fix: improve error handling, race condition and optimize page rendering logic in pdf multi tool

src/js/logic/pdf-multi-tool.ts

@@ -1,10 +1,15 @@
 import { createIcons, icons } from 'lucide';
-import { degrees, PDFDocument as PDFLibDocument } from 'pdf-lib';
+import { degrees, PDFDocument as PDFLibDocument, PDFPage } from 'pdf-lib';
 import * as pdfjsLib from 'pdfjs-dist';
 import JSZip from 'jszip';
 import Sortable from 'sortablejs';
 import { downloadFile, getPDFDocument } from '../utils/helpers';
-import { renderPagesProgressively, cleanupLazyRendering, renderPageToCanvas, createPlaceholder } from '../utils/render-utils';
+import {
+  renderPagesProgressively,
+  cleanupLazyRendering,
+  renderPageToCanvas,
+  createPlaceholder,
+} from '../utils/render-utils';
 import { initializeGlobalShortcuts } from '../utils/shortcuts-init.js';
 import { repairPdfFile } from './repair-pdf.js';
 
@@ -41,13 +46,17 @@ let sortableInstance: Sortable | null = null;
 
 const pageCanvasCache = new Map<string, HTMLCanvasElement>();
 
-type Snapshot = { allPages: PageData[]; selectedPages: number[]; splitMarkers: number[] };
+type Snapshot = {
+  allPages: PageData[];
+  selectedPages: number[];
+  splitMarkers: number[];
+};
 const undoStack: Snapshot[] = [];
 const redoStack: Snapshot[] = [];
 
 function snapshot() {
   const snap: Snapshot = {
-    allPages: allPages.map(p => ({ ...p, canvas: p.canvas })),
+    allPages: allPages.map((p) => ({ ...p, canvas: p.canvas })),
     selectedPages: Array.from(selectedPages),
     splitMarkers: Array.from(splitMarkers),
   };
@@ -56,16 +65,20 @@ function snapshot() {
 }
 
 function restore(snap: Snapshot) {
-  allPages = snap.allPages.map(p => ({
+  allPages = snap.allPages.map((p) => ({
     ...p,
-    canvas: p.canvas
+    canvas: p.canvas,
   }));
   selectedPages = new Set(snap.selectedPages);
   splitMarkers = new Set(snap.splitMarkers);
   updatePageDisplay();
 }
 
-function showModal(title: string, message: string, type: 'info' | 'error' | 'success' = 'info') {
+function showModal(
+  title: string,
+  message: string,
+  type: 'info' | 'error' | 'success' = 'info'
+) {
   const modal = document.getElementById('modal');
   const modalTitle = document.getElementById('modal-title');
   const modalMessage = document.getElementById('modal-message');
@@ -79,12 +92,12 @@ function showModal(title: string, message: string, type: 'info' | 'error' | 'suc
   const iconMap = {
     info: 'info',
     error: 'alert-circle',
-    success: 'check-circle'
+    success: 'check-circle',
   };
   const colorMap = {
     info: 'text-blue-400',
     error: 'text-red-400',
-    success: 'text-green-400'
+    success: 'text-green-400',
   };
 
   modalIcon.innerHTML = `<i data-lucide="${iconMap[type]}" class="w-12 h-12 ${colorMap[type]}"></i>`;
@@ -112,7 +125,10 @@ function showLoading(current: number, total: number) {
   text.textContent = t('multiTool.renderingPages');
 }
 
-async function withButtonLoading(buttonId: string, action: () => Promise<void>) {
+async function withButtonLoading(
+  buttonId: string,
+  action: () => Promise<void>
+) {
   const button = document.getElementById(buttonId) as HTMLButtonElement;
   if (!button) return;
 
@@ -122,7 +138,8 @@ async function withButtonLoading(buttonId: string, action: () => Promise<void>)
   try {
     button.disabled = true;
     button.style.pointerEvents = 'none';
-    button.innerHTML = '<svg class="animate-spin h-5 w-5 text-white" xmlns="http://www.w3.org/2000/svg" fill="none" viewBox="0 0 24 24"><circle class="opacity-25" cx="12" cy="12" r="10" stroke="currentColor" stroke-width="4"></circle><path class="opacity-75" fill="currentColor" d="M4 12a8 8 0 018-8V0C5.373 0 0 5.373 0 12h4zm2 5.291A7.962 7.962 0 014 12H0c0 3.042 1.135 5.824 3 7.938l3-2.647z"></path></svg>';
+    button.innerHTML =
+      '<svg class="animate-spin h-5 w-5 text-white" xmlns="http://www.w3.org/2000/svg" fill="none" viewBox="0 0 24 24"><circle class="opacity-25" cx="12" cy="12" r="10" stroke="currentColor" stroke-width="4"></circle><path class="opacity-75" fill="currentColor" d="M4 12a8 8 0 018-8V0C5.373 0 0 5.373 0 12h4zm2 5.291A7.962 7.962 0 014 12H0c0 3.042 1.135 5.824 3 7.938l3-2.647z"></path></svg>';
 
     await action();
   } finally {
@@ -143,7 +160,9 @@ if (document.readyState === 'loading') {
     initializeTool();
   });
 } else {
-  console.log('PDF Multi Tool: DOMContentLoaded already fired, initializing immediately');
+  console.log(
+    'PDF Multi Tool: DOMContentLoaded already fired, initializing immediately'
+  );
   initializeTool();
 }
 
@@ -160,16 +179,26 @@ function initializeTool() {
   document.getElementById('upload-pdfs-btn')?.addEventListener('click', () => {
     console.log('Upload button clicked, isRendering:', isRendering);
     if (isRendering) {
-      showModal(t('multiTool.pleaseWait'), t('multiTool.pagesRendering'), 'info');
+      showModal(
+        t('multiTool.pleaseWait'),
+        t('multiTool.pagesRendering'),
+        'info'
+      );
       return;
     }
     document.getElementById('pdf-file-input')?.click();
   });
 
