using System;
using System.Text.RegularExpressions;

namespace BulkArchiveMailer.Core
{
    /// <summary>Result of successfully parsing an archive file name.</summary>
    public sealed class ParsedFilename
    {
        public ParsedFilename(string login, string suffix)
        {
            Login = login;
            Suffix = suffix;
        }

        /// <summary>Lower-cased login exactly as it appears in the file name (hyphens intact).</summary>
        public string Login { get; }

        /// <summary>
        /// Lower-cased suffix exactly as it appears in the file name (the
        /// part between the login and ".7z"), e.g. "ssh_access" or
        /// "config_update" for the two built-in templates, or whatever
        /// FileSuffix a custom template in AppSettingsData.Templates uses.
        /// Whether this suffix corresponds to any *configured* template is
        /// NOT checked here - that is ArchiveScanner's job, since it is the
        /// one holding the list of templates.
        /// </summary>
        public string Suffix { get; }
    }

    /// <summary>
    /// Parses the generic "{login}_{suffix}.7z" file name shape
    /// ssh-access-tui produces (see internal/keymgr/pack.go and
    /// internal/keymgr/configonly.go in the main repo for the producing
    /// side, and config.default.json/SettingsForm for how an operator adds
    /// further suffixes via custom templates). Anything else (wrong
    /// extension, no underscore-separated suffix, stray file dropped in the
    /// export folder by a human) simply fails to parse - the caller
    /// (ArchiveScanner) is responsible for routing that into the
    /// "unrecognized" bucket instead of blocking the batch. Whether a
    /// syntactically valid suffix actually matches a configured template is
    /// also ArchiveScanner's job, not this parser's.
    /// </summary>
    public static class FilenameParser
    {
        // Matches the login part ssh-access-tui itself accepts for a Linux
        // username: lowercase alnum segments joined by single hyphens (no
        // leading/trailing/double hyphens), followed by an underscore and
        // any lowercase alnum/underscore suffix. Case-insensitive purely as
        // a defensive measure in case a file was renamed by hand on a
        // case-insensitive filesystem; the captured login/suffix are
        // normalized to lower case before use.
        private static readonly Regex Pattern = new Regex(
            @"^(?<login>[a-z0-9]+(?:-[a-z0-9]+)*)_(?<suffix>[a-z0-9_]+)\.7z$",
            RegexOptions.IgnoreCase | RegexOptions.Compiled);

        public static bool TryParse(string fileName, out ParsedFilename parsed)
        {
            parsed = null;
            if (string.IsNullOrEmpty(fileName))
            {
                return false;
            }

            var match = Pattern.Match(fileName);
            if (!match.Success)
            {
                return false;
            }

            var login = match.Groups["login"].Value.ToLowerInvariant();
            var suffix = match.Groups["suffix"].Value.ToLowerInvariant();

            parsed = new ParsedFilename(login, suffix);
            return true;
        }
    }
}