PdfStructureTreeRoot update - fixing Page linking

openpdf/src/main/java/com/lowagie/text/pdf/PdfDocument.java

@@ -977,7 +977,10 @@ public boolean newPage() {
 
             // [F12] we add tag info
             if (writer.isTagged()) {
-                page.put(PdfName.STRUCTPARENTS, new PdfNumber(writer.getCurrentPageNumber() - 1));
+                //connecting /NUMS array entry (pageIdValue) with Page via /STRUCTPARENTS value
+                int pageIdValue = writer.getStructureTreeRoot()
+                        .getOrCreatePageKey(writer.getCurrentPageNumber() - 1);
+                page.put(PdfName.STRUCTPARENTS, new PdfNumber(pageIdValue));
             }
 
             if (text.size() > textEmptySize) {

openpdf/src/main/java/com/lowagie/text/pdf/PdfStructureTreeRoot.java

@@ -130,19 +130,29 @@ public int addExistingObject(PdfIndirectReference reference) {
         return key;
     }
 
-    void setPageMark(int page, PdfIndirectReference reference) {
-        Integer entryForPageArray = pageKeysMap.get(page);
+    void setPageMark(int pageNumber, PdfIndirectReference reference) {
+        PdfArray pageArray = (PdfArray) parentTree.get(getOrCreatePageKey(pageNumber));
+        pageArray.add(reference);
+    }
+
+    /**
+     * Returns array ID for a page-related entry or creates a new one if not exists.
+     * Can be used for STRUCTPARENTS tag value
+     *
+     * @param pageNumber number of page for which the ID is required
+     * @return Optional with array ID, empty Optional otherwise
+     */
+    int getOrCreatePageKey(int pageNumber) {
+        Integer entryForPageArray = pageKeysMap.get(pageNumber);
         if (entryForPageArray == null) {
             //putting page array
             PdfArray ar = new PdfArray();
             entryForPageArray = parentTreeNextKey;
             parentTree.put(entryForPageArray, ar);
             parentTreeNextKey++;
-            pageKeysMap.put(page, entryForPageArray);
+            pageKeysMap.put(pageNumber, entryForPageArray);
         }
-
-        PdfArray pageArray = (PdfArray) parentTree.get(entryForPageArray);
-        pageArray.add(reference);
+        return entryForPageArray;
     }
 
     private void nodeProcess(PdfDictionary dictionary, PdfIndirectReference reference)
@@ -154,8 +164,7 @@ private void nodeProcess(PdfDictionary dictionary, PdfIndirectReference referenc
             for (int k = 0; k < ar.size(); ++k) {
                 PdfObject pdfObj = ar.getDirectObject(k);
 
-                if (pdfObj instanceof PdfStructureElement) {
-                    PdfStructureElement e = (PdfStructureElement) pdfObj;
+                if (pdfObj instanceof PdfStructureElement e) {
                     ar.set(k, e.getReference());
                     nodeProcess(e, e.getReference());
                 } else if (pdfObj instanceof PdfIndirectReference) {
@@ -171,12 +180,12 @@ private void nodeProcess(PdfDictionary dictionary, PdfIndirectReference referenc
     void buildTree() throws IOException {
         Map<Integer, PdfIndirectReference> numTree = new HashMap<>();
         for (Integer i : parentTree.keySet()) {
-            PdfObject ar = parentTree.get(i);
-            if (ar instanceof PdfIndirectReference) {
+            PdfObject pdfObj = parentTree.get(i);
+            if (pdfObj instanceof PdfIndirectReference pdfRef) {
                 //saving the reference to the object which was already added to the body
-                numTree.put(i, (PdfIndirectReference) ar);
+                numTree.put(i, pdfRef);
             } else {
-                numTree.put(i, writer.addToBody(ar).getIndirectReference());
+                numTree.put(i, writer.addToBody(pdfObj).getIndirectReference());
             }
         }
         PdfDictionary dicTree = PdfNumberTree.writeTree(numTree, writer);

openpdf/src/main/java/com/lowagie/text/pdf/PdfWriter.java

@@ -1093,15 +1093,26 @@ public PdfIndirectReference getPageReference(int page) {
      *
      * @return a page number
      */
-
     public int getPageNumber() {
         return pdf.getPageNumber();
     }
 
-    PdfIndirectReference getCurrentPage() {
+    /**
+     * Retrieves a reference to the current page of the document.
+     * The current page is typically the last page that was modified or accessed.
+     *
+     * @return a {@link PdfIndirectReference} object pointing to the current page in the PDF document.
+     */
+    public PdfIndirectReference getCurrentPage() {
         return getPageReference(currentPageNumber);
     }
 
+    /**
+     * Returns the number of the current page in the document.
+     * The current page is typically the last page that was modified or accessed.
+     *
+     * @return the current page number.
+     */
     public int getCurrentPageNumber() {
         return currentPageNumber;
     }

openpdf/src/test/java/com/lowagie/text/pdf/PdfStructureTreeRootTest.java

@@ -75,7 +75,7 @@ void buildTreeShouldGenerateParentTreeWithoutException() throws IOException {
 
         PdfStructureTreeRoot treeRoot = new PdfStructureTreeRoot(mockWriter);
 
-        assertDoesNotThrow(() -> treeRoot.buildTree());
+        assertDoesNotThrow(treeRoot::buildTree);
     }
 
     @Test
@@ -86,6 +86,38 @@ void buildTreeShouldHandleIOException() throws IOException {
         PdfStructureTreeRoot treeRoot = new PdfStructureTreeRoot(mockWriter);
         treeRoot.setPageMark(1, mock(PdfIndirectReference.class));
 
-        assertThrows(IOException.class, () -> treeRoot.buildTree());
+        assertThrows(IOException.class, treeRoot::buildTree);
+    }
+
+    @Test
+    void getOrCreatePageKeyShouldCreateNewPageArrayWhenNotExists() {
+        PdfWriter mockWriter = mock(PdfWriter.class);
+        PdfStructureTreeRoot treeRoot = new PdfStructureTreeRoot(mockWriter);
+
+        PdfIndirectReference mockRef = mock(PdfIndirectReference.class);
+
+        int firstKey = treeRoot.addExistingObject(mockRef);
+        assertEquals(0, firstKey);
+
+        int pageKey = treeRoot.getOrCreatePageKey(1);
+        assertEquals(1, pageKey);
+    }
+
+    @Test
+    void getOrCreatePageKeyShouldReturnExistingPageKey() {
+        PdfWriter mockWriter = mock(PdfWriter.class);
+        PdfStructureTreeRoot treeRoot = new PdfStructureTreeRoot(mockWriter);
+
+        PdfIndirectReference mockRef = mock(PdfIndirectReference.class);
+
+        int firstKey = treeRoot.addExistingObject(mockRef);
+        assertEquals(0, firstKey);
+
+        //key should be created when setting page mark
+        treeRoot.setPageMark(1, mock(PdfIndirectReference.class));
+
+        //existing key should be returned
+        int pageKey = treeRoot.getOrCreatePageKey(1);
+        assertEquals(1, pageKey);
     }
 }