Add Undo for book and chapter deletions

- Show an Undo toast after deleting a book from Home; Undo restores the
  folder from the system trash (XDG .trashinfo, URL-decoded path match).
- Chapter delete/cut now snapshots the chapter (title, color, content,
  position) and offers Undo to restore it in place.
- Add reusable showUndoToast/hideUndoToast and #undoToast UI + styles;
  expose restoreBook/restoreChapter over the preload bridge.
- Drop the now-redundant 'cannot be undone' confirm on chapter delete and
  the inaccurate 'permanently removes' wording on book delete.

src/main/chapters.ts

@@ -155,6 +155,32 @@ export function deleteChapter(bookPath: string, id: string): void {
   saveMeta(bookPath, meta);
 }
 
+// Snapshot of a deleted chapter so it can be restored in place (Undo).
+export interface ChapterSnapshot {
+  id: string;
+  title: string;
+  color?: string | null;
+  content: string;
+  index: number;
+}
+
+// Re-create a previously deleted chapter at its original position, restoring
+// its title, color, and content. The chapter is stored as Markdown so it reads
+// correctly regardless of the format it originally used.
+export function restoreChapter(bookPath: string, snap: ChapterSnapshot): ChapterEntry {
+  const meta = loadBook(bookPath);
+  const file = path.posix.join("chapters", chapterFileName(snap.id));
+  fs.mkdirSync(path.join(bookPath, "chapters"), { recursive: true });
+  fs.writeFileSync(path.join(bookPath, file), snap.content, "utf-8");
+  const entry: ChapterEntry = { id: snap.id, title: snap.title, file };
+  if (snap.color) entry.color = snap.color;
+  meta.chapters[snap.id] = entry;
+  const idx = Math.max(0, Math.min(snap.index, meta.chapterOrder.length));
+  meta.chapterOrder.splice(idx, 0, snap.id);
+  saveMeta(bookPath, meta);
+  return entry;
+}
+
 export function duplicateChapter(
   bookPath: string,
   id: string,

src/main/index.ts

@@ -22,6 +22,7 @@ import {
   reorderChapters,
   listChaptersInOrder,
   setChapterContent,
+  restoreChapter,
 } from "./chapters.js";
 import { combineMarkdown, buildZip } from "./export.js";
 import { buildDocx, buildOdt } from "./office-export.js";
@@ -309,6 +310,58 @@ ipcMain.handle("folio:deleteChapter", (_e, id: string) => {
   }
 });
 
+ipcMain.handle("folio:restoreChapter", (_e, snap: unknown) => {
+  try {
+    restoreChapter(requireBook(), snap as never);
+    notifyChange();
+    return { ok: true };
+  } catch (e) {
+    return { error: (e as Error).message };
+  }
+});
+
+// Restore a book the user just trashed (Undo for book deletion). The desktop
+// trash follows the XDG spec on Linux; we match the original path in the
+// .trashinfo and move the item back.
+function restoreBookFromTrash(p: string): { ok?: boolean; error?: string } {
+  try {
+    const home = app.getPath("home");
+    const infoDir = path.join(home, ".local", "share", "Trash", "info");
+    const filesDir = path.join(home, ".local", "share", "Trash", "files");
+    if (!fs.existsSync(infoDir)) return { error: "Trash not available." };
+    for (const infoFile of fs.readdirSync(infoDir)) {
+      if (!infoFile.endsWith(".trashinfo")) continue;
+      const txt = fs.readFileSync(path.join(infoDir, infoFile), "utf-8");
+      const m = /^Path=(.*)$/m.exec(txt);
+      if (!m) continue;
+      let orig = decodeURIComponent(m[1].trim());
+      if (!path.isAbsolute(orig)) orig = path.join(home, orig);
+      if (orig !== p) continue;
+      const base = infoFile.slice(0, -".trashinfo".length);
+      const trashed = path.join(filesDir, base);
+      if (!fs.existsSync(trashed)) return { error: "Trashed book missing." };
+      fs.mkdirSync(path.dirname(p), { recursive: true });
+      fs.renameSync(trashed, p);
+      fs.rmSync(path.join(infoDir, infoFile), { force: true });
+      try {
+        if (process.env.FOLIO_SELF_TEST !== "1") {
+          const meta = loadBook(p);
+          addRecent({ path: p, title: meta.title, lastOpened: new Date().toISOString() });
+        }
+      } catch {
+        /* recents best-effort */
+      }
+      refreshMenu();
+      return { ok: true };
+    }
+    return { error: "Book not found in trash." };
+  } catch (e) {
+    return { error: (e as Error).message };
+  }
+}
+
+ipcMain.handle("folio:restoreBook", (_e, p: string) => restoreBookFromTrash(p));
+
 ipcMain.handle("folio:duplicateChapter", (_e, id: string, title?: string) => {
   try {
     const entry = duplicateChapter(requireBook(), id, title);

