feat(prune): add prune files feature

This feature allows you to specify the n latest backups to keep in the
bucket.

pruner/pruner.go

@@ -0,0 +1,52 @@
+package pruner
+
+import (
+	"backup-tool/helpers"
+	"context"
+	"github.com/minio/minio-go/v7"
+	"log"
+	"sort"
+)
+
+func PruneFiles(bucket, endpoint string, keep int) error {
+	ctx := context.Background()
+	accessKeyID, secretAccessKey, err := helpers.GetCredentials()
+	if err != nil {
+		return err
+	}
+	client, err := helpers.CreateClient(accessKeyID, secretAccessKey, endpoint)
+	if err != nil {
+		return err
+	}
+	err = helpers.VerifyBucket(client, ctx, bucket)
+	if err != nil {
+		return err
+	}
+
+	var objects []minio.ObjectInfo
+	for obj := range client.ListObjects(ctx, bucket, minio.ListObjectsOptions{}) {
+		objects = append(objects, obj)
+	}
+
+	if len(objects) < keep {
+		return nil
+	}
+
+	sort.Sort(BucketObjects(objects)) // last modified object will be at position 0
+	for _, object := range objects[keep:] {
+		err := client.RemoveObject(ctx, bucket, object.Key, minio.RemoveObjectOptions{})
+		if err != nil {
+			log.Printf("error deleting object %q: %s", object.Key, err.Error())
+		} else {
+			log.Printf("deleted object %q", object.Key)
+		}
+	}
+
+	return nil
+}
+
+type BucketObjects []minio.ObjectInfo
+
+func (b BucketObjects) Len() int           { return len(b) }
+func (b BucketObjects) Swap(i, j int)      { b[i], b[j] = b[j], b[i] }
+func (b BucketObjects) Less(i, j int) bool { return b[i].LastModified.After(b[j].LastModified) } // return newest object first in list