From 1aa5500c64fb7099f2323e72c1062051c8f2ccfb Mon Sep 17 00:00:00 2001
From: Christopher Beckmann <chris.makas.b@gmail.com>
Date: Sun, 25 Jun 2017 20:14:34 +0200
Subject: [PATCH] Generator Changes and reworked the Saved Level Structure

---
 .idea/misc.xml                                |  88 +++++
 app/app.iml                                   |  36 +-
 app/build.gradle                              |   6 +-
 app/src/main/AndroidManifest.xml              |   4 +
 .../controller/GameController.java            |  35 ++
 .../controller/GameStateManager.java          |   1 -
 .../controller/GeneratorService.java          | 309 ++++++++++++++++++
 .../controller/NewLevelManager.java           | 206 +++++++++---
 .../controller/Symbol.java                    |   4 +-
 .../controller/database/DatabaseHelper.java   |  97 ++++++
 .../database/columns/LevelColumns.java        |  90 +++++
 .../controller/database/model/Level.java      |  65 ++++
 .../controller/qqwing/QQWing.java             |  38 ++-
 .../privacyfriendlysudoku/game/GameBoard.java |   2 +
 .../game/GameDifficulty.java                  |   4 +-
 .../ui/LoadGameActivity.java                  |   2 +
 .../ui/MainActivity.java                      |  27 +-
 .../ui/StatsActivity.java                     |  11 +-
 .../ui/view/SudokuFieldLayout.java            |  42 +--
 .../main/res/layout-land/fragment_stats.xml   |  68 +++-
 .../res/layout-xlarge-land/fragment_stats.xml |  65 ++++
 .../main/res/layout-xlarge/fragment_stats.xml |  67 +++-
 app/src/main/res/layout/fragment_stats.xml    |  70 +++-
 app/src/main/res/menu/menu_drawer_main.xml    |  13 +-
 app/src/main/res/values/strings.xml           |   4 +-
 .../main/res/xml/pref_settings_general.xml    |   5 +
 build.gradle                                  |   2 +-
 gradle/wrapper/gradle-wrapper.properties      |   4 +-
 28 files changed, 1231 insertions(+), 134 deletions(-)
 create mode 100644 .idea/misc.xml
 create mode 100644 app/src/main/java/org/secuso/privacyfriendlysudoku/controller/GeneratorService.java
 create mode 100644 app/src/main/java/org/secuso/privacyfriendlysudoku/controller/database/DatabaseHelper.java
 create mode 100644 app/src/main/java/org/secuso/privacyfriendlysudoku/controller/database/columns/LevelColumns.java
 create mode 100644 app/src/main/java/org/secuso/privacyfriendlysudoku/controller/database/model/Level.java

diff --git a/.idea/misc.xml b/.idea/misc.xml
new file mode 100644
index 0000000..50282c1
--- /dev/null
+++ b/.idea/misc.xml
@@ -0,0 +1,88 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project version="4">
+  <component name="EntryPointsManager">
+    <entry_points version="2.0" />
+  </component>
+  <component name="NullableNotNullManager">
+    <option name="myDefaultNullable" value="android.support.annotation.Nullable" />
+    <option name="myDefaultNotNull" value="android.support.annotation.NonNull" />
+    <option name="myNullables">
+      <value>
+        <list size="4">
+          <item index="0" class="java.lang.String" itemvalue="org.jetbrains.annotations.Nullable" />
+          <item index="1" class="java.lang.String" itemvalue="javax.annotation.Nullable" />
+          <item index="2" class="java.lang.String" itemvalue="edu.umd.cs.findbugs.annotations.Nullable" />
+          <item index="3" class="java.lang.String" itemvalue="android.support.annotation.Nullable" />
+        </list>
+      </value>
+    </option>
+    <option name="myNotNulls">
+      <value>
+        <list size="4">
+          <item index="0" class="java.lang.String" itemvalue="org.jetbrains.annotations.NotNull" />
+          <item index="1" class="java.lang.String" itemvalue="javax.annotation.Nonnull" />
+          <item index="2" class="java.lang.String" itemvalue="edu.umd.cs.findbugs.annotations.NonNull" />
+          <item index="3" class="java.lang.String" itemvalue="android.support.annotation.NonNull" />
+        </list>
+      </value>
+    </option>
+  </component>
+  <component name="ProjectInspectionProfilesVisibleTreeState">
+    <entry key="Project Default">
+      <profile-state>
+        <expanded-state>
+          <State>
+            <id />
+          </State>
+        </expanded-state>
+        <selected-state>
+          <State>
+            <id>Android</id>
+          </State>
+        </selected-state>
+      </profile-state>
+    </entry>
+  </component>
+  <component name="ProjectLevelVcsManager" settingsEditedManually="false">
+    <OptionsSetting value="true" id="Add" />
+    <OptionsSetting value="true" id="Remove" />
+    <OptionsSetting value="true" id="Checkout" />
+    <OptionsSetting value="true" id="Update" />
+    <OptionsSetting value="true" id="Status" />
+    <OptionsSetting value="true" id="Edit" />
+    <ConfirmationsSetting value="0" id="Add" />
+    <ConfirmationsSetting value="0" id="Remove" />
+  </component>
+  <component name="ProjectRootManager" version="2" languageLevel="JDK_1_7" default="true" assert-keyword="true" jdk-15="true" project-jdk-name="1.8" project-jdk-type="JavaSDK">
+    <output url="file://$PROJECT_DIR$/build/classes" />
+  </component>
+  <component name="ProjectType">
+    <option name="id" value="Android" />
+  </component>
+  <component name="masterDetails">
+    <states>
+      <state key="Copyright.UI">
+        <settings>
+          <splitter-proportions>
+            <option name="proportions">
+              <list>
+                <option value="0.2" />
+              </list>
+            </option>
+          </splitter-proportions>
+        </settings>
+      </state>
+      <state key="ScopeChooserConfigurable.UI">
+        <settings>
+          <splitter-proportions>
+            <option name="proportions">
+              <list>
+                <option value="0.2" />
+              </list>
+            </option>
+          </splitter-proportions>
+        </settings>
+      </state>
+    </states>
+  </component>
+</project>
\ No newline at end of file
diff --git a/app/app.iml b/app/app.iml
index bc02165..44f924e 100644
--- a/app/app.iml
+++ b/app/app.iml
@@ -9,7 +9,6 @@
     <facet type="android" name="Android">
       <configuration>
         <option name="SELECTED_BUILD_VARIANT" value="debug" />
-        <option name="SELECTED_TEST_ARTIFACT" value="_android_test_" />
         <option name="ASSEMBLE_TASK_NAME" value="assembleDebug" />
         <option name="COMPILE_JAVA_TASK_NAME" value="compileDebugSources" />
         <afterSyncTasks>
@@ -47,7 +46,6 @@
       <sourceFolder url="file://$MODULE_DIR$/src/debug/assets" type="java-resource" />
       <sourceFolder url="file://$MODULE_DIR$/src/debug/aidl" isTestSource="false" />
       <sourceFolder url="file://$MODULE_DIR$/src/debug/java" isTestSource="false" />
-      <sourceFolder url="file://$MODULE_DIR$/src/debug/jni" isTestSource="false" />
       <sourceFolder url="file://$MODULE_DIR$/src/debug/rs" isTestSource="false" />
       <sourceFolder url="file://$MODULE_DIR$/src/debug/shaders" isTestSource="false" />
       <sourceFolder url="file://$MODULE_DIR$/src/testDebug/res" type="java-test-resource" />
@@ -55,7 +53,6 @@
       <sourceFolder url="file://$MODULE_DIR$/src/testDebug/assets" type="java-test-resource" />
       <sourceFolder url="file://$MODULE_DIR$/src/testDebug/aidl" isTestSource="true" />
       <sourceFolder url="file://$MODULE_DIR$/src/testDebug/java" isTestSource="true" />
-      <sourceFolder url="file://$MODULE_DIR$/src/testDebug/jni" isTestSource="true" />
       <sourceFolder url="file://$MODULE_DIR$/src/testDebug/rs" isTestSource="true" />
       <sourceFolder url="file://$MODULE_DIR$/src/testDebug/shaders" isTestSource="true" />
       <sourceFolder url="file://$MODULE_DIR$/src/main/res" type="java-resource" />
@@ -63,43 +60,26 @@
       <sourceFolder url="file://$MODULE_DIR$/src/main/assets" type="java-resource" />
       <sourceFolder url="file://$MODULE_DIR$/src/main/aidl" isTestSource="false" />
       <sourceFolder url="file://$MODULE_DIR$/src/main/java" isTestSource="false" />
-      <sourceFolder url="file://$MODULE_DIR$/src/main/jni" isTestSource="false" />
       <sourceFolder url="file://$MODULE_DIR$/src/main/rs" isTestSource="false" />
       <sourceFolder url="file://$MODULE_DIR$/src/main/shaders" isTestSource="false" />
-      <sourceFolder url="file://$MODULE_DIR$/src/test/res" type="java-test-resource" />
-      <sourceFolder url="file://$MODULE_DIR$/src/test/resources" type="java-test-resource" />
-      <sourceFolder url="file://$MODULE_DIR$/src/test/assets" type="java-test-resource" />
-      <sourceFolder url="file://$MODULE_DIR$/src/test/aidl" isTestSource="true" />
-      <sourceFolder url="file://$MODULE_DIR$/src/test/java" isTestSource="true" />
-      <sourceFolder url="file://$MODULE_DIR$/src/test/jni" isTestSource="true" />
-      <sourceFolder url="file://$MODULE_DIR$/src/test/rs" isTestSource="true" />
-      <sourceFolder url="file://$MODULE_DIR$/src/test/shaders" isTestSource="true" />
       <sourceFolder url="file://$MODULE_DIR$/src/androidTest/res" type="java-test-resource" />
       <sourceFolder url="file://$MODULE_DIR$/src/androidTest/resources" type="java-test-resource" />
       <sourceFolder url="file://$MODULE_DIR$/src/androidTest/assets" type="java-test-resource" />
       <sourceFolder url="file://$MODULE_DIR$/src/androidTest/aidl" isTestSource="true" />
       <sourceFolder url="file://$MODULE_DIR$/src/androidTest/java" isTestSource="true" />
-      <sourceFolder url="file://$MODULE_DIR$/src/androidTest/jni" isTestSource="true" />
       <sourceFolder url="file://$MODULE_DIR$/src/androidTest/rs" isTestSource="true" />
       <sourceFolder url="file://$MODULE_DIR$/src/androidTest/shaders" isTestSource="true" />
+      <sourceFolder url="file://$MODULE_DIR$/src/test/res" type="java-test-resource" />
+      <sourceFolder url="file://$MODULE_DIR$/src/test/resources" type="java-test-resource" />
+      <sourceFolder url="file://$MODULE_DIR$/src/test/assets" type="java-test-resource" />
+      <sourceFolder url="file://$MODULE_DIR$/src/test/aidl" isTestSource="true" />
+      <sourceFolder url="file://$MODULE_DIR$/src/test/java" isTestSource="true" />
+      <sourceFolder url="file://$MODULE_DIR$/src/test/rs" isTestSource="true" />
+      <sourceFolder url="file://$MODULE_DIR$/src/test/shaders" isTestSource="true" />
       <excludeFolder url="file://$MODULE_DIR$/build/intermediates/assets" />
       <excludeFolder url="file://$MODULE_DIR$/build/intermediates/blame" />
       <excludeFolder url="file://$MODULE_DIR$/build/intermediates/builds" />
       <excludeFolder url="file://$MODULE_DIR$/build/intermediates/classes" />
-      <excludeFolder url="file://$MODULE_DIR$/build/intermediates/dependency-cache" />
-      <excludeFolder url="file://$MODULE_DIR$/build/intermediates/exploded-aar/com.android.support/animated-vector-drawable/25.0.0/jars" />
-      <excludeFolder url="file://$MODULE_DIR$/build/intermediates/exploded-aar/com.android.support/appcompat-v7/25.0.0/jars" />
-      <excludeFolder url="file://$MODULE_DIR$/build/intermediates/exploded-aar/com.android.support/design/25.0.0/jars" />
-      <excludeFolder url="file://$MODULE_DIR$/build/intermediates/exploded-aar/com.android.support/recyclerview-v7/25.0.0/jars" />
-      <excludeFolder url="file://$MODULE_DIR$/build/intermediates/exploded-aar/com.android.support/support-compat/25.0.0/jars" />
-      <excludeFolder url="file://$MODULE_DIR$/build/intermediates/exploded-aar/com.android.support/support-core-ui/25.0.0/jars" />
-      <excludeFolder url="file://$MODULE_DIR$/build/intermediates/exploded-aar/com.android.support/support-core-utils/25.0.0/jars" />
-      <excludeFolder url="file://$MODULE_DIR$/build/intermediates/exploded-aar/com.android.support/support-fragment/25.0.0/jars" />
-      <excludeFolder url="file://$MODULE_DIR$/build/intermediates/exploded-aar/com.android.support/support-media-compat/25.0.0/jars" />
-      <excludeFolder url="file://$MODULE_DIR$/build/intermediates/exploded-aar/com.android.support/support-v13/25.0.0/jars" />
-      <excludeFolder url="file://$MODULE_DIR$/build/intermediates/exploded-aar/com.android.support/support-v4/25.0.0/jars" />
-      <excludeFolder url="file://$MODULE_DIR$/build/intermediates/exploded-aar/com.android.support/support-vector-drawable/25.0.0/jars" />
-      <excludeFolder url="file://$MODULE_DIR$/build/intermediates/exploded-aar/com.android.support/transition/25.0.0/jars" />
       <excludeFolder url="file://$MODULE_DIR$/build/intermediates/incremental" />
       <excludeFolder url="file://$MODULE_DIR$/build/intermediates/incremental-classes" />
       <excludeFolder url="file://$MODULE_DIR$/build/intermediates/incremental-runtime-classes" />
@@ -109,12 +89,12 @@
       <excludeFolder url="file://$MODULE_DIR$/build/intermediates/instant-run-support" />
       <excludeFolder url="file://$MODULE_DIR$/build/intermediates/jniLibs" />
       <excludeFolder url="file://$MODULE_DIR$/build/intermediates/manifests" />
-      <excludeFolder url="file://$MODULE_DIR$/build/intermediates/pre-dexed" />
       <excludeFolder url="file://$MODULE_DIR$/build/intermediates/reload-dex" />
       <excludeFolder url="file://$MODULE_DIR$/build/intermediates/res" />
       <excludeFolder url="file://$MODULE_DIR$/build/intermediates/restart-dex" />
       <excludeFolder url="file://$MODULE_DIR$/build/intermediates/rs" />
       <excludeFolder url="file://$MODULE_DIR$/build/intermediates/shaders" />
+      <excludeFolder url="file://$MODULE_DIR$/build/intermediates/split-apk" />
       <excludeFolder url="file://$MODULE_DIR$/build/intermediates/symbols" />
       <excludeFolder url="file://$MODULE_DIR$/build/intermediates/transforms" />
       <excludeFolder url="file://$MODULE_DIR$/build/outputs" />
diff --git a/app/build.gradle b/app/build.gradle
index c1375be..87e81d7 100644
--- a/app/build.gradle
+++ b/app/build.gradle
@@ -2,7 +2,7 @@ apply plugin: 'com.android.application'
 
