theme: add multi theme provider and holder

Signed-off-by: Patrik Oldsberg <poldsberg@gmail.com>

packages/theme/src/compat/MultiThemeProvider.tsx

@@ -0,0 +1,58 @@
+/*
+ * Copyright 2022 The Backstage Authors
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+import React, { ReactNode } from 'react';
+import {
+  Theme as Mui4Theme,
+  ThemeProvider as Mui4Provider,
+} from '@material-ui/core/styles';
+import {
+  Theme as Mui5Theme,
+  ThemeProvider as Mui5Provider,
+} from '@mui/material/styles';
+import CssBaseline from '@mui/material/CssBaseline';
+import { MultiThemeHolder } from './types';
+
+interface ThemeProviderProps {
+  children: ReactNode;
+  theme: MultiThemeHolder;
+  noCssBaseline?: boolean;
+}
+
+export function MultiThemeProvider(props: ThemeProviderProps) {
+  const { children, theme, noCssBaseline } = props;
+
+  let result = noCssBaseline ? (
+    children
+  ) : (
+    <>
+      <CssBaseline />
+      {children}
+    </>
+  );
+
+  const v4Theme = theme.getThemeForVersion('v4');
+  if (v4Theme) {
+    result = <Mui4Provider theme={v4Theme as Mui4Theme}>{result}</Mui4Provider>;
+  }
+
+  const v5Theme = theme.getThemeForVersion('v5');
+  if (v5Theme) {
+    result = <Mui5Provider theme={v5Theme as Mui5Theme}>{result}</Mui5Provider>;
+  }
+
+  return result;
+}

packages/theme/src/compat/types.ts

@@ -0,0 +1,19 @@
+/*
+ * Copyright 2022 The Backstage Authors
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+export interface MultiThemeHolder {
+  getThemeForVersion(version: string): unknown | undefined;
+}