Refactor permission code

- Remove write permission (was never needed)
- Only use read permission for Android 5 and 6
- Simplify logic by mocking a valid permission result if permission
  already granted

app/src/main/java/protect/card_locker/PermissionUtils.java

@@ -0,0 +1,79 @@
+package protect.card_locker;
+
+import android.Manifest;
+import android.app.Activity;
+import android.content.pm.PackageManager;
+import android.os.Build;
+
+import androidx.core.app.ActivityCompat;
+import androidx.core.content.ContextCompat;
+
+public class PermissionUtils {
+    /**
+     * Check if storage read permission is needed.
+     *
+     * This is only necessary on Android 6.0 (Marshmallow) and below. See
+     * https://github.com/CatimaLoyalty/Android/issues/979 for more info.
+     *
+     * @param activity
+     * @return
+     */
+    private static boolean needsStorageReadPermission(Activity activity) {
+        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.N) {
+            return false;
+        }
+
+        return ContextCompat.checkSelfPermission(activity, android.Manifest.permission.READ_EXTERNAL_STORAGE) != PackageManager.PERMISSION_GRANTED;
+    }
+
+    /**
+     * Check if camera permission is needed.
+     *
+     * @param activity
+     * @return
+     */
+    public static boolean needsCameraPermission(Activity activity) {
+        // Android only introduced the runtime permission system in Marshmallow (Android 6.0)
+        if (Build.VERSION.SDK_INT < Build.VERSION_CODES.M) {
+            return false;
+        }
+
+        return ContextCompat.checkSelfPermission(activity, android.Manifest.permission.CAMERA) != PackageManager.PERMISSION_GRANTED;
+    }
+
+    /**
+     * Call onRequestPermissionsResult after storage read permission was granted.
+     * Mocks a successful grant if a grant is not necessary.
+     *
+     * @param activity
+     * @param requestCode
+     */
+    public static void requestStorageReadPermission(Activity activity, int requestCode) {
+        String[] permissions = new String[]{ android.Manifest.permission.READ_EXTERNAL_STORAGE };
+        int[] mockedResults = new int[]{ PackageManager.PERMISSION_GRANTED };
+
+        if (needsStorageReadPermission(activity)) {
+            ActivityCompat.requestPermissions(activity, permissions, requestCode);
+        } else {
+            activity.onRequestPermissionsResult(requestCode, permissions, mockedResults);
+        }
+    }
+
+    /**
+     * Call onRequestPermissionsResult after camera permission was granted.
+     * Mocks a successful grant if a grant is not necessary.
+     *
+     * @param activity
+     * @param requestCode
+     */
+    public static void requestCameraPermission(Activity activity, int requestCode) {
+        String[] permissions = new String[]{ Manifest.permission.CAMERA };
+        int[] mockedResults = new int[]{ PackageManager.PERMISSION_GRANTED };
+
+        if (needsCameraPermission(activity)) {
+            ActivityCompat.requestPermissions(activity, permissions, requestCode);
+        } else {
+            activity.onRequestPermissionsResult(requestCode, permissions, mockedResults);
+        }
+    }
+}