Roadmap, robust page refs, copy behaviour

README

@@ -1 +1,76 @@
-empty
+# PDF Workbench
+
+Browser-only PDF tools for quick page-level editing. Processing happens completely locally in the browser; files are never uploaded to a server.
+
+## Current features
+
+- load a PDF in the browser
+- generate page thumbnails progressively
+- reorder pages via drag and drop
+- select pages, including Shift range selection
+- rotate pages clockwise/counter-clockwise
+- delete pages from the working document
+- preview pages in an overlay
+- flip through preview pages with buttons or arrow keys
+- merge a second PDF by replacing, appending, or inserting at a chosen position
+- extract selected pages into a new PDF
+- export the current reordered/rotated document
+- split into single-page PDFs
+
+## Keyboard shortcuts
+
+- `CtrlA` / `⌘A`: select all pages
+- `Delete` / `Backspace`: delete selected pages
+- `Esc`: clear the current selection
+- Preview overlay: `←` / `→` flip pages, `Esc` closes the overlay
+
+Keyboard shortcuts are ignored while typing in form fields.
+
+## Current implementation focus
+
+The project is currently optimized around page-level PDF work: split, merge, reorder, rotate, preview, select, delete, extract, and export. Deep content-stream editing is intentionally out of scope for now.
+
+## Roadmap
+
+### Milestone 1: Fast preview and thumbnails
+
+- [x] Remove unused `PageList` component
+- [x] Bound thumbnail generation by width and height
+- [x] Display thumbnails progressively
+- [x] Add preview page flipping
+- [x] Attach preview controls to the modal container
+- [x] Add first keyboard shortcuts
+- [x] Cache thumbnails by page and rotation
+- [x] Regenerate only changed rotated thumbnails
+
+### Milestone 2: Real page workspace
+
+- [x] Introduce stable page references instead of only original page indices
+- [x] Support duplicate selected pages
+- [ ] Extract selection as a new active workspace
+- [ ] Add command history as a foundation for undo/redo
+- [ ] Add undo/redo
+- [ ] Add grid/list view toggle
+
+### Milestone 3: Better merge and mobile handling
+
+- [ ] Add a full multi-file merge queue
+- [ ] Support drag-and-drop of PDFs into the page grid at the hovered position
+- [ ] Add custom long-press drag on mobile
+- [ ] Consolidate actions into a toolbar
+
+### Milestone 4: Structural PDF editing
+
+- [ ] Metadata editing
+- [ ] Crop pages
+- [ ] Add tools directly in the preview overlay
+- [ ] Read/fill/flatten forms
+- [ ] Read bookmarks, then evaluate bookmark editing
+- [ ] Read annotations, then evaluate annotation writing
+
+### Milestone 5: Export and power tools
+
+- [ ] Basic text extraction
+- [ ] ZIP export for split results
+- [ ] Optimize/compress MVP
+- [ ] Carefully scoped encrypted PDF handling

src/App.tsx

@@ -1,38 +1,78 @@
-import React, { useEffect, useState } from 'react';
+import React, { useEffect, useRef, useState } from 'react';
 import Layout from './components/Layout';
 import FileLoader from './components/FileLoader';
 import ReorderPanel from './components/ReorderPanel';
 import ActionsPanel from './components/ActionsPanel';
 import PagePreviewModal from './components/PagePreviewModal';
-import type { PdfFile, SplitResult } from './pdf/pdfTypes';
+import { PDFDocument } from 'pdf-lib';
+import type { PageRef, PdfFile, SplitResult } from './pdf/pdfTypes';
 import {
   loadPdfFromFile,
   mergePdfFiles,
   splitIntoSinglePages,
-  exportReordered,
+  exportPages,
 } from './pdf/pdfService';
 import {
-  generateThumbnails,
+  generateThumbnailsProgressive,
-  generateThumbnailsWithRotations,
+  generateThumbnailsWithRotationsProgressive,
 } from './pdf/pdfThumbnailService';
 
+const THUMBNAIL_MAX_HEIGHT = 150;
+const THUMBNAIL_MAX_WIDTH = 140;
+const THUMBNAIL_CONCURRENCY = 3;
+
+function createPageRefId(): string {
+  return Math.random().toString(36).slice(2);
+}
+
+function createInitialPageRefs(pageCount: number): PageRef[] {
+  return Array.from({ length: pageCount }, (_, sourcePageIndex) => ({
+    id: createPageRefId(),
+    sourcePageIndex,
+    rotation: 0,
+  }));
+}
+
+function normalizeRotation(rotation: number | undefined): number {
+  return (((rotation ?? 0) % 360) + 360) % 360;
+}
+
+function thumbnailCacheKey(
+  pdfId: string,
+  sourcePageIndex: number,
+  rotation: number
+): string {
+  return [
+    pdfId,
+    sourcePageIndex,
+    normalizeRotation(rotation),
+    THUMBNAIL_MAX_WIDTH,
+    THUMBNAIL_MAX_HEIGHT,
+  ].join(':');
+}
+
+function isEditableKeyboardTarget(target: EventTarget | null): boolean {
+  if (!(target instanceof HTMLElement)) return false;
+
+  const tagName = target.tagName.toLowerCase();
+  return (
+    target.isContentEditable ||
+    tagName === 'input' ||
+    tagName === 'textarea' ||
+    tagName === 'select'
+  );
+}
+
 const App: React.FC = () => {
   const [pdf, setPdf] = useState<PdfFile | null>(null);
   const [isBusy, setIsBusy] = useState(false);
   const [error, setError] = useState<string | null>(null);
 
-  const [baseThumbnails, setBaseThumbnails] = useState<string[] | null>(null);
+  const [pages, setPages] = useState<PageRef[]>([]);
-  const [reorderThumbnails, setReorderThumbnails] = useState<string[] | null>(
+  const [reorderThumbnails, setReorderThumbnails] = useState<Record<string, string>>({});
-    null
-  );
 
-  const [order, setOrder] = useState<number[]>([]);
+  const [selectedPageIds, setSelectedPageIds] = useState<string[]>([]);
-  const [rotations, setRotations] = useState<Record<number, number>>({});
+  const [lastSelectedVisualIndex, setLastSelectedVisualIndex] = useState<number | null>(null);
-
-  const [selectedPages, setSelectedPages] = useState<number[]>([]);
-  const [lastSelectedVisualIndex, setLastSelectedVisualIndex] = useState<
-    number | null
-  >(null);
 
   const [splitResults, setSplitResults] = useState<SplitResult[]>([]);
   const [subsetUrl, setSubsetUrl] = useState<string | null>(null);
@@ -40,38 +80,56 @@ const App: React.FC = () => {
   const [exportUrl, setExportUrl] = useState<string | null>(null);
   const [exportFilename, setExportFilename] = useState<string | null>(null);
 
-  const [previewIndex, setPreviewIndex] = useState<number | null>(null);
+  const [previewPageId, setPreviewPageId] = useState<string | null>(null);
 
   const [pendingFile, setPendingFile] = useState<File | null>(null);
   const [showMergeOptions, setShowMergeOptions] = useState(false);
   const [mergeMode, setMergeMode] = useState<'overwrite' | 'append' | 'insertAt'>('append');
   const [mergeInsertAt, setMergeInsertAt] = useState<string>('');
 