 android {
     compileSdkVersion 25
-    buildToolsVersion '24.0.1'
+    buildToolsVersion '25.0.0'
 
     testOptions {
         unitTests.returnDefaultValues = true
@@ -12,8 +12,8 @@ android {
         applicationId "org.secuso.privacyfriendlysudoku"
         minSdkVersion 16
         targetSdkVersion 25
-        versionCode 3
-        versionName "2.0.1"
+        versionCode 4
+        versionName "2.1.1"
     }
     buildTypes {
         release {
diff --git a/app/src/main/AndroidManifest.xml b/app/src/main/AndroidManifest.xml
index 85f10a2..7a8d93b 100644
--- a/app/src/main/AndroidManifest.xml
+++ b/app/src/main/AndroidManifest.xml
@@ -38,6 +38,10 @@
         <activity
             android:name="org.secuso.privacyfriendlysudoku.ui.HelpActivity"
             android:label="@string/title_activity_help" />
+        <service
+            android:name="org.secuso.privacyfriendlysudoku.controller.GeneratorService"
+            android:enabled="true"
+            android:exported="false" />
     </application>
 
 </manifest>
\ No newline at end of file
diff --git a/app/src/main/java/org/secuso/privacyfriendlysudoku/controller/GameController.java b/app/src/main/java/org/secuso/privacyfriendlysudoku/controller/GameController.java
index 695dc06..8cb12b9 100644
--- a/app/src/main/java/org/secuso/privacyfriendlysudoku/controller/GameController.java
+++ b/app/src/main/java/org/secuso/privacyfriendlysudoku/controller/GameController.java
@@ -221,9 +221,44 @@ public class GameController implements IModelChangedListener, Parcelable {
                 updateList.addAll(gameBoard.getSection(cell.getRow(), cell.getCol()));
                 deleteNotes(updateList, value);
             }
+
+            if(settings != null && settings.getBoolean("pref_highlightInputError",true)) {
+                checkInputError(row, col);
+            }
         }
     }
 
+    private void checkInputError(int row, int col) {
+        if(isValidNumber(row+1) && isValidNumber(col+1)) {
+
+            if (errorList == null) {
+                errorList = new CellConflictList();
+            }
+
+            errorList.addAll(checkInputErrorList(gameBoard.getCell(row,col), gameBoard.getRow(row)));
+            errorList.addAll(checkInputErrorList(gameBoard.getCell(row, col), gameBoard.getColumn(col)));
+            errorList.addAll(checkInputErrorList(gameBoard.getCell(row, col), gameBoard.getSection(row, col)));
+        }
+    }
+
+
+    private CellConflictList checkInputErrorList(GameCell cell, List<GameCell> list) {
+        CellConflictList errorList = new CellConflictList();
+        for (int i = 0; i < list.size(); i++) {
+            GameCell c2 = list.get(i);
+
+            if (!cell.equals(c2) && cell.getValue() != 0 && c2.getValue() != 0) {
+
+                // Same value in one set should not exist
+                if (cell.getValue() == c2.getValue()) {
+                    // we found an error..
+                    errorList.add(new CellConflict(cell, c2));
+                }
+            }
+        }
+        return errorList;
+    }
+
     public LinkedList<GameCell> getConnectedCells(int row, int col) {
         LinkedList<GameCell> list = new LinkedList<>();
 
diff --git a/app/src/main/java/org/secuso/privacyfriendlysudoku/controller/GameStateManager.java b/app/src/main/java/org/secuso/privacyfriendlysudoku/controller/GameStateManager.java
index 64db4e8..bebec31 100644
--- a/app/src/main/java/org/secuso/privacyfriendlysudoku/controller/GameStateManager.java
+++ b/app/src/main/java/org/secuso/privacyfriendlysudoku/controller/GameStateManager.java
@@ -203,6 +203,5 @@ public class GameStateManager {
         SharedPreferences.Editor editor = settings.edit();
         editor.putBoolean("savesChanged", true);
         editor.commit();
-
     }
 }
diff --git a/app/src/main/java/org/secuso/privacyfriendlysudoku/controller/GeneratorService.java b/app/src/main/java/org/secuso/privacyfriendlysudoku/controller/GeneratorService.java
new file mode 100644
index 0000000..8fb7363
--- /dev/null
+++ b/app/src/main/java/org/secuso/privacyfriendlysudoku/controller/GeneratorService.java
@@ -0,0 +1,309 @@
+package org.secuso.privacyfriendlysudoku.controller;
+
+import android.app.IntentService;
+import android.app.PendingIntent;
+import android.app.Service;
+import android.content.Intent;
+import android.os.Handler;
+import android.os.IBinder;
+import android.support.annotation.IntDef;
+import android.support.annotation.Nullable;
+import android.support.v4.content.ContextCompat;
+import android.support.v7.app.NotificationCompat;
+import android.util.Log;
+import android.util.Pair;
+
+import org.secuso.privacyfriendlysudoku.controller.database.DatabaseHelper;
+import org.secuso.privacyfriendlysudoku.controller.database.model.Level;
+import org.secuso.privacyfriendlysudoku.controller.qqwing.Action;
+import org.secuso.privacyfriendlysudoku.controller.qqwing.PrintStyle;
+import org.secuso.privacyfriendlysudoku.controller.qqwing.QQWing;
+import org.secuso.privacyfriendlysudoku.controller.qqwing.Symmetry;
+import org.secuso.privacyfriendlysudoku.game.GameBoard;
+import org.secuso.privacyfriendlysudoku.game.GameDifficulty;
+import org.secuso.privacyfriendlysudoku.game.GameType;
+import org.secuso.privacyfriendlysudoku.ui.MainActivity;
+import org.secuso.privacyfriendlysudoku.ui.view.R;
+
+import java.util.Date;
+import java.util.LinkedList;
+import java.util.List;
+import java.util.concurrent.atomic.AtomicBoolean;
+import java.util.concurrent.atomic.AtomicInteger;
+
+import static android.app.PendingIntent.FLAG_UPDATE_CURRENT;
+import static org.secuso.privacyfriendlysudoku.controller.NewLevelManager.PRE_SAVES_MIN;
+
+/**
+ *
+ * @author Christopher Beckmann
+ */
+public class GeneratorService extends IntentService {
+
+    private static final String TAG = GeneratorService.class.getSimpleName();
+    public static final String ACTION_GENERATE = TAG + " ACTION_GENERATE";
+    public static final String ACTION_STOP = TAG + " ACTION_STOP";
+    public static final String EXTRA_GAMETYPE = TAG + " EXTRA_GAMETYPE";
+    public static final String EXTRA_DIFFICULTY = TAG + " EXTRA_DIFFICULTY";
+
+    private final QQWingOptions opts = new QQWingOptions();
+
+    private final List<Pair<GameType, GameDifficulty>> generationList = new LinkedList<>();
+    private final DatabaseHelper dbHelper = new DatabaseHelper(this);
+
+
+    public GeneratorService() {
+        super("Generator Service");
+    }
+
+    private void buildGenerationList() {
+        generationList.clear();
+
+        for(GameType validType : GameType.getValidGameTypes()) {
+            for(GameDifficulty validDifficulty : GameDifficulty.getValidDifficultyList()) {
+                int levelCount = dbHelper.getLevels(validDifficulty, validType).size();
+                Log.d(TAG, "\tType: "+ validType.name() + " Difficulty: " + validDifficulty.name() + "\t: " + levelCount);
+                // add the missing levels to the list
+                for(int i = levelCount; i < PRE_SAVES_MIN; i++) {
+                    generationList.add(new Pair<>(validType, validDifficulty));
+                }
+            }
+        }
+
+        // PrintGenerationList
+        Log.d(TAG, "### Missing Levels: ###");
+        int i = 0;
+        for(Pair<GameType, GameDifficulty> dataPair : generationList) {
+            Log.d(TAG, "\t" + i++ + ":\tType: "+ dataPair.first.name() + " Difficulty: " + dataPair.second.name());
+        }
+    }
+
+    private void handleGenerationStop() {
+        stopForeground(true);
+        stopSelf();
+    }
+
+    private void handleGenerationStart(Intent intent) {
+        GameType gameType = intent.getParcelableExtra(EXTRA_GAMETYPE);
+        GameDifficulty gameDifficulty = intent.getParcelableExtra(EXTRA_DIFFICULTY);
+
+        if(gameType == null || gameDifficulty == null) {
+            generateLevels();
+        } else {
+            generateLevel(gameType, gameDifficulty);
+        }
+    }
+
+    private void generateLevels() {
+        // if we start this service multiple times while we are already generating...
+        // we ignore this call and just keep generating
+        buildGenerationList();
+
+        // generate from the list
+        if(generationList.size() > 0) {
+
+            // generate 1 level and wait for it to be done.
+            Pair<GameType, GameDifficulty> dataPair = generationList.get(0);
+            GameType type = dataPair.first;
+            GameDifficulty diff = dataPair.second;
+
+            generateLevel(type, diff);
+        }
+    }
+
+    private void generateLevel(final GameType gameType, final GameDifficulty gameDifficulty) {
+        showNotification(gameType, gameDifficulty);
+
+        generated.clear();
+        opts.gameDifficulty = gameDifficulty;
+        opts.action = Action.GENERATE;
+        opts.needNow = true;
+        opts.printSolution = false;
+        opts.gameType = gameType;
+        if(gameDifficulty == GameDifficulty.Easy && gameType == GameType.Default_9x9) {
+            opts.symmetry = Symmetry.ROTATE90;
+        } else {
+            opts.symmetry = Symmetry.NONE;
+        }
+        if(gameType == GameType.Default_12x12 && gameDifficulty != GameDifficulty.Challenge) {
+            opts.symmetry = Symmetry.ROTATE90;
+        }
+
+        final AtomicInteger puzzleCount = new AtomicInteger(0);
+        final AtomicBoolean done = new AtomicBoolean(false);
+
+        Runnable generationRunnable = new Runnable() {
+                // Create a new puzzle board
+                // and set the options
+                private QQWing ss = createQQWing();
+
+                private QQWing createQQWing() {
+                    QQWing ss = new QQWing(opts.gameType, opts.gameDifficulty);
+                    ss.setRecordHistory(opts.printHistory || opts.printInstructions || opts.printStats || opts.gameDifficulty != GameDifficulty.Unspecified);
+                    ss.setLogHistory(opts.logHistory);
+                    ss.setPrintStyle(opts.printStyle);
+                    return ss;
+                }
+
+                @Override
+                public void run() {
+                    //android.os.Process.setThreadPriority(android.os.Process.THREAD_PRIORITY_BACKGROUND);
+                    try {
+
+                        // Solve puzzle or generate puzzles
+                        // until end of input for solving, or
+                        // until we have generated the specified number.
+                        while (!done.get()) {
+
+                            // Record whether the puzzle was possible or
+                            // not,
+                            // so that we don't try to solve impossible
+                            // givens.
+                            boolean havePuzzle;
+                            boolean solveImpossible;
+
+                            if (opts.action == Action.GENERATE) {
+                                // Generate a puzzle
+                                havePuzzle = ss.generatePuzzleSymmetry(opts.symmetry);
+
+                            } else {
+                                // Read the next puzzle on STDIN
+                                int[] puzzle = new int[QQWing.BOARD_SIZE];
+                                if (getPuzzleToSolve(puzzle)) {
+                                    havePuzzle = ss.setPuzzle(puzzle);
+                                    if (havePuzzle) {
+                                        puzzleCount.getAndDecrement();
+                                    } else {
+                                        // Puzzle to solve is impossible.
+                                        solveImpossible = true;
+                                    }
+                                } else {
+                                    // Set loop to terminate when nothing is
+                                    // left on STDIN
+                                    havePuzzle = false;
+                                    done.set(true);
+                                }
+                                puzzle = null;
+                            }
+
+                            if(opts.gameDifficulty != GameDifficulty.Unspecified) {
+                                ss.solve();
+                            }
+
+                            if (havePuzzle) {
+                                // Bail out if it didn't meet the difficulty
+                                // standards for generation
+                                if (opts.action == Action.GENERATE) {
+
+                                    // save the level anyways but keep going if the desired level is not yet generated
+                                    Level level = new Level();
+                                    level.setGameType(opts.gameType);
+                                    level.setDifficulty(ss.getDifficulty());
+                                    level.setPuzzle(ss.getPuzzle());
+                                    dbHelper.addLevel(level);
+                                    Log.d(TAG, "Generated: " + level.getGameType().name() + ",\t"+level.getDifficulty().name());
+
+                                    if (opts.gameDifficulty != GameDifficulty.Unspecified && opts.gameDifficulty != ss.getDifficulty()) {
+                                        havePuzzle = false;
+                                        // check if other threads have finished the job
+                                        if (puzzleCount.get() >= opts.numberToGenerate)
+                                            done.set(true);
+                                    } else {
+                                        int numDone = puzzleCount.incrementAndGet();
+                                        if (numDone >= opts.numberToGenerate) done.set(true);
+                                        if (numDone > opts.numberToGenerate) havePuzzle = false;
+                                    }
+                                }
+                                if (havePuzzle) {
+                                    generated.add(ss.getPuzzle());
+                                }
+                            }
+                        }
+                    } catch (Exception e) {
+                        Log.e("QQWing", "Exception Occured", e);
+                        return;
+                    }
+                    generationDone();
+                }
+            };
+
+        generationRunnable.run();
+    }
+
+    // this is called whenever a generation is done..
+    private void generationDone() {
+        // check if more can be generated
+        if(generationList.size() > 0) {
+            generateLevels();
+        } else {
+            // we are done and can close this service
+            handleGenerationStop();
+        }
+    }
+
+    private void showNotification(GameType gameType, GameDifficulty gameDifficulty) {
+        NotificationCompat.Builder builder = new NotificationCompat.Builder(this);
+        builder.setContentTitle(getString(R.string.app_name));
+        builder.setContentText(getString(R.string.generating));
+        builder.setSubText(getString(gameType.getStringResID()) + ", " + getString(gameDifficulty.getStringResID()));
+        builder.setContentIntent(PendingIntent.getActivity(this, 0, new Intent(this, MainActivity.class), FLAG_UPDATE_CURRENT));
+        builder.setColor(ContextCompat.getColor(this, R.color.colorAccent));
+        builder.setPriority(NotificationCompat.PRIORITY_HIGH);
+        builder.setWhen(0);
+        builder.setSmallIcon(R.drawable.splash_icon);
+        startForeground(50, builder.build());
+    }
+
+    @Nullable
+    @Override
+    public IBinder onBind(Intent intent) {
+        return null;
+    }
+
+    @Override
+    protected void onHandleIntent(@Nullable Intent intent) {
+        if (intent != null) {
+
+            String action = intent.getAction();
+
+            if      (ACTION_GENERATE.equals(action))    handleGenerationStart(intent);
+            else if (ACTION_STOP.equals(action))        handleGenerationStop();
+        }
+    }
+
+    private int[] level;
+    private LinkedList<int[]> generated = new LinkedList<>();
+
+    private static class QQWingOptions {
+        // defaults for options
+        boolean needNow = false;
+        boolean printPuzzle = false;
+        boolean printSolution = false;
+        boolean printHistory = false;
+        boolean printInstructions = false;
+        boolean timer = false;
+        boolean countSolutions = false;
+        Action action = Action.NONE;
+        boolean logHistory = false;
+        PrintStyle printStyle = PrintStyle.READABLE;
+        int numberToGenerate = 1;
+        boolean printStats = false;
+        GameDifficulty gameDifficulty = GameDifficulty.Unspecified;
+        GameType gameType = GameType.Unspecified;
+        Symmetry symmetry = Symmetry.NONE;
+        int threads = Runtime.getRuntime().availableProcessors();
+    }
+
+    private boolean getPuzzleToSolve(int[] puzzle) {
+        if(level != null) {
+            if(puzzle.length == level.length) {
+                for(int i = 0; i < level.length; i++) {
+                    puzzle[i] = level[i];
+                }
+            }
+            level = null;
+            return true;
+        }
+        return false;
+    }
+}
diff --git a/app/src/main/java/org/secuso/privacyfriendlysudoku/controller/NewLevelManager.java b/app/src/main/java/org/secuso/privacyfriendlysudoku/controller/NewLevelManager.java
index 79aa4a7..3ad7c9a 100644
--- a/app/src/main/java/org/secuso/privacyfriendlysudoku/controller/NewLevelManager.java
+++ b/app/src/main/java/org/secuso/privacyfriendlysudoku/controller/NewLevelManager.java
@@ -1,10 +1,13 @@
 package org.secuso.privacyfriendlysudoku.controller;
 
