Roadmap, robust page refs, copy behaviour

2026-05-16 02:37:20 +02:00
parent a649ede010
commit 2461cf3d64
9 changed files with 1588 additions and 744 deletions
--- a/src/App.tsx
+++ b/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,
-  generateThumbnailsWithRotations,
+  generateThumbnailsProgressive,
+  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 [reorderThumbnails, setReorderThumbnails] = useState<string[] | null>(
-    null
-  );
+  const [pages, setPages] = useState<PageRef[]>([]);
+  const [reorderThumbnails, setReorderThumbnails] = useState<Record<string, string>>({});

-  const [order, setOrder] = useState<number[]>([]);
-  const [rotations, setRotations] = useState<Record<number, number>>({});
-
-  const [selectedPages, setSelectedPages] = useState<number[]>([]);
-  const [lastSelectedVisualIndex, setLastSelectedVisualIndex] = useState<
-    number | null
-  >(null);
+  const [selectedPageIds, setSelectedPageIds] = useState<string[]>([]);
+  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) => {
-    setError(null);
+  const thumbnailCacheRef = useRef<Map<string, string>>(new Map());
+  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([]);
-    setLastSelectedVisualIndex(null);
-    setSubsetUrl(null);
-    setSubsetFilename(null);
-    setExportUrl(null);
-    setExportFilename(null);
-    setBaseThumbnails(null);
-    setReorderThumbnails(null);
-    setRotations({});
-    setOrder([]);
-    setPreviewIndex(null);
+    setSelectedPageIds([]);
+     setLastSelectedVisualIndex(null);
+    resetGeneratedUrls();
+    setReorderThumbnails({});
+    thumbnailCacheRef.current.clear();
+    previousPageRotationsRef.current.clear();
+    latestPagesRef.current = [];
+    setPages([]);
+    setPreviewPageId(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(
-        { length: loaded.pageCount },
-        (_, i) => i
-      );
-      setOrder(initialOrder);
+      setPdf(loaded);
+      setPages(initialPages);
+      latestPagesRef.current = initialPages;
    } 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 || order.length === 0) {
+    if (!pdf || pages.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)
-      const currentBlob = await exportReordered(pdf, order, rotations);
+      // 1) Materialize the current in-memory workspace (page refs + 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 },
-        (_, i) => i
-      );
-      setOrder(mergedOrder);
-      setRotations({});
-      setSelectedPages([]);
+
+      setPages(mergedPages);
+      latestPagesRef.current = mergedPages;
+      setSelectedPageIds([]);
      setLastSelectedVisualIndex(null);
      setSplitResults([]);
-
-      if (subsetUrl) {
-        URL.revokeObjectURL(subsetUrl);
-        setSubsetUrl(null);
-        setSubsetFilename(null);
-      }
-      if (exportUrl) {
-        URL.revokeObjectURL(exportUrl);
-        setExportUrl(null);
-        setExportFilename(null);
-      }
-
-      setBaseThumbnails(null);
-      setReorderThumbnails(null);
-      setPreviewIndex(null);
+      resetGeneratedUrls();
+      setReorderThumbnails({});
+      thumbnailCacheRef.current.clear();
+      previousPageRotationsRef.current.clear();
+      setPreviewPageId(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(null);
+      setReorderThumbnails({});
+      thumbnailCacheRef.current.clear();
+      previousPageRotationsRef.current.clear();
      return;
    }
-    let cancelled = false;

-    (async () => {
-      try {
-        const thumbs = await generateThumbnails(pdf.arrayBuffer);
-        if (!cancelled) {
-          setBaseThumbnails(thumbs);
-          setReorderThumbnails(thumbs);
+    const controller = new AbortController();
+
+    latestPagesRef.current = pages;
+    thumbnailCacheRef.current.clear();
+    previousPageRotationsRef.current = new Map(
+      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 () => {
-      try {
-        const thumbs = await generateThumbnailsWithRotations(
-          pdf.arrayBuffer,
-          rotations
-        );
-        if (!cancelled) {
-          setReorderThumbnails(thumbs);
-        }
-      } catch (e) {
-        console.error(e);
-        if (!cancelled) {
-          setError('Failed to generate rotated thumbnails (see console).');
-        }
+    const previousRotations = previousPageRotationsRef.current;
+    const changedPages = pages.filter(
+      (page) =>
+        normalizeRotation(previousRotations.get(page.id)) !==
+        normalizeRotation(page.rotation)
+    );
+
+    previousPageRotationsRef.current = new Map(
+      pages.map((page) => [page.id, normalizeRotation(page.rotation)])
+    );
+
+    if (changedPages.length === 0) return;
+
+    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) => {
-    setRotations((prev) => {
-      const current = prev[pageIndex] ?? 0;
-      const next = (current + 90) % 360;
-      return { ...prev, [pageIndex]: next };
-    });
+  const handleRotatePageClockwise = (pageId: string) => {
+    setPages((prev) =>
+      prev.map((page) =>
+        page.id === pageId
+          ? { ...page, rotation: (normalizeRotation(page.rotation) + 90) % 360 }
+          : page
+      )
+    );
  };

