From 465d405926c7e22173fe650bf2d417d4633d7990 Mon Sep 17 00:00:00 2001
From: Dan Brown <ssddanbrown@googlemail.com>
Date: Mon, 28 Sep 2020 22:26:50 +0100
Subject: [PATCH] Updated page content related links on content id changes

For #2278
---
 app/Entities/Managers/PageContent.php | 37 +++++++++++++++++++--------
 tests/Entity/PageContentTest.php      | 17 ++++++++++++
 2 files changed, 44 insertions(+), 10 deletions(-)

diff --git a/app/Entities/Managers/PageContent.php b/app/Entities/Managers/PageContent.php
index e417b1caa..a787e5d99 100644
--- a/app/Entities/Managers/PageContent.php
+++ b/app/Entities/Managers/PageContent.php
@@ -2,7 +2,6 @@
 
 use BookStack\Entities\Page;
 use DOMDocument;
-use DOMElement;
 use DOMNodeList;
 use DOMXPath;
 
@@ -44,18 +43,24 @@ class PageContent
         $container = $doc->documentElement;
         $body = $container->childNodes->item(0);
         $childNodes = $body->childNodes;
+        $xPath = new DOMXPath($doc);
 
         // Set ids on top-level nodes
         $idMap = [];
         foreach ($childNodes as $index => $childNode) {
-            $this->setUniqueId($childNode, $idMap);
+            [$oldId, $newId] = $this->setUniqueId($childNode, $idMap);
+            if ($newId && $newId !== $oldId) {
+                $this->updateLinks($xPath, '#' . $oldId, '#' . $newId);
+            }
         }
 
         // Ensure no duplicate ids within child items
-        $xPath = new DOMXPath($doc);
         $idElems = $xPath->query('//body//*//*[@id]');
         foreach ($idElems as $domElem) {
-            $this->setUniqueId($domElem, $idMap);
+            [$oldId, $newId] = $this->setUniqueId($domElem, $idMap);
+            if ($newId && $newId !== $oldId) {
+                $this->updateLinks($xPath, '#' . $oldId, '#' . $newId);
+            }
         }
 
         // Generate inner html as a string
@@ -67,23 +72,34 @@ class PageContent
         return $html;
     }
 
+    /**
+     * Update the all links to the $old location to instead point to $new.
+     */
+    protected function updateLinks(DOMXPath $xpath, string $old, string $new)
+    {
+        $old = str_replace('"', '', $old);
+        $matchingLinks = $xpath->query('//body//*//*[@href="'.$old.'"]');
+        foreach ($matchingLinks as $domElem) {
+            $domElem->setAttribute('href', $new);
+        }
+    }
+
     /**
      * Set a unique id on the given DOMElement.
      * A map for existing ID's should be passed in to check for current existence.
-     * @param DOMElement $element
-     * @param array $idMap
+     * Returns a pair of strings in the format [old_id, new_id]
      */
-    protected function setUniqueId($element, array &$idMap)
+    protected function setUniqueId(\DOMNode $element, array &$idMap): array
     {
         if (get_class($element) !== 'DOMElement') {
-            return;
+            return ['', ''];
         }
 
-        // Overwrite id if not a BookStack custom id
+        // Stop if there's an existing valid id that has not already been used.
         $existingId = $element->getAttribute('id');
         if (strpos($existingId, 'bkmrk') === 0 && !isset($idMap[$existingId])) {
             $idMap[$existingId] = true;
-            return;
+            return [$existingId, $existingId];
         }
 
         // Create an unique id for the element
@@ -100,6 +116,7 @@ class PageContent
 
         $element->setAttribute('id', $newId);
         $idMap[$newId] = true;
+        return [$existingId, $newId];
     }
 
     /**
diff --git a/tests/Entity/PageContentTest.php b/tests/Entity/PageContentTest.php
index 69b46b06e..99547fd17 100644
--- a/tests/Entity/PageContentTest.php
+++ b/tests/Entity/PageContentTest.php
@@ -262,6 +262,23 @@ class PageContentTest extends TestCase
         $this->assertEquals(substr_count($updatedPage->html, "bkmrk-test\""), 1);
     }
 
+    public function test_anchors_referencing_non_bkmrk_ids_rewritten_after_save()
+    {
+        $this->asEditor();
+        $page = Page::first();
+
+        $content = '<h1 id="non-standard-id">test</h1><p><a href="#non-standard-id">link</a></p>';
+        $this->put($page->getUrl(), [
+            'name' => $page->name,
+            'html' => $content,
+            'summary' => ''
+        ]);
+
+        $updatedPage = Page::where('id', '=', $page->id)->first();
+        $this->assertStringContainsString('id="bkmrk-test"', $updatedPage->html);
+        $this->assertStringContainsString('href="#bkmrk-test"', $updatedPage->html);
+    }
+
     public function test_get_page_nav_sets_correct_properties()
     {
         $content = '<h1 id="testa">Hello</h1><h2 id="testb">There</h2><h3 id="testc">Donkey</h3>';