component/snapshots: Create new component

This commit creates a new 'snapshots' component that is intended to
manage snapshots and backups.

internal/component/snapshots/snapshots.go

@@ -0,0 +1,72 @@
+package snapshots
+
+import (
+	"fmt"
+	"path/filepath"
+	"time"
+
+	"github.com/FAU-CDI/wisski-distillery/internal/component"
+	"github.com/FAU-CDI/wisski-distillery/pkg/environment"
+	"github.com/FAU-CDI/wisski-distillery/pkg/fsx"
+	"github.com/FAU-CDI/wisski-distillery/pkg/password"
+)
+
+// Snapshots manages snapshots and backups
+type Snapshots struct {
+	component.ComponentBase
+}
+
+func (Snapshots) Name() string { return "snapshots" }
+
+// Path returns the path that contains all snapshot related data.
+func (dis *Snapshots) Path() string {
+	return filepath.Join(dis.Config.DeployRoot, "snapshots")
+}
+
+// StagingPath returns the path to the directory containing a temporary staging area for snapshots.
+// Use NewSnapshotStagingDir to generate a new staging area.
+func (dis *Snapshots) StagingPath() string {
+	return filepath.Join(dis.Path(), "staging")
+}
+
+// ArchivePath returns the path to the directory containing all exported archives.
+// Use NewSnapshotArchivePath to generate a path to a new archive in this directory.
+func (dis *Snapshots) ArchivePath() string {
+	return filepath.Join(dis.Path(), "archives")
+}
+
+// NewArchivePath returns the path to a new archive with the provided prefix.
+// The path is guaranteed to not exist.
+func (dis *Snapshots) NewArchivePath(prefix string) (path string) {
+	// TODO: Consider moving these into a subdirectory with the provided prefix.
+	for path == "" || fsx.Exists(dis.Environment, path) {
+		name := dis.newSnapshotName(prefix) + ".tar.gz"
+		path = filepath.Join(dis.ArchivePath(), name)
+	}
+	return
+}
+
+// newSnapshot name returns a new basename for a snapshot with the provided prefix.
+// The name is guaranteed to be unique within this process.
+func (*Snapshots) newSnapshotName(prefix string) string {
+	suffix, _ := password.Password(64) // silently ignore any errors!
+	if prefix == "" {
+		prefix = "backup"
+	} else {
+		prefix = "snapshot-" + prefix
+	}
+	return fmt.Sprintf("%s-%d-%s", prefix, time.Now().Unix(), suffix)
+}
+
+// NewStagingDir returns the path to a new snapshot directory.
+// The directory is guaranteed to have been freshly created.
+func (dis *Snapshots) NewStagingDir(prefix string) (path string, err error) {
+	for path == "" || environment.IsExist(err) {
+		path = filepath.Join(dis.StagingPath(), dis.newSnapshotName(prefix))
+		err = dis.Core.Environment.Mkdir(path, environment.DefaultFilePerm)
+	}
+	if err != nil {
+		path = ""
+	}
+	return
+}