Recover page position when configuration changes

app/src/main/java/eu/kanade/mangafeed/ui/viewer/RightToLeftViewer.java

@@ -25,13 +25,8 @@ public class RightToLeftViewer extends ViewPagerViewer {
     }
 
     @Override
-    public int getCurrentPageFromPos(int position) {
-        return getTotalPages() - position;
-    }
-
-    @Override
-    public int getPosFromPage(Page page) {
-        return getTotalPages() - (page.getPageNumber() + 1);
+    public int getCurrentPageIndex(int viewerPosition) {
+        return getTotalPages() - viewerPosition - 1;
     }
 
     @Override

app/src/main/java/eu/kanade/mangafeed/ui/viewer/VerticalViewer.java

@@ -52,6 +52,12 @@ public class VerticalViewer extends BaseViewer {
         return adapter.getCount();
     }
 
+    @Override
+    public void setSelectedPage(int pageNumber) {
+        // TODO
+        return;
+    }
+
     @Override
     public void onPageListReady(List<Page> pages) {
         adapter.setPages(pages);

app/src/main/java/eu/kanade/mangafeed/ui/viewer/WebtoonViewer.java

@@ -33,6 +33,12 @@ public class WebtoonViewer extends BaseViewer {
         return adapter.getItemCount();
     }
 
+    @Override
+    public void setSelectedPage(int pageNumber) {
+        // TODO
+        return;
+    }
+
     @Override
     public void onPageListReady(List<Page> pages) {
         adapter.setPages(pages);

app/src/main/java/eu/kanade/mangafeed/ui/viewer/base/BaseViewer.java

@@ -20,18 +20,17 @@ public abstract class BaseViewer {
     }
 
     public void updatePageNumber() {
-        activity.onPageChanged(getCurrentPageFromPos(currentPosition), getTotalPages());
+        activity.onPageChanged(getCurrentPageIndex(currentPosition), getTotalPages());
     }
 
-    public int getCurrentPageFromPos(int position) {
-        return position + 1;
-    }
-
-    public int getPosFromPage(Page page) {
-        return page.getPageNumber();
+    // Returns the page index given a position in the viewer. Useful por a right to left viewer,
+    // where the current page is the inverse of the position
+    public int getCurrentPageIndex(int viewerPosition) {
+        return viewerPosition;
     }
 
     public abstract int getTotalPages();
+    public abstract void setSelectedPage(int pageNumber);
     public abstract void onPageListReady(List<Page> pages);
     public abstract boolean onImageTouch(MotionEvent motionEvent);
 }

app/src/main/java/eu/kanade/mangafeed/ui/viewer/base/ViewPagerViewer.java

@@ -65,6 +65,11 @@ public abstract class ViewPagerViewer extends BaseViewer {
         return adapter.getCount();
     }
 
+    @Override
+    public void setSelectedPage(int pageNumber) {
+        viewPager.setCurrentItem(getCurrentPageIndex(pageNumber));
+    }
+
     @Override
     public void onPageListReady(List<Page> pages) {
         adapter.setPages(pages);