Stirling-PDF/frontend/src/utils/downloadUtils.ts

import { FileMetadata } from '../types/file';
import { fileStorage } from '../services/fileStorage';
import { zipFileService } from '../services/zipFileService';

/**
 * Downloads a blob as a file using browser download API
 * @param blob - The blob to download
 * @param filename - The filename for the download
 */
export function downloadBlob(blob: Blob, filename: string): void {
  const url = URL.createObjectURL(blob);
  
  const link = document.createElement('a');
  link.href = url;
  link.download = filename;
  document.body.appendChild(link);
  link.click();
  document.body.removeChild(link);
  
  // Clean up the blob URL
  URL.revokeObjectURL(url);
}

/**
 * Downloads a single file from IndexedDB storage
 * @param file - The file object with storage information
 * @throws Error if file cannot be retrieved from storage
 */
export async function downloadFileFromStorage(file: FileMetadata): Promise<void> {
  const lookupKey = file.id;
  const storedFile = await fileStorage.getFile(lookupKey);
  
  if (!storedFile) {
    throw new Error(`File "${file.name}" not found in storage`);
  }
  
  const blob = new Blob([storedFile.data], { type: storedFile.type });
  downloadBlob(blob, storedFile.name);
}

/**
 * Downloads multiple files as individual downloads
 * @param files - Array of files to download
 */
export async function downloadMultipleFiles(files: FileMetadata[]): Promise<void> {
  for (const file of files) {
    await downloadFileFromStorage(file);
  }
}

/**
 * Downloads multiple files as a single ZIP archive
 * @param files - Array of files to include in ZIP
 * @param zipFilename - Optional custom ZIP filename (defaults to timestamped name)
 */
export async function downloadFilesAsZip(files: FileMetadata[], zipFilename?: string): Promise<void> {
  if (files.length === 0) {
    throw new Error('No files provided for ZIP download');
  }

  // Convert stored files to File objects
  const fileObjects: File[] = [];
  for (const fileWithUrl of files) {
    const lookupKey = fileWithUrl.id;
    const storedFile = await fileStorage.getFile(lookupKey);
    
    if (storedFile) {
      const file = new File([storedFile.data], storedFile.name, {
        type: storedFile.type,
        lastModified: storedFile.lastModified
      });
      fileObjects.push(file);
    }
  }
  
  if (fileObjects.length === 0) {
    throw new Error('No valid files found in storage for ZIP download');
  }

  // Generate default filename if not provided
  const finalZipFilename = zipFilename || 
    `files-${new Date().toISOString().slice(0, 19).replace(/[:-]/g, '')}.zip`;
  
  // Create and download ZIP
  const { zipFile } = await zipFileService.createZipFromFiles(fileObjects, finalZipFilename);
  downloadBlob(zipFile, finalZipFilename);
}

/**
 * Smart download function that handles single or multiple files appropriately
 * - Single file: Downloads directly
 * - Multiple files: Downloads as ZIP
 * @param files - Array of files to download
 * @param options - Download options
 */
export async function downloadFiles(
  files: FileMetadata[], 
  options: {
    forceZip?: boolean;
    zipFilename?: string;
    multipleAsIndividual?: boolean;
  } = {}
): Promise<void> {
  if (files.length === 0) {
    throw new Error('No files provided for download');
  }

  if (files.length === 1 && !options.forceZip) {
    // Single file download
    await downloadFileFromStorage(files[0]);
  } else if (options.multipleAsIndividual) {
    // Multiple individual downloads
    await downloadMultipleFiles(files);
  } else {
    // ZIP download (default for multiple files)
    await downloadFilesAsZip(files, options.zipFilename);
  }
}

/**
 * Downloads a File object directly (for files already in memory)
 * @param file - The File object to download
 * @param filename - Optional custom filename
 */
export function downloadFileObject(file: File, filename?: string): void {
  downloadBlob(file, filename || file.name);
}

/**
 * Downloads text content as a file
 * @param content - Text content to download
 * @param filename - Filename for the download
 * @param mimeType - MIME type (defaults to text/plain)
 */
export function downloadTextAsFile(
  content: string, 
  filename: string, 
  mimeType: string = 'text/plain'
): void {
  const blob = new Blob([content], { type: mimeType });
  downloadBlob(blob, filename);
}

/**
 * Downloads JSON data as a file
 * @param data - Data to serialize and download
 * @param filename - Filename for the download
 */
export function downloadJsonAsFile(data: any, filename: string): void {
  const content = JSON.stringify(data, null, 2);
  downloadTextAsFile(content, filename, 'application/json');
}