namespace Dpz.Core.Service.ObjectStorage;

/// <summary>
/// COS 空目录 marker 清理计划计算器
/// </summary>
internal static class S3DirectoryCleanupPlanner
{
    public static S3DirectoryCleanupPlan BuildPlan(IEnumerable<S3ListedObject> objects)
    {
        var directoryMarkers = new List<string>();
        var occupiedDirectories = new HashSet<string>(StringComparer.Ordinal);
        var scannedObjectCount = 0;

        foreach (var item in objects)
        {
            if (string.IsNullOrWhiteSpace(item.Key))
            {
                continue;
            }

            scannedObjectCount++;
            if (item.Size == 0 && item.Key.EndsWith('/'))
            {
                directoryMarkers.Add(item.Key);
                continue;
            }

            var slashIndex = item.Key.IndexOf('/');
            while (slashIndex >= 0)
            {
                occupiedDirectories.Add(item.Key[..(slashIndex + 1)]);
                slashIndex = item.Key.IndexOf('/', slashIndex + 1);
            }
        }

        var emptyDirectoryMarkers = directoryMarkers
            .Where(key => !occupiedDirectories.Contains(key))
            .ToList();
        return new S3DirectoryCleanupPlan(
            emptyDirectoryMarkers,
            scannedObjectCount,
            directoryMarkers.Count
        );
    }
}

internal readonly record struct S3ListedObject(string Key, long Size);

internal sealed record S3DirectoryCleanupPlan(
    IReadOnlyList<string> EmptyDirectoryMarkers,
    int ScannedObjectCount,
    int CandidateMarkerCount
);