# PDPageTree.java

    /*
     * Licensed to the Apache Software Foundation (ASF) under one or more
     * contributor license agreements.  See the NOTICE file distributed with
     * this work for additional information regarding copyright ownership.
     * The ASF licenses this file to You under the Apache License, Version 2.0
     * (the "License"); you may not use this file except in compliance with
     * the License.  You may obtain a copy of the License at
     *
     *      http://www.apache.org/licenses/LICENSE-2.0
     *
     * Unless required by applicable law or agreed to in writing, software
     * distributed under the License is distributed on an "AS IS" BASIS,
     * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
     * See the License for the specific language governing permissions and
     * limitations under the License.
     */
    package org.apache.pdfbox.pdmodel;

    import java.util.ArrayDeque;
    import java.util.Iterator;
    import java.util.Queue;
    import org.apache.pdfbox.cos.COSArray;
    import org.apache.pdfbox.cos.COSBase;
    import org.apache.pdfbox.cos.COSDictionary;
    import org.apache.pdfbox.cos.COSInteger;
    import org.apache.pdfbox.cos.COSName;

    import org.apache.pdfbox.pdmodel.common.COSObjectable;

    import java.util.ArrayList;
    import java.util.HashSet;
    import java.util.List;
    import java.util.NoSuchElementException;
    import java.util.Set;
    import org.apache.commons.logging.Log;
    import org.apache.commons.logging.LogFactory;

    /**
     * The page tree, which defines the ordering of pages in the document in an efficient manner.
     *
     * @author John Hewson
     */
    public class PDPageTree implements COSObjectable, Iterable<PDPage>
    {
        private static final Log LOG = LogFactory.getLog(PDPageTree.class);
        private final COSDictionary root;
        private final PDDocument document; // optional

        private final Set<COSDictionary> pageSet = new HashSet<>();

        /**
         * Constructor for embedding.
         */
        public PDPageTree()
        {
            root = new COSDictionary();
            root.setItem(COSName.TYPE, COSName.PAGES);
            root.setItem(COSName.KIDS, new COSArray());
            root.setItem(COSName.COUNT, COSInteger.ZERO);
            document = null;
        }

        /**
         * Constructor for reading.
         *
         * @param root A page tree root.
         */
        public PDPageTree(COSDictionary root)
        {
            this(root, null);
        }

        /**
         * Constructor for reading.
         *
         * @param root A page tree root.
         * @param document The document which contains "root".
         */
        PDPageTree(COSDictionary root, PDDocument document)
        {
            if (root == null)
            {
                throw new IllegalArgumentException("page tree root cannot be null");
            }
            // repair bad PDFs which contain a Page dict instead of a page tree, see PDFBOX-3154
            if (COSName.PAGE.equals(root.getCOSName(COSName.TYPE)))
            {
                COSArray kids = new COSArray();
                kids.add(root);
                this.root = new COSDictionary();
                this.root.setItem(COSName.KIDS, kids);
                this.root.setInt(COSName.COUNT, 1);
            }
            else
            {
                this.root = root;
            }
            this.document = document;
        }

        /**
         * Returns the given attribute, inheriting from parent tree nodes if necessary.
         *
         * @param node page object
         * @param key the key to look up
         * @return COS value for the given key
         */
        public static COSBase getInheritableAttribute(COSDictionary node, COSName key)
        {
            COSBase value = node.getDictionaryObject(key);
            if (value != null)
            {
                return value;
            }
            COSDictionary parent = node.getCOSDictionary(COSName.PARENT, COSName.P);
            if (parent != null && COSName.PAGES.equals(parent.getCOSName(COSName.TYPE)))
            {
                return getInheritableAttribute(parent, key);
            }

            return null;
        }

        /**
         * Returns an iterator which walks all pages in the tree, in order.
         */
        @Override
        public Iterator<PDPage> iterator()
        {
            return new PageIterator(root);
        }

