fix: Move content into to frontend directory

Doing this BEFORE the merge prevents a lot of merge conflicts.

Signed-off-by: Tilman Vatteroth <git@tilmanvatteroth.de>

frontend/src/components/common/show-if/__snapshots__/show-if.test.tsx.snap

@@ -0,0 +1,9 @@
+// Jest Snapshot v1, https://goo.gl/fbAQLP
+
+exports[`ShowIf does not render child if condition is false 1`] = `<div />`;
+
+exports[`ShowIf renders child if condition is true 1`] = `
+<div>
+  test
+</div>
+`;

frontend/src/components/common/show-if/show-if.test.tsx

@@ -0,0 +1,20 @@
+/*
+ * SPDX-FileCopyrightText: 2022 The HedgeDoc developers (see AUTHORS file)
+ *
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+
+import { render } from '@testing-library/react'
+import { ShowIf } from './show-if'
+
+describe('ShowIf', () => {
+  it('renders child if condition is true', () => {
+    const view = render(<ShowIf condition={true}>test</ShowIf>)
+    expect(view.container).toMatchSnapshot()
+  })
+
+  it('does not render child if condition is false', () => {
+    const view = render(<ShowIf condition={false}>test</ShowIf>)
+    expect(view.container).toMatchSnapshot()
+  })
+})

frontend/src/components/common/show-if/show-if.tsx

@@ -0,0 +1,22 @@
+/*
+ * SPDX-FileCopyrightText: 2022 The HedgeDoc developers (see AUTHORS file)
+ *
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+
+import type { PropsWithChildren } from 'react'
+import React, { Fragment } from 'react'
+
+export interface ShowIfProps {
+  condition: boolean
+}
+
+/**
+ * Renders the children if the condition is met.
+ *
+ * @param children The children to show if the condition is met.
+ * @param condition If the children should be shown
+ */
+export const ShowIf: React.FC<PropsWithChildren<ShowIfProps>> = ({ children, condition }) => {
+  return condition ? <Fragment>{children}</Fragment> : null
+}