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/application-loader/initializers/load-dark-mode.ts

@@ -0,0 +1,48 @@
+/*
+ * SPDX-FileCopyrightText: 2022 The HedgeDoc developers (see AUTHORS file)
+ *
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+import { setDarkModePreference } from '../../../redux/dark-mode/methods'
+import { Logger } from '../../../utils/logger'
+import { isClientSideRendering } from '../../../utils/is-client-side-rendering'
+import { DarkModePreference } from '../../../redux/dark-mode/types'
+import { DARK_MODE_LOCAL_STORAGE_KEY } from '../../../hooks/common/use-apply-dark-mode'
+
+const logger = new Logger('Dark mode initializer')
+
+/**
+ * Loads the saved dark mode setting or tries to derive it from the browser settings.
+ * The result is saved in the global application state.
+ *
+ * @return A promise that resolves as soon as the dark mode has been loaded.
+ */
+export const loadDarkMode = (): Promise<void> => {
+  setDarkModePreference(fetchDarkModeFromLocalStorage())
+  return Promise.resolve()
+}
+
+/**
+ * Tries to read the saved dark mode settings from the browser local storage.
+ *
+ * @return {@link true} if the local storage has saved that the user prefers dark mode.
+ *         {@link false} if the user doesn't prefer dark mode or if the value couldn't be read from local storage.
+ */
+const fetchDarkModeFromLocalStorage = (): DarkModePreference => {
+  if (!isClientSideRendering()) {
+    return DarkModePreference.AUTO
+  }
+  try {
+    const colorScheme = window.localStorage.getItem(DARK_MODE_LOCAL_STORAGE_KEY)
+    if (colorScheme === 'dark') {
+      return DarkModePreference.DARK
+    } else if (colorScheme === 'light') {
+      return DarkModePreference.LIGHT
+    } else {
+      return DarkModePreference.AUTO
+    }
+  } catch (error) {
+    logger.error('Loading from local storage failed', error)
+    return DarkModePreference.AUTO
+  }
+}