 import android.content.Context;
+import android.content.Intent;
 import android.content.SharedPreferences;
 import android.os.AsyncTask;
 import android.util.Log;
 
+import org.secuso.privacyfriendlysudoku.controller.database.DatabaseHelper;
+import org.secuso.privacyfriendlysudoku.controller.database.model.Level;
 import org.secuso.privacyfriendlysudoku.game.GameDifficulty;
 import org.secuso.privacyfriendlysudoku.game.GameType;
 
@@ -25,12 +28,14 @@ public class NewLevelManager {
     private SharedPreferences settings;
 
     private static NewLevelManager instance;
+    private DatabaseHelper dbHelper;
 
     private static String FILE_EXTENSION = ".txt";
     private static String LEVEL_PREFIX = "level_";
     private static String LEVELS_DIR = "level";
     private static File DIR;
-    private static int PRE_SAVES = 5;
+    public static int PRE_SAVES_MIN = 3;
+    public static int PRE_SAVES_MAX = 10;
 
     public static NewLevelManager getInstance(Context context, SharedPreferences settings) {
         if(instance == null) {
@@ -42,10 +47,16 @@ public class NewLevelManager {
     private NewLevelManager(Context context, SharedPreferences settings) {
         this.context = context;
         this.settings = settings;
+        this.dbHelper = new DatabaseHelper(context);
         DIR = context.getDir(LEVELS_DIR, 0);
     }
 
     public boolean isLevelLoadable(GameType type, GameDifficulty diff) {
+        return dbHelper.getLevels(diff, type).size() > 0;
+    }
+
+    @Deprecated
+    public boolean isLevelLoadableOld(GameType type, GameDifficulty diff) {
         for(File file : DIR.listFiles()) {
             if (file.isFile()) {
                 String name = file.getName().substring(0, file.getName().lastIndexOf("_"));
@@ -65,8 +76,34 @@ public class NewLevelManager {
     }
 
     public int[] loadLevel(GameType type, GameDifficulty diff) {
+        Level level = dbHelper.getLevel(diff, type);
+        dbHelper.deleteLevel(level.getId());
+        return level.getPuzzle();
+
+//        for(Level level : levels) {
+//
+//            // delete level from database
+//            dbHelper.deleteLevel(level.getId());
+//
+//            // test if it has the correct length
+//            int length = type.getSize() * type.getSize();
+//            if (level.getPuzzle().length != length) {
+//                // Level is not correctly saved -> discard it and try again
+//                continue;
+//            } else {
+//                return level.getPuzzle();
+//            }
+//        }
+//
+//        // if there is no level or every level has the wrong length
+//        throw new RuntimeException("No level to load with specified parameters");
+    }
+
+    @Deprecated
+    public int[] loadLevelOld(GameType type, GameDifficulty diff) {
         List<int[]> result = new LinkedList<>();
         LinkedList<Integer> availableFiles = new LinkedList<>();
+        Random r = new Random();
 
         // go through every file
         for(File file : DIR.listFiles()) {
@@ -117,7 +154,6 @@ public class NewLevelManager {
         }
 
         if(result.size() > 0) {
-            Random r = new Random();
             int i = r.nextInt(availableFiles.size());
             int chosen = availableFiles.get(i);
             int[] resultPuzzle = result.get(i);
@@ -144,10 +180,81 @@ public class NewLevelManager {
     }
 
     public void checkAndRestock() {
-        new AsyncGenerationTask().execute();
+        // Start Generation Service
+        Intent i = new Intent(context, GeneratorService.class);
+        i.setAction(GeneratorService.ACTION_GENERATE);
+        //i.putExtra(ProtocolService.EXTRA_PROTOCOL, current.componentName().flattenToString());
+        context.startService(i);
+
+        //new AsyncGenerationTask().execute();
     }
 
