const Database = require('better-sqlite3');
const path = require('path');
const logger = require('../utils/logger');
const { withDatabaseRetry, CircuitBreaker } = require('../utils/retry');
const { DatabaseError } = require('../middleware/errorHandler');

class DatabaseManager {
  constructor() {
    this.db = null;
    this.dbPath = path.join(__dirname, '..', 'inventory.db');
    this.isInitialized = false;
    this.circuitBreaker = new CircuitBreaker({
      failureThreshold: 5,
      resetTimeout: 30000
    });
  }

  /**
   * Initialize database connection and create tables
   */
  async initialize() {
    if (this.isInitialized) {
      logger.debug('Database already initialized');
      return;
    }

    try {
      await withDatabaseRetry(async () => {
        logger.info('Initializing database connection', { dbPath: this.dbPath });
        
        this.db = new Database(this.dbPath);
        
        // Configure database settings
        this.db.pragma('journal_mode = WAL');
        this.db.pragma('synchronous = NORMAL');
        this.db.pragma('cache_size = 1000');
        this.db.pragma('temp_store = memory');
        this.db.pragma('mmap_size = 268435456'); // 256MB
        
        // Set busy timeout
        this.db.pragma('busy_timeout = 5000');
        
        await this.createTables();
        
        this.isInitialized = true;
        
        logger.info('Database initialized successfully', {
          dbPath: this.dbPath,
          journalMode: this.db.pragma('journal_mode', { simple: true }),
          cacheSize: this.db.pragma('cache_size', { simple: true })
        });
      });
    } catch (error) {
      logger.error('Database initialization failed', {
        error: error.message,
        dbPath: this.dbPath,
        stack: error.stack
      });
      throw new DatabaseError('Failed to initialize database', {
        originalError: error.message,
        dbPath: this.dbPath
      });
    }
  }

  /**
   * Create all required tables
   */
  async createTables() {
    // Products table as per design document
    const createProductsTable = `
      CREATE TABLE IF NOT EXISTS products (
        id INTEGER PRIMARY KEY AUTOINCREMENT,
        product_code VARCHAR(50) UNIQUE NOT NULL,
        description TEXT,
        category VARCHAR(100),
        unit_of_measure VARCHAR(20),
        created_at DATETIME DEFAULT CURRENT_TIMESTAMP,
        updated_at DATETIME DEFAULT CURRENT_TIMESTAMP
      )
    `;

    // Inventory table as per design document
    const createInventoryTable = `
      CREATE TABLE IF NOT EXISTS inventory (
        id INTEGER PRIMARY KEY AUTOINCREMENT,
        product_id INTEGER NOT NULL,
        current_level INTEGER NOT NULL DEFAULT 0,
        minimum_level INTEGER DEFAULT 0,
        maximum_level INTEGER,
        last_updated DATETIME DEFAULT CURRENT_TIMESTAMP,
        updated_by VARCHAR(100),
        version INTEGER DEFAULT 1,
        FOREIGN KEY (product_id) REFERENCES products(id) ON DELETE CASCADE
      )
    `;

    // Inventory history table as per design document
    const createInventoryHistoryTable = `
      CREATE TABLE IF NOT EXISTS inventory_history (
        id INTEGER PRIMARY KEY AUTOINCREMENT,
        product_id INTEGER NOT NULL,
        old_level INTEGER,
        new_level INTEGER NOT NULL,
        change_reason VARCHAR(200),
        updated_by VARCHAR(100),
        updated_at DATETIME DEFAULT CURRENT_TIMESTAMP,
        FOREIGN KEY (product_id) REFERENCES products(id) ON DELETE CASCADE
      )
    `;

    // Import sessions table as per design document
    const createImportSessionsTable = `
      CREATE TABLE IF NOT EXISTS import_sessions (
        id INTEGER PRIMARY KEY AUTOINCREMENT,
        filename VARCHAR(255),
        total_records INTEGER,
        successful_imports INTEGER,
        failed_imports INTEGER,
        import_date DATETIME DEFAULT CURRENT_TIMESTAMP,
        status VARCHAR(20) DEFAULT 'completed'
      )
    `;

