/**
 * SMTP Validation Utilities
 * Provides validation functions for SMTP server
 */

import { SmtpState } from '../interfaces.js';
import { SMTP_PATTERNS } from '../constants.js';

/**
 * Validates an email address
 * @param email - Email address to validate
 * @returns Whether the email address is valid
 */
export function isValidEmail(email: string): boolean {
  if (!email || typeof email !== 'string') {
    return false;
  }
  
  return SMTP_PATTERNS.EMAIL.test(email);
}

/**
 * Validates the MAIL FROM command syntax
 * @param args - Arguments string from the MAIL FROM command
 * @returns Object with validation result and extracted data
 */
export function validateMailFrom(args: string): {
  isValid: boolean;
  address?: string;
  params?: Record<string, string>;
  errorMessage?: string;
} {
  if (!args) {
    return { isValid: false, errorMessage: 'Missing arguments' };
  }
  
  const match = args.match(SMTP_PATTERNS.MAIL_FROM);
  if (!match) {
    return { isValid: false, errorMessage: 'Invalid syntax' };
  }
  
  const [, address, paramsString] = match;
  
  if (!isValidEmail(address)) {
    return { isValid: false, errorMessage: 'Invalid email address' };
  }
  
  // Parse parameters if they exist
  const params: Record<string, string> = {};
  if (paramsString) {
    let paramMatch;
    const paramRegex = SMTP_PATTERNS.PARAM;
    paramRegex.lastIndex = 0; // Reset the regex
    
    while ((paramMatch = paramRegex.exec(paramsString)) !== null) {
      const [, name, value = ''] = paramMatch;
      params[name.toUpperCase()] = value;
    }
  }
  
  return { isValid: true, address, params };
}

/**
 * Validates the RCPT TO command syntax
 * @param args - Arguments string from the RCPT TO command
 * @returns Object with validation result and extracted data
 */
export function validateRcptTo(args: string): {
  isValid: boolean;
  address?: string;
  params?: Record<string, string>;
  errorMessage?: string;
} {
  if (!args) {
    return { isValid: false, errorMessage: 'Missing arguments' };
  }
  
  const match = args.match(SMTP_PATTERNS.RCPT_TO);
  if (!match) {
    return { isValid: false, errorMessage: 'Invalid syntax' };
  }
  
  const [, address, paramsString] = match;
  
  if (!isValidEmail(address)) {
    return { isValid: false, errorMessage: 'Invalid email address' };
  }
  
  // Parse parameters if they exist
  const params: Record<string, string> = {};
  if (paramsString) {
    let paramMatch;
    const paramRegex = SMTP_PATTERNS.PARAM;
    paramRegex.lastIndex = 0; // Reset the regex
    
    while ((paramMatch = paramRegex.exec(paramsString)) !== null) {
      const [, name, value = ''] = paramMatch;
      params[name.toUpperCase()] = value;
    }
  }
  
  return { isValid: true, address, params };
}

/**
 * Validates the EHLO command syntax
 * @param args - Arguments string from the EHLO command
 * @returns Object with validation result and extracted data
 */
export function validateEhlo(args: string): {
  isValid: boolean;
  hostname?: string;
  errorMessage?: string;
} {
  if (!args) {
    return { isValid: false, errorMessage: 'Missing domain name' };
  }
  
  const match = args.match(SMTP_PATTERNS.EHLO);
  if (!match) {
    return { isValid: false, errorMessage: 'Invalid syntax' };
  }
  
  const hostname = match[1];
  
  // Check for invalid characters in hostname
  if (hostname.includes('@') || hostname.includes('<')) {
    return { isValid: false, errorMessage: 'Invalid domain name format' };
  }
  
  return { isValid: true, hostname };
}

/**
 * Validates command in the current SMTP state
 * @param command - SMTP command
 * @param currentState - Current SMTP state
 * @returns Whether the command is valid in the current state
 */
export function isValidCommandSequence(command: string, currentState: SmtpState): boolean {
  const upperCommand = command.toUpperCase();
  
  // Some commands are valid in any state
  if (upperCommand === 'QUIT' || upperCommand === 'RSET' || upperCommand === 'NOOP' || upperCommand === 'HELP') {
    return true;
  }
  
  // State-specific validation
  switch (currentState) {
    case SmtpState.GREETING:
      return upperCommand === 'EHLO' || upperCommand === 'HELO';
      
    case SmtpState.AFTER_EHLO:
      return upperCommand === 'MAIL' || upperCommand === 'STARTTLS' || upperCommand === 'AUTH';
      
    case SmtpState.MAIL_FROM:
    case SmtpState.RCPT_TO:
      if (upperCommand === 'RCPT') {
        return true;
      }
      return currentState === SmtpState.RCPT_TO && upperCommand === 'DATA';
      
    case SmtpState.DATA:
      // In DATA state, only the data content is accepted, not commands
      return false;
      
    case SmtpState.DATA_RECEIVING:
      // In DATA_RECEIVING state, only the data content is accepted, not commands
      return false;
      
    case SmtpState.FINISHED:
      // After data is received, only new transactions or session end
      return upperCommand === 'MAIL' || upperCommand === 'QUIT' || upperCommand === 'RSET';
      
    default:
      return false;
  }
}

/**
 * Validates if a hostname is valid according to RFC 5321
 * @param hostname - Hostname to validate
 * @returns Whether the hostname is valid
 */
export function isValidHostname(hostname: string): boolean {
  if (!hostname || typeof hostname !== 'string') {
    return false;
  }
  
  // Basic hostname validation
  // This is a simplified check, full RFC compliance would be more complex
  return /^[a-zA-Z0-9]([a-zA-Z0-9\-]{0,61}[a-zA-Z0-9])?(\.[a-zA-Z0-9]([a-zA-Z0-9\-]{0,61}[a-zA-Z0-9])?)*$/.test(hostname);
}