     public void loadFirstStartLevels() {
+        saveToDb(GameType.Default_9x9, GameDifficulty.Moderate, "000208090027000000000400000090100706408090201000030080200001000100300469000000007");
+        saveToDb(GameType.Default_9x9, GameDifficulty.Moderate, "000000052000003007500206830002040700070000046640508003000400000000005000050301008");
+        saveToDb(GameType.Default_9x9, GameDifficulty.Moderate, "950710600063200500100300200078000032016000000000000050000001869029000000800003000");
+        saveToDb(GameType.Default_9x9, GameDifficulty.Moderate, "679000300000000050000700020020300001000006000167240000030020004004000500001003792");
+        saveToDb(GameType.Default_9x9, GameDifficulty.Moderate, "000465000000000008000320500060000709900006053000043200600000902024070600000030005");
+
+        saveToDb(GameType.Default_9x9, GameDifficulty.Hard, "000800400008004093009003060000700000000400000060002900091000670200000100403006802");
+        saveToDb(GameType.Default_9x9, GameDifficulty.Hard, "000006040000050000600040080043000200500810000100300605209080460004500000001030000");
+        saveToDb(GameType.Default_9x9, GameDifficulty.Hard, "080000000040000000000071300050130700004006000003508014000000081012600405070000002");
+        saveToDb(GameType.Default_9x9, GameDifficulty.Hard, "030200000008000096700600050013720009006000700802009000000903082500010070000000000");
+        saveToDb(GameType.Default_9x9, GameDifficulty.Hard, "007500200120093700004007050000000305500800090040300018000000009000715000000400030");
+
+        saveToDb(GameType.Default_9x9, GameDifficulty.Challenge, "086000000000000070090000304968027030000100060200900000072006100000000296000000740");
+        saveToDb(GameType.Default_9x9, GameDifficulty.Challenge, "450900001001400000600010004006700000500000000100024060002000030000062400040005700");
+        saveToDb(GameType.Default_9x9, GameDifficulty.Challenge, "100000020006020091000600000030070000260040000008010000000380060700000049040100002");
+        saveToDb(GameType.Default_9x9, GameDifficulty.Challenge, "040100800059408061700000002500000009080700000007004000000000090801009200000000685");
+        saveToDb(GameType.Default_9x9, GameDifficulty.Challenge, "007000050300710000140000000000500406001000907000370005790030001060004000005620000");
+
+        saveToDb(GameType.Default_12x12, GameDifficulty.Moderate, "B30050A100701600070030800002894000007008000000B550100004020300B0000090000060000A010000000032050C0407008006A000000000400001000C290000000008005000");
+        saveToDb(GameType.Default_12x12, GameDifficulty.Moderate, "00B4008A09C002A030C00008007850003000030C000408AB000B00052000000000000070069500030C00B00010467000008000000A100000000800000C0020700001700000095400");
+        saveToDb(GameType.Default_12x12, GameDifficulty.Moderate, "90B08A00300100A000007B500054000B90000320000C05B0A00C0000090200050200000000000094C2000006000200303140000008006C0800000000003000C0010050007009AC60");
+        saveToDb(GameType.Default_12x12, GameDifficulty.Moderate, "74000010000B000005400000900000000000000090000005000B075A0C240208B00007000009000C000207020B000860800300020190C000A000604800470009B00000A068003200");
+        saveToDb(GameType.Default_12x12, GameDifficulty.Moderate, "00B000003050000AC06000700000030001800500000040000008A50402000A00100070000000069B200009130A0000000070020195C000A409000300003600000B21B00030000800");
+
+        saveToDb(GameType.Default_12x12, GameDifficulty.Hard, "00600500000004000000002050004C00800A28049000050000A900C000000000B00000A00B0560000C900C708A00000B0002000000769000008000B002B0C6000017C00107400908");
+        saveToDb(GameType.Default_12x12, GameDifficulty.Hard, "020000B000A608070530000B9050200A03800030980010B001000B6C30900000032000CAB0000000000000067000B000000500000A000C09000081302B0100070950836000100000");
+        saveToDb(GameType.Default_12x12, GameDifficulty.Hard, "0A00070050B107B0060A8000005090020C0A500040001060000000A000040B00219000000107B000602C8090C000001700400A00058B00000000000620000B400090090400800000");
+        saveToDb(GameType.Default_12x12, GameDifficulty.Hard, "000000908A0002900080006B0000C000007005800B2C00006020300000043B090806500C090400C000300060A700040500A00400002800000CA0000900000060B000A0B0003970C6");
+        saveToDb(GameType.Default_12x12, GameDifficulty.Hard, "0070000000000020009B0100000A030000000C039002004800904005000B100B008070507040C20005A0000870B32000C5000810070980100000000000000A070C000A0500000090");
+
+        saveToDb(GameType.Default_12x12, GameDifficulty.Challenge, "2000000000000B070C00000000AC100000000020050CA00BB60002097800079001000C60400000B0070A0000A7000298005048000010004000070009A10600C00B000C00B0000020");
+        saveToDb(GameType.Default_12x12, GameDifficulty.Challenge, "01000002000C00640A800070000A0000082020000008100B0C081090000050A0060C079009BC000A04010500097000000000000000000000904000866070B100020000000C00B009");
+        saveToDb(GameType.Default_12x12, GameDifficulty.Challenge, "000C0B020600400900600A020800140000C000000013050000040600900300000C0500B49A0250000000B0C0002000300143C000B0060000800064000000000B10000000020A8B09");
+        saveToDb(GameType.Default_12x12, GameDifficulty.Challenge, "08060000000100000765A0000C00400000B0605001C7000019C0A4000002A000000B0040000000000100B500000080740020100005690A000000048B706000009020000020807000");
+        saveToDb(GameType.Default_12x12, GameDifficulty.Challenge, "B000730000000000090040000C00B00000003A07180000C00000000CB0000000400A200040B2000000A8000020006700710A06000C00000BA0200170A700603002B0043000090060");
+
+        saveToDb(GameType.Default_6x6, GameDifficulty.Moderate, "000000050004013000004003006050040010");
+        saveToDb(GameType.Default_6x6, GameDifficulty.Moderate, "000450000600104306630000060005010000");
+        saveToDb(GameType.Default_6x6, GameDifficulty.Moderate, "020003040006000000406000000050060042");
+        saveToDb(GameType.Default_6x6, GameDifficulty.Moderate, "024000510042002054000020000060600000");
+        saveToDb(GameType.Default_6x6, GameDifficulty.Moderate, "610030400001004000000200060000002600");
+
+        saveToDb(GameType.Default_6x6, GameDifficulty.Hard, "630010002000001000040020400006003040");
+        saveToDb(GameType.Default_6x6, GameDifficulty.Hard, "000000060130006000050603030005000041");
+        saveToDb(GameType.Default_6x6, GameDifficulty.Hard, "502360000040430050000030650000000000");
+        saveToDb(GameType.Default_6x6, GameDifficulty.Hard, "000004300050006010001003000561000000");
+        saveToDb(GameType.Default_6x6, GameDifficulty.Hard, "000000042000003140064030000320200000");
+
+        saveToDb(GameType.Default_6x6, GameDifficulty.Challenge, "004200200000003002600050300400046000");
+        saveToDb(GameType.Default_6x6, GameDifficulty.Challenge, "003050200003502000000000640002000045");
+        saveToDb(GameType.Default_6x6, GameDifficulty.Challenge, "004030000000003020205004400000006500");
+        saveToDb(GameType.Default_6x6, GameDifficulty.Challenge, "001650000320100000000060000000065000");
+        saveToDb(GameType.Default_6x6, GameDifficulty.Challenge, "500004013005004020000000042500100000");
+    }
+
+    private void saveToDb(GameType gametype, GameDifficulty difficulty, String levelString) {
+        Level level = new Level();
+        level.setDifficulty(difficulty);
+        level.setGameType(gametype);
+        level.setPuzzle(levelString);
+        dbHelper.addLevel(level);
+    }
+
+    @Deprecated
+    public void loadFirstStartLevelsOld() {
         // Default_9x9
         // Default_12x12
         // Default_6x6
@@ -159,62 +266,63 @@ public class NewLevelManager {
         // 0
         // 1
 
-        saveToFile(GameType.Default_9x9, GameDifficulty.Easy, 0, "000208090027000000000400000090100706408090201000030080200001000100300469000000007");
-        saveToFile(GameType.Default_9x9, GameDifficulty.Easy, 1, "000000052000003007500206830002040700070000046640508003000400000000005000050301008");
-        saveToFile(GameType.Default_9x9, GameDifficulty.Easy, 2, "950710600063200500100300200078000032016000000000000050000001869029000000800003000");
-        saveToFile(GameType.Default_9x9, GameDifficulty.Easy, 3, "679000300000000050000700020020300001000006000167240000030020004004000500001003792");
-        saveToFile(GameType.Default_9x9, GameDifficulty.Easy, 4, "000465000000000008000320500060000709900006053000043200600000902024070600000030005");
+        saveToFile(GameType.Default_9x9, GameDifficulty.Moderate, 0, "000208090027000000000400000090100706408090201000030080200001000100300469000000007");
+        saveToFile(GameType.Default_9x9, GameDifficulty.Moderate, 1, "000000052000003007500206830002040700070000046640508003000400000000005000050301008");
+        saveToFile(GameType.Default_9x9, GameDifficulty.Moderate, 2, "950710600063200500100300200078000032016000000000000050000001869029000000800003000");
+        saveToFile(GameType.Default_9x9, GameDifficulty.Moderate, 3, "679000300000000050000700020020300001000006000167240000030020004004000500001003792");
+        saveToFile(GameType.Default_9x9, GameDifficulty.Moderate, 4, "000465000000000008000320500060000709900006053000043200600000902024070600000030005");
 
-        saveToFile(GameType.Default_9x9, GameDifficulty.Moderate, 0, "000800400008004093009003060000700000000400000060002900091000670200000100403006802");
-        saveToFile(GameType.Default_9x9, GameDifficulty.Moderate, 1, "000006040000050000600040080043000200500810000100300605209080460004500000001030000");
-        saveToFile(GameType.Default_9x9, GameDifficulty.Moderate, 2, "080000000040000000000071300050130700004006000003508014000000081012600405070000002");
-        saveToFile(GameType.Default_9x9, GameDifficulty.Moderate, 3, "030200000008000096700600050013720009006000700802009000000903082500010070000000000");
-        saveToFile(GameType.Default_9x9, GameDifficulty.Moderate, 4, "007500200120093700004007050000000305500800090040300018000000009000715000000400030");
+        saveToFile(GameType.Default_9x9, GameDifficulty.Hard, 0, "000800400008004093009003060000700000000400000060002900091000670200000100403006802");
+        saveToFile(GameType.Default_9x9, GameDifficulty.Hard, 1, "000006040000050000600040080043000200500810000100300605209080460004500000001030000");
+        saveToFile(GameType.Default_9x9, GameDifficulty.Hard, 2, "080000000040000000000071300050130700004006000003508014000000081012600405070000002");
+        saveToFile(GameType.Default_9x9, GameDifficulty.Hard, 3, "030200000008000096700600050013720009006000700802009000000903082500010070000000000");
+        saveToFile(GameType.Default_9x9, GameDifficulty.Hard, 4, "007500200120093700004007050000000305500800090040300018000000009000715000000400030");
 
-        saveToFile(GameType.Default_9x9, GameDifficulty.Hard, 0, "086000000000000070090000304968027030000100060200900000072006100000000296000000740");
-        saveToFile(GameType.Default_9x9, GameDifficulty.Hard, 1, "450900001001400000600010004006700000500000000100024060002000030000062400040005700");
-        saveToFile(GameType.Default_9x9, GameDifficulty.Hard, 2, "100000020006020091000600000030070000260040000008010000000380060700000049040100002");
-        saveToFile(GameType.Default_9x9, GameDifficulty.Hard, 3, "040100800059408061700000002500000009080700000007004000000000090801009200000000685");
-        saveToFile(GameType.Default_9x9, GameDifficulty.Hard, 4, "007000050300710000140000000000500406001000907000370005790030001060004000005620000");
+        saveToFile(GameType.Default_9x9, GameDifficulty.Challenge, 0, "086000000000000070090000304968027030000100060200900000072006100000000296000000740");
+        saveToFile(GameType.Default_9x9, GameDifficulty.Challenge, 1, "450900001001400000600010004006700000500000000100024060002000030000062400040005700");
+        saveToFile(GameType.Default_9x9, GameDifficulty.Challenge, 2, "100000020006020091000600000030070000260040000008010000000380060700000049040100002");
+        saveToFile(GameType.Default_9x9, GameDifficulty.Challenge, 3, "040100800059408061700000002500000009080700000007004000000000090801009200000000685");
+        saveToFile(GameType.Default_9x9, GameDifficulty.Challenge, 4, "007000050300710000140000000000500406001000907000370005790030001060004000005620000");
 
-        saveToFile(GameType.Default_12x12, GameDifficulty.Easy, 0, "B30050A100701600070030800002894000007008000000B550100004020300B0000090000060000A010000000032050C0407008006A000000000400001000C290000000008005000");
-        saveToFile(GameType.Default_12x12, GameDifficulty.Easy, 1, "00B4008A09C002A030C00008007850003000030C000408AB000B00052000000000000070069500030C00B00010467000008000000A100000000800000C0020700001700000095400");
-        saveToFile(GameType.Default_12x12, GameDifficulty.Easy, 2, "90B08A00300100A000007B500054000B90000320000C05B0A00C0000090200050200000000000094C2000006000200303140000008006C0800000000003000C0010050007009AC60");
-        saveToFile(GameType.Default_12x12, GameDifficulty.Easy, 3, "74000010000B000005400000900000000000000090000005000B075A0C240208B00007000009000C000207020B000860800300020190C000A000604800470009B00000A068003200");
-        saveToFile(GameType.Default_12x12, GameDifficulty.Easy, 4, "00B000003050000AC06000700000030001800500000040000008A50402000A00100070000000069B200009130A0000000070020195C000A409000300003600000B21B00030000800");
+        saveToFile(GameType.Default_12x12, GameDifficulty.Moderate, 0, "B30050A100701600070030800002894000007008000000B550100004020300B0000090000060000A010000000032050C0407008006A000000000400001000C290000000008005000");
+        saveToFile(GameType.Default_12x12, GameDifficulty.Moderate, 1, "00B4008A09C002A030C00008007850003000030C000408AB000B00052000000000000070069500030C00B00010467000008000000A100000000800000C0020700001700000095400");
+        saveToFile(GameType.Default_12x12, GameDifficulty.Moderate, 2, "90B08A00300100A000007B500054000B90000320000C05B0A00C0000090200050200000000000094C2000006000200303140000008006C0800000000003000C0010050007009AC60");
+        saveToFile(GameType.Default_12x12, GameDifficulty.Moderate, 3, "74000010000B000005400000900000000000000090000005000B075A0C240208B00007000009000C000207020B000860800300020190C000A000604800470009B00000A068003200");
+        saveToFile(GameType.Default_12x12, GameDifficulty.Moderate, 4, "00B000003050000AC06000700000030001800500000040000008A50402000A00100070000000069B200009130A0000000070020195C000A409000300003600000B21B00030000800");
 