-  document.getElementById('pdf-file-input')?.addEventListener('change', handlePdfUpload);
+  document
-  document.getElementById('insert-pdf-input')?.addEventListener('change', handleInsertPdf);
+    .getElementById('pdf-file-input')
+    ?.addEventListener('change', handlePdfUpload);
+  document
+    .getElementById('insert-pdf-input')
+    ?.addEventListener('change', handleInsertPdf);
 
-  document.getElementById('bulk-rotate-left-btn')?.addEventListener('click', () => {
+  document
+    .getElementById('bulk-rotate-left-btn')
+    ?.addEventListener('click', () => {
       if (isRendering) return;
       snapshot();
       bulkRotate(-90);
@@ -184,7 +213,9 @@ function initializeTool() {
     snapshot();
     bulkDelete();
   });
-  document.getElementById('bulk-duplicate-btn')?.addEventListener('click', () => {
+  document
+    .getElementById('bulk-duplicate-btn')
+    ?.addEventListener('click', () => {
       if (isRendering) return;
       snapshot();
       bulkDuplicate();
@@ -194,15 +225,24 @@ function initializeTool() {
     snapshot();
     bulkSplit();
   });
-  document.getElementById('bulk-download-btn')?.addEventListener('click', () => {
+  document
+    .getElementById('bulk-download-btn')
+    ?.addEventListener('click', () => {
       if (isRendering) return;
       if (isRendering) return;
       if (selectedPages.size === 0) {
-      showModal(t('multiTool.noPagesSelected'), t('multiTool.selectOnePage'), 'info');
+        showModal(
+          t('multiTool.noPagesSelected'),
+          t('multiTool.selectOnePage'),
+          'info'
+        );
         return;
       }
       withButtonLoading('bulk-download-btn', async () => {
-      await downloadPagesAsPdf(Array.from(selectedPages).sort((a, b) => a - b), 'selected-pages.pdf');
+        await downloadPagesAsPdf(
+          Array.from(selectedPages).sort((a, b) => a - b),
+          'selected-pages.pdf'
+        );
       });
     });
 
@@ -229,7 +269,9 @@ function initializeTool() {
       await downloadAll();
     });
   });
-  document.getElementById('add-blank-page-btn')?.addEventListener('click', () => {
+  document
+    .getElementById('add-blank-page-btn')
+    ?.addEventListener('click', () => {
       if (isRendering) return;
       snapshot();
       addBlankPage();
@@ -239,7 +281,7 @@ function initializeTool() {
     const last = undoStack.pop();
     if (last) {
       const current: Snapshot = {
-        allPages: allPages.map(p => ({ ...p })),
+        allPages: allPages.map((p) => ({ ...p })),
         selectedPages: Array.from(selectedPages),
         splitMarkers: Array.from(splitMarkers),
       };
@@ -252,7 +294,7 @@ function initializeTool() {
     const next = redoStack.pop();
     if (next) {
       const current: Snapshot = {
-        allPages: allPages.map(p => ({ ...p })),
+        allPages: allPages.map((p) => ({ ...p })),
         selectedPages: Array.from(selectedPages),
         splitMarkers: Array.from(splitMarkers),
       };
@@ -269,7 +311,9 @@ function initializeTool() {
     }
   });
 
-  document.getElementById('modal-close-btn')?.addEventListener('click', hideModal);
+  document
+    .getElementById('modal-close-btn')
+    ?.addEventListener('click', hideModal);
   document.getElementById('modal')?.addEventListener('click', (e) => {
     if (e.target === document.getElementById('modal')) {
       hideModal();
@@ -288,7 +332,9 @@ function initializeTool() {
     uploadArea.addEventListener('drop', (e) => {
       e.preventDefault();
       uploadArea.classList.remove('border-indigo-500');
-      const files = Array.from(e.dataTransfer?.files || []).filter(f => f.type === 'application/pdf');
+      const files = Array.from(e.dataTransfer?.files || []).filter(
+        (f) => f.type === 'application/pdf'
+      );
       if (files.length > 0) {
         loadPdfs(files);
       }
@@ -361,27 +407,38 @@ async function loadPdfs(files: File[]) {
         try {
           console.log(`Repairing ${file.name}...`);
           const loadingText = document.getElementById('loading-text');
-          if (loadingText) loadingText.textContent = `Repairing ${file.name}...`;
+          if (loadingText)
+            loadingText.textContent = `Repairing ${file.name}...`;
 
           const repairedData = await repairPdfFile(file);
           if (repairedData) {
             arrayBuffer = repairedData.buffer as ArrayBuffer;
             console.log(`Successfully repaired ${file.name} before loading.`);
           } else {
-            console.warn(`Repair returned null for ${file.name}, using original file.`);
+            console.warn(
+              `Repair returned null for ${file.name}, using original file.`
+            );
             arrayBuffer = await file.arrayBuffer();
           }
         } catch (repairError) {
-          console.warn(`Failed to repair ${file.name}, attempting to load original:`, repairError);
+          console.warn(
+            `Failed to repair ${file.name}, attempting to load original:`,
+            repairError
+          );
           arrayBuffer = await file.arrayBuffer();
         }
 
-        const pdfDoc = await PDFLibDocument.load(arrayBuffer, { ignoreEncryption: true, throwOnInvalidObject: false });
+        const pdfDoc = await PDFLibDocument.load(arrayBuffer, {
+          ignoreEncryption: true,
+          throwOnInvalidObject: false,
+        });
         currentPdfDocs.push(pdfDoc);
         const pdfIndex = currentPdfDocs.length - 1;
 
         const pdfBytes = await pdfDoc.save();
-        const pdfjsDoc = await getPDFDocument({ data: new Uint8Array(pdfBytes) }).promise;
+        const pdfjsDoc = await getPDFDocument({
+          data: new Uint8Array(pdfBytes),
+        }).promise;
         const numPages = pdfjsDoc.numPages;
 