    // Legacy tables for backward compatibility (will be migrated)
    const createItemsTable = `
      CREATE TABLE IF NOT EXISTS items (
        id INTEGER PRIMARY KEY AUTOINCREMENT,
        name TEXT NOT NULL,
        description TEXT,
        category TEXT,
        quantity INTEGER NOT NULL DEFAULT 0,
        unit TEXT,
        barcode TEXT UNIQUE,
        qr_code TEXT,
        location TEXT,
        min_stock_level INTEGER DEFAULT 0,
        created_at DATETIME DEFAULT CURRENT_TIMESTAMP,
        updated_at DATETIME DEFAULT CURRENT_TIMESTAMP
      )
    `;

    const createTransactionsTable = `
      CREATE TABLE IF NOT EXISTS transactions (
        id INTEGER PRIMARY KEY AUTOINCREMENT,
        item_id INTEGER NOT NULL,
        type TEXT NOT NULL CHECK (type IN ('in', 'out', 'adjustment')),
        quantity INTEGER NOT NULL,
        reason TEXT,
        user_name TEXT,
        created_at DATETIME DEFAULT CURRENT_TIMESTAMP,
        FOREIGN KEY (item_id) REFERENCES items (id) ON DELETE CASCADE
      )
    `;

    const createIndexes = [
      // New schema indexes - optimized for performance
      'CREATE UNIQUE INDEX IF NOT EXISTS idx_products_product_code ON products(product_code)',
      'CREATE INDEX IF NOT EXISTS idx_products_category ON products(category)',
      'CREATE INDEX IF NOT EXISTS idx_products_description ON products(description)',
      'CREATE INDEX IF NOT EXISTS idx_products_created_at ON products(created_at)',
      
      // Inventory indexes - optimized for common queries
      'CREATE UNIQUE INDEX IF NOT EXISTS idx_inventory_product_id ON inventory(product_id)',
      'CREATE INDEX IF NOT EXISTS idx_inventory_current_level ON inventory(current_level)',
      'CREATE INDEX IF NOT EXISTS idx_inventory_low_stock ON inventory(current_level, minimum_level) WHERE current_level <= minimum_level',
      'CREATE INDEX IF NOT EXISTS idx_inventory_last_updated ON inventory(last_updated)',
      'CREATE INDEX IF NOT EXISTS idx_inventory_updated_by ON inventory(updated_by)',
      'CREATE INDEX IF NOT EXISTS idx_inventory_version ON inventory(version)', // For optimistic locking
      
      // Inventory history indexes - optimized for audit queries
      'CREATE INDEX IF NOT EXISTS idx_inventory_history_product_id ON inventory_history(product_id)',
      'CREATE INDEX IF NOT EXISTS idx_inventory_history_updated_at ON inventory_history(updated_at)',
      'CREATE INDEX IF NOT EXISTS idx_inventory_history_updated_by ON inventory_history(updated_by)',
      'CREATE INDEX IF NOT EXISTS idx_inventory_history_product_date ON inventory_history(product_id, updated_at)',
      
      // Import sessions indexes
      'CREATE INDEX IF NOT EXISTS idx_import_sessions_date ON import_sessions(import_date)',
      'CREATE INDEX IF NOT EXISTS idx_import_sessions_status ON import_sessions(status)',
      
      // Composite indexes for complex queries
      'CREATE INDEX IF NOT EXISTS idx_products_category_code ON products(category, product_code)',
      'CREATE INDEX IF NOT EXISTS idx_inventory_product_level ON inventory(product_id, current_level)',
      'CREATE INDEX IF NOT EXISTS idx_inventory_levels_range ON inventory(current_level, minimum_level, maximum_level)',
      
      // Legacy schema indexes
      'CREATE INDEX IF NOT EXISTS idx_items_barcode ON items(barcode)',
      'CREATE INDEX IF NOT EXISTS idx_items_name ON items(name)',
      'CREATE INDEX IF NOT EXISTS idx_items_category ON items(category)',
      'CREATE INDEX IF NOT EXISTS idx_items_quantity ON items(quantity)',
      'CREATE INDEX IF NOT EXISTS idx_transactions_item_id ON transactions(item_id)',
      'CREATE INDEX IF NOT EXISTS idx_transactions_created_at ON transactions(created_at)',
      'CREATE INDEX IF NOT EXISTS idx_transactions_type ON transactions(type)',
      'CREATE INDEX IF NOT EXISTS idx_transactions_item_date ON transactions(item_id, created_at)'
    ];

    try {
      logger.info('Creating database tables and indexes');
      
      const startTime = Date.now();
      
