using System;

namespace BulkArchiveMailer.Core
{
    /// <summary>
    /// Derives the recipient's email address from the login embedded in an
    /// archive file name. Rule (see repo README/plan, confirmed with the
    /// operator): a Linux login such as "a-makarov" maps to
    /// "a.makarov@&lt;domain&gt;" by replacing every hyphen with a dot -
    /// there is no separate mapping table.
    ///
    /// Known accepted limitation (do NOT try to fix this with an override
    /// mechanism): if a real login contains a literal hyphen that is not
    /// an initial/surname separator, this produces the wrong local part.
    /// That is out of scope for this tool - see README.md.
    /// </summary>
    public static class EmailAddressBuilder
    {
        public static string BuildEmail(string login, string domain)
        {
            if (string.IsNullOrWhiteSpace(login))
            {
                throw new ArgumentException("login must not be empty.", nameof(login));
            }

            if (string.IsNullOrWhiteSpace(domain))
            {
                throw new ArgumentException("domain must not be empty.", nameof(domain));
            }

            var localPart = login.Trim().ToLowerInvariant().Replace('-', '.');
            var cleanDomain = domain.Trim().TrimStart('@');
            return $"{localPart}@{cleanDomain}";
        }
    }
}