backup: Prune old backups

This commit updates the backup command to prune old backups.

env/backup.go

@@ -6,6 +6,7 @@ import (
 	"os"
 	"path/filepath"
 	"sync"
+	"time"
 
 	"github.com/FAU-CDI/wisski-distillery/internal/fsx"
 	"github.com/FAU-CDI/wisski-distillery/internal/logging"
@@ -187,3 +188,46 @@ func (backup Backup) WriteReport(io stream.IOStream) error {
 		return err
 	}, io, "Writing backup report")
 }
+
+// ShouldPrune determines if a file with the provided modtime
+func (dis *Distillery) ShouldPrune(modtime time.Time) bool {
+	return time.Since(modtime) > time.Duration(dis.Config.MaxBackupAge)*24*time.Hour
+}
+
+// PruneBackups prunes all backups older than the maximum backup age
+func (dis *Distillery) PruneBackups(io stream.IOStream) error {
+	sPath := dis.SnapshotsArchivePath()
+
+	// list all the files
+	entries, err := os.ReadDir(sPath)
+	if err != nil {
+		return err
+	}
+
+	for _, entry := range entries {
+		// skip directories
+		if entry.IsDir() {
+			continue
+		}
+
+		// grab info about the file
+		info, err := entry.Info()
+		if err != nil {
+			return err
+		}
+
+		// check if it should be pruned!
+		if !dis.ShouldPrune(info.ModTime()) {
+			continue
+		}
+
+		// assemble path, and then remove the file!
+		path := filepath.Join(sPath, entry.Name())
+		io.Printf("Removing %s cause it is older than %d days", path, dis.Config.MaxBackupAge)
+
+		if err := os.Remove(path); err != nil {
+			return err
+		}
+	}
+	return nil
+}