-        saveToFile(GameType.Default_12x12, GameDifficulty.Moderate, 0, "00600500000004000000002050004C00800A28049000050000A900C000000000B00000A00B0560000C900C708A00000B0002000000769000008000B002B0C6000017C00107400908");
-        saveToFile(GameType.Default_12x12, GameDifficulty.Moderate, 1, "020000B000A608070530000B9050200A03800030980010B001000B6C30900000032000CAB0000000000000067000B000000500000A000C09000081302B0100070950836000100000");
-        saveToFile(GameType.Default_12x12, GameDifficulty.Moderate, 2, "0A00070050B107B0060A8000005090020C0A500040001060000000A000040B00219000000107B000602C8090C000001700400A00058B00000000000620000B400090090400800000");
-        saveToFile(GameType.Default_12x12, GameDifficulty.Moderate, 3, "000000908A0002900080006B0000C000007005800B2C00006020300000043B090806500C090400C000300060A700040500A00400002800000CA0000900000060B000A0B0003970C6");
-        saveToFile(GameType.Default_12x12, GameDifficulty.Moderate, 4, "0070000000000020009B0100000A030000000C039002004800904005000B100B008070507040C20005A0000870B32000C5000810070980100000000000000A070C000A0500000090");
+        saveToFile(GameType.Default_12x12, GameDifficulty.Hard, 0, "00600500000004000000002050004C00800A28049000050000A900C000000000B00000A00B0560000C900C708A00000B0002000000769000008000B002B0C6000017C00107400908");
+        saveToFile(GameType.Default_12x12, GameDifficulty.Hard, 1, "020000B000A608070530000B9050200A03800030980010B001000B6C30900000032000CAB0000000000000067000B000000500000A000C09000081302B0100070950836000100000");
+        saveToFile(GameType.Default_12x12, GameDifficulty.Hard, 2, "0A00070050B107B0060A8000005090020C0A500040001060000000A000040B00219000000107B000602C8090C000001700400A00058B00000000000620000B400090090400800000");
+        saveToFile(GameType.Default_12x12, GameDifficulty.Hard, 3, "000000908A0002900080006B0000C000007005800B2C00006020300000043B090806500C090400C000300060A700040500A00400002800000CA0000900000060B000A0B0003970C6");
+        saveToFile(GameType.Default_12x12, GameDifficulty.Hard, 4, "0070000000000020009B0100000A030000000C039002004800904005000B100B008070507040C20005A0000870B32000C5000810070980100000000000000A070C000A0500000090");
 
-        saveToFile(GameType.Default_12x12, GameDifficulty.Hard, 0, "2000000000000B070C00000000AC100000000020050CA00BB60002097800079001000C60400000B0070A0000A7000298005048000010004000070009A10600C00B000C00B0000020");
-        saveToFile(GameType.Default_12x12, GameDifficulty.Hard, 1, "01000002000C00640A800070000A0000082020000008100B0C081090000050A0060C079009BC000A04010500097000000000000000000000904000866070B100020000000C00B009");
-        saveToFile(GameType.Default_12x12, GameDifficulty.Hard, 2, "000C0B020600400900600A020800140000C000000013050000040600900300000C0500B49A0250000000B0C0002000300143C000B0060000800064000000000B10000000020A8B09");
-        saveToFile(GameType.Default_12x12, GameDifficulty.Hard, 3, "08060000000100000765A0000C00400000B0605001C7000019C0A4000002A000000B0040000000000100B500000080740020100005690A000000048B706000009020000020807000");
-        saveToFile(GameType.Default_12x12, GameDifficulty.Hard, 4, "B000730000000000090040000C00B00000003A07180000C00000000CB0000000400A200040B2000000A8000020006700710A06000C00000BA0200170A700603002B0043000090060");
+        saveToFile(GameType.Default_12x12, GameDifficulty.Challenge, 0, "2000000000000B070C00000000AC100000000020050CA00BB60002097800079001000C60400000B0070A0000A7000298005048000010004000070009A10600C00B000C00B0000020");
+        saveToFile(GameType.Default_12x12, GameDifficulty.Challenge, 1, "01000002000C00640A800070000A0000082020000008100B0C081090000050A0060C079009BC000A04010500097000000000000000000000904000866070B100020000000C00B009");
+        saveToFile(GameType.Default_12x12, GameDifficulty.Challenge, 2, "000C0B020600400900600A020800140000C000000013050000040600900300000C0500B49A0250000000B0C0002000300143C000B0060000800064000000000B10000000020A8B09");
+        saveToFile(GameType.Default_12x12, GameDifficulty.Challenge, 3, "08060000000100000765A0000C00400000B0605001C7000019C0A4000002A000000B0040000000000100B500000080740020100005690A000000048B706000009020000020807000");
+        saveToFile(GameType.Default_12x12, GameDifficulty.Challenge, 4, "B000730000000000090040000C00B00000003A07180000C00000000CB0000000400A200040B2000000A8000020006700710A06000C00000BA0200170A700603002B0043000090060");
 
-        saveToFile(GameType.Default_6x6, GameDifficulty.Easy, 0, "000000050004013000004003006050040010");
-        saveToFile(GameType.Default_6x6, GameDifficulty.Easy, 1, "000450000600104306630000060005010000");
-        saveToFile(GameType.Default_6x6, GameDifficulty.Easy, 2, "020003040006000000406000000050060042");
-        saveToFile(GameType.Default_6x6, GameDifficulty.Easy, 3, "024000510042002054000020000060600000");
-        saveToFile(GameType.Default_6x6, GameDifficulty.Easy, 4, "610030400001004000000200060000002600");
+        saveToFile(GameType.Default_6x6, GameDifficulty.Moderate, 0, "000000050004013000004003006050040010");
+        saveToFile(GameType.Default_6x6, GameDifficulty.Moderate, 1, "000450000600104306630000060005010000");
+        saveToFile(GameType.Default_6x6, GameDifficulty.Moderate, 2, "020003040006000000406000000050060042");
+        saveToFile(GameType.Default_6x6, GameDifficulty.Moderate, 3, "024000510042002054000020000060600000");
+        saveToFile(GameType.Default_6x6, GameDifficulty.Moderate, 4, "610030400001004000000200060000002600");
 
-        saveToFile(GameType.Default_6x6, GameDifficulty.Moderate, 0, "630010002000001000040020400006003040");
-        saveToFile(GameType.Default_6x6, GameDifficulty.Moderate, 1, "000000060130006000050603030005000041");
-        saveToFile(GameType.Default_6x6, GameDifficulty.Moderate, 2, "502360000040430050000030650000000000");
-        saveToFile(GameType.Default_6x6, GameDifficulty.Moderate, 3, "000004300050006010001003000561000000");
-        saveToFile(GameType.Default_6x6, GameDifficulty.Moderate, 4, "000000042000003140064030000320200000");
+        saveToFile(GameType.Default_6x6, GameDifficulty.Hard, 0, "630010002000001000040020400006003040");
+        saveToFile(GameType.Default_6x6, GameDifficulty.Hard, 1, "000000060130006000050603030005000041");
+        saveToFile(GameType.Default_6x6, GameDifficulty.Hard, 2, "502360000040430050000030650000000000");
+        saveToFile(GameType.Default_6x6, GameDifficulty.Hard, 3, "000004300050006010001003000561000000");
+        saveToFile(GameType.Default_6x6, GameDifficulty.Hard, 4, "000000042000003140064030000320200000");
 
-        saveToFile(GameType.Default_6x6, GameDifficulty.Hard, 0, "004200200000003002600050300400046000");
-        saveToFile(GameType.Default_6x6, GameDifficulty.Hard, 1, "003050200003502000000000640002000045");
-        saveToFile(GameType.Default_6x6, GameDifficulty.Hard, 2, "004030000000003020205004400000006500");
-        saveToFile(GameType.Default_6x6, GameDifficulty.Hard, 3, "001650000320100000000060000000065000");
-        saveToFile(GameType.Default_6x6, GameDifficulty.Hard, 4, "500004013005004020000000042500100000");
+        saveToFile(GameType.Default_6x6, GameDifficulty.Challenge, 0, "004200200000003002600050300400046000");
+        saveToFile(GameType.Default_6x6, GameDifficulty.Challenge, 1, "003050200003502000000000640002000045");
+        saveToFile(GameType.Default_6x6, GameDifficulty.Challenge, 2, "004030000000003020205004400000006500");
+        saveToFile(GameType.Default_6x6, GameDifficulty.Challenge, 3, "001650000320100000000060000000065000");
+        saveToFile(GameType.Default_6x6, GameDifficulty.Challenge, 4, "500004013005004020000000042500100000");
     }
 
     /** Don't use this if you don't know what you are doing! **/
+    @Deprecated
     private void saveToFile(GameType gameType, GameDifficulty gameDifficulty, int saveNumber, String puzzle) {
         StringBuilder sb = new StringBuilder();
         sb.append(LEVEL_PREFIX);
@@ -249,7 +357,7 @@ public class NewLevelManager {
 
         @Override
         protected String doInBackground(int[][] ... params) {
-            int preSaves = PRE_SAVES;
+            int preSaves = PRE_SAVES_MIN;
             // init
             final LinkedList<GameType> gameTypes = GameType.getValidGameTypes();
             final LinkedList<GameDifficulty> gameDifficulties = GameDifficulty.getValidDifficultyList();
diff --git a/app/src/main/java/org/secuso/privacyfriendlysudoku/controller/Symbol.java b/app/src/main/java/org/secuso/privacyfriendlysudoku/controller/Symbol.java
index 4135a30..96265f0 100644
--- a/app/src/main/java/org/secuso/privacyfriendlysudoku/controller/Symbol.java
+++ b/app/src/main/java/org/secuso/privacyfriendlysudoku/controller/Symbol.java
@@ -10,8 +10,8 @@ public enum Symbol {
     Roman(new String[] {"I", "II", "III", "IV", "V", "VI", "VII", "VIII", "IX", "X", "XI", "XII", "XIII", "XIV", "XV", "XVI", "XVII", "XVIII", "XIX", "XX", "XXI", "XXII"}),
     Fancy(new String[] {"♪", "♫", "☼", "♥", "♦", "♣", "♠", "•", "○", "A", "B", "C", "D", "E", "F", "G", "H", "J", "K", "L", "M", "N" }),
     Chinese(new String[] {"一", "二", "三", "四", "五", "六", "七", "八", "九", "十", "十一", "十二", "十三", "十四", "十五", "十六" }),
-    Greek(new String[] { "α", "β", "γ", "δ", "ε", "ϛ", "ζ", "η", "θ", "ι", "ια", "ιβ", "ιγ", "ιδ", "ιε", "ιϛ", "ιζ", "ιη", "ιθ", "κ"}),
-    Indian(new String[] { "१", "२", "३", "४", "५", "६", "७", "८", "९", "१०", "११", "१२", "१३", "१४", "१५", "१६", "१७"});
+    Greek(new String[] {"α", "β", "γ", "δ", "ε", "ϛ", "ζ", "η", "θ", "ι", "ια", "ιβ", "ιγ", "ιδ", "ιε", "ιϛ", "ιζ", "ιη", "ιθ", "κ"}),
+    Indian(new String[] {"१", "२", "३", "४", "५", "६", "७", "८", "९", "१०", "११", "१२", "१३", "१४", "१५", "१६", "१७"});
 
     private String[] map;
 
