feat: fetch frontend config in server side rendering

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

frontend/src/utils/frontend-config-fetcher.ts

@@ -0,0 +1,35 @@
+/*
+ * SPDX-FileCopyrightText: 2023 The HedgeDoc developers (see AUTHORS file)
+ *
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+import { getConfig } from '../api/config'
+import type { FrontendConfig } from '../api/config/types'
+import type { BaseUrls } from '../components/common/base-url/base-url-context-provider'
+import { Logger } from './logger'
+
+/**
+ * Fetches and caches the {@link FrontendConfig frontend config} from the backend.
+ */
+export class FrontendConfigFetcher {
+  private readonly logger = new Logger('Frontend config fetcher')
+
+  private frontendConfig: FrontendConfig | undefined = undefined
+
+  public async fetch(baseUrls: BaseUrls | undefined): Promise<FrontendConfig | undefined> {
+    if (!this.frontendConfig) {
+      if (baseUrls === undefined) {
+        return undefined
+      }
+      const baseUrl = baseUrls.editor.toString()
+      try {
+        this.frontendConfig = await getConfig(baseUrl)
+      } catch (error) {
+        this.logger.error(`Couldn't fetch frontend configuration from ${baseUrl}`, error)
+        return undefined
+      }
+      this.logger.info(`Fetched frontend config from ${baseUrl}`)
+    }
+    return this.frontendConfig
+  }
+}