         // Pre-fill allPages with placeholders to maintain order/state
@@ -425,10 +482,13 @@ async function loadPdfs(files: File[]) {
             shouldCancel: () => renderCancelled, // Pass cancellation check
           }
         );
-
       } catch (e) {
         console.error(`Failed to load PDF ${file.name}:`, e);
-        showModal(t('multiTool.error'), `${t('multiTool.failedToLoad')} ${file.name}.`, 'error');
+        showModal(
+          t('multiTool.error'),
+          `${t('multiTool.failedToLoad')} ${file.name}.`,
+          'error'
+        );
       }
     }
 
@@ -439,7 +499,9 @@ async function loadPdfs(files: File[]) {
   } finally {
     hideLoading();
     isRendering = false;
-    console.log('PDF Multi Tool: Render finished/cancelled, isRendering set to false');
+    console.log(
+      'PDF Multi Tool: Render finished/cancelled, isRendering set to false'
+    );
     if (renderCancelled) {
       renderCancelled = false;
     }
@@ -464,7 +526,10 @@ function createPageCard(pageData: PageData, index: number) {
 }
 
 // Modified to return the element instead of appending it
-function createPageElement(canvas: HTMLCanvasElement | null, index: number): HTMLElement {
+function createPageElement(
+  canvas: HTMLCanvasElement | null,
+  index: number
+): HTMLElement {
   const pageData = allPages[index];
   if (!pageData) {
     console.error(`Page data not found for index ${index}`);
@@ -472,7 +537,8 @@ function createPageElement(canvas: HTMLCanvasElement | null, index: number): HTM
   }
 
   const card = document.createElement('div');
-  card.className = 'bg-gray-800 rounded-lg border-2 border-gray-700 p-2 relative group cursor-move';
+  card.className =
+    'bg-gray-800 rounded-lg border-2 border-gray-700 p-2 relative group cursor-move';
   card.dataset.pageIndex = index.toString();
   card.dataset.pageId = pageData.id; // Set ID for reconciliation
 
@@ -490,7 +556,8 @@ function createPageElement(canvas: HTMLCanvasElement | null, index: number): HTM
   }
 
   const preview = document.createElement('div');
-  preview.className = 'bg-white rounded mb-2 overflow-hidden w-full flex items-center justify-center relative h-36 sm:h-64';
+  preview.className =
+    'bg-white rounded mb-2 overflow-hidden w-full flex items-center justify-center relative h-36 sm:h-64';
 
   if (canvas) {
     const previewCanvas = canvas;
@@ -502,7 +569,8 @@ function createPageElement(canvas: HTMLCanvasElement | null, index: number): HTM
   } else {
     // Show loading placeholder if canvas is null
     const loading = document.createElement('div');
-    loading.className = 'flex flex-col items-center justify-center text-gray-400';
+    loading.className =
+      'flex flex-col items-center justify-center text-gray-400';
     loading.innerHTML = `
       <i data-lucide="loader" class="w-8 h-8 animate-spin mb-2"></i>
       <span class="text-xs">${t('common.loading')}</span>
@@ -518,15 +586,18 @@ function createPageElement(canvas: HTMLCanvasElement | null, index: number): HTM
 
   // Actions toolbar
   const actions = document.createElement('div');
-  actions.className = 'flex items-center justify-center gap-1 sm:opacity-0 group-hover:opacity-100 transition-opacity absolute bottom-2 left-0 right-0';
+  actions.className =
+    'flex items-center justify-center gap-1 sm:opacity-0 group-hover:opacity-100 transition-opacity absolute bottom-2 left-0 right-0';
 
   const actionsInner = document.createElement('div');
-  actionsInner.className = 'flex items-center gap-1 bg-gray-900/90 rounded px-2 py-1';
+  actionsInner.className =
+    'flex items-center gap-1 bg-gray-900/90 rounded px-2 py-1';
   actions.appendChild(actionsInner);
 
   // Select checkbox
   const selectBtn = document.createElement('button');
-  selectBtn.className = 'absolute top-2 right-2 p-1 rounded bg-gray-900/70 hover:bg-gray-800 z-10';
+  selectBtn.className =
+    'absolute top-2 right-2 p-1 rounded bg-gray-900/70 hover:bg-gray-800 z-10';
   selectBtn.innerHTML = selectedPages.has(index)
     ? '<i data-lucide="check-square" class="w-4 h-4 text-indigo-400"></i>'
     : '<i data-lucide="square" class="w-4 h-4 text-gray-200"></i>';
@@ -538,14 +609,16 @@ function createPageElement(canvas: HTMLCanvasElement | null, index: number): HTM
   // Rotate button
   const rotateBtn = document.createElement('button');
   rotateBtn.className = 'p-1 rounded hover:bg-gray-700';
-  rotateBtn.innerHTML = '<i data-lucide="rotate-cw" class="w-4 h-4 text-gray-300"></i>';
+  rotateBtn.innerHTML =
+    '<i data-lucide="rotate-cw" class="w-4 h-4 text-gray-300"></i>';
   rotateBtn.onclick = (e) => {
     e.stopPropagation();
     rotatePage(index, 90);
   };
   const rotateLeftBtn = document.createElement('button');
   rotateLeftBtn.className = 'p-1 rounded hover:bg-gray-700';
-  rotateLeftBtn.innerHTML = '<i data-lucide="rotate-ccw" class="w-4 h-4 text-gray-300"></i>';
+  rotateLeftBtn.innerHTML =
+    '<i data-lucide="rotate-ccw" class="w-4 h-4 text-gray-300"></i>';
   rotateLeftBtn.onclick = (e) => {
     e.stopPropagation();
     rotatePage(index, -90);
@@ -554,7 +627,8 @@ function createPageElement(canvas: HTMLCanvasElement | null, index: number): HTM
   // Duplicate button
   const duplicateBtn = document.createElement('button');
   duplicateBtn.className = 'p-1 rounded hover:bg-gray-700';
-  duplicateBtn.innerHTML = '<i data-lucide="copy" class="w-4 h-4 text-gray-300"></i>';
+  duplicateBtn.innerHTML =
+    '<i data-lucide="copy" class="w-4 h-4 text-gray-300"></i>';
   duplicateBtn.title = t('multiTool.actions.duplicatePage');
   duplicateBtn.onclick = (e) => {
     e.stopPropagation();
@@ -565,7 +639,8 @@ function createPageElement(canvas: HTMLCanvasElement | null, index: number): HTM
   // Delete button
   const deleteBtn = document.createElement('button');
   deleteBtn.className = 'p-1 rounded hover:bg-gray-700';
-  deleteBtn.innerHTML = '<i data-lucide="trash-2" class="w-4 h-4 text-red-400"></i>';
+  deleteBtn.innerHTML =
+    '<i data-lucide="trash-2" class="w-4 h-4 text-red-400"></i>';
   deleteBtn.title = t('multiTool.actions.deletePage');
   deleteBtn.onclick = (e) => {
     e.stopPropagation();
@@ -576,7 +651,8 @@ function createPageElement(canvas: HTMLCanvasElement | null, index: number): HTM
   // Insert PDF button
   const insertBtn = document.createElement('button');
   insertBtn.className = 'p-1 rounded hover:bg-gray-700';
-  insertBtn.innerHTML = '<i data-lucide="file-plus" class="w-4 h-4 text-gray-300"></i>';
+  insertBtn.innerHTML =
+    '<i data-lucide="file-plus" class="w-4 h-4 text-gray-300"></i>';
   insertBtn.title = t('multiTool.actions.insertPdf');
   insertBtn.onclick = (e) => {
     e.stopPropagation();
@@ -587,7 +663,8 @@ function createPageElement(canvas: HTMLCanvasElement | null, index: number): HTM
   // Split button
   const splitBtn = document.createElement('button');
   splitBtn.className = 'p-1 rounded hover:bg-gray-700';
-  splitBtn.innerHTML = '<i data-lucide="scissors" class="w-4 h-4 text-gray-300"></i>';
+  splitBtn.innerHTML =
+    '<i data-lucide="scissors" class="w-4 h-4 text-gray-300"></i>';
   splitBtn.title = t('multiTool.actions.toggleSplit');
   splitBtn.onclick = (e) => {
     e.stopPropagation();
@@ -596,14 +673,23 @@ function createPageElement(canvas: HTMLCanvasElement | null, index: number): HTM
     renderSplitMarkers();
   };
 