-    const loadFileAsNew = async (file: File) => {
+  const thumbnailCacheRef = useRef<Map<string, string>>(new Map());
-    setError(null);
+  const latestPagesRef = useRef<PageRef[]>([]);
+  const previousPageRotationsRef = useRef<Map<string, number>>(new Map());
+
+  const resetGeneratedUrls = () => {
+    if (subsetUrl) {
+      URL.revokeObjectURL(subsetUrl);
+      setSubsetUrl(null);
+      setSubsetFilename(null);
+    }
+
+    if (exportUrl) {
+      URL.revokeObjectURL(exportUrl);
+      setExportUrl(null);
+      setExportFilename(null);
+    }
+  };
+
+  const resetWorkspaceState = () => {
     setSplitResults([]);
-    setSelectedPages([]);
+    setSelectedPageIds([]);
-    setLastSelectedVisualIndex(null);
+     setLastSelectedVisualIndex(null);
-    setSubsetUrl(null);
+    resetGeneratedUrls();
-    setSubsetFilename(null);
+    setReorderThumbnails({});
-    setExportUrl(null);
+    thumbnailCacheRef.current.clear();
-    setExportFilename(null);
+    previousPageRotationsRef.current.clear();
-    setBaseThumbnails(null);
+    latestPagesRef.current = [];
-    setReorderThumbnails(null);
+    setPages([]);
-    setRotations({});
+    setPreviewPageId(null);
-    setOrder([]);
+  };
-    setPreviewIndex(null);
+
+  const loadFileAsNew = async (file: File) => {
+    setError(null);
+    resetWorkspaceState();
 
     setIsBusy(true);
     try {
       const loaded = await loadPdfFromFile(file);
-      setPdf(loaded);
+      const initialPages = createInitialPageRefs(loaded.pageCount);
 
-      const initialOrder = Array.from(
+      setPdf(loaded);
-        { length: loaded.pageCount },
+      setPages(initialPages);
-        (_, i) => i
+      latestPagesRef.current = initialPages;
-      );
-      setOrder(initialOrder);
     } catch (e) {
       console.error(e);
       setError('Failed to load PDF (see console).');
@@ -81,15 +139,13 @@ const App: React.FC = () => {
   };
 
   const handleFileLoaded = (file: File) => {
-    // If no PDF loaded yet, just open it as before
+    if (!pdf || pages.length === 0) {
-    if (!pdf || order.length === 0) {
       void loadFileAsNew(file);
     } else {
-      // Otherwise, ask whether to merge or replace
       setPendingFile(file);
       setShowMergeOptions(true);
       setMergeMode('append');
-      setMergeInsertAt(String(order.length + 1));
+      setMergeInsertAt(String(pages.length + 1));
     }
   };
 
@@ -101,7 +157,6 @@ const App: React.FC = () => {
   const handleMergeConfirm = async () => {
     if (!pendingFile) return;
 
-    // If there's no current PDF or the user chose overwrite, just load normally
     if (!pdf || mergeMode === 'overwrite') {
       await loadFileAsNew(pendingFile);
       setPendingFile(null);
@@ -113,58 +168,49 @@ const App: React.FC = () => {
     setIsBusy(true);
 
     try {
-      // 1) Materialize the current in-memory state (order + rotations)
+      // 1) Materialize the current in-memory workspace (page refs + rotations)
-      const currentBlob = await exportReordered(pdf, order, rotations);
+      const currentBlob = await exportPages(pdf, pages);
       const currentArrayBuffer = await currentBlob.arrayBuffer();
+      const currentDoc = await PDFDocument.load(currentArrayBuffer);
       const currentPdf: PdfFile = {
+        id: pdf.id,
         name: pdf.name,
+        doc: currentDoc,
         arrayBuffer: currentArrayBuffer,
-        pageCount: order.length,
+        pageCount: pages.length,
       };
 
       // 2) Load the new PDF
       const newPdf = await loadPdfFromFile(pendingFile);
 
       // 3) Determine insert position (0-based)
-      let insertAt = order.length; // default: append at end
+      let insertAt = pages.length; // default: append at end
       if (mergeMode === 'insertAt') {
         const parsed = parseInt(mergeInsertAt, 10);
         if (Number.isFinite(parsed)) {
-          insertAt = Math.min(Math.max(parsed - 1, 0), order.length);
+          insertAt = Math.min(Math.max(parsed - 1, 0), pages.length);
         }
       } else if (mergeMode === 'append') {
-        insertAt = order.length;
+        insertAt = pages.length;
       }
 
       // 4) Merge
       const mergedPdf = await mergePdfFiles(currentPdf, newPdf, insertAt);
+      const mergedPages = createInitialPageRefs(mergedPdf.pageCount);
 
       // 5) Reset state to the merged document
       setPdf(mergedPdf);
-      const mergedOrder = Array.from(
+
-        { length: mergedPdf.pageCount },
+      setPages(mergedPages);
-        (_, i) => i
+      latestPagesRef.current = mergedPages;
-      );
+      setSelectedPageIds([]);
-      setOrder(mergedOrder);
-      setRotations({});
-      setSelectedPages([]);
       setLastSelectedVisualIndex(null);
       setSplitResults([]);
-
+      resetGeneratedUrls();
-      if (subsetUrl) {
+      setReorderThumbnails({});
-        URL.revokeObjectURL(subsetUrl);
+      thumbnailCacheRef.current.clear();
-        setSubsetUrl(null);
+      previousPageRotationsRef.current.clear();
-        setSubsetFilename(null);
+      setPreviewPageId(null);
-      }
-      if (exportUrl) {
-        URL.revokeObjectURL(exportUrl);
-        setExportUrl(null);
-        setExportFilename(null);
-      }
-
-      setBaseThumbnails(null);
-      setReorderThumbnails(null);
-      setPreviewIndex(null);
     } catch (e) {
       console.error(e);
       setError('Failed to merge PDF (see console).');
@@ -175,146 +221,404 @@ const App: React.FC = () => {
     }
   };
 
+  useEffect(() => {
+    latestPagesRef.current = pages;
+  }, [pages]);
+
   useEffect(() => {
     if (!pdf) {
-      setBaseThumbnails(null);
+      setReorderThumbnails({});
-      setReorderThumbnails(null);
+      thumbnailCacheRef.current.clear();
+      previousPageRotationsRef.current.clear();
       return;
     }
-    let cancelled = false;
 
-    (async () => {
+    const controller = new AbortController();
-      try {
+
-        const thumbs = await generateThumbnails(pdf.arrayBuffer);
+    latestPagesRef.current = pages;
-        if (!cancelled) {
+    thumbnailCacheRef.current.clear();
-          setBaseThumbnails(thumbs);
+    previousPageRotationsRef.current = new Map(
-          setReorderThumbnails(thumbs);
+      pages.map((page) => [page.id, normalizeRotation(page.rotation)])
+    );
+    setReorderThumbnails({});
+
+    void generateThumbnailsProgressive(pdf.arrayBuffer, {
+      maxHeight: THUMBNAIL_MAX_HEIGHT,
+      maxWidth: THUMBNAIL_MAX_WIDTH,
+      concurrency: THUMBNAIL_CONCURRENCY,
+      signal: controller.signal,
+      onThumbnail: ({ pageIndex, dataUrl }) => {
+        if (controller.signal.aborted) return;
+
+        thumbnailCacheRef.current.set(
+          thumbnailCacheKey(pdf.id, pageIndex, 0),
+          dataUrl
+        );
+
+        const currentPages = latestPagesRef.current;
+        const updates: Record<string, string> = {};
+
+        for (const page of currentPages) {
+          if (
+            page.sourcePageIndex === pageIndex &&
+            normalizeRotation(page.rotation) === 0
+          ) {
+            updates[page.id] = dataUrl;
+          }
         }
-      } catch (e) {
+
+        if (Object.keys(updates).length === 0) return;
+
+        setReorderThumbnails((prev) => ({
+          ...prev,
+          ...updates,
+        }));
+      },
+    }).catch((e) => {
+      if (!controller.signal.aborted) {
         console.error(e);
-        if (!cancelled) {
+        setError('Failed to generate thumbnails (see console).');
-          setError('Failed to generate thumbnails (see console).');
-        }
       }
-    })();
+    });
 
     return () => {
-      cancelled = true;
+      controller.abort();
     };
   }, [pdf]);
 
   useEffect(() => {
     if (!pdf) {
-      setReorderThumbnails(null);
+      previousPageRotationsRef.current.clear();
       return;
     }
-    let cancelled = false;
 
