Network Operations

/**
 * Downloads a file from a URL to a specified destination
 * @param url URL of the file to download
 * @param destination Target directory or file path
 * @param options Download configuration options
 * @returns Promise resolving to the downloaded File instance
 */
static downloadFileAsync(
  url: string,
  destination: Directory | File,
  options?: DownloadOptions
): Promise<File>;

interface DownloadOptions {
  /** HTTP headers to send with the download request */
  headers?: { [key: string]: string };
}

import { File, Directory, Paths } from "expo-file-system";

// Basic file download to directory
const downloadDir = new Directory(Paths.document, "downloads");
downloadDir.create();

const imageUrl = "https://example.com/images/photo.jpg";
const downloadedImage = await File.downloadFileAsync(imageUrl, downloadDir);

console.log(`Downloaded: ${downloadedImage.name}`);
console.log(`Size: ${downloadedImage.size} bytes`);
console.log(`Location: ${downloadedImage.uri}`);

// Download to specific file path
const specificFile = new File(Paths.document, "profile-picture.jpg");
const profileImage = await File.downloadFileAsync(imageUrl, specificFile);

// Download with custom headers
const authenticatedDownload = await File.downloadFileAsync(
  "https://api.example.com/secure/document.pdf",
  downloadDir,
  {
    headers: {
      "Authorization": "Bearer your-auth-token",
      "User-Agent": "MyApp/1.0.0",
      "Accept": "application/pdf"
    }
  }
);

import { File, Directory, Paths } from "expo-file-system";

// Download with progress monitoring
async function downloadWithProgress(
  url: string,
  destination: Directory,
  onProgress?: (bytesDownloaded: number, totalBytes: number) => void
) {
  console.log(`Starting download: ${url}`);
  
  try {
    // Start download
    const downloadedFile = await File.downloadFileAsync(url, destination);
    
    // Note: Progress tracking would typically be implemented with
    // custom networking libraries or by checking file size periodically
    console.log(`Download completed: ${downloadedFile.name}`);
    console.log(`Final size: ${downloadedFile.size} bytes`);
    
    return downloadedFile;
    
  } catch (error) {
    console.error("Download failed:", error);
    throw error;
  }
}

// Download queue management
class DownloadManager {
  private downloadQueue: Array<{
    url: string;
    destination: Directory | File;
    options?: DownloadOptions;
  }> = [];
  
  private activeDownloads = 0;
  private maxConcurrentDownloads = 3;
  
  async addDownload(
    url: string, 
    destination: Directory | File, 
    options?: DownloadOptions
  ) {
    this.downloadQueue.push({ url, destination, options });
    this.processQueue();
  }
  
  private async processQueue() {
    if (this.activeDownloads >= this.maxConcurrentDownloads || this.downloadQueue.length === 0) {
      return;
    }
    
    const download = this.downloadQueue.shift()!;
    this.activeDownloads++;
    
    try {
      console.log(`Starting download: ${download.url}`);
      const file = await File.downloadFileAsync(
        download.url, 
        download.destination, 
        download.options
      );
      console.log(`Completed download: ${file.name}`);
      
    } catch (error) {
      console.error(`Download failed: ${download.url}`, error);
      
    } finally {
      this.activeDownloads--;
      // Process next item in queue
      setTimeout(() => this.processQueue(), 100);
    }
  }
}

// Usage
const downloadManager = new DownloadManager();
const downloadDir = new Directory(Paths.document, "downloads");

await downloadManager.addDownload("https://example.com/file1.zip", downloadDir);
await downloadManager.addDownload("https://example.com/file2.pdf", downloadDir);
await downloadManager.addDownload("https://example.com/file3.jpg", downloadDir);

import { File, Directory, Paths } from "expo-file-system";

// Download with retry logic
async function downloadWithRetry(
  url: string,
  destination: Directory | File,
  options?: DownloadOptions,
  maxRetries: number = 3
): Promise<File> {
  let lastError: Error;
  
  for (let attempt = 1; attempt <= maxRetries; attempt++) {
    try {
      console.log(`Download attempt ${attempt}/${maxRetries}: ${url}`);
      
      const file = await File.downloadFileAsync(url, destination, options);
      console.log(`Download successful on attempt ${attempt}`);
      return file;
      
    } catch (error) {
      lastError = error as Error;
      console.warn(`Download attempt ${attempt} failed:`, error);
      
      if (attempt < maxRetries) {
        // Exponential backoff
        const delay = Math.pow(2, attempt) * 1000;
        console.log(`Retrying in ${delay}ms...`);
        await new Promise(resolve => setTimeout(resolve, delay));
      }
    }
  }
  
  throw new Error(`Download failed after ${maxRetries} attempts: ${lastError.message}`);
}

// Validate downloaded files
async function downloadAndValidate(
  url: string,
  destination: Directory,
  expectedSize?: number,
  expectedChecksum?: string
): Promise<File> {
  const downloadedFile = await downloadWithRetry(url, destination);
  