        /**
         * Helper to get kids from malformed PDFs.
         * @param node page tree node
         * @return list of kids
         */
        private List<COSDictionary> getKids(COSDictionary node)
        {
            List<COSDictionary> result = new ArrayList<>();

            COSArray kids = node.getCOSArray(COSName.KIDS);
            if (kids == null)
            {
                // probably a malformed PDF
                return result;
            }

            for (int i = 0, size = kids.size(); i < size; i++)
            {
                COSBase base = kids.getObject(i);
                if (base instanceof COSDictionary)
                {
                    result.add((COSDictionary) base);
                }
                else
                {
                    LOG.warn("COSDictionary expected, but got " +
                            (base == null ? "null" : base.getClass().getSimpleName()));
                }
            }

            return result;
        }

        /**
         * Iterator which walks all pages in the tree, in order.
         */
        private final class PageIterator implements Iterator<PDPage>
        {
            private final Queue<COSDictionary> queue = new ArrayDeque<>();
            private Set<COSDictionary> set = new HashSet<>();

            private PageIterator(COSDictionary node)
            {
                enqueueKids(node);
                set = null; // release memory, we don't use this anymore
            }

            private void enqueueKids(COSDictionary node)
            {
                if (isPageTreeNode(node))
                {
                    List<COSDictionary> kids = getKids(node);
                    for (COSDictionary kid : kids)
                    {
                        if (set.contains(kid))
                        {
                            // PDFBOX-5009, PDFBOX-3953: prevent stack overflow with malformed PDFs
                            LOG.error("This page tree node has already been visited");
                            continue;
                        }
                        else if (kid.containsKey(COSName.KIDS))
                        {
                            set.add(kid);
                        }
                        enqueueKids(kid);
                    }
                }
                else
                {
                    if (COSName.PAGE.equals(node.getCOSName(COSName.TYPE)))
                    {
                        queue.add(node);
                    }
                    else
                    {
                        LOG.error("Page skipped due to an invalid or missing type "
                                + node.getCOSName(COSName.TYPE));
                    }
                }
            }

            @Override
            public boolean hasNext()
            {
                return !queue.isEmpty();
            }

            @Override
            public PDPage next()
            {
                if (!hasNext())
                {
                    throw new NoSuchElementException();
                }
                COSDictionary next = queue.poll();

                sanitizeType(next);

                ResourceCache resourceCache = document != null ? document.getResourceCache() : null;
                return new PDPage(next, resourceCache);
            }

            @Override
            public void remove()
            {
                throw new UnsupportedOperationException();
            }
        }

        /**
         * Returns the page at the given index.
         *
         * @param index zero-based index
         *
         * @throws IllegalStateException if the requested index isn't found or doesn't point to a valid
         * page dictionary
         * @throws IndexOutOfBoundsException if the requested index is higher than the page count
         */
        public PDPage get(int index)
        {
            COSDictionary dict = get(index + 1, root, 0);

            sanitizeType(dict);

            ResourceCache resourceCache = document != null ? document.getResourceCache() : null;
            return new PDPage(dict, resourceCache);
        }

        private static void sanitizeType(COSDictionary dictionary)
        {
            COSName type = dictionary.getCOSName(COSName.TYPE);
            if (type == null)
            {
                dictionary.setItem(COSName.TYPE, COSName.PAGE);
                return;
            }
            if (!COSName.PAGE.equals(type))
            {
                throw new IllegalStateException("Expected 'Page' but found " + type);
            }
        }