-    (async () => {
+    const previousRotations = previousPageRotationsRef.current;
-      try {
+    const changedPages = pages.filter(
-        const thumbs = await generateThumbnailsWithRotations(
+      (page) =>
-          pdf.arrayBuffer,
+        normalizeRotation(previousRotations.get(page.id)) !==
-          rotations
+        normalizeRotation(page.rotation)
-        );
+    );
-        if (!cancelled) {
+
-          setReorderThumbnails(thumbs);
+    previousPageRotationsRef.current = new Map(
-        }
+      pages.map((page) => [page.id, normalizeRotation(page.rotation)])
-      } catch (e) {
+    );
-        console.error(e);
+
-        if (!cancelled) {
+    if (changedPages.length === 0) return;
-          setError('Failed to generate rotated thumbnails (see console).');
+
-        }
+    const cachedUpdates: Record<string, string> = {};
+    const pagesToRender: PageRef[] = [];
+
+    for (const page of changedPages) {
+      const rotation = normalizeRotation(page.rotation);
+      const cached = thumbnailCacheRef.current.get(
+        thumbnailCacheKey(pdf.id, page.sourcePageIndex, rotation)
+      );
+
+      if (cached) {
+        cachedUpdates[page.id] = cached;
+      } else {
+        pagesToRender.push(page);
       }
-    })();
+    }
+
+    if (Object.keys(cachedUpdates).length > 0) {
+      setReorderThumbnails((prev) => ({
+        ...prev,
+        ...cachedUpdates,
+      }));
+    }
+
+    if (pagesToRender.length === 0) return;
+
+    const controller = new AbortController();
+    const groups = new Map<number, PageRef[]>();
+
+    for (const page of pagesToRender) {
+      const rotation = normalizeRotation(page.rotation);
+      const group = groups.get(rotation) ?? [];
+      group.push(page);
+      groups.set(rotation, group);
+    }
+
+    const renderGroups = async () => {
+      for (const [rotation, groupPages] of groups) {
+        if (controller.signal.aborted) return;
+
+        const pageIndices = Array.from(
+          new Set(groupPages.map((page) => page.sourcePageIndex))
+        );
+        const rotationsBySourcePage: Record<number, number> = {};
+
+        for (const pageIndex of pageIndices) {
+          rotationsBySourcePage[pageIndex] = rotation;
+        }
+
+        await generateThumbnailsWithRotationsProgressive(
+          pdf.arrayBuffer,
+          rotationsBySourcePage,
+          {
+            maxHeight: THUMBNAIL_MAX_HEIGHT,
+            maxWidth: THUMBNAIL_MAX_WIDTH,
+            concurrency: Math.min(THUMBNAIL_CONCURRENCY, pageIndices.length),
+            pageIndices,
+            signal: controller.signal,
+            onThumbnail: ({ pageIndex, dataUrl }) => {
+              if (controller.signal.aborted) return;
+
+              thumbnailCacheRef.current.set(
+                thumbnailCacheKey(pdf.id, pageIndex, rotation),
+                dataUrl
+              );
+
+              const updates: Record<string, string> = {};
+
+              for (const page of latestPagesRef.current) {
+                if (
+                  page.sourcePageIndex === pageIndex &&
+                  normalizeRotation(page.rotation) === rotation
+                ) {
+                  updates[page.id] = dataUrl;
+                }
+              }
+
+              if (Object.keys(updates).length === 0) return;
+
+              setReorderThumbnails((prev) => ({
+                ...prev,
+                ...updates,
+              }));
+            },
+          }
+        );
+      }
+    };
+
+    void renderGroups().catch((e) => {
+      if (!controller.signal.aborted) {
+        console.error(e);
+        setError('Failed to generate rotated thumbnails (see console).');
+      }
+    });
 
     return () => {
-      cancelled = true;
+      controller.abort();
     };
-  }, [pdf, rotations]);
+  }, [pdf, pages]);
+
+  useEffect(() => {
+    if (previewPageId != null && !pages.some((page) => page.id === previewPageId)) {
+      setPreviewPageId(null);
+    }
+  }, [previewPageId, pages]);
 
   const hasPdf = !!pdf;
-  const pageCount = pdf?.pageCount ?? 0;
 
   // === UI interactions ===
 
-  const handleRotatePageClockwise = (pageIndex: number) => {
+  const handleRotatePageClockwise = (pageId: string) => {
-    setRotations((prev) => {
+    setPages((prev) =>
-      const current = prev[pageIndex] ?? 0;
+      prev.map((page) =>
-      const next = (current + 90) % 360;
+        page.id === pageId
-      return { ...prev, [pageIndex]: next };
+          ? { ...page, rotation: (normalizeRotation(page.rotation) + 90) % 360 }
-    });
+          : page
+      )
+    );
   };
 
-  const handleRotatePageCounterclockwise = (pageIndex: number) => {
+  const handleRotatePageCounterclockwise = (pageId: string) => {
-    setRotations((prev) => {
+    setPages((prev) =>
-      const current = prev[pageIndex] ?? 0;
+      prev.map((page) =>
-      const next = (current + 270) % 360;
+        page.id === pageId
-      return { ...prev, [pageIndex]: next };
+          ? { ...page, rotation: (normalizeRotation(page.rotation) + 270) % 360 }
-    });
+          : page
+      )
+    );
   };
 
-  const handleDeletePage = (pageIndex: number) => {
+  const handleDeletePage = (pageId: string) => {
-    setOrder((prev) => prev.filter((p) => p !== pageIndex));
+    setPages((prev) => prev.filter((page) => page.id !== pageId));
-    setSelectedPages((prev) => prev.filter((p) => p !== pageIndex));
+    setSelectedPageIds((prev) => prev.filter((id) => id !== pageId));
   };
 
-  const handleReorder = (newOrder: number[]) => {
+  const handleReorder = (newPages: PageRef[]) => {
-    setOrder(newOrder);
+    setPages(newPages);
   };
 
   const handleToggleSelect = (
-    pageIndex: number,
+    pageId: string,
     visualIndex: number,
     e: React.MouseEvent<HTMLButtonElement>
   ) => {
-    setSelectedPages((prev) => {
+    setSelectedPageIds((prev) => {
-      // Shift: add a range (visual positions) to the existing selection
+      if (e.shiftKey && lastSelectedVisualIndex !== null && pages.length > 0) {
-      if (e.shiftKey && lastSelectedVisualIndex !== null && order.length > 0) {
         const from = Math.min(lastSelectedVisualIndex, visualIndex);
         const to = Math.max(lastSelectedVisualIndex, visualIndex);
-        const rangeIndices = order.slice(from, to + 1); // original page indices
+        const rangeIds = pages.slice(from, to + 1).map((page) => page.id);
 
         const set = new Set(prev);
-        rangeIndices.forEach((idx) => set.add(idx));
+        rangeIds.forEach((id) => set.add(id));
         return Array.from(set);
       }
 
