Let the user choose theme (#1499)

libraries/theme/src/main/kotlin/io/element/android/libraries/theme/theme/Theme.kt

@@ -0,0 +1,46 @@
+/*
+ * Copyright (c) 2023 New Vector Ltd
+ *
+ * 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.
+ */
+
+package io.element.android.libraries.theme.theme
+
+import androidx.compose.foundation.isSystemInDarkTheme
+import androidx.compose.runtime.Composable
+import kotlinx.coroutines.flow.Flow
+import kotlinx.coroutines.flow.map
+
+enum class Theme {
+    System,
+    Dark,
+    Light;
+}
+
+val themes = listOf(Theme.System, Theme.Dark, Theme.Light)
+
+@Composable
+fun Theme.isDark(): Boolean {
+    return when (this) {
+        Theme.System -> isSystemInDarkTheme()
+        Theme.Dark -> true
+        Theme.Light -> false
+    }
+}
+
+fun Flow<String?>.mapToTheme(): Flow<Theme> = map {
+    when (it) {
+        null -> Theme.System
+        else -> Theme.valueOf(it)
+    }
+}