-  actionsInner.append(rotateLeftBtn, rotateBtn, duplicateBtn, insertBtn, splitBtn, deleteBtn);
+  actionsInner.append(
+    rotateLeftBtn,
+    rotateBtn,
+    duplicateBtn,
+    insertBtn,
+    splitBtn,
+    deleteBtn
+  );
   card.append(preview, info, actions, selectBtn);
 
   // Check for split marker
   if (splitMarkers.has(index)) {
     const marker = document.createElement('div');
-    marker.className = 'split-marker absolute -right-3 top-0 bottom-0 w-6 flex items-center justify-center z-20 pointer-events-none';
+    marker.className =
-    marker.innerHTML = '<div class="h-full w-0.5 border-l-2 border-dashed border-blue-400"></div>';
+      'split-marker absolute -right-3 top-0 bottom-0 w-6 flex items-center justify-center z-20 pointer-events-none';
+    marker.innerHTML =
+      '<div class="h-full w-0.5 border-l-2 border-dashed border-blue-400"></div>';
     card.appendChild(marker);
   }
 
@@ -655,15 +741,19 @@ function toggleSelectOptimized(index: number) {
   const card = pagesContainer.children[index] as HTMLElement;
   if (!card) return;
 
-  const selectBtn = card.querySelector('button[class*="absolute top-2 right-2"]');
+  const selectBtn = card.querySelector(
+    'button[class*="absolute top-2 right-2"]'
+  );
   if (!selectBtn) return;
 
   if (selectedPages.has(index)) {
     card.classList.add('border-indigo-500', 'ring-2', 'ring-indigo-500');
-    selectBtn.innerHTML = '<i data-lucide="check-square" class="w-4 h-4 text-indigo-400"></i>';
+    selectBtn.innerHTML =
+      '<i data-lucide="check-square" class="w-4 h-4 text-indigo-400"></i>';
   } else {
     card.classList.remove('border-indigo-500', 'ring-2', 'ring-indigo-500');
-    selectBtn.innerHTML = '<i data-lucide="square" class="w-4 h-4 text-gray-200"></i>';
+    selectBtn.innerHTML =
+      '<i data-lucide="square" class="w-4 h-4 text-gray-200"></i>';
   }
 
   createIcons({ icons });
@@ -730,7 +820,7 @@ function deletePage(index: number) {
   allPages.splice(index, 1);
   selectedPages.delete(index);
   const newSelected = new Set<number>();
-  selectedPages.forEach(i => {
+  selectedPages.forEach((i) => {
     if (i > index) newSelected.add(i - 1);
     else if (i < index) newSelected.add(i);
   });
@@ -759,13 +849,17 @@ async function handleInsertPdf(e: Event) {
 
   try {
     const arrayBuffer = await file.arrayBuffer();
-    const pdfDoc = await PDFLibDocument.load(arrayBuffer, { ignoreEncryption: true, throwOnInvalidObject: false });
+    const pdfDoc = await PDFLibDocument.load(arrayBuffer, {
+      ignoreEncryption: true,
+      throwOnInvalidObject: false,
+    });
     currentPdfDocs.push(pdfDoc);
     const pdfIndex = currentPdfDocs.length - 1;
 
     // Load PDF.js document for rendering
     const pdfBytes = await pdfDoc.save();
-    const pdfjsDoc = await getPDFDocument({ data: new Uint8Array(pdfBytes) }).promise;
+    const pdfjsDoc = await getPDFDocument({ data: new Uint8Array(pdfBytes) })
+      .promise;
     const numPages = pdfjsDoc.numPages;
 
     const newPages: PageData[] = [];
@@ -802,13 +896,18 @@ async function handleInsertPdf(e: Event) {
 