-  const handleRotatePageCounterclockwise = (pageIndex: number) => {
-    setRotations((prev) => {
-      const current = prev[pageIndex] ?? 0;
-      const next = (current + 270) % 360;
-      return { ...prev, [pageIndex]: next };
-    });
+  const handleRotatePageCounterclockwise = (pageId: string) => {
+    setPages((prev) =>
+      prev.map((page) =>
+        page.id === pageId
+          ? { ...page, rotation: (normalizeRotation(page.rotation) + 270) % 360 }
+          : page
+      )
+    );
  };

-  const handleDeletePage = (pageIndex: number) => {
-    setOrder((prev) => prev.filter((p) => p !== pageIndex));
-    setSelectedPages((prev) => prev.filter((p) => p !== pageIndex));
+  const handleDeletePage = (pageId: string) => {
+    setPages((prev) => prev.filter((page) => page.id !== pageId));
+    setSelectedPageIds((prev) => prev.filter((id) => id !== pageId));
  };

-  const handleReorder = (newOrder: number[]) => {
-    setOrder(newOrder);
+  const handleReorder = (newPages: PageRef[]) => {
+    setPages(newPages);
  };

  const handleToggleSelect = (
-    pageIndex: number,
+    pageId: string,
    visualIndex: number,
    e: React.MouseEvent<HTMLButtonElement>
  ) => {
-    setSelectedPages((prev) => {
-      // Shift: add a range (visual positions) to the existing selection
-      if (e.shiftKey && lastSelectedVisualIndex !== null && order.length > 0) {
+    setSelectedPageIds((prev) => {
+      if (e.shiftKey && lastSelectedVisualIndex !== null && pages.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(pageIndex)) {
-        return prev.filter((p) => p !== pageIndex);
+      if (prev.includes(pageId)) {
+        return prev.filter((id) => id !== pageId);
      }

-      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;
-    setOrder((prev) => prev.filter((p) => !selectedPages.includes(p)));
-    setSelectedPages([]);
+    if (selectedPageIds.length === 0) return;
+    const selectedSet = new Set(selectedPageIds);
+    setPages((prev) => prev.filter((page) => !selectedSet.has(page.id)));
+    setSelectedPageIds([]);
    setLastSelectedVisualIndex(null);
  };

-  const handleOpenPreview = (pageIndex: number) => {
-    setPreviewIndex(pageIndex);
+  const handleCopyPagesToSlot = (pageIds: string[], insertSlot: number) => {
+    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) =>
-        selectedPages.includes(idx)
-      );
-      const blob = await exportReordered(pdf, selectedOrder, rotations);
+      const selectedSet = new Set(selectedPageIds);
+      const selectedPages = pages.filter((page) => selectedSet.has(page.id));
+      const blob = await exportPages(pdf, selectedPages);
      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}
-        selectedPages={selectedPages}
+        selectedPageIds={selectedPageIds}
        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}
-        rotation={previewIndex != null ? rotations[previewIndex] ?? 0 : 0}
+        pageIndex={previewPage?.sourcePageIndex ?? null}
+        rotation={previewPage?.rotation ?? 0}
+        visualIndex={previewVisualIndex >= 0 ? previewVisualIndex : null}
+        totalPages={pages.length}
+        canGoPrevious={canPreviewPrevious}
+        canGoNext={canPreviewNext}
+        onPrevious={handlePreviewPrevious}
+        onNext={handlePreviewNext}
        onClose={handleClosePreview}
      />
    </Layout>
--- a/src/components/PageList.tsx
+++ b/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;
--- a/src/components/PagePreviewModal.tsx
+++ b/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;
-        if (!canvas) return;
-        const ctx = canvas.getContext('2d');
-        if (!ctx) return;
+        const visibleCanvas = canvasRef.current;
+        if (!visibleCanvas) 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;
-        canvas.height = canvasHeight;
+        visibleCanvas.width = canvasWidth;
+        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
-        ctx.save();
+        visibleCtx.save();