        /**
         * Returns the given COS page using a depth-first search.
         *
         * @param pageNum 1-based page number
         * @param node page tree node to search
         * @param encountered number of pages encountered so far
         * @return COS dictionary of the Page object
         * @throws IllegalStateException if the requested page number isn't found
         * @throws IndexOutOfBoundsException if the requested page number is higher than the page count
         */
        private COSDictionary get(int pageNum, COSDictionary node, int encountered)
        {
            if (pageNum < 1)
            {
                throw new IndexOutOfBoundsException("Index out of bounds: " + pageNum);
            }
            if (pageSet.contains(node))
            {
                pageSet.clear();
                throw new IllegalStateException(
                        "Possible recursion found when searching for page " + pageNum);
            }
            else
            {
                // collect already processed pages to detect possible recursions
                // to avoid a StackOverflowError
                pageSet.add(node);
            }
            if (isPageTreeNode(node))
            {
                int count = node.getInt(COSName.COUNT, 0);
                if (pageNum <= encountered + count)
                {
                    // it's a kid of this node
                    for (COSDictionary kid : getKids(node))
                    {
                        // which kid?
                        if (isPageTreeNode(kid))
                        {
                            int kidCount = kid.getInt(COSName.COUNT, 0);
                            if (pageNum <= encountered + kidCount)
                            {
                                // it's this kid
                                return get(pageNum, kid, encountered);
                            }
                            else
                            {
                                encountered += kidCount;
                            }
                        }
                        else
                        {
                            // single page
                            encountered++;
                            if (pageNum == encountered)
                            {
                                // it's this page
                                return get(pageNum, kid, encountered);
                            }
                        }
                    }

                    throw new IllegalStateException("1-based index not found: " + pageNum);
                }
                else
                {
                    throw new IndexOutOfBoundsException("1-based index out of bounds: " + pageNum);
                }
            }
            else
            {
                if (encountered == pageNum)
                {
                    pageSet.clear();
                    return node;
                }
                else
                {
                    throw new IllegalStateException("1-based index not found: " + pageNum);
                }
            }
        }

        /**
         * Returns true if the node is a page tree node (i.e. and intermediate).
         */
        private boolean isPageTreeNode(COSDictionary node)
        {
            // some files such as PDFBOX-2250-229205.pdf don't have Pages set as the Type, so we have
            // to check for the presence of Kids too
            return node != null &&
                    (COSName.PAGES.equals(node.getCOSName(COSName.TYPE))
                            || node.containsKey(COSName.KIDS));
        }

        /**
         * Returns the index of the given page, or -1 if it does not exist.
         *
         * @param page The page to search for.
         * @return the zero-based index of the given page, or -1 if the page is not found.
         */
        public int indexOf(PDPage page)
        {
            SearchContext context = new SearchContext(page);
            if (findPage(context, root))
            {
                return context.index;
            }
            return -1;
        }

        private boolean findPage(SearchContext context, COSDictionary node)
        {
            for (COSDictionary kid : getKids(node))
            {
                if (context.found)
                {
                    break;
                }
                if (isPageTreeNode(kid))
                {
                    findPage(context, kid);
                }
                else
                {
                    context.visitPage(kid);
                }
            }
            return context.found;
        }

        private static final class SearchContext
        {
            private final COSDictionary searched;
            private int index = -1;
            private boolean found;

            private SearchContext(PDPage page)
            {
                searched = page.getCOSObject();
            }

            private void visitPage(COSDictionary current)
            {
                index++;
                found = searched == current;
            }
        }

        /**
         * Returns the number of leaf nodes (page objects) that are descendants of this root within the
         * page tree.
         */
        public int getCount()
        {
            return root.getInt(COSName.COUNT, 0);
        }

        @Override
        public COSDictionary getCOSObject()
        {
            return root;
        }

        /**
         * Removes the page with the given index from the page tree.
         * @param index zero-based page index
         */
        public void remove(int index)
        {
            COSDictionary node = get(index + 1, root, 0);
            remove(node);
        }

        /**
         * Removes the given page from the page tree.
         *
         * @param page The page to remove.
         */
        public void remove(PDPage page)
        {
            remove(page.getCOSObject());
        }