diff --git a/app/src/main/java/org/secuso/privacyfriendlysudoku/controller/database/DatabaseHelper.java b/app/src/main/java/org/secuso/privacyfriendlysudoku/controller/database/DatabaseHelper.java
new file mode 100644
index 0000000..59fdae0
--- /dev/null
+++ b/app/src/main/java/org/secuso/privacyfriendlysudoku/controller/database/DatabaseHelper.java
@@ -0,0 +1,97 @@
+package org.secuso.privacyfriendlysudoku.controller.database;
+
+import android.content.ContentValues;
+import android.content.Context;
+import android.database.Cursor;
+import android.database.sqlite.SQLiteDatabase;
+import android.database.sqlite.SQLiteOpenHelper;
+
+import org.secuso.privacyfriendlysudoku.controller.database.columns.LevelColumns;
+import org.secuso.privacyfriendlysudoku.controller.database.model.Level;
+import org.secuso.privacyfriendlysudoku.game.GameDifficulty;
+import org.secuso.privacyfriendlysudoku.game.GameType;
+
+import java.util.ArrayList;
+import java.util.HashMap;
+import java.util.LinkedList;
+import java.util.List;
+
+public class DatabaseHelper extends SQLiteOpenHelper {
+
+    public static final int DATABASE_VERSION = 1;
+    public static final String DATABASE_NAME = "Database.db";
+
+    public DatabaseHelper(Context context) {
+        super(context, DATABASE_NAME, null, DATABASE_VERSION);
+    }
+
+    @Override
+    public void onCreate(SQLiteDatabase db) {
+        db.execSQL(LevelColumns.SQL_CREATE_ENTRIES);
+    }
+
+    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
+        db.execSQL(LevelColumns.SQL_DELETE_ENTRIES);
+        onCreate(db);
+    }
+
+    public void onDowngrade(SQLiteDatabase db, int oldVersion, int newVersion) {
+        onUpgrade(db, oldVersion, newVersion);
+    }
+
+    public List<Level> getLevels(GameDifficulty difficulty, GameType gameType) {
+        if(difficulty == null || gameType == null) {
+            throw new IllegalArgumentException("Arguments may not be null");
+        }
+
+        List<Level> levelList = new LinkedList<Level>();
+
+        SQLiteDatabase database = getWritableDatabase();
+
+        String selection = LevelColumns.DIFFICULTY + " = ? AND " + LevelColumns.GAMETYPE + " = ?";
+        String[] selectionArgs = {difficulty.name(), gameType.name()};
+
+        // How you want the results sorted in the resulting Cursor
+        Cursor c = database.query(
+                LevelColumns.TABLE_NAME,         // The table to query
+                LevelColumns.PROJECTION,                // The columns to return
+                selection,                                // The columns for the WHERE clause
+                selectionArgs,                            // The values for the WHERE clause
+                null,                                     // don't group the rows
+                null,                                     // don't filter by row groups
+                null                                    // The sort order
+        );
+
+        if (c != null) {
+            while(c.moveToNext()) {
+                levelList.add(LevelColumns.getLevel(c));
+            }
+        }
+
+        c.close();
+        return levelList;
+    }
+
+    public Level getLevel(GameDifficulty difficulty, GameType gameType) {
+        List<Level> levelList = getLevels(difficulty, gameType);
+        if(levelList.size() == 0) {
+            throw new IllegalArgumentException("There is no level");
+        }
+        return levelList.get(0);
+    }
+
+    public void deleteLevel(int id) {
+        SQLiteDatabase database = getWritableDatabase();
+
+        String selection = LevelColumns._ID + " = ?";
+        String[] selectionArgs = {id+""};
+
+        database.delete(LevelColumns.TABLE_NAME, selection, selectionArgs);
+    }
+
+    public long addLevel(Level level) {
+        SQLiteDatabase database = getWritableDatabase();
+        return database.insert(LevelColumns.TABLE_NAME, null, LevelColumns.getValues(level));
+    }
+}
+
diff --git a/app/src/main/java/org/secuso/privacyfriendlysudoku/controller/database/columns/LevelColumns.java b/app/src/main/java/org/secuso/privacyfriendlysudoku/controller/database/columns/LevelColumns.java
new file mode 100644
index 0000000..d6deebc
--- /dev/null
+++ b/app/src/main/java/org/secuso/privacyfriendlysudoku/controller/database/columns/LevelColumns.java
@@ -0,0 +1,90 @@
+package org.secuso.privacyfriendlysudoku.controller.database.columns;
+
+import android.content.ContentValues;
+import android.database.Cursor;
+import android.provider.BaseColumns;
+
+import org.secuso.privacyfriendlysudoku.controller.Symbol;
+import org.secuso.privacyfriendlysudoku.controller.database.model.*;
+import org.secuso.privacyfriendlysudoku.game.GameDifficulty;
+import org.secuso.privacyfriendlysudoku.game.GameType;
+
+public class LevelColumns implements BaseColumns {
+
+    public static final String TABLE_NAME = "levels";
+
+    public static final String DIFFICULTY = "level_difficulty";
+    public static final String GAMETYPE = "level_gametype";
+    public static final String PUZZLE = "level_puzzle";
+
+    private static final String TEXT_TYPE = " TEXT ";
+    private static final String INTEGER_TYPE = " INTEGER ";
+    private static final String COMMA_SEP = ",";
+
+    public static final String[] PROJECTION = {
+            _ID,
+            DIFFICULTY,
+            GAMETYPE,
+            PUZZLE
+    };
+
+    public static String SQL_CREATE_ENTRIES =
+            "CREATE TABLE " + TABLE_NAME + " (" +
+                    _ID         + INTEGER_TYPE + " PRIMARY KEY AUTOINCREMENT" + COMMA_SEP +
+                    DIFFICULTY        + TEXT_TYPE + COMMA_SEP +
+                    GAMETYPE  + TEXT_TYPE + COMMA_SEP +
+                    PUZZLE     + TEXT_TYPE + " )";
+    public static String SQL_DELETE_ENTRIES =
+            "DROP TABLE IF EXISTS " + TABLE_NAME;
+
+    public static Level getLevel(Cursor c) {
+        Level level = new Level();
+
+        // *** ID ***
+        level.setId(c.getInt(c.getColumnIndexOrThrow(LevelColumns._ID)));
+
+        // *** GAME TYPE ***
+        String gameTypeString = c.getString(c.getColumnIndexOrThrow(LevelColumns.GAMETYPE));
+        GameType gameType = GameType.valueOf(gameTypeString);
+        level.setGameType(gameType);
+
+        // *** DIFFICULTY ***
+        String difficultyString = c.getString(c.getColumnIndexOrThrow(LevelColumns.DIFFICULTY));
+        level.setDifficulty(GameDifficulty.valueOf(difficultyString));
+
+        // *** PUZZLE ***
+        String puzzleString = c.getString(c.getColumnIndexOrThrow(LevelColumns.PUZZLE));
+        int[] puzzle = new int[gameType.getSize()*gameType.getSize()];
+
+        if(puzzle.length != puzzleString.length()) {
+            throw new IllegalArgumentException("Saved level does not have the correct size.");
+        }
+
+        for(int i = 0; i < puzzleString.length(); i++) {
+            puzzle[i] = Symbol.getValue(Symbol.SaveFormat, String.valueOf(puzzleString.charAt(i)))+1;
+        }
+        level.setPuzzle(puzzle);
+
+        return level;
+    }
+
+    public static ContentValues getValues(Level record) {
+        ContentValues values = new ContentValues();
+        if(record.getId() != -1) {
+            values.put(LevelColumns._ID, record.getId());
+        }
+        values.put(LevelColumns.GAMETYPE, record.getGameType().name());
+        values.put(LevelColumns.DIFFICULTY, record.getDifficulty().name());
+
+        StringBuilder sb = new StringBuilder();
+        for(int i = 0; i < record.getPuzzle().length; i++) {
+            if (record.getPuzzle()[i] == 0) {
+                sb.append(0);
+            } else {
+                sb.append(Symbol.getSymbol(Symbol.SaveFormat, record.getPuzzle()[i]-1));
+            }
+        }
+        values.put(LevelColumns.PUZZLE, sb.toString());
+        return values;
+    }
+}
diff --git a/app/src/main/java/org/secuso/privacyfriendlysudoku/controller/database/model/Level.java b/app/src/main/java/org/secuso/privacyfriendlysudoku/controller/database/model/Level.java
new file mode 100644
index 0000000..589d365
--- /dev/null
+++ b/app/src/main/java/org/secuso/privacyfriendlysudoku/controller/database/model/Level.java
@@ -0,0 +1,65 @@
+package org.secuso.privacyfriendlysudoku.controller.database.model;
+
+import org.secuso.privacyfriendlysudoku.controller.Symbol;
+import org.secuso.privacyfriendlysudoku.game.GameDifficulty;
+import org.secuso.privacyfriendlysudoku.game.GameType;
+
+public class Level {
+    private int id = -1;
+    private GameDifficulty difficulty = GameDifficulty.Unspecified;
+    private GameType gameType = GameType.Unspecified;
+    private int[] puzzle;
+
+    public Level() {}
+
+    public Level(int id, GameDifficulty difficulty, GameType gameType, int[] puzzle) {
+        this.id = id;
+        this.difficulty = difficulty;
+        this.gameType = gameType;
+        this.puzzle = puzzle;
+    }
+
+    public int getId() {
+        return id;
+    }
+
+    public void setId(int id) {
+        this.id = id;
+    }
+
+    public GameDifficulty getDifficulty() {
+        return difficulty;
+    }
+
+    public void setDifficulty(GameDifficulty difficulty) {
+        this.difficulty = difficulty;
+    }
+
+    public GameType getGameType() {
+        return gameType;
+    }
+
+    public void setGameType(GameType gameType) {
+        this.gameType = gameType;
+    }
+
+    public int[] getPuzzle() {
+        return puzzle;
+    }
+
+    public void setPuzzle(int[] puzzle) {
+        this.puzzle = puzzle;
+    }
+    public void setPuzzle(String puzzleString) {
+        int[] puzzle = new int[gameType.getSize()*gameType.getSize()];
+
+        if(puzzle.length != puzzleString.length()) {
+            throw new IllegalArgumentException("Saved level does not have the correct size.");
+        }
+
+        for(int i = 0; i < puzzleString.length(); i++) {
+            puzzle[i] = Symbol.getValue(Symbol.SaveFormat, String.valueOf(puzzleString.charAt(i)))+1;
+        }
+        this.puzzle = puzzle;
+    }
+}
diff --git a/app/src/main/java/org/secuso/privacyfriendlysudoku/controller/qqwing/QQWing.java b/app/src/main/java/org/secuso/privacyfriendlysudoku/controller/qqwing/QQWing.java
index 2e152f9..f57efd5 100644
--- a/app/src/main/java/org/secuso/privacyfriendlysudoku/controller/qqwing/QQWing.java
+++ b/app/src/main/java/org/secuso/privacyfriendlysudoku/controller/qqwing/QQWing.java
@@ -22,6 +22,8 @@
 // @formatter:on
 package org.secuso.privacyfriendlysudoku.controller.qqwing;
 
+import android.util.Log;
+
 import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.Collections;
@@ -228,17 +230,33 @@ public class QQWing {
 	 */
 	public GameDifficulty getDifficulty() {
 		if (getGuessCount() > 0)
-            return GameDifficulty.Hard;
+            return GameDifficulty.Challenge;
 		if (getBoxLineReductionCount() > 0)
-            return GameDifficulty.Moderate;
+            return GameDifficulty.Hard;
 		if (getPointingPairTripleCount() > 0)
-            return GameDifficulty.Moderate;
+            return GameDifficulty.Hard;
 		if (getHiddenPairCount() > 0)
-            return GameDifficulty.Moderate;
+            return GameDifficulty.Hard;
 		if (getNakedPairCount() > 0)
-            return GameDifficulty.Moderate;
-		if (getHiddenSingleCount() > 0)
-            return GameDifficulty.Easy;
+            return GameDifficulty.Hard;
+		switch (gameType) {
+			case Default_6x6:
+				if (getHiddenSingleCount() > 0)
+					return GameDifficulty.Moderate;
+				break;
+			case Default_9x9:
+				if (getHiddenSingleCount() > 10)
+					return GameDifficulty.Moderate;
+				break;
+			case Default_12x12:
+				Log.d("GeneratorService", "# HiddenSingleCount: "+ getHiddenSingleCount());
+				if (getHiddenSingleCount() > 20)
+					return GameDifficulty.Moderate;
+				break;
+			default:
+				if(getHiddenSingleCount() > 10)
+					return GameDifficulty.Moderate;
+		}
 		if (getSingleCount() > 0)
             return GameDifficulty.Easy;
 
@@ -450,9 +468,9 @@ public class QQWing {
 			rollbackRound(i);
 
             // Some hack to make easy levels on 12x12 .. because the generator wasn't able to create some
-            if(gameType == GameType.Default_12x12 &&  difficulty == GameDifficulty.Easy ) {
-                i += 4; // skip every 2nd round to find "easy" levels more frequent. Still takes about 20 Seconds.
-            }
+            //if(difficulty == GameDifficulty.Easy && gameType == GameType.Default_12x12) {
+            //    i += 2; // skip every 2nd round to find "easy" levels more frequent. Still takes about 20 Seconds.
+            //}
         }
 	}
 
diff --git a/app/src/main/java/org/secuso/privacyfriendlysudoku/game/GameBoard.java b/app/src/main/java/org/secuso/privacyfriendlysudoku/game/GameBoard.java
index 95f5081..ba7c64f 100644
--- a/app/src/main/java/org/secuso/privacyfriendlysudoku/game/GameBoard.java
+++ b/app/src/main/java/org/secuso/privacyfriendlysudoku/game/GameBoard.java
@@ -145,6 +145,8 @@ public class GameBoard implements Cloneable, Parcelable {
         return solved;
     }
 
+
+
     /**
      * Checks the given list if every number occurs only once.
      * This method will automatically build the errorList.
diff --git a/app/src/main/java/org/secuso/privacyfriendlysudoku/game/GameDifficulty.java b/app/src/main/java/org/secuso/privacyfriendlysudoku/game/GameDifficulty.java
index 44dfe0d..fbf9f9c 100644
--- a/app/src/main/java/org/secuso/privacyfriendlysudoku/game/GameDifficulty.java
+++ b/app/src/main/java/org/secuso/privacyfriendlysudoku/game/GameDifficulty.java
@@ -16,7 +16,8 @@ public enum GameDifficulty implements Parcelable {
     Unspecified(R.string.gametype_unspecified),
     Easy(R.string.difficulty_easy),
     Moderate(R.string.difficulty_moderate),
-    Hard(R.string.difficulty_hard);
+    Hard(R.string.difficulty_hard),
+    Challenge(R.string.difficulty_challenge);
 
     private int resID;
 