-      // Plain click: toggle this page
+      if (prev.includes(pageId)) {
-      if (prev.includes(pageIndex)) {
+        return prev.filter((id) => id !== pageId);
-        return prev.filter((p) => p !== pageIndex);
       }
 
-      return [...prev, pageIndex];
+      return [...prev, pageId];
     });
 
     setLastSelectedVisualIndex(visualIndex);
   };
 
   const handleSelectAll = () => {
-    setSelectedPages([...order]);
+    setSelectedPageIds(pages.map((page) => page.id));
     setLastSelectedVisualIndex(null);
   };
 
   const handleClearSelection = () => {
-    setSelectedPages([]);
+    setSelectedPageIds([]);
     setLastSelectedVisualIndex(null);
   };
   
   const handleDeleteSelected = () => {
-    if (selectedPages.length === 0) return;
+    if (selectedPageIds.length === 0) return;
-    setOrder((prev) => prev.filter((p) => !selectedPages.includes(p)));
+    const selectedSet = new Set(selectedPageIds);
-    setSelectedPages([]);
+    setPages((prev) => prev.filter((page) => !selectedSet.has(page.id)));
+    setSelectedPageIds([]);
     setLastSelectedVisualIndex(null);
   };
 
-  const handleOpenPreview = (pageIndex: number) => {
+  const handleCopyPagesToSlot = (pageIds: string[], insertSlot: number) => {
-    setPreviewIndex(pageIndex);
+    if (!pdf || pageIds.length === 0) return;
+
+    const pageIdSet = new Set(pageIds);
+
+    // Copy in current visual order, not in arbitrary selectedPageIds order.
+    const sourcePages = pages.filter((page) => pageIdSet.has(page.id));
+
+    if (sourcePages.length === 0) return;
+
+    const copiedPages: PageRef[] = sourcePages.map((page) => ({
+      ...page,
+      id: createPageRefId(),
+    }));
+
+    const clampedSlot = Math.min(Math.max(insertSlot, 0), pages.length);
+
+    const thumbnailUpdates: Record<string, string> = {};
+
+    sourcePages.forEach((sourcePage, index) => {
+      const copiedPage = copiedPages[index];
+
+      const thumbnail =
+        reorderThumbnails[sourcePage.id] ??
+        thumbnailCacheRef.current.get(
+          thumbnailCacheKey(
+            pdf.id,
+            sourcePage.sourcePageIndex,
+            sourcePage.rotation
+          )
+        );
+
+      if (thumbnail) {
+        thumbnailUpdates[copiedPage.id] = thumbnail;
+      }
+    });
+
+    setPages((prev) => {
+      const slot = Math.min(Math.max(clampedSlot, 0), prev.length);
+
+      return [
+        ...prev.slice(0, slot),
+        ...copiedPages,
+        ...prev.slice(slot),
+      ];
+    });
+
+    // Select the newly created copies.
+    setSelectedPageIds(copiedPages.map((page) => page.id));
+    setLastSelectedVisualIndex(null);
+
+    if (Object.keys(thumbnailUpdates).length > 0) {
+      setReorderThumbnails((prev) => ({
+        ...prev,
+        ...thumbnailUpdates,
+      }));
+    }
+
+    // Existing generated outputs no longer represent the current workspace.
+    setSplitResults([]);
+    resetGeneratedUrls();
+  };
+
+  const handleOpenPreview = (pageId: string) => {
+    setPreviewPageId(pageId);
   };
 
   const handleClosePreview = () => {
-    setPreviewIndex(null);
+    setPreviewPageId(null);
   };
 
+  const handlePreviewPrevious = () => {
+    setPreviewPageId((current) => {
+      if (current == null || pages.length === 0) return current;
+
+      const visualIndex = pages.findIndex((page) => page.id === current);
+      if (visualIndex <= 0) return current;
+
+      return pages[visualIndex - 1].id;
+    });
+  };
+
+  const handlePreviewNext = () => {
+    setPreviewPageId((current) => {
+      if (current == null || pages.length === 0) return current;
+
+      const visualIndex = pages.findIndex((page) => page.id === current);
+      if (visualIndex < 0 || visualIndex >= pages.length - 1) return current;
+
+      return pages[visualIndex + 1].id;
+    });
+  };
+
+  useEffect(() => {
+    if (!hasPdf || previewPageId !== null) return;
+
+    const handleKeyDown = (e: KeyboardEvent) => {
+      if (isEditableKeyboardTarget(e.target)) return;
+
+      const key = e.key.toLowerCase();
+
+      if ((e.ctrlKey || e.metaKey) && key === 'a') {
+        e.preventDefault();
+        setSelectedPageIds(pages.map((page) => page.id));
+        setLastSelectedVisualIndex(null);
+        return;
+      }
+
+      if ((e.key === 'Delete' || e.key === 'Backspace') && selectedPageIds.length > 0) {
+        e.preventDefault();
+        const selectedSet = new Set(selectedPageIds);
+        setPages((prev) => prev.filter((page) => !selectedSet.has(page.id)));
+        setSelectedPageIds([]);
+        setLastSelectedVisualIndex(null);
+        return;
+      }
+
+      if (e.key === 'Escape' && selectedPageIds.length > 0) {
+        e.preventDefault();
+        setSelectedPageIds([]);
+        setLastSelectedVisualIndex(null);
+      }
+    };
+
+    window.addEventListener('keydown', handleKeyDown);
+
+    return () => {
+      window.removeEventListener('keydown', handleKeyDown);
+    };
+  }, [hasPdf, previewPageId, pages, selectedPageIds]);
+
   const handleSplit = async () => {
     if (!pdf) return;
     setError(null);
@@ -331,7 +635,7 @@ const App: React.FC = () => {
   };
 
   const handleExtractSelected = async () => {
-    if (!pdf || selectedPages.length === 0) return;
+    if (!pdf || selectedPageIds.length === 0) return
     setError(null);
     setIsBusy(true);
 
@@ -342,10 +646,9 @@ const App: React.FC = () => {
     }
 
     try {
-      const selectedOrder = order.filter((idx) =>
+      const selectedSet = new Set(selectedPageIds);
-        selectedPages.includes(idx)
+      const selectedPages = pages.filter((page) => selectedSet.has(page.id));
-      );
+      const blob = await exportPages(pdf, selectedPages);
-      const blob = await exportReordered(pdf, selectedOrder, rotations);
       const url = URL.createObjectURL(blob);
       const base = pdf.name.replace(/\.pdf$/i, '');
       const filename = `${base}_selected.pdf`;
@@ -360,7 +663,7 @@ const App: React.FC = () => {
   };
 
   const handleExportReordered = async () => {
-    if (!pdf || order.length === 0) return;
+    if (!pdf || pages.length === 0) return;
     setError(null);
     setIsBusy(true);
 
@@ -371,7 +674,7 @@ const App: React.FC = () => {
     }
 
     try {
-      const blob = await exportReordered(pdf, order, rotations);
+      const blob = await exportPages(pdf, pages);
       const url = URL.createObjectURL(blob);
       const base = pdf.name.replace(/\.pdf$/i, '');
       const filename = `${base}_reordered.pdf`;
@@ -385,18 +688,29 @@ const App: React.FC = () => {
     }
   };
 
