStrategy' && (
@@ -345,9 +429,9 @@ export const StrategyChange: FC<{
                     change={change}
                     changeRequestState={changeRequestState}
                     currentStrategy={currentStrategy}
-                    actions={actions}
+                    actions={Actions}
                 />
             )}
-        </>
+        </Tabs>
     );
 };

frontend/src/component/changeRequest/ChangeRequest/StrategyTooltipLink/StrategyTooltipLink.tsx

@@ -58,8 +58,12 @@ export const StrategyDiff: FC<{
         return (
             <NewEventDiff
                 entry={{
-                    preData: omit(sortedCurrentStrategy, 'sortOrder'),
-                    data: omit(sortedChangeRequestStrategy, 'snapshot'),
+                    preData: sortedCurrentStrategy
+                        ? omit(sortedCurrentStrategy, 'sortOrder')
+                        : undefined,
+                    data: sortedChangeRequestStrategy
+                        ? omit(sortedChangeRequestStrategy, 'snapshot')
+                        : undefined,
                 }}
             />
         );