      // Create new schema tables
      this.db.exec(createProductsTable);
      this.db.exec(createInventoryTable);
      this.db.exec(createInventoryHistoryTable);
      this.db.exec(createImportSessionsTable);
      
      // Create legacy tables for backward compatibility
      this.db.exec(createItemsTable);
      this.db.exec(createTransactionsTable);
      
      // Create indexes
      createIndexes.forEach((indexQuery, index) => {
        try {
          this.db.exec(indexQuery);
          logger.debug('Index created', { index: index + 1, total: createIndexes.length });
        } catch (indexError) {
          logger.warn('Index creation failed', {
            query: indexQuery,
            error: indexError.message
          });
        }
      });

      const duration = Date.now() - startTime;
      logger.info('Database tables created successfully', { duration: `${duration}ms` });
    } catch (error) {
      logger.error('Error creating database tables', {
        error: error.message,
        stack: error.stack
      });
      throw new DatabaseError('Failed to create database tables', {
        originalError: error.message
      });
    }
  }

  /**
   * Get database instance with circuit breaker protection
   */
  getDatabase() {
    if (!this.db || !this.isInitialized) {
      throw new DatabaseError('Database not initialized. Call initialize() first.');
    }
    return this.db;
  }

  /**
   * Execute database operation with circuit breaker and retry logic
   */
  async executeWithProtection(operation, operationName = 'database_operation') {
    return await this.circuitBreaker.execute(async () => {
      return await withDatabaseRetry(async () => {
        const startTime = Date.now();
        
        try {
          const result = await operation();
          const duration = Date.now() - startTime;
          
          logger.logDbOperation(operationName, 'unknown', {}, duration);
          
          return result;
        } catch (error) {
          const duration = Date.now() - startTime;
          
          logger.error('Database operation failed', {
            operation: operationName,
            duration: `${duration}ms`,
            error: error.message,
            code: error.code
          });
          
          throw error;
        }
      });
    });
  }

  /**
   * Close database connection
   */
  close() {
    if (this.db) {
      try {
        logger.info('Closing database connection');
        this.db.close();
        this.db = null;
        this.isInitialized = false;
        logger.info('Database connection closed successfully');
      } catch (error) {
        logger.error('Error closing database connection', {
          error: error.message
        });
      }
    }
  }

  /**
   * Execute a transaction with rollback support and error handling
   */
  async executeTransaction(callback, transactionName = 'transaction') {
    return await this.executeWithProtection(async () => {
      const startTime = Date.now();
      
      try {
        logger.debug('Starting database transaction', { name: transactionName });
        
        const transaction = this.db.transaction(callback);
        const result = transaction();
        
        const duration = Date.now() - startTime;
        logger.debug('Database transaction completed', {
          name: transactionName,
          duration: `${duration}ms`
        });
        
        return result;
      } catch (error) {
        const duration = Date.now() - startTime;
        logger.error('Database transaction failed', {
          name: transactionName,
          duration: `${duration}ms`,
          error: error.message
        });
        
        throw new DatabaseError(`Transaction failed: ${transactionName}`, {
          originalError: error.message,
          transactionName
        });
      }
    }, `transaction_${transactionName}`);
  }

  /**
   * Health check for database connection
   */
  async healthCheck() {
    try {
      const result = this.db.prepare('SELECT 1 as health').get();
      return {
        status: 'healthy',
        connected: true,
        result: result.health === 1
      };
    } catch (error) {
      logger.error('Database health check failed', {
        error: error.message
      });
      return {
        status: 'unhealthy',
        connected: false,
        error: error.message
      };
    }
  }

  /**
   * Get database statistics
   */
  getStats() {
    try {
      const stats = {
        isInitialized: this.isInitialized,
        dbPath: this.dbPath,
        circuitBreakerState: this.circuitBreaker.getState()
      };

      if (this.db) {
        stats.pragmas = {
          journalMode: this.db.pragma('journal_mode', { simple: true }),
          synchronous: this.db.pragma('synchronous', { simple: true }),
          cacheSize: this.db.pragma('cache_size', { simple: true }),
          busyTimeout: this.db.pragma('busy_timeout', { simple: true })
        };