+  const previewVisualIndex =
+    previewPageId != null
+      ? pages.findIndex((page) => page.id === previewPageId)
+      : -1;
+  const previewPage =
+    previewVisualIndex >= 0 ? pages[previewVisualIndex] : null;
+
+  const canPreviewPrevious = previewVisualIndex > 0;
+  const canPreviewNext =
+    previewVisualIndex >= 0 && previewVisualIndex < pages.length - 1;
+
   return (
     <Layout>
-            <FileLoader pdf={pdf} onFileLoaded={handleFileLoaded} />
+      <FileLoader pdf={pdf} onFileLoaded={handleFileLoaded} />
 
-      {showMergeOptions && pendingFile && pdf && order.length > 0 && (
+      {showMergeOptions && pendingFile && pdf && pages.length > 0 && (
         <div
           className="card"
           style={{ border: '1px solid #bfdbfe', background: '#eff6ff' }}
         >
           <h2>Open file: merge or replace?</h2>
           <p style={{ fontSize: '0.85rem', color: '#374151' }}>
-            You already have <strong>{pdf.name}</strong> with {order.length}{' '}
+            You already have <strong>{pdf.name}</strong> with {pages.length}{' '}
             pages open. What should happen with{' '}
             <strong>{pendingFile.name}</strong>?
           </p>
@@ -451,7 +765,7 @@ const App: React.FC = () => {
                 <input
                   type="number"
                   min={1}
-                  max={order.length + 1}
+                  max={pages.length + 1}
                   value={mergeInsertAt}
                   onChange={(e) => setMergeInsertAt(e.target.value)}
                   style={{
@@ -461,7 +775,7 @@ const App: React.FC = () => {
                   }}
                 />{' '}
                 <span style={{ color: '#6b7280' }}>
-                  (1 = before first page, {order.length + 1} = after last page)
+                  (1 = before first page, {pages.length + 1} = after last page)
                 </span>
               </span>
             </label>
@@ -489,16 +803,16 @@ const App: React.FC = () => {
       )}
 
       <ReorderPanel
-        order={order}
+        pages={pages}
         thumbnails={reorderThumbnails}
         isBusy={isBusy}
         hasPdf={hasPdf}
-        rotations={rotations}
+        selectedPageIds={selectedPageIds}
-        selectedPages={selectedPages}
         onRotateClockwise={handleRotatePageClockwise}
         onRotateCounterclockwise={handleRotatePageCounterclockwise}
         onDelete={handleDeletePage}
         onReorder={handleReorder}
+        onCopyPagesToSlot={handleCopyPagesToSlot}
         onToggleSelect={handleToggleSelect}
         onSelectAll={handleSelectAll}
         onOpenPreview={handleOpenPreview}
@@ -510,7 +824,7 @@ const App: React.FC = () => {
       <ActionsPanel
         hasPdf={hasPdf}
         isBusy={isBusy}
-        selectedCount={selectedPages.length}
+        selectedCount={selectedPageIds.length}
         onSplit={handleSplit}
         onExtractSelected={handleExtractSelected}
         onExportReordered={handleExportReordered}
@@ -531,10 +845,16 @@ const App: React.FC = () => {
       )}
 
       <PagePreviewModal
-        isOpen={previewIndex !== null}
+        isOpen={previewPage !== null}
         pdf={pdf}
-        pageIndex={previewIndex}
+        pageIndex={previewPage?.sourcePageIndex ?? null}
-        rotation={previewIndex != null ? rotations[previewIndex] ?? 0 : 0}
+        rotation={previewPage?.rotation ?? 0}
+        visualIndex={previewVisualIndex >= 0 ? previewVisualIndex : null}
+        totalPages={pages.length}
+        canGoPrevious={canPreviewPrevious}
+        canGoNext={canPreviewNext}
+        onPrevious={handlePreviewPrevious}
+        onNext={handlePreviewNext}
         onClose={handleClosePreview}
       />
     </Layout>

src/components/PageList.tsx

@@ -1,79 +0,0 @@
-import React from 'react';
-
-interface PageListProps {
-  pageCount: number;
-  selectedPages: number[];
-  onTogglePage: (index: number) => void;
-  thumbnails: string[] | null;
-}
-
-const PageList: React.FC<PageListProps> = ({
-  pageCount,
-  selectedPages,
-  onTogglePage,
-  thumbnails,
-}) => {
-  if (pageCount === 0) return null;
-
-  const pages = Array.from({ length: pageCount }, (_, i) => i);
-
-  return (
-    <div className="card">
-      <h2>2. Pages</h2>
-      <p>
-        Thumbnails are generated in your browser. Click to select pages (used by
-        future tools).
-      </p>
-      <div className="page-list">
-        {pages.map((i) => {
-          const selected = selectedPages.includes(i);
-          const thumb = thumbnails?.[i];
-
-          return (
-            <button
-              key={i}
-              type="button"
-              className={`page-pill ${selected ? 'selected' : ''}`}
-              onClick={() => onTogglePage(i)}
-              style={{
-                display: 'flex',
-                flexDirection: 'column',
-                alignItems: 'center',
-                gap: '0.25rem',
-                padding: '0.4rem',
-                minWidth: '90px',
-              }}
-            >
-              {thumb ? (
-                <img
-                  src={thumb}
-                  alt={`Page ${i + 1}`}
-                  style={{
-                    maxHeight: '100px',
-                    width: 'auto',
-                    borderRadius: '0.25rem',
-                    border: '1px solid #e5e7eb',
-                    background: 'white',
-                  }}
-                />
-              ) : (
-                <div
-                  style={{
-                    width: '60px',
-                    height: '80px',
-                    borderRadius: '0.25rem',
-                    border: '1px dashed #d1d5db',
-                    background: '#f3f4f6',
-                  }}
-                />
-              )}
-              <span>Page {i + 1}</span>
-            </button>
-          );
-        })}
-      </div>
-    </div>
-  );
-};
-
-export default PageList;

src/components/PagePreviewModal.tsx

@@ -10,8 +10,17 @@ import pdfjsWorker from 'pdfjs-dist/build/pdf.worker?worker&url';
 interface PagePreviewModalProps {
   isOpen: boolean;
   pdf: PdfFile | null;
-  pageIndex: number | null;        // original page index (0-based)
+  pageIndex: number | null;        // original page index, 0-based
   rotation: number;                // degrees
+
+  visualIndex: number | null;      // current position in order, 0-based
+  totalPages: number;
+
+  canGoPrevious: boolean;
+  canGoNext: boolean;
+  onPrevious: () => void;
+  onNext: () => void;
+
   onClose: () => void;
 }
 
@@ -20,10 +29,45 @@ const PagePreviewModal: React.FC<PagePreviewModalProps> = ({
   pdf,
   pageIndex,
   rotation,
+  visualIndex,
+  totalPages,
+  canGoPrevious,
+  canGoNext,
+  onPrevious,
+  onNext,
   onClose,
 }) => {
   const canvasRef = useRef<HTMLCanvasElement | null>(null);
 
+  useEffect(() => {
+    if (!isOpen) return;
+
+    const handleKeyDown = (e: KeyboardEvent) => {
+      if (e.key === 'Escape') {
+        e.preventDefault();
+        onClose();
+        return;
+      }
+
+      if (e.key === 'ArrowLeft' && canGoPrevious) {
+        e.preventDefault();
+        onPrevious();
+        return;
+      }
+
+      if (e.key === 'ArrowRight' && canGoNext) {
+        e.preventDefault();
+        onNext();
+      }
+    };
+
+    window.addEventListener('keydown', handleKeyDown);
+
+    return () => {
+      window.removeEventListener('keydown', handleKeyDown);
+    };
+  }, [isOpen, canGoPrevious, canGoNext, onPrevious, onNext, onClose]);
+
   useEffect(() => {
     if (!isOpen || !pdf || pageIndex == null) return;
 