@@ -34,6 +35,7 @@ public enum GameDifficulty implements Parcelable {
         validList.add(Easy);
         validList.add(Moderate);
         validList.add(Hard);
+        validList.add(Challenge);
         return validList;
     }
 
diff --git a/app/src/main/java/org/secuso/privacyfriendlysudoku/ui/LoadGameActivity.java b/app/src/main/java/org/secuso/privacyfriendlysudoku/ui/LoadGameActivity.java
index 8de62ad..0ead53c 100644
--- a/app/src/main/java/org/secuso/privacyfriendlysudoku/ui/LoadGameActivity.java
+++ b/app/src/main/java/org/secuso/privacyfriendlysudoku/ui/LoadGameActivity.java
@@ -217,6 +217,8 @@ public class LoadGameActivity extends BaseActivity implements IDeleteDialogFragm
             }
             gameType.setText(gic.getGameType().getStringResID());
             difficulty.setText(gic.getDifficulty().getStringResID());
+            difficultyBar.setNumStars(GameDifficulty.getValidDifficultyList().size());
+            difficultyBar.setMax(GameDifficulty.getValidDifficultyList().size());
             difficultyBar.setRating(GameDifficulty.getValidDifficultyList().indexOf(gic.getDifficulty())+1);
 
             int time = gic.getTimePlayed();
diff --git a/app/src/main/java/org/secuso/privacyfriendlysudoku/ui/MainActivity.java b/app/src/main/java/org/secuso/privacyfriendlysudoku/ui/MainActivity.java
index 9c05354..7bbc155 100644
--- a/app/src/main/java/org/secuso/privacyfriendlysudoku/ui/MainActivity.java
+++ b/app/src/main/java/org/secuso/privacyfriendlysudoku/ui/MainActivity.java
@@ -48,6 +48,7 @@ public class MainActivity extends BaseActivity implements NavigationView.OnNavig
     SharedPreferences settings;
     ImageView arrowLeft, arrowRight;
     DrawerLayout drawer;
+    NavigationView mNavigationView;
 
     /**
      * The {@link ViewPager} that will host the section contents.
@@ -168,8 +169,10 @@ public class MainActivity extends BaseActivity implements NavigationView.OnNavig
         drawer.setDrawerListener(toggle);
         toggle.syncState();
 
-        NavigationView navigationView = (NavigationView) findViewById(R.id.nav_view_main);
-        navigationView.setNavigationItemSelectedListener(this);
+        mNavigationView = (NavigationView) findViewById(R.id.nav_view_main);
+        mNavigationView.setNavigationItemSelectedListener(this);
+
+        selectNavigationItem(R.id.nav_newgame_main);
 
         overridePendingTransition(0, 0);
     }
@@ -247,6 +250,8 @@ public class MainActivity extends BaseActivity implements NavigationView.OnNavig
     public void onResume() {
         super.onResume();
 
+        selectNavigationItem(R.id.nav_newgame_main);
+
         refreshContinueButton();
     }
 
@@ -269,6 +274,13 @@ public class MainActivity extends BaseActivity implements NavigationView.OnNavig
         // Handle navigation view item clicks here.
         final int id = item.getItemId();
 
+        drawer.closeDrawer(GravityCompat.START);
+
+        // return if we are not going to another page
+        if(id == R.id.nav_newgame_main) {
+            return true;
+        }
+
         // delay transition so the drawer can close
         mHandler.postDelayed(new Runnable() {
             @Override
@@ -277,16 +289,23 @@ public class MainActivity extends BaseActivity implements NavigationView.OnNavig
             }
         }, NAVDRAWER_LAUNCH_DELAY);
 
-        drawer.closeDrawer(GravityCompat.START);
-
         // fade out the active activity
         View mainContent = findViewById(R.id.main_content);
         if (mainContent != null) {
             mainContent.animate().alpha(0).setDuration(MAIN_CONTENT_FADEOUT_DURATION);
         }
+
         return true;
     }
 
+    // set active navigation item
+    private void selectNavigationItem(int itemId) {
+        for(int i = 0 ; i < mNavigationView.getMenu().size(); i++) {
+            boolean b = itemId == mNavigationView.getMenu().getItem(i).getItemId();
+            mNavigationView.getMenu().getItem(i).setChecked(b);
+        }
+    }
+
     private boolean goToNavigationItem(int id) {
         Intent intent;
 
diff --git a/app/src/main/java/org/secuso/privacyfriendlysudoku/ui/StatsActivity.java b/app/src/main/java/org/secuso/privacyfriendlysudoku/ui/StatsActivity.java
index 93c0ef5..fe29654 100644
--- a/app/src/main/java/org/secuso/privacyfriendlysudoku/ui/StatsActivity.java
+++ b/app/src/main/java/org/secuso/privacyfriendlysudoku/ui/StatsActivity.java
@@ -21,6 +21,7 @@ import android.widget.TextView;
 
 import org.secuso.privacyfriendlysudoku.controller.SaveLoadStatistics;
 import org.secuso.privacyfriendlysudoku.controller.helper.HighscoreInfoContainer;
+import org.secuso.privacyfriendlysudoku.game.GameDifficulty;
 import org.secuso.privacyfriendlysudoku.game.GameType;
 import org.secuso.privacyfriendlysudoku.ui.view.R;
 
@@ -243,9 +244,17 @@ public class StatsActivity extends BaseActivity {
                     averageTimeView = (TextView) rootView.findViewById(R.id.third_ava_time);
                     minTimeView = (TextView) rootView.findViewById(R.id.third_min_time);
                     break;
+                case 3:
+                    difficultyBarView = (RatingBar) rootView.findViewById(R.id.fourth_diff_bar);
+                    difficultyView = (TextView) rootView.findViewById(R.id.fourth_diff_text);
+                    averageTimeView = (TextView) rootView.findViewById(R.id.fourth_ava_time);
+                    minTimeView = (TextView) rootView.findViewById(R.id.fourth_min_time);
+                    break;
                 default: return;
             }
-            difficultyBarView.setRating(pos+1);
+            difficultyBarView.setMax(GameDifficulty.getValidDifficultyList().size());
+            difficultyBarView.setNumStars(GameDifficulty.getValidDifficultyList().size());
+            difficultyBarView.setRating(infos.getDifficulty().ordinal());
             difficultyView.setText(rootView.getResources().getString(infos.getDifficulty().getStringResID()));
             t= (infos.getTimeNoHints() == 0)?0:(infos.getTimeNoHints() / infos.getNumberOfGamesNoHints());
             averageTimeView.setText(formatTime(t));
diff --git a/app/src/main/java/org/secuso/privacyfriendlysudoku/ui/view/SudokuFieldLayout.java b/app/src/main/java/org/secuso/privacyfriendlysudoku/ui/view/SudokuFieldLayout.java
index 4e3783d..7b997fd 100644
--- a/app/src/main/java/org/secuso/privacyfriendlysudoku/ui/view/SudokuFieldLayout.java
+++ b/app/src/main/java/org/secuso/privacyfriendlysudoku/ui/view/SudokuFieldLayout.java
@@ -216,48 +216,42 @@ public class SudokuFieldLayout extends RelativeLayout implements IHighlightChang
         p.setStrokeWidth(4);
         p.setColor(Color.RED);
 
-        float offset1=0;
-        float offset2= 0;
+        float offsetX = 0;
+        float offsetY = 0;
         int row;
         int col;
         int row2;
         int col2;
-        float radius;
+
+        float radius = gameCellWidth / 2 - gameCellWidth / 16;
+
         for(CellConflict conflict : gameController.getErrorList()) {
 
-            //gamecells[conflict.getRowCell1()][conflict.getColCell1()].
-
+            // draw the circles around the numbers
             row = conflict.getRowCell1();
             col = conflict.getColCell1();
-            radius = gameCellWidth/2 - gameCellWidth / 8;
             canvas.drawCircle(gameCellWidth * col + gameCellWidth / 2, gameCellHeight * row + gameCellHeight / 2, radius, p);
 
             row2 = conflict.getRowCell2();
             col2 = conflict.getColCell2();
             canvas.drawCircle(gameCellWidth * col2 + gameCellWidth / 2, gameCellHeight * row2 + gameCellHeight / 2, radius, p);
 
+            // draw the line between the circles
+            // either offset is 0 or it is the radius pointing in the direction of the other cell
+            offsetX = (col == col2) ? 0f : (col < col2) ? radius : -radius;
+            offsetY = (row == row2) ? 0f : (row < row2) ? radius : -radius;
 
-
-
-            if (col == col2 || row == row2) {
-                offset1 = (col > col2)? 0-radius:radius;
-                offset2 = (row > row2)? 0-radius:radius;
-                offset1 = (col == col2)?0f:offset1;
-                offset2 = (row == row2)?0f:offset2;
-            } else {
-                double alpha = Math.atan((Math.abs(col2-col))/(Math.abs(row2 - row)));
-                offset1 = (col > col2)? 0-radius:radius;
-                offset2 = (row > row2)? 0-radius:radius;
-                offset1*=Math.sin(alpha);
-                offset2*=Math.cos(alpha);
+            if(col != col2 && row != row2) {
+                double alpha = Math.atan(((float)Math.abs(col2 - col))/((float)Math.abs(row2 - row)));
+                offsetX *= Math.sin(alpha);
+                offsetY *= Math.cos(alpha);
             }
 
-
             canvas.drawLine(
-                    (gameCellWidth * col + gameCellWidth / 2)+offset1,
-                    (gameCellHeight * row + gameCellHeight / 2)+offset2,
-                    (gameCellWidth * col2 + gameCellWidth / 2)-offset1,
-                    (gameCellHeight * row2 + gameCellHeight / 2)-offset2, p);
+                    (gameCellWidth * col + gameCellWidth / 2)+offsetX,
+                    (gameCellHeight * row + gameCellHeight / 2)+offsetY,
+                    (gameCellWidth * col2 + gameCellWidth / 2)-offsetX,
+                    (gameCellHeight * row2 + gameCellHeight / 2)-offsetY, p);
         }
     }
 }
diff --git a/app/src/main/res/layout-land/fragment_stats.xml b/app/src/main/res/layout-land/fragment_stats.xml
index bc719a9..80160d4 100644
--- a/app/src/main/res/layout-land/fragment_stats.xml
+++ b/app/src/main/res/layout-land/fragment_stats.xml
@@ -128,7 +128,7 @@
             android:layout_height="match_parent"
             android:orientation="vertical"
             android:layout_weight="5.5"
-            android:weightSum="3">
+            android:weightSum="4">
             <!-- ### first row -->
             <LinearLayout
                 android:layout_width="match_parent"
@@ -324,6 +324,72 @@
                     android:layout_below="@+id/third_min_text"/>
             </RelativeLayout>
         </LinearLayout>
+
+            <LinearLayout
+                android:layout_width="match_parent"
+                android:layout_height="0dp"
+                android:layout_weight="1">
+
+                <RelativeLayout
+                    android:layout_width="0dp"
+                    android:layout_height="fill_parent"
+                    android:layout_weight="1"
+                    android:gravity="center_vertical">
+                    <RatingBar
+                        android:layout_width="wrap_content"
+                        android:layout_height="wrap_content"
+                        android:numStars="3"
+                        android:layout_gravity="center"
+                        android:id="@+id/fourth_diff_bar"
+                        android:layout_below="@+id/fourth_diff_text"
+                        style="?android:attr/ratingBarStyleSmall"/>
+                    <TextView
+                        android:layout_width="wrap_content"
+                        android:layout_height="wrap_content"
+                        android:text="diffi"
+                        android:id="@+id/fourth_diff_text"
+                        android:gravity="center_vertical"/>
+                </RelativeLayout>
+
+                <RelativeLayout
+                    android:layout_width="0dp"
+                    android:layout_height="fill_parent"
+                    android:layout_weight="1"
+                    android:gravity="center_vertical">
+                    <TextView
+                        android:layout_width="wrap_content"
+                        android:layout_height="wrap_content"
+                        android:text="@string/average_time"
+                        android:id="@+id/fourth_av_text"/>
+                    <TextView
+                        android:layout_width="wrap_content"
+                        android:layout_height="wrap_content"
+                        android:text="0"
+                        android:id="@+id/fourth_ava_time"
+                        android:gravity="center_vertical"
+                        android:layout_below="@+id/fourth_av_text"/>
+                </RelativeLayout>
+                <RelativeLayout
+                    android:layout_width="0dp"
+                    android:layout_height="fill_parent"
+                    android:layout_weight="1"
+                    android:gravity="center_vertical">
+                    <TextView
+                        android:layout_width="wrap_content"
+                        android:layout_height="wrap_content"
+                        android:text="@string/min_time"
+                        android:id="@+id/fourth_min_text"/>
+                    <TextView
+                        android:layout_width="wrap_content"
+                        android:layout_height="wrap_content"
+                        android:text="0"
+                        android:id="@+id/fourth_min_time"
+                        android:gravity="center_vertical"
+                        android:layout_below="@+id/fourth_min_text"/>
+                </RelativeLayout>
+
+            </LinearLayout>
+
         </LinearLayout>
 
 
diff --git a/app/src/main/res/layout-xlarge-land/fragment_stats.xml b/app/src/main/res/layout-xlarge-land/fragment_stats.xml
index 34a4496..035860f 100644
--- a/app/src/main/res/layout-xlarge-land/fragment_stats.xml
+++ b/app/src/main/res/layout-xlarge-land/fragment_stats.xml
@@ -309,6 +309,71 @@
 
