make theme depend on dark/night mode on android 10+

closes #3611

build.gradle

@@ -85,7 +85,7 @@ ext {
 }
 
 android {
-    compileSdkVersion 28
+    compileSdkVersion 29
 
     defaultConfig {
         minSdkVersion 16

src/main/java/eu/siacs/conversations/utils/ThemeHelper.java

@@ -31,8 +31,10 @@ package eu.siacs.conversations.utils;
 
 import android.content.Context;
 import android.content.SharedPreferences;
+import android.content.res.Configuration;
 import android.content.res.Resources;
 import android.content.res.TypedArray;
+import android.os.Build;
 import android.preference.PreferenceManager;
 import android.support.annotation.StyleRes;
 import android.support.design.widget.Snackbar;
@@ -45,10 +47,10 @@ import eu.siacs.conversations.ui.SettingsActivity;
 
 public class ThemeHelper {
 
-	public static int find(Context context) {
+	public static int find(final Context context) {
 		final SharedPreferences sharedPreferences = PreferenceManager.getDefaultSharedPreferences(context);
 		final Resources resources = context.getResources();
-		final boolean dark = sharedPreferences.getString(SettingsActivity.THEME, resources.getString(R.string.theme)).equals("dark");
+		final boolean dark = isDark(sharedPreferences, resources);
 		final String fontSize = sharedPreferences.getString("font_size", resources.getString(R.string.default_font_size));
 		switch (fontSize) {
 			case "medium":
@@ -63,7 +65,7 @@ public class ThemeHelper {
 	public static int findDialog(Context context) {
 		final SharedPreferences sharedPreferences = PreferenceManager.getDefaultSharedPreferences(context);
 		final Resources resources = context.getResources();
-		final boolean dark = sharedPreferences.getString(SettingsActivity.THEME, resources.getString(R.string.theme)).equals("dark");
+		final boolean dark = isDark(sharedPreferences, resources);
 		final String fontSize = sharedPreferences.getString("font_size", resources.getString(R.string.default_font_size));
 		switch (fontSize) {
 			case "medium":
@@ -75,6 +77,15 @@ public class ThemeHelper {
 		}
 	}
 
+	private static boolean isDark(final SharedPreferences sharedPreferences, final Resources resources) {
+		final String setting = sharedPreferences.getString(SettingsActivity.THEME, resources.getString(R.string.theme));
+		if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.Q && "automatic".equals(setting)) {
+			return (resources.getConfiguration().uiMode & Configuration.UI_MODE_NIGHT_MASK) == Configuration.UI_MODE_NIGHT_YES;
+		} else {
+			return "dark".equals(setting);
+		}
+	}
+
 	public static boolean isDark(@StyleRes int id) {
 		switch (id) {
 			case R.style.ConversationsTheme_Dark:

src/main/res/values-v29/theme-settings.xml

@@ -0,0 +1,16 @@
+<?xml version="1.0" encoding="utf-8"?>
+<resources xmlns:tools="http://schemas.android.com/tools">
+
+    <string name="theme">automatic</string>
+    <string-array name="themes" tools:ignore="InconsistentArrays">
+        <item>@string/pref_theme_automatic</item>
+        <item>@string/pref_theme_light</item>
+        <item>@string/pref_theme_dark</item>
+    </string-array>
+    <string-array name="themes_values" tools:ignore="InconsistentArrays">
+        <item>automatic</item>
+		<item>light</item>
+		<item>dark</item>
+	</string-array>
+
+</resources>

src/main/res/values/arrays.xml

@@ -1,14 +1,6 @@
 <?xml version="1.0" encoding="utf-8"?>
 <resources>
 
-	<string-array name="themes">
-		<item>@string/pref_theme_light</item>
-		<item>@string/pref_theme_dark</item>
-	</string-array>
-	<string-array name="themes_values">
-		<item>light</item>
-		<item>dark</item>
-	</string-array>
 	<string-array name="filesizes">
 		<item>@string/never</item>
 		<item>256 KiB</item>

src/main/res/values/defaults.xml

@@ -17,7 +17,6 @@
     <integer name="grace_period">144</integer>
     <integer name="auto_accept_filesize">524288</integer>
     <string name="picture_compression">auto</string>
-    <string name="theme">light</string>
     <bool name="use_green_background">true</bool>
     <string name="quick_action">recent</string>
     <bool name="show_dynamic_tags">false</bool>

src/main/res/values/strings.xml

@@ -559,6 +559,7 @@
     <string name="pref_privacy">Privacy</string>
     <string name="pref_theme_options">Theme</string>
     <string name="pref_theme_options_summary">Select the color palette</string>
+    <string name="pref_theme_automatic">Automatic</string>
     <string name="pref_theme_light">Light theme</string>
     <string name="pref_theme_dark">Dark theme</string>
     <string name="pref_use_green_background">Green Background</string>

src/main/res/values/theme-settings.xml

@@ -0,0 +1,14 @@
+<?xml version="1.0" encoding="utf-8"?>
+<resources>
+
+    <string name="theme">light</string>
+    <string-array name="themes">
+        <item>@string/pref_theme_light</item>
+        <item>@string/pref_theme_dark</item>
+    </string-array>
+    <string-array name="themes_values">
+		<item>light</item>
+		<item>dark</item>
+	</string-array>
+
+</resources>