/**
 * FRONTEND SERVICE
 * 
 * This service communicates with the Node.js backend (server.js).
 * It supports Batch Uploading to maximize speed.
 */

// Use relative URL so Vite proxy can forward it to localhost:3001
const BACKEND_URL = '/api/upload';

interface BatchItem {
  id: string; // Used for tracking
  file: File;
  path: string;
}

/**
 * Uploads multiple files in a single request.
 * 
 * @param items Array of files and their destination paths
 * @returns Array of public URLs for the uploaded files
 */
export const uploadBatchToHub = async (items: BatchItem[]): Promise<string[]> => {
  const formData = new FormData();

  // Append all files and paths to FormData
  // Multer on the backend will receive these as arrays
  items.forEach(item => {
    formData.append('paths', item.path);
    formData.append('files', item.file);
  });

  try {
    const response = await fetch(BACKEND_URL, {
      method: 'POST',
      body: formData,
    });

    // Handle non-JSON responses (like 404 or 502 from proxy)
    const contentType = response.headers.get("content-type");
    if (!contentType || !contentType.includes("application/json")) {
        throw new Error(`Server returned unexpected ${response.status} ${response.statusText}. Is the backend running?`);
    }

    const data = await response.json();

    if (!response.ok || !data.success) {
      throw new Error(data.error || 'Upload failed on server');
    }

    return data.urls;
    
  } catch (err: any) {
    console.error("[FE] Batch Upload Failed:", err);
    const errorMessage = err?.message || "Unknown error";
    
    if (errorMessage.includes('Failed to fetch') || errorMessage.includes('backend running')) {
        throw new Error("Cannot connect to Backend. Make sure 'npm run server' is running.");
    }
    throw new Error(errorMessage);
  }
};