         // Update UI if card exists
         const pagesContainer = document.getElementById('pages-container');
-        const card = pagesContainer?.querySelector(`div[data-page-index="${globalIndex}"]`);
+        const card = pagesContainer?.querySelector(
+          `div[data-page-index="${globalIndex}"]`
+        );
         if (card) {
-          const preview = card.querySelector('.bg-gray-700') || card.querySelector('.bg-white');
+          const preview =
+            card.querySelector('.bg-gray-700') ||
+            card.querySelector('.bg-white');
           if (preview) {
             // Re-create the preview content
             preview.innerHTML = '';
-            preview.className = 'bg-white rounded mb-2 overflow-hidden w-full flex items-center justify-center relative h-36 sm:h-64';
+            preview.className =
+              'bg-white rounded mb-2 overflow-hidden w-full flex items-center justify-center relative h-36 sm:h-64';
 
             const previewCanvas = canvas;
             previewCanvas.className = 'max-w-full max-h-full object-contain';
@@ -819,10 +918,13 @@ async function handleInsertPdf(e: Event) {
         }
       }
     }
-
   } catch (e) {
     console.error('Failed to insert PDF:', e);
-    showModal('Error', 'Failed to insert PDF. The file may be corrupted.', 'error');
+    showModal(
+      'Error',
+      'Failed to insert PDF. The file may be corrupted.',
+      'error'
+    );
   }
 
   input.value = '';
@@ -837,13 +939,15 @@ function renderSplitMarkers() {
   const pagesContainer = document.getElementById('pages-container');
   if (!pagesContainer) return;
 
-  pagesContainer.querySelectorAll('.split-marker').forEach(m => m.remove());
+  pagesContainer.querySelectorAll('.split-marker').forEach((m) => m.remove());
 
   Array.from(pagesContainer.children).forEach((cardEl, i) => {
     if (splitMarkers.has(i)) {
       const marker = document.createElement('div');
-      marker.className = 'split-marker absolute -right-3 top-0 bottom-0 w-6 flex items-center justify-center z-20 pointer-events-none';
+      marker.className =
-      marker.innerHTML = '<div class="h-full w-0.5 border-l-2 border-dashed border-blue-400"></div>';
+        'split-marker absolute -right-3 top-0 bottom-0 w-6 flex items-center justify-center z-20 pointer-events-none';
+      marker.innerHTML =
+        '<div class="h-full w-0.5 border-l-2 border-dashed border-blue-400"></div>';
       (cardEl as HTMLElement).appendChild(marker);
     }
   });
@@ -881,7 +985,7 @@ function bulkRotate(delta: number) {
     return;
   }
 
-  selectedPages.forEach(index => {
+  selectedPages.forEach((index) => {
     const pageData = allPages[index];
     if (pageData) {
       // Update state
@@ -890,7 +994,9 @@ function bulkRotate(delta: number) {
 
       // Update DOM immediately if it exists
       const pagesContainer = document.getElementById('pages-container');
-      const card = pagesContainer?.querySelector(`div[data-page-index="${index}"]`);
+      const card = pagesContainer?.querySelector(
+        `div[data-page-index="${index}"]`
+      );
       if (card) {
         const canvas = card.querySelector('canvas');
         if (canvas) {
@@ -911,7 +1017,7 @@ function bulkDelete() {
     return;
   }
   const indices = Array.from(selectedPages).sort((a, b) => b - a);
-  indices.forEach(index => allPages.splice(index, 1));
+  indices.forEach((index) => allPages.splice(index, 1));
   selectedPages.clear();
 
   if (allPages.length === 0) {
@@ -928,7 +1034,7 @@ function bulkDuplicate() {
     return;
   }
   const indices = Array.from(selectedPages).sort((a, b) => b - a);
-  indices.forEach(index => {
+  indices.forEach((index) => {
     duplicatePage(index);
   });
   selectedPages.clear();
@@ -937,11 +1043,15 @@ function bulkDuplicate() {
 
 function bulkSplit() {
   if (selectedPages.size === 0) {
-    showModal('No Selection', 'Please select pages to mark for splitting.', 'info');
+    showModal(
+      'No Selection',
+      'Please select pages to mark for splitting.',
+      'info'
+    );
     return;
   }
   const indices = Array.from(selectedPages);
-  indices.forEach(index => {
+  indices.forEach((index) => {
     if (!splitMarkers.has(index)) {
       splitMarkers.add(index);
     }
@@ -951,7 +1061,6 @@ function bulkSplit() {
   updatePageDisplay();
 }
 
-
 async function downloadAll() {
   if (allPages.length === 0) {
     showModal('No Pages', 'Please upload PDFs first.', 'info');
@@ -993,24 +1102,63 @@ async function downloadSplitPdfs() {
       segments.push(currentSegment);
     }
 
-    // Create PDFs for each segment
     for (let segIndex = 0; segIndex < segments.length; segIndex++) {
       const segment = segments[segIndex];
       const newPdf = await PDFLibDocument.create();
 
+      const segSpecs: (
+        | {
+            type: 'pdf';
+            pdfDoc: PDFLibDocument;
+            originalPageIndex: number;
+            rotation: number;
+          }
+        | { type: 'blank' }
+      )[] = [];
       for (const index of segment) {
         const pageData = allPages[index];
-        if (!pageData) {
+        if (!pageData) continue;
-          console.warn(`Page data missing for index ${index}`);
-          continue;
-        }
         if (pageData.pdfDoc && pageData.originalPageIndex >= 0) {
-          const [copiedPage] = await newPdf.copyPages(pageData.pdfDoc, [pageData.originalPageIndex]);
+          segSpecs.push({
-          const page = newPdf.addPage(copiedPage);
+            type: 'pdf',
+            pdfDoc: pageData.pdfDoc,
+            originalPageIndex: pageData.originalPageIndex,
+            rotation: pageData.rotation,
+          });
+        } else {
+          segSpecs.push({ type: 'blank' });
+        }
+      }
 
