using System.Text.RegularExpressions;

namespace SharepointToolbox.Web.Core.Helpers;

public static class PermissionEntryHelper
{
    private static readonly Regex LimitedAccessWebRegex = new(
        @"^Limited Access System Group For Web\s+(?<id>[0-9a-fA-F-]{36})\s*$",
        RegexOptions.Compiled | RegexOptions.IgnoreCase);

    private static readonly Regex LimitedAccessListRegex = new(
        @"^Limited Access System Group For List\s+(?<id>[0-9a-fA-F-]{36})\s*$",
        RegexOptions.Compiled | RegexOptions.IgnoreCase);

    private static readonly Regex SharingLinkRegex = new(
        @"^SharingLinks\.(?<item>[0-9a-fA-F-]{36})\.(?<type>[^.]+)\.(?<share>[0-9a-fA-F-]{36})\s*$",
        RegexOptions.Compiled | RegexOptions.IgnoreCase);

    public static bool IsExternalUser(string loginName) =>
        loginName.Contains("#EXT#", StringComparison.OrdinalIgnoreCase);

    public static IReadOnlyList<string> FilterPermissionLevels(IEnumerable<string> levels) =>
        levels.Where(l => !string.Equals(l, "Limited Access", StringComparison.OrdinalIgnoreCase)).ToList();

    public static bool IsBareLimitedAccessSystemGroup(string name) =>
        name.Equals("Limited Access System Group", StringComparison.OrdinalIgnoreCase);

    public static SystemGroupClassification Classify(string groupTitle)
    {
        if (string.IsNullOrWhiteSpace(groupTitle))
            return new SystemGroupClassification(SystemGroupKind.None, null, null, null, null, null);

        var trimmed = groupTitle.Trim();

        if (IsBareLimitedAccessSystemGroup(trimmed))
            return new SystemGroupClassification(SystemGroupKind.LimitedAccessBare, null, null, null, null, null);

        var mWeb = LimitedAccessWebRegex.Match(trimmed);
        if (mWeb.Success && Guid.TryParse(mWeb.Groups["id"].Value, out var webId))
            return new SystemGroupClassification(SystemGroupKind.LimitedAccessWeb, webId, null, null, null, null);

        var mList = LimitedAccessListRegex.Match(trimmed);
        if (mList.Success && Guid.TryParse(mList.Groups["id"].Value, out var listId))
            return new SystemGroupClassification(SystemGroupKind.LimitedAccessList, null, listId, null, null, null);

        var mShare = SharingLinkRegex.Match(trimmed);
        if (mShare.Success
            && Guid.TryParse(mShare.Groups["item"].Value, out var itemId)
            && Guid.TryParse(mShare.Groups["share"].Value, out var shareId))
        {
            return new SystemGroupClassification(
                SystemGroupKind.SharingLink, null, null, itemId, mShare.Groups["type"].Value, shareId);
        }

        return new SystemGroupClassification(SystemGroupKind.None, null, null, null, null, null);
    }
}

public enum SystemGroupKind
{
    None,
    LimitedAccessBare,
    LimitedAccessWeb,
    LimitedAccessList,
    SharingLink
}

public readonly record struct SystemGroupClassification(
    SystemGroupKind Kind,
    Guid?   WebId,
    Guid?   ListId,
    Guid?   ItemUniqueId,
    string? LinkType,
    Guid?   ShareId);