feat(pdf-tools): add alternate merge tool for mixing pdf pages

Implement new tool that allows users to combine PDFs by alternating pages from each document. Includes UI components, logic for processing, and test coverage.

- Add new tool to configuration arrays and categories
- Create UI with drag-and-drop file ordering
- Implement core logic for alternating pages
- Add comprehensive unit tests

src/tests/alternate-merge.test.ts

@@ -0,0 +1,158 @@
+import { describe, it, expect, vi, beforeEach, afterEach } from 'vitest';
+import { state } from '@/js/state';
+import { PDFDocument } from 'pdf-lib';
+import Sortable from 'sortablejs';
+import * as helpers from '@/js/utils/helpers';
+import * as ui from '@/js/ui';
+import { setupAlternateMergeTool, alternateMerge } from '@/js/logic/alternate-merge';
+
+vi.mock('pdf-lib', () => ({
+  PDFDocument: {
+    create: vi.fn(),
+    load: vi.fn(),
+  },
+}));
+
+vi.mock('sortablejs', () => ({
+  default: { create: vi.fn() },
+}));
+
+vi.mock('@/js/utils/helpers', () => ({
+  readFileAsArrayBuffer: vi.fn(),
+  downloadFile: vi.fn(),
+}));
+
+vi.mock('@/js/ui', () => ({
+  showLoader: vi.fn(),
+  hideLoader: vi.fn(),
+  showAlert: vi.fn(),
+}));
+
+describe('Alternate Merge Tool', () => {
+  let mockPdfDoc1: any;
+  let mockPdfDoc2: any;
+
+  beforeEach(() => {
+    document.body.innerHTML = `
+      <div id="alternate-merge-options" class="hidden"></div>
+      <button id="process-btn"></button>
+      <ul id="alternate-file-list"></ul>
+    `;
+
+    state.files = [
+      new File(['dummy1'], 'file1.pdf'),
+      new File(['dummy2'], 'file2.pdf'),
+    ];
+
+    mockPdfDoc1 = { getPageCount: vi.fn(() => 2) };
+    mockPdfDoc2 = { getPageCount: vi.fn(() => 3) };
+
+    vi.mocked(helpers.readFileAsArrayBuffer).mockResolvedValue(new ArrayBuffer(8));
+    vi.mocked(PDFDocument.load)
+      .mockResolvedValueOnce(mockPdfDoc1)
+      .mockResolvedValueOnce(mockPdfDoc2);
+
+    vi.clearAllMocks();
+  });
+
+  afterEach(() => {
+    vi.clearAllMocks();
+  });
+
+  describe('setupAlternateMergeTool()', () => {
+    it('should initialize UI and load PDF files', async () => {
+      await setupAlternateMergeTool();
+
+      expect(ui.showLoader).toHaveBeenCalledWith('Loading PDF documents...');
+      expect(ui.hideLoader).toHaveBeenCalled();
+      expect(PDFDocument.load).toHaveBeenCalledTimes(2);
+      expect(document.querySelectorAll('#alternate-file-list li').length).toBe(2);
+      expect(Sortable.create).toHaveBeenCalled();
+    });
+
+    it('should show alert on load failure', async () => {
+      vi.mocked(PDFDocument.load).mockReset();
+      vi.mocked(PDFDocument.load).mockRejectedValueOnce(new Error('bad pdf'));
+      
+      await setupAlternateMergeTool();
+      
+      expect(ui.showAlert).toHaveBeenCalledWith(
+        'Error',
+        expect.stringContaining('Failed to load one or more PDF files')
+      );
+      expect(ui.hideLoader).toHaveBeenCalled();
+    });
+  });
+
+  describe('alternateMerge()', () => {
+    it('should show alert if less than 2 PDFs loaded', async () => {
+      // Setup with only 1 file - need to call setup first to populate internal state
+      state.files = [new File(['dummy1'], 'file1.pdf')];
+      vi.mocked(PDFDocument.load).mockReset();
+      vi.mocked(PDFDocument.load).mockResolvedValueOnce(mockPdfDoc1);
+      
+      await setupAlternateMergeTool();
+      vi.clearAllMocks(); // Clear the setup calls
+      
+      await alternateMerge();
+      
+      expect(ui.showAlert).toHaveBeenCalledWith(
+        'Not Enough Files',
+        expect.stringContaining('Please upload at least two PDF files')
+      );
+    });
+
+    it('should merge pages alternately and download file', async () => {
+      // First setup the tool to populate internal state
+      await setupAlternateMergeTool();
+      vi.clearAllMocks(); // Clear setup calls
+      
+      const mockCopyPages = vi.fn(() =>
+        Promise.resolve([{ page: 'mockPage' }] as any)
+      );
+      const mockAddPage = vi.fn();
+      const mockSave = vi.fn(() => Promise.resolve(new Uint8Array([1, 2, 3])));
+
+      vi.mocked(PDFDocument.create).mockResolvedValue({
+        copyPages: mockCopyPages,
+        addPage: mockAddPage,
+        save: mockSave,
+      } as any);
+
+      const fileList = document.getElementById('alternate-file-list')!;
+      // The list should already be populated by setupAlternateMergeTool
+      // But ensure it has the correct structure
+      fileList.innerHTML = `
+        <li data-file-name="file1.pdf"></li>
+        <li data-file-name="file2.pdf"></li>
+      `;
+
+      await alternateMerge();
+
+      expect(ui.showLoader).toHaveBeenCalledWith(expect.stringContaining('Alternating'));
+      expect(mockCopyPages).toHaveBeenCalled();
+      expect(mockAddPage).toHaveBeenCalled();
+      expect(mockSave).toHaveBeenCalled();
+      expect(helpers.downloadFile).toHaveBeenCalled();
+      expect(ui.showAlert).toHaveBeenCalledWith('Success', expect.stringContaining('mixed successfully'));
+      expect(ui.hideLoader).toHaveBeenCalled();
+    });
+
+    it('should show alert on merge error', async () => {
+      // Setup the tool first to populate internal state with 2 PDFs
+      await setupAlternateMergeTool();
+      vi.clearAllMocks(); // Clear setup calls
+      
+      // Mock PDFDocument.create to reject
+      vi.mocked(PDFDocument.create).mockRejectedValue(new Error('broken'));
+
+      await alternateMerge();
+
+      expect(ui.showAlert).toHaveBeenCalledWith(
+        'Error',
+        expect.stringContaining('An error occurred while mixing')
+      );
+      expect(ui.hideLoader).toHaveBeenCalled();
+    });
+  });
+});

src/tests/pdf-tools.test.ts

@@ -58,7 +58,7 @@ describe('Tool Configuration Arrays', () => {
     });
 
     it('should have the correct number of tools', () => {
-      expect(multiFileTools).toHaveLength(10);
+      expect(multiFileTools).toHaveLength(11);
     });
 
     it('should not contain any duplicate tools', () => {