Fix scroll- and page change handlers

invui/src/main/java/xyz/xenondevs/invui/gui/AbstractPagedGui.java

@@ -47,14 +47,29 @@ public abstract class AbstractPagedGui<C> extends AbstractGui implements PagedGu
     
     @Override
     public void setPage(int page) {
-        int previous = currentPage;
+        int previousPage = currentPage;
-        currentPage = page;
+        int newPage = correctPage(page);
+        
+        if (previousPage == newPage)
+            return;
+        
+        currentPage = newPage;
         update();
-        if (previous != currentPage) {
+        
-            pageChangeHandlers.forEach(handler -> handler.accept(previous, page));
+        if (pageChangeHandlers != null) {
+            pageChangeHandlers.forEach(handler -> handler.accept(previousPage, newPage));
         }
     }
     
+    private int correctPage(int page) {
+        // page 0 always exist, every positive page exist for infinite pages
+        if (page == 0 || (infinitePages && page > 0))
+            return page;
+        
+        // 0 <= page < pageAmount
+        return Math.max(0, Math.min(page, getPageAmount() - 1));
+    }
+    
     @Override
     public boolean hasNextPage() {
         return currentPage < getPageAmount() - 1 || infinitePages;
@@ -66,19 +81,10 @@ public abstract class AbstractPagedGui<C> extends AbstractGui implements PagedGu
     }
     
     protected void update() {
-        correctPage();
         updateControlItems();
         updatePageContent();
     }
     
-    private void correctPage() {
-        if (currentPage == 0 || infinitePages) return;
-        
-        int pageAmount = getPageAmount();
-        if (currentPage < 0 || pageAmount <= 0) currentPage = 0;
-        else if (currentPage >= pageAmount) currentPage = pageAmount - 1;
-    }
-    
     private void updatePageContent() {
         List<SlotElement> slotElements = getPageElements(currentPage);
         

invui/src/main/java/xyz/xenondevs/invui/gui/AbstractScrollGui.java

@@ -20,6 +20,7 @@ public abstract class AbstractScrollGui<C> extends AbstractGui implements Scroll
     private final int lineLength;
     private final int lineAmount;
     private final int[] contentListSlots;
+    private int currentLine;
     private int offset;
     
     private List<BiConsumer<Integer, Integer>> scrollHandlers;
@@ -50,12 +51,33 @@ public abstract class AbstractScrollGui<C> extends AbstractGui implements Scroll
     
     @Override
     public int getCurrentLine() {
-        return offset / lineLength;
+        return currentLine;
     }
     
     @Override
     public void setCurrentLine(int line) {
+        int previousLine = currentLine;
+        int newLine = correctLine(line);
+        
+        if (previousLine == newLine)
+            return;
+        
+        this.currentLine = line;
         this.offset = line * lineLength;
+        update();
+        
+        if (scrollHandlers != null) {
+            scrollHandlers.forEach(handler -> handler.accept(previousLine, newLine));
+        }
+    }
+    
+    private int correctLine(int line) {
+        // line 0 always exists, every positive line exists for infinite lines
+        if (line == 0 || (infiniteLines && line > 0))
+            return 0;
+        
+        // 0 <= line <= maxLine
+        return Math.max(0, Math.min(line, getMaxLine()));
     }
     
     @Override
@@ -69,39 +91,23 @@ public abstract class AbstractScrollGui<C> extends AbstractGui implements Scroll
     
     @Override
     public void scroll(int lines) {
-        if (lines == 0) return;
+        if (lines == 0)
+            return;
         
         if (canScroll(lines)) {
             setCurrentLine(getCurrentLine() + lines);
-            update();
         } else if (lines > 1) {
             setCurrentLine(getMaxLine());
-            update();
         } else if (lines < -1) {
             setCurrentLine(0);
-            update();
         }
-        
     }
     
     protected void update() {
-        correctLine();
         updateControlItems();
         updateContent();
     }
     
-    private void correctLine() {
-        if (offset == 0 || infiniteLines) return;
-        
-        if (offset < 0) {
-            offset = 0;
-        } else {
-            int currentLine = getCurrentLine();
-            int maxLineIndex = getMaxLine();
-            if (currentLine >= maxLineIndex) setCurrentLine(maxLineIndex);
-        }
-    }
-    
     private void updateContent() {
         List<? extends SlotElement> slotElements = getElements(offset, contentListSlots.length + offset);