Allow merging when moving pages

assets/page/actions.js

@@ -13,6 +13,11 @@ function encodePickedPath(p) {
 // re-fetching, so a server-side mutation wouldn't be reflected. Instead,
 // rewrite the current entry's URL via history.replaceState, then reload — the
 // reload always re-fetches and preserves the (new) URL including its fragment.
+function navigateReplace(target) {
+    window.history.replaceState(null, '', target);
+    window.location.reload();
+}
+
 function postReplace(action, body, target) {
     var init = { method: 'POST', redirect: 'manual' };
     if (body) {
@@ -21,8 +26,7 @@ function postReplace(action, body, target) {
     }
     fetch(action, init).then(function (res) {
         if (res.type === 'opaqueredirect' || res.ok) {
-            window.history.replaceState(null, '', target);
+            navigateReplace(target);
-            window.location.reload();
             return;
         }
         return res.text().then(function (msg) {
@@ -71,6 +75,38 @@ function newPage() {
     });
 }
 
+// submitMove POSTs a move and navigates on success. When the server reports
+// the destination folder already exists but can be merged (the source carries
+// a page and the destination has none), it asks the user to confirm and
+// retries the same move with &merge=1.
+function submitMove(action, target) {
+    fetch(action, { method: 'POST', redirect: 'manual' }).then(function (res) {
+        if (res.type === 'opaqueredirect' || res.ok) {
+            navigateReplace(target);
+            return;
+        }
+        if (res.status === 409 && res.headers.get('X-Merge-Available') === '1') {
+            openModal({
+                title: 'Merge folders?',
+                body: 'The destination folder already exists but has no page of its own. Merge this page and its contents into it?',
+                confirm: {
+                    label: 'MERGE',
+                    onConfirm: function () {
+                        closeModal();
+                        submitMove(action + '&merge=1', target);
+                    }
+                }
+            });
+            return;
+        }
+        return res.text().then(function (msg) {
+            alert(msg || ('Request failed (' + res.status + ')'));
+        });
+    }).catch(function () {
+        alert('Network error');
+    });
+}
+
 function movePage() {
     var current = decodeURIComponent(window.location.pathname).replace(/\/+$/, '');
     if (!current) return;
@@ -121,7 +157,7 @@ function movePage() {
                         if (linksCheckbox.checked) action += '&links=1';
                         var target = encodePickedPath(dest) + '/';
                         closeModal();
-                        postReplace(action, null, target);
+                        submitMove(action, target);
                     }
                 }
             });

main.go

@@ -360,7 +360,7 @@ func (h *handler) handlePost(w http.ResponseWriter, r *http.Request, urlPath, fs
 		return
 	}
 	if _, ok := query["move"]; ok {
-		h.handleMove(w, r, urlPath, fsPath, query.Get("move"), query.Has("links"))
+		h.handleMove(w, r, urlPath, fsPath, query.Get("move"), query.Has("links"), query.Has("merge"))
 		return
 	}
 	if query.Has("toggle") {

moves.go

@@ -14,7 +14,14 @@ import (
 // updateLinks is true it also rewrites every [[...]] wiki link across the
 // tree that targets the old path or any descendant; rewritten files are held
 // in memory for rollback.
-func (h *handler) handleMove(w http.ResponseWriter, r *http.Request, srcURL, srcFsPath, dstURL string, updateLinks bool) {
+//
+// If the destination folder already exists it is normally a hard conflict.
+// The one exception is a merge: when the source carries a page (index.md) and
+// the destination folder has none, the source's contents can fill the empty
+// container without clobbering anything. That merge only proceeds when merge
+// is true; otherwise the client is told a merge is available so it can ask the
+// user to confirm.
+func (h *handler) handleMove(w http.ResponseWriter, r *http.Request, srcURL, srcFsPath, dstURL string, updateLinks, merge bool) {
 	oldPath := normalizeMovePath(srcURL)
 	if oldPath == "/" {
 		http.Error(w, "cannot move wiki root", http.StatusBadRequest)
@@ -40,9 +47,31 @@ func (h *handler) handleMove(w http.ResponseWriter, r *http.Request, srcURL, src
 		return
 	}
 	dstFsPath := filepath.Join(h.root, filepath.FromSlash(strings.TrimPrefix(newPath, "/")))
-	if _, err := os.Stat(dstFsPath); err == nil {
+
-		http.Error(w, "destination already exists", http.StatusConflict)
+	// Decide between a plain rename and a merge into an existing destination.
-		return
+	merging := false
+	if dstInfo, err := os.Stat(dstFsPath); err == nil {
+		if !canMergeMove(srcFsPath, dstFsPath, dstInfo) {
+			http.Error(w, "destination already exists", http.StatusConflict)
+			return
+		}
+		if !merge {
+			// Ask the client to confirm the merge. The header lets it tell
+			// this apart from an ordinary conflict.
+			w.Header().Set("X-Merge-Available", "1")
+			http.Error(w, "destination already exists — merge folders?", http.StatusConflict)
+			return
+		}
+		conflict, err := firstMergeConflict(srcFsPath, dstFsPath)
+		if err != nil {
+			http.Error(w, "merge check failed: "+err.Error(), http.StatusInternalServerError)
+			return
+		}
+		if conflict != "" {
+			http.Error(w, "cannot merge: "+conflict+" exists in both folders", http.StatusConflict)
+			return
+		}
+		merging = true
 	}
 
 	// Phase 1: optionally walk the tree and rewrite every index.md that
@@ -88,17 +117,84 @@ func (h *handler) handleMove(w http.ResponseWriter, r *http.Request, srcURL, src
 		}
 	}
 