        /**
         * Removes the given COS page.
         */
        private void remove(COSDictionary node)
        {
            // remove from parent's kids
            COSDictionary parent = node.getCOSDictionary(COSName.PARENT, COSName.P);
            COSArray kids = parent.getCOSArray(COSName.KIDS);
            if (kids.removeObject(node))
            {
                // update ancestor counts
                do
                {
                    node = node.getCOSDictionary(COSName.PARENT, COSName.P);
                    if (node != null)
                    {
                        node.setInt(COSName.COUNT, node.getInt(COSName.COUNT) - 1);
                    }
                }
                while (node != null);
            }
        }

        /**
         * Adds the given page to this page tree.
         *
         * @param page The page to add.
         */
        public void add(PDPage page)
        {
            // set parent
            COSDictionary node = page.getCOSObject();
            node.setItem(COSName.PARENT, root);

            // todo: re-balance tree? (or at least group new pages into tree nodes of e.g. 20)

            // add to parent's kids
            COSArray kids = root.getCOSArray(COSName.KIDS);
            kids.add(node);

            // update ancestor counts
            do
            {
                node = node.getCOSDictionary(COSName.PARENT, COSName.P);
                if (node != null)
                {
                    node.setInt(COSName.COUNT, node.getInt(COSName.COUNT) + 1);
                }
            }
            while (node != null);
        }

        /**
         * Insert a page before another page within a page tree.
         *
         * @param newPage the page to be inserted.
         * @param nextPage the page that is to be after the new page.
         * @throws IllegalArgumentException if one attempts to insert a page that isn't part of a page
         * tree.
         */
        public void insertBefore(PDPage newPage, PDPage nextPage)
        {
            COSDictionary nextPageDict = nextPage.getCOSObject();
            COSDictionary parentDict = nextPageDict.getCOSDictionary(COSName.PARENT, COSName.P);
            COSArray kids = parentDict.getCOSArray(COSName.KIDS);
            boolean found = false;
            for (int i = 0; i < kids.size(); ++i)
            {
                COSDictionary pageDict = (COSDictionary) kids.getObject(i);
                if (pageDict == nextPage.getCOSObject())
                {
                    kids.add(i, newPage.getCOSObject());
                    newPage.getCOSObject().setItem(COSName.PARENT, parentDict);
                    found = true;
                    break;
                }
            }
            if (!found)
            {
                throw new IllegalArgumentException("attempted to insert before orphan page");
            }
            increaseParents(parentDict);
        }

        /**
         * Insert a page after another page within a page tree.
         *
         * @param newPage the page to be inserted.
         * @param prevPage the page that is to be before the new page.
         * @throws IllegalArgumentException if one attempts to insert a page that isn't part of a page
         * tree.
         */
        public void insertAfter(PDPage newPage, PDPage prevPage)
        {
            COSDictionary prevPageDict = prevPage.getCOSObject();
            COSDictionary parentDict = prevPageDict.getCOSDictionary(COSName.PARENT, COSName.P);
            COSArray kids = parentDict.getCOSArray(COSName.KIDS);
            boolean found = false;
            for (int i = 0; i < kids.size(); ++i)
            {
                COSDictionary pageDict = (COSDictionary) kids.getObject(i);
                if (pageDict == prevPage.getCOSObject())
                {
                    kids.add(i + 1, newPage.getCOSObject());
                    newPage.getCOSObject().setItem(COSName.PARENT, parentDict);
                    found = true;
                    break;
                }
            }
            if (!found)
            {
                throw new IllegalArgumentException("attempted to insert before orphan page");
            }
            increaseParents(parentDict);
        }

        private void increaseParents(COSDictionary parentDict)
        {
            do
            {
                int cnt = parentDict.getInt(COSName.COUNT);
                parentDict.setInt(COSName.COUNT, cnt + 1);
                parentDict = parentDict.getCOSDictionary(COSName.PARENT, COSName.P);
            }
            while (parentDict != null);
        }
    }