validateEmail function

String? validateEmail({ required String email, String? emptyMessage, String? invalidFormatMessage, bool trimWhitespace = true, List<String>? existingEmails, String? alreadyExistsMessage, })

Validates an email address format and checks for duplicates.

Performs RFC-compliant email format validation and optional duplicate checking. Returns null if valid, or an error message if invalid.

Parameters:

• email: The email address to validate
• emptyMessage: Custom message when empty
• invalidFormatMessage: Custom message for invalid format
• trimWhitespace: Whether to trim whitespace (default: true)
• existingEmails: List of existing emails to check against
• alreadyExistsMessage: Custom message when email already exists

Implementation

String? validateEmail({
  required String email,
  String? emptyMessage,
  String? invalidFormatMessage,
  bool trimWhitespace = true,
  List<String>? existingEmails,
  String? alreadyExistsMessage,
}) {
  final String input = trimWhitespace ? email.trim() : email;

  if (input.isEmpty) {
    return emptyMessage ?? "Please enter your email.";
  }

  if (!PatternType.email.isValid(input)) {
    return invalidFormatMessage ?? "The email address is badly formatted.";
  }

  if (existingEmails != null && existingEmails.contains(input)) {
    return alreadyExistsMessage ?? "This email is already registered.";
  }

  return null;
}