/**
 * Shattered Void MMO - Comprehensive Startup Checks
 * 
 * This module performs thorough pre-flight checks to ensure all dependencies,
 * configurations, and system requirements are met before starting the game.
 */

const fs = require('fs').promises;
const path = require('path');
const { exec } = require('child_process');
const { promisify } = require('util');
const net = require('net');

const execAsync = promisify(exec);

class StartupChecks {
  constructor() {
    this.checks = [];
    this.results = {};
  }

  /**
   * Add a check to the validation suite
   */
  addCheck(name, checkFunction, required = true) {
    this.checks.push({
      name,
      function: checkFunction,
      required
    });
  }

  /**
   * Run all registered checks
   */
  async runAllChecks() {
    const startTime = Date.now();
    const results = {
      success: true,
      checks: {},
      failures: [],
      duration: 0
    };

    // Register all standard checks
    this.registerStandardChecks();

    console.log(`🔍 Running ${this.checks.length} startup checks...`);

    for (const check of this.checks) {
      try {
        console.log(`  ⏳ ${check.name}...`);
        const checkResult = await check.function();
        
        results.checks[check.name] = {
          success: true,
          required: check.required,
          details: checkResult
        };
        
        console.log(`  ✅ ${check.name}`);
      } catch (error) {
        const failure = {
          name: check.name,
          required: check.required,
          error: error.message
        };
        
        results.checks[check.name] = {
          success: false,
          required: check.required,
          error: error.message
        };
        
        results.failures.push(failure);
        
        if (check.required) {
          results.success = false;
          console.log(`  ❌ ${check.name}: ${error.message}`);
        } else {
          console.log(`  ⚠️  ${check.name}: ${error.message} (optional)`);
        }
      }
    }

    results.duration = Date.now() - startTime;
    return results;
  }

  /**
   * Register all standard checks
   */
  registerStandardChecks() {
    // Node.js version check
    this.addCheck('Node.js Version', this.checkNodeVersion, true);
    
    // NPM availability
    this.addCheck('NPM Availability', this.checkNpmAvailability, true);
    
    // Environment configuration
    this.addCheck('Environment Configuration', this.checkEnvironmentConfig, true);
    
    // Required directories
    this.addCheck('Directory Structure', this.checkDirectoryStructure, true);
    
    // Package dependencies
    this.addCheck('Package Dependencies', this.checkPackageDependencies, true);
    
    // Port availability
    this.addCheck('Port Availability', this.checkPortAvailability, true);
    
    // Database configuration
    this.addCheck('Database Configuration', this.checkDatabaseConfig, true);
    
    // Redis configuration
    this.addCheck('Redis Configuration', this.checkRedisConfig, false);
    
    // Log directories
    this.addCheck('Log Directories', this.checkLogDirectories, true);
    
    // Frontend availability
    this.addCheck('Frontend Dependencies', this.checkFrontendDependencies, false);
    
    // Memory availability
    this.addCheck('System Memory', this.checkSystemMemory, true);
    
    // Disk space
    this.addCheck('Disk Space', this.checkDiskSpace, true);
    
    // File permissions
    this.addCheck('File Permissions', this.checkFilePermissions, true);
  }

  /**
   * Check Node.js version requirements
   */
  async checkNodeVersion() {
    const requiredMajor = 18;
    const currentVersion = process.version;
    const major = parseInt(currentVersion.slice(1).split('.')[0]);
    
    if (major < requiredMajor) {
      throw new Error(`Node.js ${requiredMajor}+ required, found ${currentVersion}`);
    }
    
    return {
      current: currentVersion,
      required: `>=${requiredMajor}.0.0`,
      valid: true
    };
  }

  /**
   * Check NPM availability
   */
  async checkNpmAvailability() {
    try {
      const { stdout } = await execAsync('npm --version');
      const version = stdout.trim();
      
      return {
        version,
        available: true
      };
    } catch (error) {
      throw new Error('NPM not found in PATH');
    }
  }

  /**
   * Check environment configuration
   */
  async checkEnvironmentConfig() {
    const envFile = path.join(process.cwd(), '.env');
    const config = {
      hasEnvFile: false,
      requiredVars: [],
      missingVars: [],
      warnings: []
    };

    // Check for .env file
    try {
      await fs.access(envFile);
      config.hasEnvFile = true;
    } catch {
      config.warnings.push('No .env file found, using defaults');
    }