@@ -31,6 +75,14 @@ const PagePreviewModal: React.FC<PagePreviewModalProps> = ({
 
     (async () => {
       try {
+        const canvas = canvasRef.current;
+        if (canvas) {
+          const ctx = canvas.getContext('2d');
+          if (ctx) {
+            ctx.clearRect(0, 0, canvas.width, canvas.height);
+          }
+        }
+
         // copy data for pdf.js (avoid detaching original ArrayBuffer)
         const src = new Uint8Array(pdf.arrayBuffer);
         const copy = new Uint8Array(src.byteLength);
@@ -44,16 +96,23 @@ const PagePreviewModal: React.FC<PagePreviewModalProps> = ({
         if (cancelled) return;
 
         const viewport = page.getViewport({ scale: 1 });
+
         const maxWidth = Math.min(window.innerWidth * 0.9, 800);
-        const scale = maxWidth / viewport.width;
+        const maxHeight = window.innerHeight * 0.75;
+
+        const scale = Math.min(
+          maxWidth / viewport.width,
+          maxHeight / viewport.height
+        );
+
         const scaledViewport = page.getViewport({ scale });
 
-        const canvas = canvasRef.current;
+        const visibleCanvas = canvasRef.current;
-        if (!canvas) return;
+        if (!visibleCanvas) return;
-        const ctx = canvas.getContext('2d');
+
-        if (!ctx) return;
+        const visibleCtx = visibleCanvas.getContext('2d');
+        if (!visibleCtx) return;
 
-        // base size
         let canvasWidth = scaledViewport.width;
         let canvasHeight = scaledViewport.height;
 
@@ -64,10 +123,9 @@ const PagePreviewModal: React.FC<PagePreviewModalProps> = ({
           canvasHeight = scaledViewport.width;
         }
 
-        canvas.width = canvasWidth;
+        visibleCanvas.width = canvasWidth;
-        canvas.height = canvasHeight;
+        visibleCanvas.height = canvasHeight;
 
-        // render into an offscreen canvas first
         const baseCanvas = document.createElement('canvas');
         const baseCtx = baseCanvas.getContext('2d');
         if (!baseCtx) return;
@@ -79,31 +137,29 @@ const PagePreviewModal: React.FC<PagePreviewModalProps> = ({
           canvasContext: baseCtx,
           viewport: scaledViewport,
         });
+
         await renderTask.promise;
         if (cancelled) return;
 
-        // draw rotated onto visible canvas
+        visibleCtx.save();
-        ctx.save();
 
         switch (angle) {
           case 90:
-            ctx.translate(canvasWidth, 0);
+            visibleCtx.translate(canvasWidth, 0);
-            ctx.rotate((angle * Math.PI) / 180);
+            visibleCtx.rotate((angle * Math.PI) / 180);
             break;
           case 180:
-            ctx.translate(canvasWidth, canvasHeight);
+            visibleCtx.translate(canvasWidth, canvasHeight);
-            ctx.rotate((angle * Math.PI) / 180);
+            visibleCtx.rotate((angle * Math.PI) / 180);
             break;
           case 270:
-            ctx.translate(0, canvasHeight);
+            visibleCtx.translate(0, canvasHeight);
-            ctx.rotate((angle * Math.PI) / 180);
+            visibleCtx.rotate((angle * Math.PI) / 180);
-            break;
-          default:
             break;
         }
 
-        ctx.drawImage(baseCanvas, 0, 0);
+        visibleCtx.drawImage(baseCanvas, 0, 0);
-        ctx.restore();
+        visibleCtx.restore();
       } catch (e) {
         console.error('Error rendering preview', e);
       }
@@ -116,6 +172,11 @@ const PagePreviewModal: React.FC<PagePreviewModalProps> = ({
 
   if (!isOpen || !pdf || pageIndex == null) return null;
 
+  const positionLabel =
+    visualIndex != null && visualIndex >= 0
+      ? `${visualIndex + 1} / ${totalPages}`
+      : `Page ${pageIndex + 1}`;
+
   return (
     <div
       onClick={onClose}
@@ -133,6 +194,7 @@ const PagePreviewModal: React.FC<PagePreviewModalProps> = ({
       <div
         onClick={(e) => e.stopPropagation()}
         style={{
+          position: 'relative',
           background: '#111827',
           borderRadius: '0.75rem',
           padding: '0.75rem',
@@ -142,25 +204,107 @@ const PagePreviewModal: React.FC<PagePreviewModalProps> = ({
           flexDirection: 'column',
           alignItems: 'center',
           gap: '0.5rem',
+          overflow: 'visible',
         }}
       >
-        <div style={{ alignSelf: 'flex-end' }}>
+        {/* Previous page */}
-          <button
+        <button
-            type="button"
+          type="button"
-            onClick={onClose}
+          onClick={(e) => {
-            style={{
+            e.stopPropagation();
-              border: 'none',
+            onPrevious();
-              borderRadius: '999px',
+          }}
-              padding: '0.25rem 0.5rem',
+          disabled={!canGoPrevious}
-              fontSize: '0.8rem',
+          style={{
-              background: '#374151',
+            position: 'absolute',
-              color: '#e5e7eb',
+            left: 0,
-              cursor: 'pointer',
+            top: '50%',
-            }}
+            transform: 'translate(-50%, -50%)',
-          >
+            width: '2.5rem',
-            ✕ Close
+            height: '2.5rem',
-          </button>
+            borderRadius: '999px',
-        </div>
+            border: 'none',
+            background: canGoPrevious ? '#374151' : '#1f2937',
+            color: canGoPrevious ? '#e5e7eb' : '#6b7280',
+            cursor: canGoPrevious ? 'pointer' : 'default',
+            fontSize: '1.35rem',
+            lineHeight: 1,
+            display: 'flex',
+            alignItems: 'center',
+            justifyContent: 'center',
+            zIndex: 2,
+          }}
+          title="Previous page (←)"
+          aria-label="Previous page"
+        >
+          ◀
+        </button>
+
+        {/* Next page */}
+        <button
+          type="button"
+          onClick={(e) => {
+            e.stopPropagation();
+            onNext();
+          }}
+          disabled={!canGoNext}
+          style={{
+            position: 'absolute',
+            right: 0,
+            top: '50%',
+            transform: 'translate(50%, -50%)',
+            width: '2.5rem',
+            height: '2.5rem',
+            borderRadius: '999px',
+            border: 'none',
+            background: canGoNext ? '#374151' : '#1f2937',
+            color: canGoNext ? '#e5e7eb' : '#6b7280',
+            cursor: canGoNext ? 'pointer' : 'default',
+            fontSize: '1.35rem',
+            lineHeight: 1,
+            display: 'flex',
+            alignItems: 'center',
+            justifyContent: 'center',
+            zIndex: 2,
+          }}
+          title="Next page (→)"
+          aria-label="Next page"
+        >
+          ▶
+        </button>
+
+        {/* Close */}
+        <button
+          type="button"
+          onClick={(e) => {
+            e.stopPropagation();
+            onClose();
+          }}
+          style={{
+            position: 'absolute',
+            top: 0,
+            right: 0,
+            transform: 'translate(50%, -50%)',
+            width: '2.25rem',
+            height: '2.25rem',
+            borderRadius: '999px',
+            border: 'none',
+            background: '#374151',
+            color: '#e5e7eb',
+            cursor: 'pointer',
+            fontSize: '1.2rem',
+            lineHeight: 1,
+            display: 'flex',
+            alignItems: 'center',
+            justifyContent: 'center',
+            zIndex: 3,
+          }}
+          title="Close preview (Esc)"
+          aria-label="Close preview"
+        >
+          ×
+        </button>
+
         <canvas
           ref={canvasRef}
           style={{
@@ -170,8 +314,9 @@ const PagePreviewModal: React.FC<PagePreviewModalProps> = ({
             borderRadius: '0.5rem',
           }}
         />
+
         <div style={{ color: '#e5e7eb', fontSize: '0.85rem' }}>
-          Page {pageIndex + 1} · Rot {rotation}°
+          {positionLabel} · Original page {pageIndex + 1} · Rot {rotation}°
         </div>
       </div>
     </div>