-	// Phase 3: rename the source folder into place.
+	// Phase 3: move the source into place. A plain move renames the whole
-	if err := os.Rename(srcFsPath, dstFsPath); err != nil {
+	// folder; a merge moves the source's entries into the existing
-		rollbackRewrites(rewritten)
+	// destination and drops the emptied source.
-		http.Error(w, "rename failed: "+err.Error(), http.StatusInternalServerError)
+	if merging {
-		return
+		if err := mergeFolder(srcFsPath, dstFsPath); err != nil {
+			rollbackRewrites(rewritten)
+			http.Error(w, "merge failed: "+err.Error(), http.StatusInternalServerError)
+			return
+		}
+		folderIndexMergeSubtree(strings.TrimPrefix(oldPath, "/"), strings.TrimPrefix(newPath, "/"))
+	} else {
+		if err := os.Rename(srcFsPath, dstFsPath); err != nil {
+			rollbackRewrites(rewritten)
+			http.Error(w, "rename failed: "+err.Error(), http.StatusInternalServerError)
+			return
+		}
+		folderIndexRenameSubtree(strings.TrimPrefix(oldPath, "/"), strings.TrimPrefix(newPath, "/"))
 	}
-	folderIndexRenameSubtree(strings.TrimPrefix(oldPath, "/"), strings.TrimPrefix(newPath, "/"))
 
 	http.Redirect(w, r, wikiTargetHref(newPath), http.StatusSeeOther)
 }
 
+// canMergeMove reports whether moving onto an existing destination should
+// merge rather than conflict. Merging is allowed only when the destination is
+// a folder with no page of its own (no index.md) and the source has one — so
+// the source's page fills the empty destination without overwriting content.
+func canMergeMove(srcFsPath, dstFsPath string, dstInfo os.FileInfo) bool {
+	if !dstInfo.IsDir() {
+		return false
+	}
+	return hasIndexFile(srcFsPath) && !hasIndexFile(dstFsPath)
+}
+
+// hasIndexFile reports whether dir contains a regular index.md.
+func hasIndexFile(dir string) bool {
+	info, err := os.Stat(filepath.Join(dir, "index.md"))
+	return err == nil && info.Mode().IsRegular()
+}
+
+// firstMergeConflict returns the name of the first source entry that already
+// exists in the destination, or "" when the merge can proceed without
+// overwriting anything. index.md cannot collide here: canMergeMove already
+// established the destination has none.
+func firstMergeConflict(srcFsPath, dstFsPath string) (string, error) {
+	entries, err := os.ReadDir(srcFsPath)
+	if err != nil {
+		return "", err
+	}
+	for _, e := range entries {
+		_, err := os.Lstat(filepath.Join(dstFsPath, e.Name()))
+		if err == nil {
+			return e.Name(), nil
+		}
+		if !os.IsNotExist(err) {
+			return "", err
+		}
+	}
+	return "", nil
+}
+
+// mergeFolder moves every entry from srcFsPath into dstFsPath, then removes
+// the now-empty source. Callers must run firstMergeConflict beforehand so no
+// rename overwrites an existing destination entry.
+func mergeFolder(srcFsPath, dstFsPath string) error {
+	entries, err := os.ReadDir(srcFsPath)
+	if err != nil {
+		return err
+	}
+	for _, e := range entries {
+		from := filepath.Join(srcFsPath, e.Name())
+		to := filepath.Join(dstFsPath, e.Name())
+		if err := os.Rename(from, to); err != nil {
+			return fmt.Errorf("move %s: %w", e.Name(), err)
+		}
+	}
+	return os.Remove(srcFsPath)
+}
+
 // handleDelete removes the folder at fsPath (URL urlPath) and redirects to
 // the parent. Refuses to touch the wiki root.
 func (h *handler) handleDelete(w http.ResponseWriter, r *http.Request, urlPath, fsPath string) {

search.go

@@ -335,6 +335,38 @@ func folderIndexRenameSubtree(oldRel, newRel string) {
 	folderIndex.entries = out
 }
 
+// folderIndexMergeSubtree updates the index after a merge move: it drops the
+// source root entry (that folder is gone) and rewrites every descendant's
+// prefix to live under newRel. Unlike folderIndexRenameSubtree it does not add
+// a newRel entry, since the destination folder already exists in the index.
+func folderIndexMergeSubtree(oldRel, newRel string) {
+	oldRel = strings.Trim(oldRel, "/")
+	newRel = strings.Trim(newRel, "/")
+	if oldRel == "" || newRel == "" {
+		return
+	}
+	oldPrefix := oldRel + "/"
+	folderIndex.Lock()
+	defer folderIndex.Unlock()
+	old := folderIndex.entries
+	out := make([]folderEntry, 0, len(old))
+	for _, e := range old {
+		switch {
+		case e.Path == oldRel:
+			continue
+		case strings.HasPrefix(e.Path, oldPrefix):
+			out = append(out, folderEntry{
+				Path:       newRel + "/" + strings.TrimPrefix(e.Path, oldPrefix),
+				NameLower:  e.NameLower,
+				NameTokens: e.NameTokens,
+			})
+		default:
+			out = append(out, e)
+		}
+	}
+	folderIndex.entries = out
+}
+
 // resolveWalkRoot resolves symlinks so WalkDir descends into the real tree
 // even when the configured wiki root is itself a symlink (as on the NAS).
 func resolveWalkRoot(root string) string {