    // Required environment variables (with defaults)
    const requiredVars = [
      { name: 'NODE_ENV', default: 'development' },
      { name: 'PORT', default: '3000' },
      { name: 'DB_HOST', default: 'localhost' },
      { name: 'DB_PORT', default: '5432' },
      { name: 'DB_NAME', default: 'shattered_void_dev' },
      { name: 'DB_USER', default: 'postgres' }
    ];

    for (const varConfig of requiredVars) {
      const value = process.env[varConfig.name];
      if (!value) {
        config.missingVars.push({
          name: varConfig.name,
          default: varConfig.default
        });
      } else {
        config.requiredVars.push({
          name: varConfig.name,
          value: varConfig.name.includes('PASSWORD') ? '[HIDDEN]' : value
        });
      }
    }

    return config;
  }

  /**
   * Check directory structure
   */
  async checkDirectoryStructure() {
    const requiredDirs = [
      'src',
      'src/controllers',
      'src/services',
      'src/routes',
      'src/database',
      'src/database/migrations',
      'config',
      'scripts'
    ];

    const optionalDirs = [
      'frontend',
      'frontend/src',
      'frontend/dist',
      'logs',
      'tests'
    ];

    const results = {
      required: [],
      optional: [],
      missing: []
    };

    // Check required directories
    for (const dir of requiredDirs) {
      try {
        const stats = await fs.stat(dir);
        if (stats.isDirectory()) {
          results.required.push(dir);
        } else {
          results.missing.push(dir);
        }
      } catch {
        results.missing.push(dir);
      }
    }

    // Check optional directories
    for (const dir of optionalDirs) {
      try {
        const stats = await fs.stat(dir);
        if (stats.isDirectory()) {
          results.optional.push(dir);
        }
      } catch {
        // Optional directories are not reported as missing
      }
    }

    if (results.missing.length > 0) {
      throw new Error(`Missing required directories: ${results.missing.join(', ')}`);
    }

    return results;
  }

  /**
   * Check package dependencies
   */
  async checkPackageDependencies() {
    const packageJsonPath = path.join(process.cwd(), 'package.json');
    const nodeModulesPath = path.join(process.cwd(), 'node_modules');
    
    try {
      // Check package.json exists
      const packageJson = JSON.parse(await fs.readFile(packageJsonPath, 'utf8'));
      
      // Check node_modules exists
      await fs.access(nodeModulesPath);
      
      // Check critical dependencies
      const criticalDeps = [
        'express',
        'pg',
        'knex',
        'winston',
        'dotenv',
        'socket.io'
      ];
      
      const missing = [];
      for (const dep of criticalDeps) {
        try {
          await fs.access(path.join(nodeModulesPath, dep));
        } catch {
          missing.push(dep);
        }
      }
      
      if (missing.length > 0) {
        throw new Error(`Missing critical dependencies: ${missing.join(', ')}`);
      }
      
      return {
        packageJson: packageJson.name,
        version: packageJson.version,
        dependencies: Object.keys(packageJson.dependencies || {}).length,
        devDependencies: Object.keys(packageJson.devDependencies || {}).length,
        criticalDeps: criticalDeps.length
      };
    } catch (error) {
      throw new Error(`Package validation failed: ${error.message}`);
    }
  }

  /**
   * Check port availability
   */
  async checkPortAvailability() {
    const backendPort = process.env.PORT || 3000;
    const frontendPort = process.env.FRONTEND_PORT || 5173;
    
    const checkPort = (port) => {
      return new Promise((resolve, reject) => {
        const server = net.createServer();
        
        server.listen(port, (err) => {
          if (err) {
            reject(new Error(`Port ${port} is in use`));
          } else {
            server.close(() => resolve(port));
          }
        });
        
        server.on('error', (err) => {
          reject(new Error(`Port ${port} is in use`));
        });
      });
    };
    
    const results = {
      backend: await checkPort(backendPort),
      frontend: null
    };
    
    // Only check frontend port if frontend is enabled
    if (process.env.ENABLE_FRONTEND !== 'false') {
      try {
        results.frontend = await checkPort(frontendPort);
      } catch (error) {
        // Frontend port check is not critical
        results.frontendError = error.message;
      }
    }
    
    return results;
  }

  /**
   * Check database configuration
   */
  async checkDatabaseConfig() {
    const config = {
      host: process.env.DB_HOST || 'localhost',
      port: process.env.DB_PORT || 5432,
      database: process.env.DB_NAME || 'shattered_void_dev',
      user: process.env.DB_USER || 'postgres'
    };
    
    // Check if database connection parameters are reasonable
    if (!config.host || !config.port || !config.database || !config.user) {
      throw new Error('Incomplete database configuration');
    }
    
    // Validate port number
    const port = parseInt(config.port);
    if (isNaN(port) || port < 1 || port > 65535) {
      throw new Error(`Invalid database port: ${config.port}`);
    }
    
    return {
      host: config.host,
      port: config.port,
      database: config.database,
      user: config.user,
      configured: true
    };
  }