  // Validate file size
  if (expectedSize && downloadedFile.size !== expectedSize) {
    downloadedFile.delete();
    throw new Error(`File size mismatch: expected ${expectedSize}, got ${downloadedFile.size}`);
  }
  
  // Validate checksum
  if (expectedChecksum) {
    const fileInfo = downloadedFile.info({ md5: true });
    if (fileInfo.md5 !== expectedChecksum) {
      downloadedFile.delete();
      throw new Error(`Checksum mismatch: expected ${expectedChecksum}, got ${fileInfo.md5}`);
    }
  }
  
  console.log("File validation successful");
  return downloadedFile;
}

// Usage with validation
try {
  const validatedFile = await downloadAndValidate(
    "https://example.com/important-document.pdf",
    new Directory(Paths.document, "verified"),
    1024 * 1024, // Expected 1MB
    "5d41402abc4b2a76b9719d911017c592" // Expected MD5
  );
  
  console.log(`Verified download: ${validatedFile.name}`);
} catch (error) {
  console.error("Download validation failed:", error);
}

import { File, Directory, Paths } from "expo-file-system";

interface DownloadTask {
  url: string;
  filename?: string;
  headers?: { [key: string]: string };
}

// Batch download with comprehensive tracking
async function batchDownload(
  tasks: DownloadTask[],
  destination: Directory,
  onProgress?: (completed: number, total: number, currentFile?: string) => void
): Promise<File[]> {
  const results: File[] = [];
  const errors: Array<{ task: DownloadTask; error: Error }> = [];
  
  for (let i = 0; i < tasks.length; i++) {
    const task = tasks[i];
    
    try {
      onProgress?.(i, tasks.length, task.filename || task.url);
      
      const targetFile = task.filename 
        ? new File(destination, task.filename)
        : destination;
        
      const downloadedFile = await File.downloadFileAsync(
        task.url,
        targetFile,
        { headers: task.headers }
      );
      
      results.push(downloadedFile);
      console.log(`Downloaded ${i + 1}/${tasks.length}: ${downloadedFile.name}`);
      
    } catch (error) {
      console.error(`Failed to download ${task.url}:`, error);
      errors.push({ task, error: error as Error });
    }
  }
  
  onProgress?.(tasks.length, tasks.length);
  
  if (errors.length > 0) {
    console.warn(`Batch download completed with ${errors.length} errors`);
    // Optionally retry failed downloads or report errors
  }
  
  return results;
}

// Download manifest file and process contents
async function downloadFromManifest(manifestUrl: string): Promise<File[]> {
  const manifestFile = await File.downloadFileAsync(
    manifestUrl,
    new File(Paths.cache, "download-manifest.json")
  );
  
  const manifestContent = await manifestFile.text();
  const manifest = JSON.parse(manifestContent);
  
  const downloadTasks: DownloadTask[] = manifest.files.map((item: any) => ({
    url: item.url,
    filename: item.name,
    headers: item.headers
  }));
  
  const downloadDir = new Directory(Paths.document, "manifest-downloads");
  downloadDir.create();
  
  const downloadedFiles = await batchDownload(
    downloadTasks,
    downloadDir,
    (completed, total, currentFile) => {
      console.log(`Progress: ${completed}/${total} - ${currentFile}`);
    }
  );
  
  // Clean up manifest file
  manifestFile.delete();
  
  return downloadedFiles;
}

// Smart caching with download fallback
async function getFileWithCache(
  url: string,
  cacheKey: string,
  maxAge: number = 24 * 60 * 60 * 1000 // 24 hours
): Promise<File> {
  const cacheDir = new Directory(Paths.cache, "downloaded-files");
  cacheDir.create();
  
  const cachedFile = new File(cacheDir, `${cacheKey}.cached`);
  
  // Check if cached file exists and is fresh
  if (cachedFile.exists) {
    const fileInfo = cachedFile.info();
    const age = Date.now() - (fileInfo.modificationTime || 0);
    
    if (age < maxAge) {
      console.log(`Using cached file: ${cacheKey}`);
      return cachedFile;
    } else {
      console.log(`Cache expired for: ${cacheKey}`);
      cachedFile.delete();
    }
  }
  
  // Download fresh copy
  console.log(`Downloading fresh copy: ${url}`);
  const downloadedFile = await File.downloadFileAsync(url, cachedFile);
  
  return downloadedFile;
}

// Usage examples
async function demonstrateNetworkOperations() {
  // Batch download example
  const downloadTasks: DownloadTask[] = [
    { 
      url: "https://example.com/image1.jpg", 
      filename: "image1.jpg" 
    },
    { 
      url: "https://api.example.com/data.json", 
      filename: "api-data.json",
      headers: { "Authorization": "Bearer token123" }
    },
    { 
      url: "https://example.com/document.pdf", 
      filename: "document.pdf" 
    }
  ];
  
  const downloadDir = new Directory(Paths.document, "batch-downloads");
  downloadDir.create();
  
  const downloadedFiles = await batchDownload(downloadTasks, downloadDir);
  console.log(`Successfully downloaded ${downloadedFiles.length} files`);
  
