/**
 * Environment Variable Validation
 * 
 * Validates required environment variables at startup and provides
 * helpful error messages for production deployments.
 */

/**
 * Required environment variables for production
 */
const REQUIRED_ENV_VARS = {
  // Server Configuration
  NODE_ENV: {
    required: true,
    description: 'Environment mode (development, production)',
    validate: (val) => ['development', 'production', 'test'].includes(val)
  },
  PORT: {
    required: true,
    description: 'Server port number',
    validate: (val) => !isNaN(parseInt(val)) && parseInt(val) > 0 && parseInt(val) < 65536
  },
  
  // Optional but recommended for production
  SESSION_SECRET: {
    required: false,
    description: 'Secret key for session encryption',
    warn: (val) => !val || val.length < 32 ? 'SESSION_SECRET should be at least 32 characters for security' : null
  },
  FRONTEND_URL: {
    required: false,
    description: 'Frontend URL for CORS (required in production)',
    warn: (val, env) => env.NODE_ENV === 'production' && !val ? 'FRONTEND_URL should be set in production for proper CORS' : null
  },
  
  // Challonge OAuth (optional)
  CHALLONGE_CLIENT_ID: {
    required: false,
    description: 'Challonge OAuth client ID'
  },
  CHALLONGE_CLIENT_SECRET: {
    required: false,
    description: 'Challonge OAuth client secret'
  },
  CHALLONGE_REDIRECT_URI: {
    required: false,
    description: 'OAuth redirect URI'
  }
};

/**
 * Validate environment variables
 * @returns {Object} Validation result with errors and warnings
 */
export function validateEnvironment() {
  const errors = [];
  const warnings = [];
  const missing = [];
  
  // Check required variables
  for (const [key, config] of Object.entries(REQUIRED_ENV_VARS)) {
    const value = process.env[key];
    
    // Check if required variable is missing
    if (config.required && !value) {
      errors.push(`Missing required environment variable: ${key} - ${config.description}`);
      missing.push(key);
      continue;
    }
    
    // Validate value if present
    if (value && config.validate && !config.validate(value)) {
      errors.push(`Invalid value for ${key}: "${value}" - ${config.description}`);
    }
    
    // Check for warnings
    if (config.warn) {
      const warning = config.warn(value, process.env);
      if (warning) {
        warnings.push(`${key}: ${warning}`);
      }
    }
  }
  
  return {
    valid: errors.length === 0,
    errors,
    warnings,
    missing
  };
}

/**
 * Validate environment and exit if critical errors found
 * @param {boolean} exitOnError - Whether to exit process on validation errors (default: true)
 */
export function validateOrExit(exitOnError = true) {
  const result = validateEnvironment();
  
  // Print validation results
  console.log('\n🔍 Environment Validation:');
  console.log(`   NODE_ENV: ${process.env.NODE_ENV || 'not set'}`);
  console.log(`   PORT: ${process.env.PORT || 'not set'}`);
  
  // Show errors
  if (result.errors.length > 0) {
    console.error('\n❌ Environment Validation Errors:');
    result.errors.forEach(error => console.error(`   - ${error}`));
    
    if (result.missing.length > 0) {
      console.error('\n💡 Tip: Create a .env file with these variables:');
      result.missing.forEach(key => {
        console.error(`   ${key}=your_value_here`);
      });
      console.error('\n   See .env.example for reference');
    }
    
    if (exitOnError) {
      console.error('\n❌ Server cannot start due to environment errors\n');
      process.exit(1);
    }
  } else {
    console.log('   ✅ All required variables present');
  }
  
  // Show warnings
  if (result.warnings.length > 0) {
    console.warn('\n⚠️  Environment Warnings:');
    result.warnings.forEach(warning => console.warn(`   - ${warning}`));
  }
  
  console.log('');
  return result;
}

/**
 * Get configuration object with validated environment variables
 * @returns {Object} Configuration object
 */
export function getConfig() {
  return {
    nodeEnv: process.env.NODE_ENV || 'development',
    port: parseInt(process.env.PORT || '3001'),
    isProduction: process.env.NODE_ENV === 'production',
    isDevelopment: process.env.NODE_ENV === 'development',
    
    // Challonge OAuth
    challonge: {
      clientId: process.env.CHALLONGE_CLIENT_ID,
      clientSecret: process.env.CHALLONGE_CLIENT_SECRET,
      redirectUri: process.env.CHALLONGE_REDIRECT_URI,
      configured: !!(process.env.CHALLONGE_CLIENT_ID && process.env.CHALLONGE_CLIENT_SECRET)
    },
    
    // CORS
    cors: {
      origin: process.env.NODE_ENV === 'production'
        ? process.env.FRONTEND_URL
        : ['http://localhost:5173', 'http://localhost:5174', 'http://localhost:5175']
    },
    
    // Security
    session: {
      secret: process.env.SESSION_SECRET || 'dev-secret-change-in-production'
    }
  };
}