-          if (pageData.rotation !== 0) {
+      const docPageIndices = new Map<PDFLibDocument, number[]>();
+      for (const spec of segSpecs) {
+        if (spec.type === 'pdf') {
+          if (!docPageIndices.has(spec.pdfDoc)) {
+            docPageIndices.set(spec.pdfDoc, []);
+          }
+          docPageIndices.get(spec.pdfDoc)!.push(spec.originalPageIndex);
+        }
+      }
+
+      const copiedPagesMap = new Map<PDFLibDocument, PDFPage[]>();
+      for (const [doc, pageIdxs] of Array.from(docPageIndices)) {
+        const copied = await newPdf.copyPages(doc, pageIdxs);
+        copiedPagesMap.set(doc, copied);
+      }
+
+      const docConsumeIndex = new Map<PDFLibDocument, number>();
+      docPageIndices.forEach((_, doc) => docConsumeIndex.set(doc, 0));
+
+      for (const spec of segSpecs) {
+        if (spec.type === 'pdf') {
+          const idx = docConsumeIndex.get(spec.pdfDoc)!;
+          const copiedPage = copiedPagesMap.get(spec.pdfDoc)![idx];
+          docConsumeIndex.set(spec.pdfDoc, idx + 1);
+
+          const page = newPdf.addPage(copiedPage);
+          if (spec.rotation !== 0) {
             const currentRotation = page.getRotation().angle;
-            page.setRotation(degrees(currentRotation + pageData.rotation));
+            page.setRotation(degrees(currentRotation + spec.rotation));
           }
         } else {
           newPdf.addPage([595, 842]);
@@ -1025,7 +1173,11 @@ async function downloadSplitPdfs() {
     const zipBlob = await zip.generateAsync({ type: 'blob' });
     downloadFile(zipBlob, 'split-documents.zip');
 
-    showModal('Success', `Downloaded ${segments.length} PDF files in a ZIP archive.`, 'success');
+    showModal(
+      'Success',
+      `Downloaded ${segments.length} PDF files in a ZIP archive.`,
+      'success'
+    );
   } catch (e) {
     console.error('Failed to create split PDFs:', e);
     showModal('Error', 'Failed to create split PDFs.', 'error');
@@ -1038,20 +1190,59 @@ async function downloadPagesAsPdf(indices: number[], filename: string) {
   try {
     const newPdf = await PDFLibDocument.create();
 
+    const pageSpecs: (
+      | {
+          type: 'pdf';
+          pdfDoc: PDFLibDocument;
+          originalPageIndex: number;
+          rotation: number;
+        }
+      | { type: 'blank' }
+    )[] = [];
     for (const index of indices) {
       const pageData = allPages[index];
-      if (!pageData) {
+      if (!pageData) continue;
-        console.warn(`Page data missing for index ${index}`);
-        continue;
-      }
       if (pageData.pdfDoc && pageData.originalPageIndex >= 0) {
-        // Copy page from original PDF
+        pageSpecs.push({
-        const [copiedPage] = await newPdf.copyPages(pageData.pdfDoc, [pageData.originalPageIndex]);
+          type: 'pdf',
-        const page = newPdf.addPage(copiedPage);
+          pdfDoc: pageData.pdfDoc,
+          originalPageIndex: pageData.originalPageIndex,
+          rotation: pageData.rotation,
+        });
+      } else {
+        pageSpecs.push({ type: 'blank' });
+      }
+    }
 
-        if (pageData.rotation !== 0) {
+    const docPageIndices = new Map<PDFLibDocument, number[]>();
+    for (const spec of pageSpecs) {
+      if (spec.type === 'pdf') {
+        if (!docPageIndices.has(spec.pdfDoc)) {
+          docPageIndices.set(spec.pdfDoc, []);
+        }
+        docPageIndices.get(spec.pdfDoc)!.push(spec.originalPageIndex);
+      }
+    }
+
+    const copiedPagesMap = new Map<PDFLibDocument, PDFPage[]>();
+    for (const [doc, pageIdxs] of Array.from(docPageIndices)) {
+      const copied = await newPdf.copyPages(doc, pageIdxs);
+      copiedPagesMap.set(doc, copied);
+    }
+
+    const docConsumeIndex = new Map<PDFLibDocument, number>();
+    docPageIndices.forEach((_, doc) => docConsumeIndex.set(doc, 0));
+
+    for (const spec of pageSpecs) {
+      if (spec.type === 'pdf') {
+        const idx = docConsumeIndex.get(spec.pdfDoc)!;
+        const copiedPage = copiedPagesMap.get(spec.pdfDoc)![idx];
+        docConsumeIndex.set(spec.pdfDoc, idx + 1);
+
+        const page = newPdf.addPage(copiedPage);
+        if (spec.rotation !== 0) {
           const currentRotation = page.getRotation().angle;
-          page.setRotation(degrees(currentRotation + pageData.rotation));
+          page.setRotation(degrees(currentRotation + spec.rotation));
         }
       } else {
         newPdf.addPage([595, 842]);
@@ -1059,7 +1250,9 @@ async function downloadPagesAsPdf(indices: number[], filename: string) {
     }
 
     const pdfBytes = await newPdf.save();
-    const blob = new Blob([new Uint8Array(pdfBytes)], { type: 'application/pdf' });
+    const blob = new Blob([new Uint8Array(pdfBytes)], {
+      type: 'application/pdf',
+    });
 
     downloadFile(blob, filename);
     showModal('Success', 'PDF downloaded successfully.', 'success');
@@ -1101,18 +1294,28 @@ function updatePageDisplay() {
 
       // Update index-dependent attributes
       card.dataset.pageIndex = index.toString();
-      const info = card.querySelector('.text-xs.text-gray-400.text-center.mb-2');
+      const info = card.querySelector(
+        '.text-xs.text-gray-400.text-center.mb-2'
+      );
       if (info) info.textContent = `Page ${index + 1} `;
 
