Implement purchase check

Author: patzly

app/build.gradle

@@ -52,4 +52,5 @@ android {
 }
 
 dependencies {
+    implementation 'androidx.appcompat:appcompat:1.3.1'
 }

app/src/main/AndroidManifest.xml

@@ -25,6 +25,20 @@
   <application
     android:allowBackup="false"
     android:icon="@mipmap/ic_launcher"
-    android:label="@string/app_name" />
+    android:label="@string/app_name"
+    android:theme="@style/Theme.AppCompat">
+
+    <activity
+      android:name=".MainActivity"
+      android:exported="true">
+
+      <intent-filter>
+        <action android:name="android.intent.action.MAIN" />
+        <category android:name="android.intent.category.INFO" />
+      </intent-filter>
+
+    </activity>
+
+  </application>
 
 </manifest>

app/src/main/java/xyz/zedler/patrick/grocy/unlock/MainActivity.java

@@ -0,0 +1,51 @@
+/*
+ * This file is part of Grocy Android.
+ *
+ * Grocy Android is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * Grocy Android is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with Grocy Android. If not, see http://www.gnu.org/licenses/.
+ *
+ * Copyright (c) 2020-2021 by Patrick Zedler and Dominic Zedler
+ */
+
+package xyz.zedler.patrick.grocy.unlock;
+
+import android.content.pm.PackageManager.NameNotFoundException;
+import android.os.Build;
+import android.os.Bundle;
+import androidx.annotation.Nullable;
+import androidx.appcompat.app.AppCompatActivity;
+
+public class MainActivity extends AppCompatActivity {
+
+  private final static int PURCHASED = 1;
+  private final static int NOT_PURCHASED = 0;
+
+  @Override
+  protected void onCreate(@Nullable Bundle savedInstanceState) {
+    super.onCreate(savedInstanceState);
+
+    try {
+      String packageName = getApplicationContext().getPackageName();
+      String source;
+      if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.R) {
+        source = getPackageManager().getInstallSourceInfo(packageName).getInitiatingPackageName();
+      } else {
+        source = getPackageManager().getInstallerPackageName(packageName);
+      }
+      setResult(source != null && source.equals("com.android.vending") ? PURCHASED : NOT_PURCHASED);
+    } catch (Exception ignored) {
+    }
+
+    finish();
+  }
+}