using System;
using System.Text.RegularExpressions;

namespace BulkArchiveMailer.Core
{
    /// <summary>
    /// Which kind of archive ssh-access-tui produced. See
    /// internal/keymgr/pack.go (BuildUserArchive -> "_ssh_access.7z") and
    /// internal/keymgr/configonly.go (BuildConfigOnlyArchive ->
    /// "_config_update.7z") in the main repo for the producing side.
    /// </summary>
    public enum ArchiveKind
    {
        SshAccess,
        ConfigUpdate
    }

    /// <summary>Result of successfully parsing an archive file name.</summary>
    public sealed class ParsedFilename
    {
        public ParsedFilename(string login, ArchiveKind kind)
        {
            Login = login;
            Kind = kind;
        }

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

        public ArchiveKind Kind { get; }
    }

    /// <summary>
    /// Parses the two file name shapes ssh-access-tui ever produces:
    /// "{login}_ssh_access.7z" and "{login}_config_update.7z". Anything
    /// else (wrong extension, extra suffix, typo'd kind, 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.
    /// </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). Case-insensitive purely as a
        // defensive measure in case a file was renamed by hand on a
        // case-insensitive filesystem; the captured login is normalized to
        // lower case before use.
        private static readonly Regex Pattern = new Regex(
            @"^(?<login>[a-z0-9]+(?:-[a-z0-9]+)*)_(?<kind>ssh_access|config_update)\.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 kindText = match.Groups["kind"].Value.ToLowerInvariant();
            var kind = kindText == "ssh_access" ? ArchiveKind.SshAccess : ArchiveKind.ConfigUpdate;

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