       // Update selection state
-      const selectBtn = card.querySelector('button[class*="absolute top-2 right-2"]');
+      const selectBtn = card.querySelector(
+        'button[class*="absolute top-2 right-2"]'
+      );
       if (selectBtn) {
         if (selectedPages.has(index)) {
           card.classList.add('border-indigo-500', 'ring-2', 'ring-indigo-500');
-          selectBtn.innerHTML = '<i data-lucide="check-square" class="w-4 h-4 text-indigo-400"></i>';
+          selectBtn.innerHTML =
+            '<i data-lucide="check-square" class="w-4 h-4 text-indigo-400"></i>';
         } else {
-          card.classList.remove('border-indigo-500', 'ring-2', 'ring-indigo-500');
+          card.classList.remove(
-          selectBtn.innerHTML = '<i data-lucide="square" class="w-4 h-4 text-gray-200"></i>';
+            'border-indigo-500',
+            'ring-2',
+            'ring-indigo-500'
+          );
+          selectBtn.innerHTML =
+            '<i data-lucide="square" class="w-4 h-4 text-gray-200"></i>';
         }
         // Update click handler to use new index
         (selectBtn as HTMLElement).onclick = (e) => {
@@ -1128,17 +1331,47 @@ function updatePageDisplay() {
       }
 
       // Update action buttons
-      const actionsInner = card.querySelector('.flex.items-center.gap-1.bg-gray-900\\/90');
+      const actionsInner = card.querySelector(
+        '.flex.items-center.gap-1.bg-gray-900\\/90'
+      );
       if (actionsInner) {
         const buttons = actionsInner.querySelectorAll('button');
-        if (buttons[0]) (buttons[0] as HTMLElement).onclick = (e) => { e.stopPropagation(); rotatePage(index, -90); };
+        if (buttons[0])
-        if (buttons[1]) (buttons[1] as HTMLElement).onclick = (e) => { e.stopPropagation(); rotatePage(index, 90); };
+          (buttons[0] as HTMLElement).onclick = (e) => {
-        if (buttons[2]) (buttons[2] as HTMLElement).onclick = (e) => { e.stopPropagation(); snapshot(); duplicatePage(index); };
+            e.stopPropagation();
-        if (buttons[3]) (buttons[3] as HTMLElement).onclick = (e) => { e.stopPropagation(); snapshot(); insertPdfAfter(index); };
+            rotatePage(index, -90);
-        if (buttons[4]) (buttons[4] as HTMLElement).onclick = (e) => { e.stopPropagation(); snapshot(); toggleSplitMarker(index); renderSplitMarkers(); };
+          };
-        if (buttons[5]) (buttons[5] as HTMLElement).onclick = (e) => { e.stopPropagation(); snapshot(); deletePage(index); };
+        if (buttons[1])
+          (buttons[1] as HTMLElement).onclick = (e) => {
+            e.stopPropagation();
+            rotatePage(index, 90);
+          };
+        if (buttons[2])
+          (buttons[2] as HTMLElement).onclick = (e) => {
+            e.stopPropagation();
+            snapshot();
+            duplicatePage(index);
+          };
+        if (buttons[3])
+          (buttons[3] as HTMLElement).onclick = (e) => {
+            e.stopPropagation();
+            snapshot();
+            insertPdfAfter(index);
+          };
+        if (buttons[4])
+          (buttons[4] as HTMLElement).onclick = (e) => {
+            e.stopPropagation();
+            snapshot();
+            toggleSplitMarker(index);
+            renderSplitMarkers();
+          };
+        if (buttons[5])
+          (buttons[5] as HTMLElement).onclick = (e) => {
+            e.stopPropagation();
+            snapshot();
+            deletePage(index);
+          };
       }
-
     } else {
       // Element doesn't exist, create it
       card = createPageElement(pageData.canvas, index);
@@ -1179,7 +1412,9 @@ function updatePageNumbers() {
     // We need to find the buttons and update their onclick handlers
     // This is necessary because the original handlers captured the old index
 
-    const selectBtn = card.querySelector('button[class*="absolute top-2 right-2"]') as HTMLButtonElement;
+    const selectBtn = card.querySelector(
+      'button[class*="absolute top-2 right-2"]'
+    ) as HTMLButtonElement;
     if (selectBtn) {
       selectBtn.onclick = (e) => {
         e.stopPropagation();
@@ -1187,16 +1422,47 @@ function updatePageNumbers() {
       };
     }
 
-    const actionsInner = card.querySelector('.flex.items-center.gap-1.bg-gray-900\\/90');
+    const actionsInner = card.querySelector(
+      '.flex.items-center.gap-1.bg-gray-900\\/90'
+    );
     if (actionsInner) {
       const buttons = actionsInner.querySelectorAll('button');
       // Order: Rotate Left, Rotate Right, Duplicate, Insert, Split, Delete
-      if (buttons[0]) buttons[0].onclick = (e) => { e.stopPropagation(); rotatePage(index, -90); };
+      if (buttons[0])
-      if (buttons[1]) buttons[1].onclick = (e) => { e.stopPropagation(); rotatePage(index, 90); };
+        buttons[0].onclick = (e) => {
-      if (buttons[2]) buttons[2].onclick = (e) => { e.stopPropagation(); snapshot(); duplicatePage(index); };
+          e.stopPropagation();
-      if (buttons[3]) buttons[3].onclick = (e) => { e.stopPropagation(); snapshot(); insertPdfAfter(index); };
+          rotatePage(index, -90);
-      if (buttons[4]) buttons[4].onclick = (e) => { e.stopPropagation(); snapshot(); toggleSplitMarker(index); renderSplitMarkers(); };
+        };
-      if (buttons[5]) buttons[5].onclick = (e) => { e.stopPropagation(); snapshot(); deletePage(index); };
+      if (buttons[1])
+        buttons[1].onclick = (e) => {
+          e.stopPropagation();
+          rotatePage(index, 90);
+        };
+      if (buttons[2])
+        buttons[2].onclick = (e) => {
+          e.stopPropagation();
+          snapshot();
+          duplicatePage(index);
+        };
+      if (buttons[3])
+        buttons[3].onclick = (e) => {
+          e.stopPropagation();
+          snapshot();
+          insertPdfAfter(index);
+        };
+      if (buttons[4])
+        buttons[4].onclick = (e) => {
+          e.stopPropagation();
+          snapshot();
+          toggleSplitMarker(index);
+          renderSplitMarkers();
+        };
+      if (buttons[5])
+        buttons[5].onclick = (e) => {
+          e.stopPropagation();
+          snapshot();
+          deletePage(index);
+        };
     }
   });
 }

src/js/utils/render-utils.ts

@@ -103,7 +103,10 @@ export async function renderPageToCanvas(
   canvas.height = viewport.height;
   canvas.width = viewport.width;
 
