'wdcli backup': Move to separate package

internal/component/backup.go

@@ -0,0 +1,43 @@
+package component
+
+import (
+	"io"
+
+	"github.com/tkw1536/goprogram/stream"
+)
+
+// Backupable represents a component with a Backup method
+type Backupable interface {
+	Component
+
+	// BackupName returns a new name to be used as an argument for path.
+	BackupName() string
+
+	// Backup backs up this component into the destination path path
+	Backup(context BackupContext) error
+}
+
+// BackupContext is the context for backups
+type BackupContext interface {
+	// IO returns the input output stream belonging to this backup file
+	IO() stream.IOStream
+
+	// Name creates a new directory inside the destination.
+	// Passing the empty path creates the destination as a directory.
+	//
+	// It then allows op to fill the file.
+	AddDirectory(path string, op func() error) error
+
+	// CopyFile copies a file from source to dst.
+	CopyFile(dest, src string) error
+
+	// AddFile creates a new file at the provided path inside the destination.
+	// Passing the empty path creates the destination as a file.
+	//
+	// It then allows op to write to the file.
+	//
+	// The op function must not retain file.
+	// The underlying file does not need to be closed.
+	// AddFile will not return before op has returned.
+	AddFile(path string, op func(file io.Writer) error) error
+}