const sharp = require('sharp');
const path = require('path');
const fs = require('fs').promises;
const logger = require('../utils/logger');
const { db } = require('../database/db');

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

// Default thumbnail settings
const DEFAULT_THUMBNAIL_WIDTH = 300;
const DEFAULT_THUMBNAIL_HEIGHT = 300;
const DEFAULT_THUMBNAIL_FIT = 'cover'; // 'cover' for square crops
const DEFAULT_THUMBNAIL_QUALITY = 85;
const DEFAULT_THUMBNAIL_FORMAT = 'jpeg';

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

// Get thumbnail settings from database
async function getThumbnailSettings() {
  try {
    const settings = await db('app_settings')
      .whereIn('setting_key', [
        'thumbnail_width',
        'thumbnail_height',
        'thumbnail_fit',
        'thumbnail_quality',
        'thumbnail_format'
      ])
      .select('setting_key', 'setting_value');
    
    const settingsMap = {};
    settings.forEach(s => {
      settingsMap[s.setting_key] = s.setting_value;
    });
    
    return {
      width: parseInt(settingsMap.thumbnail_width) || DEFAULT_THUMBNAIL_WIDTH,
      height: parseInt(settingsMap.thumbnail_height) || DEFAULT_THUMBNAIL_HEIGHT,
      fit: settingsMap.thumbnail_fit || DEFAULT_THUMBNAIL_FIT,
      quality: parseInt(settingsMap.thumbnail_quality) || DEFAULT_THUMBNAIL_QUALITY,
      format: settingsMap.thumbnail_format || DEFAULT_THUMBNAIL_FORMAT
    };
  } catch (error) {
    // If database is not ready or settings don't exist, use defaults
    logger.warn('Could not fetch thumbnail settings, using defaults:', error.message);
    return {
      width: DEFAULT_THUMBNAIL_WIDTH,
      height: DEFAULT_THUMBNAIL_HEIGHT,
      fit: DEFAULT_THUMBNAIL_FIT,
      quality: DEFAULT_THUMBNAIL_QUALITY,
      format: DEFAULT_THUMBNAIL_FORMAT
    };
  }
}

async function generateThumbnail(imagePath, options = {}) {
  const filename = path.basename(imagePath);
  const thumbnailFilename = `thumb_${filename}`;
  const thumbnailDir = getThumbnailPath();
  const thumbnailPath = path.join(thumbnailDir, thumbnailFilename);
  
  // Get thumbnail settings
  const settings = await getThumbnailSettings();
  
  // Ensure thumbnail directory exists
  await fs.mkdir(thumbnailDir, { recursive: true });
  
  // Check if we need to regenerate (for broken thumbnails)
  if (options.regenerate) {
    try {
      await fs.unlink(thumbnailPath);
      logger.info(`Deleted broken thumbnail: ${thumbnailPath}`);
    } catch (err) {
      // File might not exist, that's okay
    }
  }
  
  try {
    // First, verify the source image is complete and valid
    const metadata = await sharp(imagePath).metadata();
    
    if (!metadata.width || !metadata.height) {
      throw new Error('Invalid image metadata - file may be incomplete');
    }
    
    // Create sharp instance with memory-efficient settings
    let sharpInstance = sharp(imagePath, { 
      limitInputPixels: 268402689, // ~16k x 16k max
      sequentialRead: true, // More memory efficient for large images
      failOnError: false // Don't fail on minor issues
    });
    
    // Apply resize with configured settings
    // For square thumbnails with 'cover' fit, we crop to center
    sharpInstance = sharpInstance.resize(settings.width, settings.height, {
      withoutEnlargement: true,
      fit: settings.fit, // 'cover' will crop to fill the exact dimensions
      position: 'center' // Center the crop for better composition
    });
    
    // Apply format-specific options
    if (settings.format === 'jpeg') {
      sharpInstance = sharpInstance.jpeg({ 
        quality: settings.quality,
        progressive: true, // Progressive JPEG for better loading
        mozjpeg: true // Better compression
      });
    } else if (settings.format === 'png') {
      sharpInstance = sharpInstance.png({
        quality: settings.quality,
        compressionLevel: 9,
        progressive: true
      });
    } else if (settings.format === 'webp') {
      sharpInstance = sharpInstance.webp({
        quality: settings.quality,
        effort: 4 // Balance between speed and compression
      });
    }
    
    // Save the thumbnail
    await sharpInstance.toFile(thumbnailPath);
    
    // Verify the thumbnail was created successfully
    const stats = await fs.stat(thumbnailPath);
    if (stats.size === 0) {
      throw new Error('Generated thumbnail is empty');
    }
    
    return path.relative(getStoragePath(), thumbnailPath);
  } catch (error) {
    const msg = (error && error.message) ? error.message : String(error);
    logger.error(`Failed to generate thumbnail for ${filename}: ${msg}`);
    
    // Clean up any partially created file
    try {
      await fs.unlink(thumbnailPath);
    } catch (unlinkErr) {
      // Ignore unlink errors
    }
    
    // Return null if thumbnail generation fails, don't fail the whole upload
    return null;
  }
}

/**
 * Check if a thumbnail exists and is valid
 */
async function isThumbnailValid(thumbnailPath) {
  try {
    const fullPath = path.join(getStoragePath(), thumbnailPath);
    const stats = await fs.stat(fullPath);
    
    // Check if file exists and has content
    if (stats.size === 0) {
      return false;
    }
    
    // Try to read metadata to ensure it's a valid image
    await sharp(fullPath).metadata();
    return true;
  } catch (error) {
    return false;
  }
}

/**
 * Regenerate thumbnail if it's broken or missing
 */
async function ensureThumbnail(photo) {
  const { db } = require('../database/db');
  const { resolvePhotoFilePath } = require('./photoResolver');
  let originalPath;
  try {
    const event = await db('events').where('id', photo.event_id).first();
    originalPath = resolvePhotoFilePath(event, photo);
    logger.info(`Ensuring thumbnail for photo ${photo.id} from source: ${originalPath}`);
  } catch (e) {
    const msg = (e && e.message) ? e.message : String(e);
    logger.error(`Failed to resolve original path for thumbnail (photo ${photo.id}): ${msg}`);
    return null;
  }
  
  // Check if thumbnail exists and is valid
  if (photo.thumbnail_path) {
    const isValid = await isThumbnailValid(photo.thumbnail_path);
    if (isValid) {
      return photo.thumbnail_path;
    }
    logger.warn(`Invalid thumbnail detected for photo ${photo.id}, regenerating...`);
  }
  
  // Generate new thumbnail
  const newThumbnailPath = await generateThumbnail(originalPath, { regenerate: true });
  
  if (newThumbnailPath) {
    // Update database with new thumbnail path
    const { db } = require('../database/db');
    await db('photos')
      .where({ id: photo.id })
      .update({ thumbnail_path: newThumbnailPath });
    
    logger.info(`Regenerated thumbnail for photo ${photo.id}`);
    return newThumbnailPath;
  }
  
  return null;
}

module.exports = { generateThumbnail, isThumbnailValid, ensureThumbnail };