BackupRetention.cs

namespace DbBackupTool
{
    // Every run gets its own timestamped subfolder (dump/log/option-file etc
    // together), so retention counts whole backup runs, not loose files - a
    // provider that produces several files (Oracle's .dmp+.log, Mongo's whole
    // dump directory) can never desync from one that produces a single file
    // (MySQL/Postgres's .sql/.dump). This is what makes pruning itself fully
    // DB-independent: it never has to know what a "backup" looks like per engine.
    public static class BackupRetention
    {
        public static void Prune(string backupFolder, string label, int retentionCount, JobLog log)
        {
            // Folder names are "{label}_{yyyyMMdd_HHmmss}" - that format sorts
            // correctly as a plain string, so no timestamp parsing is needed here.
            var dirs = new DirectoryInfo(backupFolder)
                .GetDirectories($"{label}_*")
                .OrderByDescending(d => d.Name)
                .Skip(retentionCount)
                .ToList();

            foreach (var dir in dirs)
            {
                log.Info($"Pruning old backup: {dir.FullName}");
                try { dir.Delete(recursive: true); }
                catch (Exception ex) { log.Error($"Could not delete {dir.FullName}: {ex.Message}"); }
            }
        }
    }
}