        // Get table statistics
        stats.tables = this.getTableStats();
        
        // Get index usage statistics
        stats.indexes = this.getIndexStats();
      }

      return stats;
    } catch (error) {
      logger.error('Error getting database stats', {
        error: error.message
      });
      return {
        isInitialized: this.isInitialized,
        error: error.message
      };
    }
  }

  /**
   * Get table statistics for performance monitoring
   */
  getTableStats() {
    try {
      const tables = ['products', 'inventory', 'inventory_history', 'import_sessions'];
      const stats = {};

      tables.forEach(table => {
        try {
          const countResult = this.db.prepare(`SELECT COUNT(*) as count FROM ${table}`).get();
          stats[table] = {
            rowCount: countResult.count
          };
        } catch (error) {
          stats[table] = { error: error.message };
        }
      });

      return stats;
    } catch (error) {
      logger.error('Error getting table stats', { error: error.message });
      return {};
    }
  }

  /**
   * Get index statistics for query optimization
   */
  getIndexStats() {
    try {
      const indexes = this.db.prepare(`
        SELECT name, tbl_name, sql 
        FROM sqlite_master 
        WHERE type = 'index' AND name NOT LIKE 'sqlite_%'
        ORDER BY tbl_name, name
      `).all();

      return indexes.map(index => ({
        name: index.name,
        table: index.tbl_name,
        definition: index.sql
      }));
    } catch (error) {
      logger.error('Error getting index stats', { error: error.message });
      return [];
    }
  }

  /**
   * Analyze database performance and suggest optimizations
   */
  analyzePerformance() {
    try {
      const analysis = {
        timestamp: new Date().toISOString(),
        recommendations: []
      };

      // Check for missing indexes on frequently queried columns
      const tableStats = this.getTableStats();
      
      // Analyze query patterns (this would be enhanced with actual query logging)
      if (tableStats.products && tableStats.products.rowCount > 1000) {
        analysis.recommendations.push({
          type: 'INDEX_OPTIMIZATION',
          message: 'Consider adding composite indexes for frequently filtered product queries',
          priority: 'MEDIUM'
        });
      }

      if (tableStats.inventory_history && tableStats.inventory_history.rowCount > 10000) {
        analysis.recommendations.push({
          type: 'ARCHIVAL',
          message: 'Consider archiving old inventory history records to improve query performance',
          priority: 'LOW'
        });
      }

      // Check cache hit ratio (simplified)
      const cacheSize = this.db.pragma('cache_size', { simple: true });
      if (cacheSize < 2000) {
        analysis.recommendations.push({
          type: 'CACHE_OPTIMIZATION',
          message: 'Consider increasing cache size for better performance with large datasets',
          priority: 'HIGH'
        });
      }

      return analysis;
    } catch (error) {
      logger.error('Error analyzing database performance', { error: error.message });
      return {
        timestamp: new Date().toISOString(),
        error: error.message,
        recommendations: []
      };
    }
  }

  /**
   * Optimize database for better performance
   */
  async optimize() {
    return await this.executeWithProtection(async () => {
      logger.info('Starting database optimization');
      
      const startTime = Date.now();
      const results = {
        vacuum: false,
        analyze: false,
        reindex: false,
        pragmaUpdates: []
      };

      try {
        // Run VACUUM to reclaim space and defragment
        this.db.exec('VACUUM');
        results.vacuum = true;
        logger.debug('Database VACUUM completed');

        // Run ANALYZE to update query planner statistics
        this.db.exec('ANALYZE');
        results.analyze = true;
        logger.debug('Database ANALYZE completed');

        // Reindex all indexes
        this.db.exec('REINDEX');
        results.reindex = true;
        logger.debug('Database REINDEX completed');