  // Smart caching example
  const apiData = await getFileWithCache(
    "https://api.example.com/config.json",
    "app-config",
    30 * 60 * 1000 // 30 minutes cache
  );
  
  const config = JSON.parse(await apiData.text());
  console.log("Loaded configuration:", config);
}

import { File, Directory, Paths } from "expo-file-system";

// Authenticated download service
class AuthenticatedDownloadService {
  private authToken: string | null = null;
  private refreshTokenUrl: string;
  
  constructor(refreshTokenUrl: string) {
    this.refreshTokenUrl = refreshTokenUrl;
  }
  
  async setAuthToken(token: string) {
    this.authToken = token;
  }
  
  async refreshAuthToken(): Promise<string> {
    // Implementation would depend on your auth system
    const response = await fetch(this.refreshTokenUrl, {
      method: 'POST',
      headers: { 'Content-Type': 'application/json' },
      body: JSON.stringify({ refresh_token: this.authToken })
    });
    
    const result = await response.json();
    this.authToken = result.access_token;
    return this.authToken;
  }
  
  async downloadAuthenticatedFile(
    url: string,
    destination: Directory | File,
    additionalHeaders?: Record<string, string>
  ): Promise<File> {
    let attempts = 0;
    const maxAttempts = 2;
    
    while (attempts < maxAttempts) {
      try {
        const headers = {
          'Authorization': `Bearer ${this.authToken}`,
          'User-Agent': 'MyApp/1.0.0',
          ...additionalHeaders
        };
        
        return await File.downloadFileAsync(url, destination, { headers });
        
      } catch (error) {
        attempts++;
        
        // If unauthorized and we haven't tried refreshing, refresh token
        if (error && attempts === 1) {
          console.log("Auth failed, refreshing token...");
          await this.refreshAuthToken();
        } else {
          throw error;
        }
      }
    }
    
    throw new Error("Download failed after token refresh");
  }
}

// API-specific download patterns
class APIDownloadClient {
  private baseUrl: string;
  private apiKey: string;
  
  constructor(baseUrl: string, apiKey: string) {
    this.baseUrl = baseUrl;
    this.apiKey = apiKey;
  }
  
  async downloadReport(
    reportId: string,
    format: 'pdf' | 'xlsx' | 'csv',
    destination: Directory
  ): Promise<File> {
    const url = `${this.baseUrl}/reports/${reportId}/export?format=${format}`;
    const filename = `report-${reportId}.${format}`;
    
    const headers = {
      'X-API-Key': this.apiKey,
      'Accept': this.getContentType(format),
      'X-Request-ID': this.generateRequestId()
    };
    
    const targetFile = new File(destination, filename);
    return await File.downloadFileAsync(url, targetFile, { headers });
  }
  
  async downloadWithRateLimit(
    url: string,
    destination: Directory | File,
    rateLimitDelay: number = 1000
  ): Promise<File> {
    // Implement rate limiting
    await new Promise(resolve => setTimeout(resolve, rateLimitDelay));
    
    const headers = {
      'X-API-Key': this.apiKey,
      'X-Rate-Limit': 'respect'
    };
    
    return await File.downloadFileAsync(url, destination, { headers });
  }
  
  private getContentType(format: string): string {
    const types = {
      'pdf': 'application/pdf',
      'xlsx': 'application/vnd.openxmlformats-officedocument.spreadsheetml.sheet',
      'csv': 'text/csv'
    };
    return types[format as keyof typeof types] || 'application/octet-stream';
  }
  
  private generateRequestId(): string {
    return Math.random().toString(36).substring(2, 15);
  }
}

// Usage examples
async function demonstrateAuthenticatedDownloads() {
  // Authenticated service usage
  const authService = new AuthenticatedDownloadService("https://api.example.com/auth/refresh");
  await authService.setAuthToken("initial-token");
  
  const protectedFile = await authService.downloadAuthenticatedFile(
    "https://api.example.com/protected/document.pdf",
    new Directory(Paths.document, "secure")
  );
  
  // API client usage
  const apiClient = new APIDownloadClient("https://api.example.com", "your-api-key");
  const reportsDir = new Directory(Paths.document, "reports");
  reportsDir.create();
  
  const pdfReport = await apiClient.downloadReport("report-123", "pdf", reportsDir);
  const excelReport = await apiClient.downloadReport("report-456", "xlsx", reportsDir);
  
  console.log(`Downloaded reports: ${pdfReport.name}, ${excelReport.name}`);
}