-  const context = canvas.getContext('2d')!;
+  const context = canvas.getContext('2d');
+  if (!context) {
+    throw new Error(`Failed to get 2D context for page ${pageNumber}`);
+  }
 
   await page.render({
     canvasContext: context,
@@ -115,12 +118,9 @@ export async function renderPageToCanvas(
 }
 
 /**
- * Renders a batch of pages in parallel
+ * Renders a batch of pages
  */
-async function renderPageBatch(
+async function renderPageBatch(tasks: PageTask[]): Promise<void> {
-  tasks: PageTask[],
-  onProgress?: (current: number, total: number) => void
-): Promise<void> {
   for (const task of tasks) {
     try {
       const canvas = await renderPageToCanvas(
@@ -147,6 +147,13 @@ async function renderPageBatch(
         parent.insertBefore(wrapper, placeholder);
         parent.removeChild(placeholder);
       } else {
+        const existingRendered = task.container.querySelector(
+          `[data-page-number="${task.pageNumber}"]:not([data-lazy-load="true"])`
+        );
+        if (existingRendered) {
+          continue;
+        }
+
         const allChildren = Array.from(
           task.container.children
         ) as HTMLElement[];
@@ -207,7 +214,7 @@ function setupLazyRendering(
           task.placeholderElement = placeholder;
 
           // Render this page immediately (not waiting for isRendering flag)
-          renderPageBatch([task], config.onProgress)
+          renderPageBatch([task])
             .then(() => {
               // Trigger callback after lazy load batch
               if (config.onBatchComplete) {
@@ -263,21 +270,19 @@ export async function renderPagesProgressively(
   config: RenderConfig = {}
 ): Promise<void> {
   const {
-    batchSize = 8, // Increased from 5 to 8 for faster initial render
+    batchSize = 8,
     useLazyLoading = true,
-    eagerLoadBatches = 2, // Eagerly load 1 batch ahead by default
+    eagerLoadBatches = 2,
     onProgress,
     onBatchComplete,
   } = config;
 
   const totalPages = pdfjsDoc.numPages;
 
-  // Render more pages initially to reduce lazy loading issues
   const initialRenderCount = useLazyLoading
-    ? Math.min(20, totalPages) // Increased from 12 to 20 pages
+    ? Math.min(20, totalPages)
     : totalPages;
 
-  // CRITICAL FIX: Create placeholders for ALL pages first to maintain order
   const placeholders: HTMLElement[] = [];
   for (let i = 1; i <= totalPages; i++) {
     const placeholder = createPlaceholder(i);
@@ -293,7 +298,7 @@ export async function renderPagesProgressively(
       pageNumber: i,
       pdfjsDoc,
       container,
-      scale: config.useLazyLoading ? 0.3 : 0.5,
+      scale: useLazyLoading ? 0.3 : 0.5,
       createWrapper,
       placeholderElement: placeholders[i - 1],
     });
@@ -330,12 +335,15 @@ export async function renderPagesProgressively(
 
     const batch = initialTasks.slice(i, i + batchSize);
 
-    await new Promise<void>((resolve) => {
+    await new Promise<void>((resolve, reject) => {
-      requestIdleCallbackPolyfill(async () => {
+      requestIdleCallbackPolyfill(() => {
-        await renderPageBatch(batch, onProgress);
+        renderPageBatch(batch)
-
+          .then(() => {
             if (onProgress) {
-          onProgress(Math.min(i + batchSize, initialRenderCount), totalPages);
+              onProgress(
+                Math.min(i + batchSize, initialRenderCount),
+                totalPages
+              );
             }
 
             if (onBatchComplete) {
@@ -343,6 +351,8 @@ export async function renderPagesProgressively(
             }
 
             resolve();
+          })
+          .catch(reject);
       });
     });
   }
@@ -397,8 +407,11 @@ function renderEagerBatch(config: RenderConfig): void {
   requestIdleCallbackPolyfill(async () => {
     if (config.shouldCancel?.()) return;
 
-    // Remove these tasks from pending since we're rendering them eagerly
+    const tasksToRender = batch.filter((task) =>
-    batch.forEach((task) => {
+      lazyLoadState.pendingTasksByPageNumber.has(task.pageNumber)
+    );
+
+    tasksToRender.forEach((task) => {
       const placeholder = task.placeholderElement;
       if (placeholder && lazyLoadState.observer) {
         lazyLoadState.observer.unobserve(placeholder);
@@ -407,7 +420,18 @@ function renderEagerBatch(config: RenderConfig): void {
       }
     });
 
-    await renderPageBatch(batch, config.onProgress);
+    if (tasksToRender.length === 0) {
+      lazyLoadState.nextEagerIndex = batchEnd;
+      const remainingBatches = Math.ceil(
+        (eagerLoadQueue.length - batchEnd) / batchSize
+      );
+      if (remainingBatches > 0 && remainingBatches < eagerLoadBatches) {
+        renderEagerBatch(config);
+      }
+      return;
+    }
+
+    await renderPageBatch(tasksToRender);
 
     if (config.onBatchComplete) {
       config.onBatchComplete();
@@ -421,7 +445,6 @@ function renderEagerBatch(config: RenderConfig): void {
       (eagerLoadQueue.length - batchEnd) / batchSize
     );
     if (remainingBatches > 0 && remainingBatches < eagerLoadBatches) {
-      // Continue eager loading if we have more batches within the eager threshold
       renderEagerBatch(config);
     }
   });