const sharp = require('sharp');
const path = require('path');
const fs = require('fs').promises;

// Configure sharp for better memory management with large batches
sharp.cache(false); // Disable cache to prevent memory buildup
sharp.concurrency(2); // Limit concurrent operations

const THUMBNAIL_WIDTH = 300;
const getStoragePath = () => process.env.STORAGE_PATH || path.join(__dirname, '../../../storage');
const getThumbnailPath = () => path.join(getStoragePath(), 'thumbnails');

async function generateThumbnail(imagePath) {
  const filename = path.basename(imagePath);
  const thumbnailFilename = `thumb_${filename}`;
  const thumbnailDir = getThumbnailPath();
  const thumbnailPath = path.join(thumbnailDir, thumbnailFilename);
  
  // Ensure thumbnail directory exists
  await fs.mkdir(thumbnailDir, { recursive: true });
  
  try {
    // Generate thumbnail with memory-efficient settings
    await sharp(imagePath, { 
      limitInputPixels: 268402689, // ~16k x 16k max
      sequentialRead: true // More memory efficient for large images
    })
      .resize(THUMBNAIL_WIDTH, null, {
        withoutEnlargement: true,
        fit: 'inside'
      })
      .jpeg({ 
        quality: 80,
        progressive: true, // Progressive JPEG for better loading
        mozjpeg: true // Better compression
      })
      .toFile(thumbnailPath);
    
    return path.relative(getStoragePath(), thumbnailPath);
  } catch (error) {
    console.error(`Failed to generate thumbnail for ${filename}:`, error);
    // Return null if thumbnail generation fails, don't fail the whole upload
    return null;
  }
}

module.exports = { generateThumbnail };