/**
 * Database Backup and Recovery Utilities
 * Provides automated backup and recovery functionality for SQLite database
 */

const fs = require('fs').promises;
const path = require('path');
const { createReadStream, createWriteStream } = require('fs');
const { pipeline } = require('stream/promises');
const logger = require('./logger');
const config = require('../config/production');

class BackupManager {
  constructor() {
    this.dbPath = config.database.path;
    this.backupDir = config.database.backupPath;
    this.retentionDays = config.backup.retentionDays;
  }

  /**
   * Initialize backup directory
   */
  async initialize() {
    try {
      await fs.mkdir(this.backupDir, { recursive: true });
      logger.info('Backup directory initialized', { path: this.backupDir });
    } catch (error) {
      logger.error('Failed to initialize backup directory', { 
        error: error.message,
        path: this.backupDir 
      });
      throw error;
    }
  }

  /**
   * Create a backup of the database
   */
  async createBackup() {
    try {
      const timestamp = new Date().toISOString().replace(/[:.]/g, '-');
      const backupFileName = `inventory-backup-${timestamp}.db`;
      const backupPath = path.join(this.backupDir, backupFileName);

      // Check if source database exists
      try {
        await fs.access(this.dbPath);
      } catch (error) {
        throw new Error(`Source database not found: ${this.dbPath}`);
      }

      // Create backup using file copy
      await pipeline(
        createReadStream(this.dbPath),
        createWriteStream(backupPath)
      );

      // Verify backup file
      const stats = await fs.stat(backupPath);
      if (stats.size === 0) {
        throw new Error('Backup file is empty');
      }

      logger.info('Database backup created successfully', {
        backupPath,
        size: stats.size,
        timestamp
      });

      return {
        success: true,
        backupPath,
        size: stats.size,
        timestamp
      };
    } catch (error) {
      logger.error('Database backup failed', { error: error.message });
      throw error;
    }
  }

  /**
   * Restore database from backup
   */
  async restoreBackup(backupPath) {
    try {
      // Verify backup file exists
      try {
        await fs.access(backupPath);
      } catch (error) {
        throw new Error(`Backup file not found: ${backupPath}`);
      }

      // Create backup of current database before restore
      const currentBackupPath = `${this.dbPath}.pre-restore-${Date.now()}.bak`;
      try {
        await pipeline(
          createReadStream(this.dbPath),
          createWriteStream(currentBackupPath)
        );
        logger.info('Current database backed up before restore', { 
          path: currentBackupPath 
        });
      } catch (error) {
        logger.warn('Could not backup current database before restore', { 
          error: error.message 
        });
      }

      // Restore from backup
      await pipeline(
        createReadStream(backupPath),
        createWriteStream(this.dbPath)
      );

      // Verify restored database
      const stats = await fs.stat(this.dbPath);
      if (stats.size === 0) {
        throw new Error('Restored database is empty');
      }

      logger.info('Database restored successfully', {
        backupPath,
        restoredSize: stats.size
      });

      return {
        success: true,
        restoredFrom: backupPath,
        size: stats.size
      };
    } catch (error) {
      logger.error('Database restore failed', { 
        error: error.message,
        backupPath 
      });
      throw error;
    }
  }

  /**
   * List available backups
   */
  async listBackups() {
    try {
      const files = await fs.readdir(this.backupDir);
      const backups = [];

      for (const file of files) {
        if (file.endsWith('.db')) {
          const filePath = path.join(this.backupDir, file);
          const stats = await fs.stat(filePath);
          
          backups.push({
            filename: file,
            path: filePath,
            size: stats.size,
            created: stats.birthtime,
            modified: stats.mtime
          });
        }
      }

      // Sort by creation date (newest first)
      backups.sort((a, b) => b.created - a.created);

      return backups;
    } catch (error) {
      logger.error('Failed to list backups', { error: error.message });
      throw error;
    }
  }

  /**
   * Clean up old backups based on retention policy
   */
  async cleanupOldBackups() {
    try {
      const backups = await this.listBackups();
      const cutoffDate = new Date();
      cutoffDate.setDate(cutoffDate.getDate() - this.retentionDays);

      let deletedCount = 0;
      let deletedSize = 0;

      for (const backup of backups) {
        if (backup.created < cutoffDate) {
          try {
            await fs.unlink(backup.path);
            deletedCount++;
            deletedSize += backup.size;
            logger.info('Old backup deleted', {
              filename: backup.filename,
              age: Math.floor((Date.now() - backup.created) / (1000 * 60 * 60 * 24))
            });
          } catch (error) {
            logger.warn('Failed to delete old backup', {
              filename: backup.filename,
              error: error.message
            });
          }
        }
      }

      logger.info('Backup cleanup completed', {
        deletedCount,
        deletedSize,
        retentionDays: this.retentionDays
      });

      return { deletedCount, deletedSize };
    } catch (error) {
      logger.error('Backup cleanup failed', { error: error.message });
      throw error;
    }
  }

  /**
   * Schedule automatic backups
   */
  scheduleBackups() {
    const interval = config.database.backupInterval;
    
    if (!config.backup.enabled) {
      logger.info('Automatic backups disabled');
      return;
    }

    logger.info('Scheduling automatic backups', { 
      intervalMs: interval,
      intervalHours: interval / (1000 * 60 * 60)
    });

    setInterval(async () => {
      try {
        await this.createBackup();
        await this.cleanupOldBackups();
      } catch (error) {
        logger.error('Scheduled backup failed', { error: error.message });
      }
    }, interval);
  }

  /**
   * Get backup statistics
   */
  async getBackupStats() {
    try {
      const backups = await this.listBackups();
      const totalSize = backups.reduce((sum, backup) => sum + backup.size, 0);
      const oldestBackup = backups.length > 0 ? backups[backups.length - 1] : null;
      const newestBackup = backups.length > 0 ? backups[0] : null;

      return {
        count: backups.length,
        totalSize,
        oldestBackup: oldestBackup ? {
          filename: oldestBackup.filename,
          created: oldestBackup.created,
          size: oldestBackup.size
        } : null,
        newestBackup: newestBackup ? {
          filename: newestBackup.filename,
          created: newestBackup.created,
          size: newestBackup.size
        } : null
      };
    } catch (error) {
      logger.error('Failed to get backup statistics', { error: error.message });
      throw error;
    }
  }
}

module.exports = BackupManager;