src/main/preload.ts

@@ -4,6 +4,7 @@ contextBridge.exposeInMainWorld("folio", {
   // book / project
   newBookNamed: (name: string) => ipcRenderer.invoke("folio:newBookNamed", name),
   deleteBook: (p: string) => ipcRenderer.invoke("folio:deleteBook", p),
+  restoreBook: (p: string) => ipcRenderer.invoke("folio:restoreBook", p),
   openBook: () => ipcRenderer.invoke("folio:openBook"),
   openBookPath: (p: string) => ipcRenderer.invoke("folio:openPath", p),
   revealInFolder: (p: string) => ipcRenderer.invoke("folio:reveal", p),
@@ -24,6 +25,8 @@ contextBridge.exposeInMainWorld("folio", {
     ipcRenderer.invoke("folio:setChapterColor", id, color),
   deleteChapter: (id: string) =>
     ipcRenderer.invoke("folio:deleteChapter", id),
+  restoreChapter: (snap: unknown) =>
+    ipcRenderer.invoke("folio:restoreChapter", snap),
   duplicateChapter: (id: string, title?: string) =>
     ipcRenderer.invoke("folio:duplicateChapter", id, title),
   reorderChapters: (newOrder: string[]) =>

src/renderer/book.ts

@@ -17,9 +17,18 @@ import {
   nativeNodeText,
 } from "./native-assembly.js";
 
+export interface ChapterSnapshot {
+  id: string;
+  title: string;
+  color?: string | null;
+  content: string;
+  index: number;
+}
+
 export type FolioAPI = {
   newBookNamed: (name: string) => Promise<any>;
   deleteBook: (p: string) => Promise<any>;
+  restoreBook: (p: string) => Promise<any>;
   openBook: () => Promise<any>;
   openBookPath: (p: string) => Promise<any>;
   revealInFolder: (p: string) => Promise<boolean>;
@@ -33,6 +42,7 @@ export type FolioAPI = {
   renameChapter: (id: string, title: string) => Promise<any>;
   setChapterColor: (id: string, color: string | null) => Promise<any>;
   deleteChapter: (id: string) => Promise<any>;
+  restoreChapter: (snap: ChapterSnapshot) => Promise<any>;
   duplicateChapter: (id: string, title?: string) => Promise<any>;
   reorderChapters: (newOrder: string[]) => Promise<any>;
   saveChapter: (id: string, content: string) => Promise<any>;
@@ -937,6 +947,34 @@ export function initBook(api: FolioAPI) {
     }, 1400);
   }
 
+  // Toast with an Undo action, used after destructive operations (delete book,
+  // delete/cut chapter). Auto-dismisses; the action runs once if tapped.
+  let undoToastTimer: ReturnType<typeof setTimeout> | null = null;
+  function hideUndoToast(): void {
+    const el = $("undoToast");
+    if (!el) return;
+    el.classList.remove("show");
+    setTimeout(() => el.classList.add("hidden"), 200);
+  }
+  function showUndoToast(msg: string, onUndo: () => void, timeout = 9000): void {
+    const el = $("undoToast");
+    if (!el) {
+      onUndo();
+      return;
+    }
+    const msgEl = $("undoToastMsg");
+    const btn = $("undoToastBtn") as HTMLButtonElement | null;
+    if (msgEl) msgEl.textContent = msg;
+    if (btn) btn.onclick = () => {
+      hideUndoToast();
+      onUndo();
+    };
+    el.classList.remove("hidden");
+    el.classList.add("show");
+    if (undoToastTimer) clearTimeout(undoToastTimer);
+    undoToastTimer = setTimeout(hideUndoToast, timeout);
+  }
+
   async function saveCurrentChapter(): Promise<void> {
     if (!selectedId) return;
     const res = await api.saveChapterDoc(selectedId, getEditorDoc(editor));
@@ -1285,14 +1323,31 @@ export function initBook(api: FolioAPI) {
   async function del(id: string) {
     if (!meta || !meta.chapters[id]) return;
     const entry = meta.chapters[id];
-    const confirmed = await confirmMessage(`Delete "${entry.title}"?`, "This cannot be undone.");
+    const index = meta.chapterOrder.indexOf(id);
-    if (!confirmed) return;
+    const content = (await api.getChapterContent(id)) as string;
     const res = await api.deleteChapter(id);
-    if (res && "error" in res) await alertMessage("Could not delete chapter", (res as { error: string }).error);
+    if (res && "error" in res) {
-    else {
+      await alertMessage("Could not delete chapter", (res as { error: string }).error);
-      if (selectedId === id) { selectedId = null; showPlaceholder(); }
+      return;
-      await refreshMeta();
     }
+    const wasSelected = selectedId === id;
+    if (wasSelected) { selectedId = null; showPlaceholder(); }
+    await refreshMeta();
+    showUndoToast(`Deleted "${entry.title}"`, async () => {
+      const r = await api.restoreChapter({
+        id,
+        title: entry.title,
+        color: entry.color ?? null,
+        content,
+        index,
+      });
+      if (r && "error" in r) {
+        await alertMessage("Could not restore chapter", (r as { error: string }).error);
+        return;
+      }
+      await refreshMeta();
+      if (wasSelected) await selectChapter(id);
+    });
   }
 
