automatically adapt to system theme

added two new theme options:
SYSTEM: dynamically switches between light and dark
SYSTEM_AMOLED: dynamically switches between light and amoled

reversed workaround for amoled themed preferences
launch screen now always follows the system theme

app/src/main/java/com/beemdevelopment/aegis/Preferences.java

@@ -90,7 +90,7 @@ public class Preferences {
     }
 
     public Theme getCurrentTheme() {
-        return Theme.fromInteger(_prefs.getInt("pref_current_theme", 0));
+        return Theme.fromInteger(_prefs.getInt("pref_current_theme", Theme.SYSTEM.ordinal()));
     }
 
     public void setCurrentTheme(Theme theme) {

app/src/main/java/com/beemdevelopment/aegis/Theme.java

@@ -3,7 +3,9 @@ package com.beemdevelopment.aegis;
 public enum Theme {
     LIGHT,
     DARK,
-    AMOLED;
+    AMOLED,
+    SYSTEM,
+    SYSTEM_AMOLED;
 
     private static Theme[] _values;
 

app/src/main/java/com/beemdevelopment/aegis/ui/AegisActivity.java

@@ -89,6 +89,19 @@ public abstract class AegisActivity extends AppCompatActivity implements AegisAp
     }
 
     protected void setPreferredTheme(Theme theme) {
+        if (theme == Theme.SYSTEM || theme == Theme.SYSTEM_AMOLED) {
+            // set the theme based on the system theme
+            int currentNightMode = getResources().getConfiguration().uiMode & Configuration.UI_MODE_NIGHT_MASK;
+            switch (currentNightMode) {
+                case Configuration.UI_MODE_NIGHT_NO:
+                    theme = Theme.LIGHT;
+                    break;
+                case Configuration.UI_MODE_NIGHT_YES:
+                    theme = theme == Theme.SYSTEM_AMOLED ? Theme.AMOLED : Theme.DARK;
+                    break;
+            }
+        }
+
         _currentTheme = theme;
 
         switch (theme) {

app/src/main/java/com/beemdevelopment/aegis/ui/PreferencesActivity.java

@@ -39,21 +39,4 @@ public class PreferencesActivity extends AegisActivity {
         outState.putParcelable("result", _fragment.getResult());
         super.onSaveInstanceState(outState);
     }
-
-    @Override
-    protected void setPreferredTheme(Theme theme) {
-        switch (theme) {
-            case LIGHT:
-                setTheme(R.style.AppTheme);
-                break;
-
-            case DARK:
-                setTheme(R.style.AppTheme_Dark);
-                break;
-
-            case AMOLED:
-                setTheme(R.style.AppTheme_TrueBlack_Preferences);
-                break;
-        }
-    }
 }

app/src/main/res/values-v29/strings.xml

@@ -0,0 +1,5 @@
+<?xml version="1.0" encoding="utf-8"?>
+<resources>
+    <string name="system_theme_title">System default</string>
+    <string name="system_amoled_theme_title">System default (AMOLED)</string>
+</resources>

app/src/main/res/values/arrays.xml

@@ -22,6 +22,8 @@
         <item>@string/light_theme_title</item>
         <item>@string/dark_theme_title</item>
         <item>@string/amoled_theme_title</item>
+        <item>@string/system_theme_title</item>
+        <item>@string/system_amoled_theme_title</item>
     </string-array>
 
     <string-array name="view_mode_titles">

app/src/main/res/values/strings.xml

@@ -189,6 +189,8 @@
     <string name="dark_theme_title">Dark theme</string>
     <string name="light_theme_title">Light theme</string>
     <string name="amoled_theme_title">AMOLED theme</string>
+    <string name="system_theme_title">Set by Battery Saver</string>
+    <string name="system_amoled_theme_title">Set by Battery Saver (AMOLED)</string>
     <string name="normal_viewmode_title">Normal</string>
     <string name="compact_mode_title">Compact</string>
     <string name="small_mode_title">Small</string>

app/src/main/res/values/styles.xml

@@ -70,9 +70,7 @@
         <item name="android:textColor">@android:color/white</item>
     </style>
 
-    <style name="AppTheme.NoActionBar">
+    <style name="AppTheme.NoActionBar" parent="Theme.AppCompat.DayNight.NoActionBar">
-        <item name="windowActionBar">false</item>
-        <item name="windowNoTitle">true</item>
         <item name="android:windowDrawsSystemBarBackgrounds" tools:targetApi="lollipop">true</item>
         <item name="android:statusBarColor" tools:targetApi="lollipop">@android:color/transparent</item>
     </style>
@@ -123,9 +121,7 @@
 
         <item name="android:navigationBarColor" tools:targetApi="lollipop">@color/background_true_dark</item>
         <item name="android:windowLightNavigationBar" tools:targetApi="o_mr1">false</item>
-    </style>
 
-    <style name="AppTheme.TrueBlack.Preferences" parent="AppTheme.TrueBlack">
         <item name="android:windowBackground">@color/background_true_dark</item>
     </style>