feat(pdf-tools): add attachments feature to embed files in PDFs

Implement new functionality to allow embedding attachments into PDF documents. The feature includes:
- UI for selecting PDF and files to attach
- Logic to embed files while preserving metadata
- Display of attached files with size information
- Download of modified PDF with embedded files

src/js/logic/add-attachments.ts

@@ -0,0 +1,125 @@
+import { showLoader, hideLoader, showAlert } from '../ui';
+import { readFileAsArrayBuffer, downloadFile } from '../utils/helpers';
+import { state } from '../state';
+let attachments: File[] = [];
+
+export async function addAttachments() {
+  if (!state.pdfDoc) {
+    showAlert('Error', 'Main PDF is not loaded.');
+    return;
+  }
+  if (attachments.length === 0) {
+    showAlert('No Files', 'Please select at least one file to attach.');
+    return;
+  }
+
+  showLoader('Embedding files into PDF...');
+  try {
+    const pdfDoc = state.pdfDoc;
+
+    for (let i = 0; i < attachments.length; i++) {
+      const file = attachments[i];
+      showLoader(`Attaching ${file.name} (${i + 1}/${attachments.length})...`);
+
+      const fileBytes = await readFileAsArrayBuffer(file);
+
+      await pdfDoc.attach(fileBytes as ArrayBuffer, file.name, {
+        mimeType: file.type || 'application/octet-stream',
+        description: `Attached file: ${file.name}`,
+        creationDate: new Date(),
+        modificationDate: new Date(file.lastModified),
+      });
+    }
+
+    const pdfBytes = await pdfDoc.save();
+    downloadFile(
+      new Blob([pdfBytes], { type: 'application/pdf' }),
+      `attached-${state.files[0].name}`
+    );
+
+    showAlert(
+      'Success',
+      `${attachments.length} file(s) attached successfully.`
+    );
+  } catch (error: any) {
+    console.error('Error attaching files:', error);
+    showAlert('Error', `Failed to attach files: ${error.message}`);
+  } finally {
+    hideLoader();
+    clearAttachments(); 
+  }
+}
+
+function clearAttachments() {
+  attachments = [];
+  const fileListDiv = document.getElementById('attachment-file-list');
+  const attachmentInput = document.getElementById(
+    'attachment-files-input'
+  ) as HTMLInputElement;
+  const processBtn = document.getElementById(
+    'process-btn'
+  ) as HTMLButtonElement;
+
+  if (fileListDiv) fileListDiv.innerHTML = '';
+  if (attachmentInput) attachmentInput.value = '';
+  if (processBtn) {
+    processBtn.disabled = true;
+    processBtn.classList.add('hidden');
+  }
+}
+
+let isSetup = false; // Prevent duplicate setup
+
+export function setupAddAttachmentsTool() {
+  if (isSetup) return; // Already set up
+  isSetup = true;
+
+  const optionsDiv = document.getElementById('attachment-options');
+  const attachmentInput = document.getElementById(
+    'attachment-files-input'
+  ) as HTMLInputElement;
+  const fileListDiv = document.getElementById('attachment-file-list');
+  const processBtn = document.getElementById(
+    'process-btn'
+  ) as HTMLButtonElement;
+
+  if (!optionsDiv || !attachmentInput || !fileListDiv || !processBtn) {
+    console.error('Attachment tool UI elements not found.');
+    return;
+  }
+
+  optionsDiv.classList.remove('hidden');
+
+  attachmentInput.addEventListener('change', (e) => {
+    const files = (e.target as HTMLInputElement).files;
+    if (files && files.length > 0) {
+      attachments = Array.from(files);
+
+      fileListDiv.innerHTML = '';
+      attachments.forEach((file) => {
+        const div = document.createElement('div');
+        div.className =
+          'flex justify-between items-center p-2 bg-gray-800 rounded-md text-white';
+
+        const nameSpan = document.createElement('span');
+        nameSpan.className = 'truncate text-sm';
+        nameSpan.textContent = file.name; 
+
+        const sizeSpan = document.createElement('span');
+        sizeSpan.className = 'text-xs text-gray-400';
+        sizeSpan.textContent = `${Math.round(file.size / 1024)} KB`;
+
+        div.appendChild(nameSpan);
+        div.appendChild(sizeSpan);
+        fileListDiv.appendChild(div);
+      });
+
+      processBtn.disabled = false;
+      processBtn.classList.remove('hidden');
+    } else {
+      clearAttachments();
+    }
+  });
+
+  processBtn.onclick = addAttachments;
+}