require('dotenv').config();

/**
 * Application Configuration
 * Centralized configuration management for all environment variables
 */

const config = {
  // Server Configuration
  server: {
    nodeEnv: process.env.NODE_ENV || 'development',
    port: parseInt(process.env.PORT) || 3000,
    apiPrefix: process.env.API_PREFIX || '/api',
    isDevelopment: (process.env.NODE_ENV || 'development') === 'development',
    isProduction: process.env.NODE_ENV === 'production',
    isTest: process.env.NODE_ENV === 'test'
  },

  // Database Configuration
  database: {
    host: process.env.DB_HOST || 'localhost',
    port: parseInt(process.env.DB_PORT) || 3306,
    name: process.env.DB_NAME || 'interview_quiz_db',
    user: process.env.DB_USER || 'root',
    password: process.env.DB_PASSWORD || '',
    dialect: process.env.DB_DIALECT || 'mysql',
    pool: {
      max: parseInt(process.env.DB_POOL_MAX) || 10,
      min: parseInt(process.env.DB_POOL_MIN) || 0,
      acquire: parseInt(process.env.DB_POOL_ACQUIRE) || 30000,
      idle: parseInt(process.env.DB_POOL_IDLE) || 10000
    }
  },

  // JWT Configuration
  jwt: {
    secret: process.env.JWT_SECRET,
    expire: process.env.JWT_EXPIRE || '24h',
    algorithm: 'HS256'
  },

  // Rate Limiting Configuration
  rateLimit: {
    windowMs: parseInt(process.env.RATE_LIMIT_WINDOW_MS) || 900000, // 15 minutes
    maxRequests: parseInt(process.env.RATE_LIMIT_MAX_REQUESTS) || 100,
    message: 'Too many requests from this IP, please try again later.'
  },

  // CORS Configuration
  cors: {
    origin: process.env.CORS_ORIGIN || 'http://localhost:4200',
    credentials: true
  },

  // Guest Session Configuration
  guest: {
    sessionExpireHours: parseInt(process.env.GUEST_SESSION_EXPIRE_HOURS) || 24,
    maxQuizzes: parseInt(process.env.GUEST_MAX_QUIZZES) || 3
  },

  // Logging Configuration
  logging: {
    level: process.env.LOG_LEVEL || 'info'
  },

  // Pagination Defaults
  pagination: {
    defaultLimit: 10,
    maxLimit: 100
  },

  // Security Configuration
  security: {
    bcryptRounds: 10,
    maxLoginAttempts: 5,
    lockoutDuration: 15 * 60 * 1000 // 15 minutes
  }
};

/**
 * Validate critical configuration values
 */
function validateConfig() {
  const errors = [];

  if (!config.jwt.secret) {
    errors.push('JWT_SECRET is not configured');
  }

  if (!config.database.name) {
    errors.push('DB_NAME is not configured');
  }

  if (config.server.isProduction && !config.database.password) {
    errors.push('DB_PASSWORD is required in production');
  }

  if (errors.length > 0) {
    throw new Error(`Configuration errors:\n  - ${errors.join('\n  - ')}`);
  }

  return true;
}

// Validate on module load
try {
  validateConfig();
} catch (error) {
  console.error('❌ Configuration Error:', error.message);
  process.exit(1);
}

module.exports = config;