From bbe7eac13df60bd924b9e2b2e4c0306e2bdd3904 Mon Sep 17 00:00:00 2001
From: Jean-Baptiste Meyer <jeanbaptiste.meyer@gmail.com>
Date: Sun, 17 May 2026 12:16:36 +0200
Subject: [PATCH] Fix anchor navigation in preview: add heading IDs and
 intercept #fragment clicks (issue #73)

- Add processHeadingIds() to inject GitHub-style id attributes on <h1>-<h6>
  tags so that #fragment anchors have a target element to scroll to
- Intercept #fragment navigation in the SCHEDULED state listener: cancel the
  full page reload and use scrollIntoView() via executeScript instead,
  preventing flicker and correctly scrolling to the heading

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
---
 src/main/java/ui/PreviewPanel.java | 49 ++++++++++++++++++++++++++++++
 1 file changed, 49 insertions(+)

diff --git a/src/main/java/ui/PreviewPanel.java b/src/main/java/ui/PreviewPanel.java
index c7321f8..54b0349 100644
--- a/src/main/java/ui/PreviewPanel.java
+++ b/src/main/java/ui/PreviewPanel.java
@@ -184,6 +184,18 @@ public PreviewPanel() {
             if (newState == Worker.State.SCHEDULED) {
                 String location = webView.getEngine().getLocation();
                 if (location != null && !location.isEmpty() && !location.equals("about:blank")) {
+                    // Ancre interne (#fragment) : défiler vers l'élément sans recharger la page
+                    if (location.contains("#")) {
+                        String fragment = location.substring(location.indexOf('#') + 1);
+                        if (!fragment.isEmpty()) {
+                            webView.getEngine().getLoadWorker().cancel();
+                            webView.getEngine().executeScript(
+                                "var el = document.getElementById('" + fragment.replace("'", "\\'") + "');" +
+                                "if (el) el.scrollIntoView({behavior: 'smooth', block: 'start'});"
+                            );
+                        }
+                        return;
+                    }
                     // Vérifier si c'est un lien vers un fichier .md
                     if (location.toLowerCase().endsWith(".md") || location.toLowerCase().endsWith(".markdown")) {
                         // Annuler la navigation
@@ -267,6 +279,9 @@ private void updatePreview(String markdown, boolean addToHistory) {
         
         String html = htmlRenderer.render(markdownParser.parse(body));
 
+        // ── IDs sur les titres : nécessaires pour la navigation par ancres (#fragment)
+        html = processHeadingIds(html);
+
         // ── Checkboxes : convertir [ ] et [x] en éléments checkbox HTML
         html = processCheckboxes(html);
 
@@ -527,6 +542,40 @@ private String loadResourceAsString(String resourcePath) {
         });
     }
 
+    /**
+     * Injecte un attribut {@code id} GitHub-compatible sur chaque titre HTML ({@code <h1>}–{@code <h6>})
+     * qui n'en possède pas encore. Requis pour que la navigation par ancres (#fragment) fonctionne.
+     */
+    private String processHeadingIds(String html) {
+        Pattern p = Pattern.compile(
+                "<(h[1-6])(\\s[^>]*)?>(.+?)</h[1-6]>",
+                Pattern.CASE_INSENSITIVE | Pattern.DOTALL);
+        Matcher m = p.matcher(html);
+        StringBuffer sb = new StringBuffer();
+        java.util.Map<String, Integer> seen = new java.util.HashMap<>();
+        while (m.find()) {
+            String tag     = m.group(1);
+            String attrs   = m.group(2) != null ? m.group(2) : "";
+            String content = m.group(3);
+            if (attrs.contains("id=")) {
+                m.appendReplacement(sb, Matcher.quoteReplacement(m.group(0)));
+                continue;
+            }
+            String text = content.replaceAll("<[^>]+>", "").trim();
+            String id = text.toLowerCase()
+                    .replaceAll("[^\\w\\s-]", "")
+                    .trim()
+                    .replaceAll("\\s+", "-");
+            int count = seen.getOrDefault(id, 0);
+            seen.put(id, count + 1);
+            String uid = count == 0 ? id : id + "-" + count;
+            m.appendReplacement(sb, Matcher.quoteReplacement(
+                    "<" + tag + attrs + " id=\"" + uid + "\">" + content + "</" + tag + ">"));
+        }
+        m.appendTail(sb);
+        return sb.toString();
+    }
+
     /**
      * Convertit les marqueurs de checkbox Markdown ([ ] et [x]) en éléments HTML checkbox.
      *