   async function duplicate(id: string) {
@@ -1394,17 +1449,20 @@ export function initBook(api: FolioAPI) {
       del.textContent = "×";
       del.addEventListener("click", async (e) => {
         e.stopPropagation();
-        const ok = await confirmMessage(
-          "Delete book",
-          `Delete "${r.title || r.path}"? This permanently removes the book folder.`
-        );
-        if (!ok) return;
         const res = await api.deleteBook(r.path);
         if (res && "error" in res) {
           await alertMessage("Could not delete", (res as { error: string }).error);
           return;
         }
         await renderRecents();
+        showUndoToast(`Deleted "${r.title || r.path}"`, async () => {
+          const rr = await api.restoreBook(r.path);
+          if (rr && "error" in rr) {
+            await alertMessage("Could not restore", (rr as { error: string }).error);
+            return;
+          }
+          await renderRecents();
+        });
       });
       li.appendChild(label);
       li.appendChild(del);

src/renderer/index.css

@@ -1067,10 +1067,30 @@ body.dragging-active * {
   transition: opacity 0.18s ease, transform 0.18s ease;
   z-index: 1000;
 }
-.toast.show {
+ .toast.show {
-  opacity: 1;
+   opacity: 1;
-  transform: translateX(-50%) translateY(0);
+   transform: translateX(-50%) translateY(0);
-}
+ }
+
+ .undo-toast {
+   display: flex;
+   align-items: center;
+   gap: 14px;
+   pointer-events: auto;
+ }
+ .undo-toast .toast-action {
+   background: rgba(255, 255, 255, 0.18);
+   color: #fff;
+   border: 1px solid rgba(255, 255, 255, 0.35);
+   border-radius: 6px;
+   font: inherit;
+   font-weight: 700;
+   padding: 5px 14px;
+   cursor: pointer;
+ }
+ .undo-toast .toast-action:hover {
+   background: rgba(255, 255, 255, 0.3);
+ }
 
 /* ---- toolbar dropdowns ---- */
 .toolbar-dropdown {

src/renderer/index.html

@@ -273,6 +273,10 @@
       </div>
     </div>
     <div class="toast hidden" id="toast"></div>
+    <div class="toast undo-toast hidden" id="undoToast" role="status" aria-live="polite">
+      <span id="undoToastMsg"></span>
+      <button type="button" class="toast-action" id="undoToastBtn">Undo</button>
+    </div>
     <div class="modal-backdrop hidden" id="searchModal">
       <div class="modal search-modal" role="dialog" aria-modal="true" aria-label="Search all chapters">
         <h3 class="modal-title">Search</h3>

tests/selftest-scenario.js

@@ -170,7 +170,33 @@
         }
         step("exports", ex);
 
-        // New book auto-creates a folder inside Documents; then delete it.
+        // Chapter delete + undo (snapshot restore).
+        try {
+          const before = (await api.getChapterList()).length;
+          const cc = await api.getChapterContent("ch-one");
+          const delc = await api.deleteChapter("ch-one");
+          const afterDel = (await api.getChapterList()).length;
+          const restc = await api.restoreChapter({
+            id: "ch-one",
+            title: "Book_The_Lab",
+            color: null,
+            content: cc,
+            index: 0,
+          });
+          const afterRest = (await api.getChapterList()).length;
+          const cc2 = await api.getChapterContent("ch-one");
+          step("chapterUndo", {
+            before,
+            afterDel,
+            afterRest,
+            restored: cc2 === cc,
+            ok: !!(delc && delc.ok) && !!(restc && restc.ok),
+          });
+        } catch (e) {
+          step("chapterUndoErr", String(e));
+        }
+
+        // New book auto-creates a folder inside Documents; delete then undo.
         const nb = await api.newBookNamed("Folio Selftest Temp");
         step("newBookNamed", {
           ok: !!(nb && nb.path && nb.title),
@@ -180,6 +206,10 @@
         if (nb && nb.path) {
           const del = await api.deleteBook(nb.path);
           step("deleteBook", del && del.ok ? "ok" : del && del.error);
+          if (del && del.ok) {
+            const rest = await api.restoreBook(nb.path);
+            step("restoreBook", rest && rest.ok ? "ok" : rest && rest.error);
+          }
         }
 
         out.ok = true;