        // Optimize pragma settings for performance
        const optimizations = [
          { pragma: 'optimize', value: null }, // SQLite auto-optimization
          { pragma: 'cache_size', value: 2000 },
          { pragma: 'temp_store', value: 'memory' },
          { pragma: 'mmap_size', value: 268435456 } // 256MB
        ];

        optimizations.forEach(opt => {
          try {
            if (opt.value !== null) {
              this.db.pragma(`${opt.pragma} = ${opt.value}`);
            } else {
              this.db.pragma(opt.pragma);
            }
            results.pragmaUpdates.push(opt.pragma);
          } catch (error) {
            logger.warn(`Failed to update pragma ${opt.pragma}`, { error: error.message });
          }
        });

        const duration = Date.now() - startTime;
        logger.info('Database optimization completed', {
          duration: `${duration}ms`,
          results
        });

        return {
          success: true,
          duration,
          results
        };
      } catch (error) {
        const duration = Date.now() - startTime;
        logger.error('Database optimization failed', {
          duration: `${duration}ms`,
          error: error.message,
          partialResults: results
        });
        
        throw new DatabaseError('Database optimization failed', {
          originalError: error.message,
          partialResults: results
        });
      }
    }, 'database_optimization');
  }

  /**
   * Prepare optimized statements for common queries
   */
  prepareOptimizedStatements() {
    if (!this.db) {
      throw new DatabaseError('Database not initialized');
    }

    try {
      // Cache frequently used prepared statements
      this.preparedStatements = {
        // Product queries
        findProductByCode: this.db.prepare(`
          SELECT p.*, i.current_level, i.minimum_level, i.maximum_level
          FROM products p
          LEFT JOIN inventory i ON p.id = i.product_id
          WHERE p.product_code = ?
        `),
        
        findProductsByCategory: this.db.prepare(`
          SELECT p.*, i.current_level, i.minimum_level, i.maximum_level
          FROM products p
          LEFT JOIN inventory i ON p.id = i.product_id
          WHERE p.category = ?
          ORDER BY p.product_code
          LIMIT ? OFFSET ?
        `),

        // Inventory queries
        getInventorySummary: this.db.prepare(`
          SELECT 
            p.id,
            p.product_code,
            p.description,
            p.category,
            i.current_level,
            i.minimum_level,
            i.maximum_level,
            i.last_updated,
            i.updated_by,
            CASE 
              WHEN i.current_level <= i.minimum_level THEN 'low'
              WHEN i.current_level >= i.maximum_level THEN 'high'
              ELSE 'normal'
            END as stock_status
          FROM products p
          INNER JOIN inventory i ON p.id = i.product_id
          ORDER BY p.product_code
          LIMIT ? OFFSET ?
        `),

        getLowStockItems: this.db.prepare(`
          SELECT 
            p.id,
            p.product_code,
            p.description,
            p.category,
            i.current_level,
            i.minimum_level,
            i.last_updated
          FROM products p
          INNER JOIN inventory i ON p.id = i.product_id
          WHERE i.current_level <= i.minimum_level
          ORDER BY (i.current_level - i.minimum_level), p.product_code
        `),

        // History queries
        getInventoryHistory: this.db.prepare(`
          SELECT 
            ih.*,
            p.product_code,
            p.description
          FROM inventory_history ih
          INNER JOIN products p ON ih.product_id = p.id
          WHERE ih.product_id = ?
          ORDER BY ih.updated_at DESC
          LIMIT ? OFFSET ?
        `),

        // Update queries with optimistic locking
        updateInventoryLevel: this.db.prepare(`
          UPDATE inventory 
          SET current_level = ?, 
              last_updated = datetime('now'), 
              updated_by = ?,
              version = version + 1
          WHERE product_id = ? AND version = ?
        `),

        insertInventoryHistory: this.db.prepare(`
          INSERT INTO inventory_history (product_id, old_level, new_level, change_reason, updated_by)
          VALUES (?, ?, ?, ?, ?)
        `)
      };

      logger.info('Optimized prepared statements created');
      return this.preparedStatements;
    } catch (error) {
      logger.error('Failed to prepare optimized statements', { error: error.message });
      throw new DatabaseError('Failed to prepare optimized statements', {
        originalError: error.message
      });
    }
  }

  /**
   * Get prepared statement by name
   */
  getPreparedStatement(name) {
    if (!this.preparedStatements) {
      this.prepareOptimizedStatements();
    }
    
    const statement = this.preparedStatements[name];
    if (!statement) {
      throw new DatabaseError(`Prepared statement '${name}' not found`);
    }
    
    return statement;
  }
}

module.exports = new DatabaseManager();