src/pdf/pdfService.ts

@@ -1,5 +1,5 @@
 import { PDFDocument, degrees } from 'pdf-lib';
-import type { PdfFile, SplitResult, Range } from './pdfTypes';
+import type { PdfFile, PageRef, SplitResult, Range } from './pdfTypes';
 
 function createId() {
   return Math.random().toString(36).slice(2);
@@ -53,19 +53,18 @@ export async function mergePdfFiles(
   }
 
   const bytes = await mergedDoc.save();
-  const buffer = bytes.buffer.slice(
+  const buffer = new ArrayBuffer(bytes.byteLength);
-    bytes.byteOffset,
+  new Uint8Array(buffer).set(bytes);
-    bytes.byteOffset + bytes.byteLength
-  );
 
   const baseName = basePdf.name.replace(/\.pdf$/i, '');
   const newName = newPdf.name.replace(/\.pdf$/i, '');
 
   return {
+    id: createId(),
     name: `${baseName}_plus_${newName}.pdf`,
     arrayBuffer: buffer,
     pageCount: mergedDoc.getPageCount(),
-    doc: mergedDoc, // 👈 important
+    doc: mergedDoc,
   };
 }
 
@@ -93,7 +92,7 @@ export async function splitIntoSinglePages(
     if (title) newDoc.setTitle(title);
     if (author) newDoc.setAuthor(author);
     if (subject) newDoc.setSubject(subject);
-    if (keywords) newDoc.setKeywords(keywords);
+    if (keywords) newDoc.setKeywords([keywords]);
     if (producer) newDoc.setProducer(producer);
     if (creator) newDoc.setCreator(creator);
     if (creationDate) newDoc.setCreationDate(creationDate);
@@ -154,30 +153,32 @@ export async function mergePdfs(pdfs: PdfFile[]): Promise<Blob> {
   return new Blob([bytes], { type: 'application/pdf' });
 }
 
-export async function exportReordered(
+export async function exportPages(
   pdf: PdfFile,
-  order: number[],
+  pages: PageRef[]
-  rotations?: Record<number, number>
 ): Promise<Blob> {
   const { doc } = pdf;
   const pageCount = doc.getPageCount();
 
-  if (order.length === 0) {
+  if (pages.length === 0) {
-    throw new Error('Order must contain at least one page');
+    throw new Error('Pages must contain at least one page');
   }
 
-  if (order.some((i) => i < 0 || i >= pageCount)) {
+  if (
-    throw new Error('Order contains invalid page indices');
+    pages.some(
+      (page) => page.sourcePageIndex < 0 || page.sourcePageIndex >= pageCount
+    )
+  ) {
+    throw new Error('Pages contain invalid source page indices');
   }
 
   const newDoc = await PDFDocument.create();
-  const indices = [...order];
+  const indices = pages.map((page) => page.sourcePageIndex);
 
   const copiedPages = await newDoc.copyPages(doc, indices);
 
   copiedPages.forEach((page, idx) => {
-    const originalIndex = indices[idx];
+    const angle = pages[idx].rotation;
-    const angle = rotations?.[originalIndex];
 
     if (typeof angle === 'number' && angle % 360 !== 0) {
       page.setRotation(degrees(angle));
@@ -189,3 +190,18 @@ export async function exportReordered(
   const bytes = await newDoc.save();
   return new Blob([bytes], { type: 'application/pdf' });
 }
+
+export async function exportReordered(
+  pdf: PdfFile,
+  order: number[],
+  rotations?: Record<number, number>
+): Promise<Blob> {
+  return exportPages(
+    pdf,
+    order.map((sourcePageIndex) => ({
+      id: String(sourcePageIndex),
+      sourcePageIndex,
+      rotation: rotations?.[sourcePageIndex] ?? 0,
+    }))
+  );
+}

src/pdf/pdfThumbnailService.ts

@@ -19,115 +19,190 @@ function makePdfJsDataCopy(arrayBuffer: ArrayBuffer): Uint8Array {
   return copy;
 }
 
+interface ThumbnailUpdate {
+  pageIndex: number;
+  dataUrl: string;
+}
+
+interface ThumbnailGenerationOptions {
+  maxHeight?: number;
+  maxWidth?: number;
+  concurrency?: number;
+  /**
+   * Optional subset of 0-based page indices to render.
+   * If omitted, all pages are rendered.
+   */
+  pageIndices?: number[];
+  signal?: AbortSignal;
+  onThumbnail?: (update: ThumbnailUpdate) => void;
+}
+
+
 /**
  * Unrotated thumbnails – used e.g. in the Split/Extract view.
  */
-export async function generateThumbnails(
+export async function generateThumbnailsProgressive(
   arrayBuffer: ArrayBuffer,
-  maxHeight = 150
+  options: ThumbnailGenerationOptions = {}
 ): Promise<string[]> {
-  return generateThumbnailsInternal(arrayBuffer, {}, maxHeight);
+  return generateThumbnailsInternal(arrayBuffer, {}, options);
 }
 
 /**
  * Thumbnails that respect per-page rotations (for the Reorder view).
  */
-export async function generateThumbnailsWithRotations(
+export async function generateThumbnailsWithRotationsProgressive(
   arrayBuffer: ArrayBuffer,
   rotations: RotationsMap,
-  maxHeight = 150
+  options: ThumbnailGenerationOptions = {}
 ): Promise<string[]> {
-  return generateThumbnailsInternal(arrayBuffer, rotations, maxHeight);
+  return generateThumbnailsInternal(arrayBuffer, rotations, options);
 }
 
 async function generateThumbnailsInternal(
   arrayBuffer: ArrayBuffer,
   rotations: RotationsMap,
-  maxHeight: number
+  options: ThumbnailGenerationOptions = {}
 ): Promise<string[]> {
-  // IMPORTANT: use a COPY so pdf.js can detach it without breaking future calls
+  const maxHeight = options.maxHeight ?? 150;
-  const dataCopy = makePdfJsDataCopy(arrayBuffer);
+  const maxWidth = options.maxWidth ?? 140;
+  const concurrency = Math.max(1, Math.min(options.concurrency ?? 3, 6));
+  const signal = options.signal;
 
+  const dataCopy = makePdfJsDataCopy(arrayBuffer);
   const loadingTask = pdfjsLib.getDocument({ data: dataCopy });
   const pdf = await loadingTask.promise;
 
-  const thumbs: string[] = [];
+  const thumbs = Array<string>(pdf.numPages).fill('');
+
+  const pageNums = options.pageIndices
+    ? Array.from(
+        new Set(
+          options.pageIndices
+            .filter((pageIndex) => pageIndex >= 0 && pageIndex < pdf.numPages)
+            .map((pageIndex) => pageIndex + 1)
+        )
+      )
+    : Array.from({ length: pdf.numPages }, (_, index) => index + 1);
+
+  let nextPageIndex = 0;
+
+  const renderOne = async (pageNum: number) => {
+    if (signal?.aborted) return;
 