        switch (angle) {
          case 90:
-            ctx.translate(canvasWidth, 0);
-            ctx.rotate((angle * Math.PI) / 180);
+            visibleCtx.translate(canvasWidth, 0);
+            visibleCtx.rotate((angle * Math.PI) / 180);
            break;
          case 180:
-            ctx.translate(canvasWidth, canvasHeight);
-            ctx.rotate((angle * Math.PI) / 180);
+            visibleCtx.translate(canvasWidth, canvasHeight);
+            visibleCtx.rotate((angle * Math.PI) / 180);
            break;
          case 270:
-            ctx.translate(0, canvasHeight);
-            ctx.rotate((angle * Math.PI) / 180);
-            break;
-          default:
+            visibleCtx.translate(0, canvasHeight);
+            visibleCtx.rotate((angle * Math.PI) / 180);
            break;
        }

-        ctx.drawImage(baseCanvas, 0, 0);
-        ctx.restore();
+        visibleCtx.drawImage(baseCanvas, 0, 0);
+        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' }}>
-          <button
-            type="button"
-            onClick={onClose}
-            style={{
-              border: 'none',
-              borderRadius: '999px',
-              padding: '0.25rem 0.5rem',
-              fontSize: '0.8rem',
-              background: '#374151',
-              color: '#e5e7eb',
-              cursor: 'pointer',
-            }}
-          >
-            ✕ Close
-          </button>
-        </div>
+        {/* Previous page */}
+        <button
+          type="button"
+          onClick={(e) => {
+            e.stopPropagation();
+            onPrevious();
+          }}
+          disabled={!canGoPrevious}
+          style={{
+            position: 'absolute',
+            left: 0,
+            top: '50%',
+            transform: 'translate(-50%, -50%)',
+            width: '2.5rem',
+            height: '2.5rem',
+            borderRadius: '999px',
+            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={{
@@ -170,12 +314,13 @@ 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>
  );
 };

-export default PagePreviewModal;
+export default PagePreviewModal;
--- a/src/components/ReorderPanel.tsx
+++ b/src/components/ReorderPanel.tsx
--- a/src/pdf/pdfService.ts
+++ b/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(
-    bytes.byteOffset,
-    bytes.byteOffset + bytes.byteLength
-  );
+  const buffer = new ArrayBuffer(bytes.byteLength);
+  new Uint8Array(buffer).set(bytes);

  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[],
-  rotations?: Record<number, number>
+  pages: PageRef[]
 ): Promise<Blob> {
  const { doc } = pdf;
  const pageCount = doc.getPageCount();

-  if (order.length === 0) {
-    throw new Error('Order must contain at least one page');
+  if (pages.length === 0) {
+    throw new Error('Pages must contain at least one page');
  }

-  if (order.some((i) => i < 0 || i >= pageCount)) {
-    throw new Error('Order contains invalid page indices');
+  if (
+    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 = rotations?.[originalIndex];
+    const angle = pages[idx].rotation;

    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,
+    }))
+  );
+}
--- a/src/pdf/pdfThumbnailService.ts
+++ b/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 dataCopy = makePdfJsDataCopy(arrayBuffer);
+  const maxHeight = options.maxHeight ?? 150;
+  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 });
-    const scale = maxHeight / viewport.height;
-    const scaledViewport = page.getViewport({ scale });
+    if (signal?.aborted) return;

-    // First render unrotated page into a canvas
-    const baseCanvas = document.createElement('canvas');
-    const baseCtx = baseCanvas.getContext('2d');
-    if (!baseCtx) {
-      thumbs.push('');
-      continue;
+    const pageIndex = pageNum - 1;
+    const dataUrl = await renderPageThumbnail(
+      page,
+      pageIndex,
+      rotations,
+      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;
-    baseCanvas.height = scaledViewport.height;
+  const workerCount = Math.min(concurrency, pageNums.length);
+  if (workerCount === 0) return thumbs;

-    const renderTask = page.render({
-      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'));
-  }
+  await Promise.all(Array.from({ length: workerCount }, worker));

  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');
+}
--- a/src/pdf/pdfTypes.ts
+++ b/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;
--- a/src/styles.css
+++ b/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;