         </LinearLayout>
 
+        <LinearLayout
+            android:layout_width="match_parent"
+            android:layout_height="0dp"
+            android:layout_weight="1">
+
+            <RelativeLayout
+                android:layout_width="0dp"
+                android:layout_height="fill_parent"
+                android:layout_weight="1"
+                android:gravity="center_vertical">
+                <RatingBar
+                    android:layout_width="wrap_content"
+                    android:layout_height="wrap_content"
+                    android:numStars="3"
+                    android:layout_gravity="center"
+                    android:id="@+id/fourth_diff_bar"
+                    android:layout_below="@+id/fourth_diff_text"
+                    style="?android:attr/ratingBarStyleSmall"/>
+                <TextView
+                    android:layout_width="wrap_content"
+                    android:layout_height="wrap_content"
+                    android:text="diffi"
+                    android:id="@+id/fourth_diff_text"
+                    android:gravity="center_vertical"/>
+            </RelativeLayout>
+
+            <RelativeLayout
+                android:layout_width="0dp"
+                android:layout_height="fill_parent"
+                android:layout_weight="1"
+                android:gravity="center_vertical">
+                <TextView
+                    android:layout_width="wrap_content"
+                    android:layout_height="wrap_content"
+                    android:text="@string/average_time"
+                    android:id="@+id/fourth_av_text"/>
+                <TextView
+                    android:layout_width="wrap_content"
+                    android:layout_height="wrap_content"
+                    android:text="0"
+                    android:id="@+id/fourth_ava_time"
+                    android:gravity="center_vertical"
+                    android:layout_below="@+id/fourth_av_text"/>
+            </RelativeLayout>
+            <RelativeLayout
+                android:layout_width="0dp"
+                android:layout_height="fill_parent"
+                android:layout_weight="1"
+                android:gravity="center_vertical">
+                <TextView
+                    android:layout_width="wrap_content"
+                    android:layout_height="wrap_content"
+                    android:text="@string/min_time"
+                    android:id="@+id/fourth_min_text"/>
+                <TextView
+                    android:layout_width="wrap_content"
+                    android:layout_height="wrap_content"
+                    android:text="0"
+                    android:id="@+id/fourth_min_time"
+                    android:gravity="center_vertical"
+                    android:layout_below="@+id/fourth_min_text"/>
+            </RelativeLayout>
+
+        </LinearLayout>
+
 
     </LinearLayout>
 
diff --git a/app/src/main/res/layout-xlarge/fragment_stats.xml b/app/src/main/res/layout-xlarge/fragment_stats.xml
index 34a4496..26997f5 100644
--- a/app/src/main/res/layout-xlarge/fragment_stats.xml
+++ b/app/src/main/res/layout-xlarge/fragment_stats.xml
@@ -105,7 +105,7 @@
         android:layout_width="fill_parent"
         android:layout_height="0dp"
         android:layout_weight="4"
-        android:weightSum="3"
+        android:weightSum="4"
         android:orientation="vertical">
         <!-- ### first row -->
         <LinearLayout
@@ -309,6 +309,71 @@
 
         </LinearLayout>
 
+        <LinearLayout
+            android:layout_width="match_parent"
+            android:layout_height="0dp"
+            android:layout_weight="1">
+
+            <RelativeLayout
+                android:layout_width="0dp"
+                android:layout_height="fill_parent"
+                android:layout_weight="1"
+                android:gravity="center_vertical">
+                <RatingBar
+                    android:layout_width="wrap_content"
+                    android:layout_height="wrap_content"
+                    android:numStars="3"
+                    android:layout_gravity="center"
+                    android:id="@+id/fourth_diff_bar"
+                    android:layout_below="@+id/fourth_diff_text"
+                    style="?android:attr/ratingBarStyleSmall"/>
+                <TextView
+                    android:layout_width="wrap_content"
+                    android:layout_height="wrap_content"
+                    android:text="diffi"
+                    android:id="@+id/fourth_diff_text"
+                    android:gravity="center_vertical"/>
+            </RelativeLayout>
+
+            <RelativeLayout
+                android:layout_width="0dp"
+                android:layout_height="fill_parent"
+                android:layout_weight="1"
+                android:gravity="center_vertical">
+                <TextView
+                    android:layout_width="wrap_content"
+                    android:layout_height="wrap_content"
+                    android:text="@string/average_time"
+                    android:id="@+id/fourth_av_text"/>
+                <TextView
+                    android:layout_width="wrap_content"
+                    android:layout_height="wrap_content"
+                    android:text="0"
+                    android:id="@+id/fourth_ava_time"
+                    android:gravity="center_vertical"
+                    android:layout_below="@+id/fourth_av_text"/>
+            </RelativeLayout>
+            <RelativeLayout
+                android:layout_width="0dp"
+                android:layout_height="fill_parent"
+                android:layout_weight="1"
+                android:gravity="center_vertical">
+                <TextView
+                    android:layout_width="wrap_content"
+                    android:layout_height="wrap_content"
+                    android:text="@string/min_time"
+                    android:id="@+id/fourth_min_text"/>
+                <TextView
+                    android:layout_width="wrap_content"
+                    android:layout_height="wrap_content"
+                    android:text="0"
+                    android:id="@+id/fourth_min_time"
+                    android:gravity="center_vertical"
+                    android:layout_below="@+id/fourth_min_text"/>
+            </RelativeLayout>
+
+        </LinearLayout>
+
 
     </LinearLayout>
 
diff --git a/app/src/main/res/layout/fragment_stats.xml b/app/src/main/res/layout/fragment_stats.xml
index 34a4496..9e12962 100644
--- a/app/src/main/res/layout/fragment_stats.xml
+++ b/app/src/main/res/layout/fragment_stats.xml
@@ -6,7 +6,7 @@
     android:paddingBottom="@dimen/activity_vertical_margin"
     android:weightSum="10"
     android:orientation="vertical"
-    tools:context="tu_darmstadt.sudoku.ui.StatsActivity$PlaceholderFragment">
+    tools:context="org.secuso.privacyfriendlysudoku.ui.StatsActivity$PlaceholderFragment">
 
     <LinearLayout
         android:layout_width="fill_parent"
@@ -86,6 +86,7 @@
         </LinearLayout>
     </LinearLayout>
 
+
     <LinearLayout
         android:layout_width="fill_parent"
         android:layout_height="0dp"
@@ -105,7 +106,7 @@
         android:layout_width="fill_parent"
         android:layout_height="0dp"
         android:layout_weight="4"
-        android:weightSum="3"
+        android:weightSum="4"
         android:orientation="vertical">
         <!-- ### first row -->
         <LinearLayout
@@ -310,6 +311,71 @@
         </LinearLayout>
 
 
+        <LinearLayout
+            android:layout_width="match_parent"
+            android:layout_height="0dp"
+            android:layout_weight="1">
+
+            <RelativeLayout
+                android:layout_width="0dp"
+                android:layout_height="fill_parent"
+                android:layout_weight="1"
+                android:gravity="center_vertical">
+                <RatingBar
+                    android:layout_width="wrap_content"
+                    android:layout_height="wrap_content"
+                    android:numStars="3"
+                    android:layout_gravity="center"
+                    android:id="@+id/fourth_diff_bar"
+                    android:layout_below="@+id/fourth_diff_text"
+                    style="?android:attr/ratingBarStyleSmall"/>
+                <TextView
+                    android:layout_width="wrap_content"
+                    android:layout_height="wrap_content"
+                    android:text="diffi"
+                    android:id="@+id/fourth_diff_text"
+                    android:gravity="center_vertical"/>
+            </RelativeLayout>
+
+            <RelativeLayout
+                android:layout_width="0dp"
+                android:layout_height="fill_parent"
+                android:layout_weight="1"
+                android:gravity="center_vertical">
+                <TextView
+                    android:layout_width="wrap_content"
+                    android:layout_height="wrap_content"
+                    android:text="@string/average_time"
+                    android:id="@+id/fourth_av_text"/>
+                <TextView
+                    android:layout_width="wrap_content"
+                    android:layout_height="wrap_content"
+                    android:text="0"
+                    android:id="@+id/fourth_ava_time"
+                    android:gravity="center_vertical"
+                    android:layout_below="@+id/fourth_av_text"/>
+            </RelativeLayout>
+            <RelativeLayout
+                android:layout_width="0dp"
+                android:layout_height="fill_parent"
+                android:layout_weight="1"
+                android:gravity="center_vertical">
+                <TextView
+                    android:layout_width="wrap_content"
+                    android:layout_height="wrap_content"
+                    android:text="@string/min_time"
+                    android:id="@+id/fourth_min_text"/>
+                <TextView
+                    android:layout_width="wrap_content"
+                    android:layout_height="wrap_content"
+                    android:text="0"
+                    android:id="@+id/fourth_min_time"
+                    android:gravity="center_vertical"
+                    android:layout_below="@+id/fourth_min_text"/>
+            </RelativeLayout>
+
+        </LinearLayout>
+
     </LinearLayout>
 
 
diff --git a/app/src/main/res/menu/menu_drawer_main.xml b/app/src/main/res/menu/menu_drawer_main.xml
index 222c2a7..f47ca5a 100644
--- a/app/src/main/res/menu/menu_drawer_main.xml
+++ b/app/src/main/res/menu/menu_drawer_main.xml
@@ -1,9 +1,16 @@
 <?xml version="1.0" encoding="utf-8"?>
 <menu xmlns:android="http://schemas.android.com/apk/res/android">
-    <item android:id="@+id/nav_highscore_main" android:icon="@android:drawable/ic_menu_myplaces"
-        android:title="@string/menu_highscore" />
 
-    <group android:id="@+id/group2">
+    <group android:id="@+id/group4"
+        android:checkableBehavior="all">
+        <item android:id="@+id/nav_newgame_main" android:icon="@android:drawable/ic_menu_today"
+            android:title="@string/menu_main" />
+        <item android:id="@+id/nav_highscore_main" android:icon="@android:drawable/ic_menu_myplaces"
+            android:title="@string/menu_highscore" />
+    </group>
+
+    <group android:id="@+id/group2"
+        android:checkableBehavior="all">
         <item android:id="@+id/menu_settings_main" android:icon="@android:drawable/ic_menu_manage"
             android:title="@string/menu_settings" />
         <item android:id="@+id/menu_help_main" android:icon="@android:drawable/ic_menu_help"
diff --git a/app/src/main/res/values/strings.xml b/app/src/main/res/values/strings.xml
index 2e4138c..35fed86 100644
--- a/app/src/main/res/values/strings.xml
+++ b/app/src/main/res/values/strings.xml
@@ -57,7 +57,7 @@
 
     <!-- ###ABOUT### -->
     <string name="app_name_long" translatable="false">Privacy Friendly Sudoku</string>
-    <string name="version_number" translatable="false">2.0.1</string>
+    <string name="version_number" translatable="false">2.1.1</string>
     <string name="about_author">Author:</string>
     <string name="about_author_names" translatable="false">Christopher Beckmann, Timm Lippert</string>
     <string name="about_author_contributors">and contributors.</string>
@@ -140,4 +140,6 @@
     <string name="help_permissions_summary">Privacy Friendly Sudoku does not use any permissions.</string>
     <string name="okay">Okay</string>
     <string name="view_help">View Help</string>
+    <string name="difficulty_challenge">Challenge</string>
+    <string name="pref_highlightInputError">Highlight input mistakes</string>
 </resources>
diff --git a/app/src/main/res/xml/pref_settings_general.xml b/app/src/main/res/xml/pref_settings_general.xml
index 173e752..793e450 100644
--- a/app/src/main/res/xml/pref_settings_general.xml
+++ b/app/src/main/res/xml/pref_settings_general.xml
@@ -41,6 +41,11 @@
             android:title="@string/pref_highlight_notes"
             android:summary=""
             android:defaultValue="true"/>
+        <SwitchPreference android:id="@+id/pref_highlightInputError"
+            android:key="pref_highlightInputError"
+            android:title="@string/pref_highlightInputError"
+            android:summary=""
+            android:defaultValue="true"/>
     </PreferenceCategory>
 
     <!-- NOTE: EditTextPreference accepts EditText attributes. -->
diff --git a/build.gradle b/build.gradle
index c20bca1..d0aa704 100644
--- a/build.gradle
+++ b/build.gradle
@@ -5,7 +5,7 @@ buildscript {
         jcenter()
     }
     dependencies {
-        classpath 'com.android.tools.build:gradle:2.2.2'
+        classpath 'com.android.tools.build:gradle:2.3.2'
 
         // NOTE: Do not place your application dependencies here; they belong
         // in the individual module build.gradle files
diff --git a/gradle/wrapper/gradle-wrapper.properties b/gradle/wrapper/gradle-wrapper.properties
index deccf0c..2509f5b 100644
--- a/gradle/wrapper/gradle-wrapper.properties
+++ b/gradle/wrapper/gradle-wrapper.properties
@@ -1,6 +1,6 @@
-#Wed Oct 05 22:51:31 CEST 2016
+#Thu May 18 12:33:34 CEST 2017
 distributionBase=GRADLE_USER_HOME
 distributionPath=wrapper/dists
 zipStoreBase=GRADLE_USER_HOME
 zipStorePath=wrapper/dists
-distributionUrl=https\://services.gradle.org/distributions/gradle-2.14.1-all.zip
+distributionUrl=https\://services.gradle.org/distributions/gradle-3.3-all.zip