-  for (let pageNum = 1; pageNum <= pdf.numPages; pageNum++) {
     const page = await pdf.getPage(pageNum);
-    const viewport = page.getViewport({ scale: 1 });
+    if (signal?.aborted) return;
-    const scale = maxHeight / viewport.height;
-    const scaledViewport = page.getViewport({ scale });
 
-    // First render unrotated page into a canvas
+    const pageIndex = pageNum - 1;
-    const baseCanvas = document.createElement('canvas');
+    const dataUrl = await renderPageThumbnail(
-    const baseCtx = baseCanvas.getContext('2d');
+      page,
-    if (!baseCtx) {
+      pageIndex,
-      thumbs.push('');
+      rotations,
-      continue;
+      maxHeight,
+      maxWidth
+    );
+
+    if (signal?.aborted) return;
+
+    thumbs[pageIndex] = dataUrl;
+    options.onThumbnail?.({ pageIndex, dataUrl });
+  };
+
+  const worker = async () => {
+    while (!signal?.aborted) {
+      const pageNum = pageNums[nextPageIndex];
+      nextPageIndex += 1;
+ 
+      if (pageNum == null) return;
+
+      await renderOne(pageNum);
+
+      // Let React/browser paint between batches.
+      await new Promise<void>((resolve) => {
+        requestAnimationFrame(() => resolve());
+      });
     }
+  };
 
-    baseCanvas.width = scaledViewport.width;
+  const workerCount = Math.min(concurrency, pageNums.length);
-    baseCanvas.height = scaledViewport.height;
+  if (workerCount === 0) return thumbs;
 
-    const renderTask = page.render({
+  await Promise.all(Array.from({ length: workerCount }, worker));
-      canvasContext: baseCtx,
-      viewport: scaledViewport,
-    });
-    await renderTask.promise;
-
-    const originalIndex = pageNum - 1;
-    const rotationDegRaw = rotations[originalIndex] ?? 0;
-    const rotationDeg = ((rotationDegRaw % 360) + 360) % 360; // normalize 0–359
-
-    if (rotationDeg === 0) {
-      thumbs.push(baseCanvas.toDataURL('image/png'));
-      continue;
-    }
-
-    // Re-render onto a second canvas with rotation applied
-    const rotatedCanvas = document.createElement('canvas');
-    const rotatedCtx = rotatedCanvas.getContext('2d');
-    if (!rotatedCtx) {
-      thumbs.push(baseCanvas.toDataURL('image/png'));
-      continue;
-    }
-
-    const rad = (rotationDeg * Math.PI) / 180;
-
-    if (rotationDeg === 90 || rotationDeg === 270) {
-      rotatedCanvas.width = baseCanvas.height;
-      rotatedCanvas.height = baseCanvas.width;
-    } else {
-      rotatedCanvas.width = baseCanvas.width;
-      rotatedCanvas.height = baseCanvas.height;
-    }
-
-    rotatedCtx.save();
-
-    switch (rotationDeg) {
-      case 90:
-        rotatedCtx.translate(rotatedCanvas.width, 0);
-        rotatedCtx.rotate(rad);
-        break;
-      case 180:
-        rotatedCtx.translate(rotatedCanvas.width, rotatedCanvas.height);
-        rotatedCtx.rotate(rad);
-        break;
-      case 270:
-        rotatedCtx.translate(0, rotatedCanvas.height);
-        rotatedCtx.rotate(rad);
-        break;
-      default:
-        // fallback: no rotation
-        break;
-    }
-
-    rotatedCtx.drawImage(baseCanvas, 0, 0);
-    rotatedCtx.restore();
-
-    thumbs.push(rotatedCanvas.toDataURL('image/png'));
-  }
 
   return thumbs;
 }
+
+async function renderPageThumbnail(
+  page: Awaited<ReturnType<Awaited<ReturnType<typeof pdfjsLib.getDocument>['promise']>['getPage']>>,
+  originalIndex: number,
+  rotations: RotationsMap,
+  maxHeight: number,
+  maxWidth: number
+): Promise<string> {
+  const viewport = page.getViewport({ scale: 1 });
+  const scaleH = maxHeight / viewport.height;
+  const scaleW = maxWidth / viewport.width;
+  const scale = Math.min(scaleH, scaleW);
+  const scaledViewport = page.getViewport({ scale });
+
+  const baseCanvas = document.createElement('canvas');
+  const baseCtx = baseCanvas.getContext('2d');
+
+  if (!baseCtx) return '';
+
+  baseCanvas.width = scaledViewport.width;
+  baseCanvas.height = scaledViewport.height;
+
+  const renderTask = page.render({
+    canvasContext: baseCtx,
+    viewport: scaledViewport,
+  });
+
+  await renderTask.promise;
+
+  const rotationDegRaw = rotations[originalIndex] ?? 0;
+  const rotationDeg = ((rotationDegRaw % 360) + 360) % 360;
+
+  if (rotationDeg === 0) {
+    return baseCanvas.toDataURL('image/png');
+  }
+
+  const rotatedCanvas = document.createElement('canvas');
+  const rotatedCtx = rotatedCanvas.getContext('2d');
+
+  if (!rotatedCtx) {
+    return baseCanvas.toDataURL('image/png');
+  }
+
+  const rad = (rotationDeg * Math.PI) / 180;
+
+  if (rotationDeg === 90 || rotationDeg === 270) {
+    rotatedCanvas.width = baseCanvas.height;
+    rotatedCanvas.height = baseCanvas.width;
+  } else {
+    rotatedCanvas.width = baseCanvas.width;
+    rotatedCanvas.height = baseCanvas.height;
+  }
+
+  rotatedCtx.save();
+
+  switch (rotationDeg) {
+    case 90:
+      rotatedCtx.translate(rotatedCanvas.width, 0);
+      rotatedCtx.rotate(rad);
+      break;
+    case 180:
+      rotatedCtx.translate(rotatedCanvas.width, rotatedCanvas.height);
+      rotatedCtx.rotate(rad);
+      break;
+    case 270:
+      rotatedCtx.translate(0, rotatedCanvas.height);
+      rotatedCtx.rotate(rad);
+      break;
+  }
+
+  rotatedCtx.drawImage(baseCanvas, 0, 0);
+  rotatedCtx.restore();
+
+  return rotatedCanvas.toDataURL('image/png');
+}

src/pdf/pdfTypes.ts

@@ -8,6 +8,12 @@ export interface PdfFile {
   arrayBuffer: ArrayBuffer;
 }
 
+export interface PageRef {
+  id: string;
+  sourcePageIndex: number;
+  rotation: number;
+}
+
 export interface SplitResult {
   pageIndex: number;
   blob: Blob;

src/styles.css

@@ -120,12 +120,6 @@ button.secondary {
   margin-top: 0.5rem;
 }
 
-.page-list {
-  display: flex;
-  flex-wrap: wrap;
-  gap: 0.5rem;
-}
-
 .app-root {
   min-height: 100vh;
   background-color: #f3f4f6;
@@ -175,20 +169,6 @@ button.secondary {
   width: 100%;
 }
 
-/* Slightly less rounded page pills so they look like rectangles */
-.page-pill {
-  padding: 0.2rem 0.5rem;
-  border-radius: 0.5rem; /* was 999px */
-  border: 1px solid #e5e7eb;
-  font-size: 0.8rem;
-  background: #f9fafb;
-}
-
-.page-pill.selected {
-  background: #dbeafe;
-  border-color: #93c5fd;
-}
-
 .download-link {
   display: inline-block;
   margin: 0.15rem 0;