  /**
   * Check Redis configuration (optional)
   */
  async checkRedisConfig() {
    const config = {
      host: process.env.REDIS_HOST || 'localhost',
      port: process.env.REDIS_PORT || 6379,
      enabled: process.env.DISABLE_REDIS !== 'true'
    };
    
    if (!config.enabled) {
      return {
        enabled: false,
        message: 'Redis disabled by configuration'
      };
    }
    
    // Validate port number
    const port = parseInt(config.port);
    if (isNaN(port) || port < 1 || port > 65535) {
      throw new Error(`Invalid Redis port: ${config.port}`);
    }
    
    return {
      host: config.host,
      port: config.port,
      enabled: true
    };
  }

  /**
   * Check log directories
   */
  async checkLogDirectories() {
    const logDir = path.join(process.cwd(), 'logs');
    
    try {
      // Check if logs directory exists
      await fs.access(logDir);
      
      // Check if it's writable
      await fs.access(logDir, fs.constants.W_OK);
      
      return {
        directory: logDir,
        exists: true,
        writable: true
      };
    } catch {
      // Create logs directory if it doesn't exist
      try {
        await fs.mkdir(logDir, { recursive: true });
        return {
          directory: logDir,
          exists: true,
          writable: true,
          created: true
        };
      } catch (error) {
        throw new Error(`Cannot create logs directory: ${error.message}`);
      }
    }
  }

  /**
   * Check frontend dependencies (optional)
   */
  async checkFrontendDependencies() {
    const frontendDir = path.join(process.cwd(), 'frontend');
    
    try {
      // Check if frontend directory exists
      await fs.access(frontendDir);
      
      // Check package.json
      const packageJsonPath = path.join(frontendDir, 'package.json');
      const packageJson = JSON.parse(await fs.readFile(packageJsonPath, 'utf8'));
      
      // Check node_modules
      const nodeModulesPath = path.join(frontendDir, 'node_modules');
      await fs.access(nodeModulesPath);
      
      return {
        directory: frontendDir,
        name: packageJson.name,
        version: packageJson.version,
        dependencies: Object.keys(packageJson.dependencies || {}).length,
        hasNodeModules: true
      };
    } catch (error) {
      throw new Error(`Frontend not available: ${error.message}`);
    }
  }

  /**
   * Check system memory
   */
  async checkSystemMemory() {
    const totalMemory = require('os').totalmem();
    const freeMemory = require('os').freemem();
    const usedMemory = totalMemory - freeMemory;
    
    const totalGB = totalMemory / (1024 * 1024 * 1024);
    const freeGB = freeMemory / (1024 * 1024 * 1024);
    const usedGB = usedMemory / (1024 * 1024 * 1024);
    
    // Minimum 1GB free memory recommended
    if (freeGB < 1) {
      throw new Error(`Low memory: ${freeGB.toFixed(2)}GB free, 1GB+ recommended`);
    }
    
    return {
      total: `${totalGB.toFixed(2)}GB`,
      used: `${usedGB.toFixed(2)}GB`,
      free: `${freeGB.toFixed(2)}GB`,
      usage: `${((usedGB / totalGB) * 100).toFixed(1)}%`
    };
  }

  /**
   * Check disk space
   */
  async checkDiskSpace() {
    try {
      const { stdout } = await execAsync('df -h .');
      const lines = stdout.trim().split('\n');
      const data = lines[1].split(/\s+/);
      
      const size = data[1];
      const used = data[2];
      const available = data[3];
      const usage = data[4];
      
      // Extract numeric percentage
      const usagePercent = parseInt(usage.replace('%', ''));
      
      // Warn if disk usage is over 90%
      if (usagePercent > 90) {
        throw new Error(`High disk usage: ${usage} used, <10% available`);
      }
      
      return {
        size,
        used,
        available,
        usage: `${usagePercent}%`
      };
    } catch (error) {
      // Fallback for non-Unix systems or when df is not available
      return {
        message: 'Disk space check not available on this system',
        available: true
      };
    }
  }

  /**
   * Check file permissions
   */
  async checkFilePermissions() {
    const criticalFiles = [
      'src/server.js',
      'package.json',
      'knexfile.js'
    ];
    
    const results = {
      readable: [],
      unreadable: []
    };
    
    for (const file of criticalFiles) {
      try {
        await fs.access(file, fs.constants.R_OK);
        results.readable.push(file);
      } catch {
        results.unreadable.push(file);
      }
    }
    
    if (results.unreadable.length > 0) {
      throw new Error(`Cannot read critical files: ${results.unreadable.join(', ')}`);
    }
    
    return results;
  }
}

module.exports = StartupChecks;