client io architecture

client/storage/storage.go

@@ -0,0 +1,48 @@
+package storage
+
+import (
+	"errors"
+	"fmt"
+	"galaxy/util"
+	"path/filepath"
+)
+
+const (
+	// Name of the file under the storage's root where [model.State] is stored.
+	stateFileName = "state.dat"
+
+	// Suffix of a Game's file inder the storage's root where [model.GameData] is stored.
+	gameDataFileSuffix = ".dat"
+)
+
+type storage struct {
+	root string
+}
+
+// NewStorage returns implementation of the "galaxy/client.Storage" interface
+// or nil with a non-nil error when filesystem storage initialisation failed.
+func NewStorage(rootPath string) (*storage, error) {
+	ok, err := util.Writable(rootPath)
+	if err != nil {
+		return nil, err
+	}
+	if !ok {
+		return nil, errors.New("user does not have write permissions to the storage root")
+	}
+	s := &storage{
+		root: rootPath,
+	}
+	return s, nil
+}
+
+// StateFilePath returns client's state file path relative to the root,
+// file name and extension are pre-defined constant.
+func StateFilePath(root string) string {
+	return filepath.Join(root, stateFileName)
+}
+
+// GameDataPath returns game's data file path relative to the root,
+// data file name is GameID string representation and extension is a pre-defined constant.
+func GameDataFilePath(root string, id fmt.Stringer) string {
+	return filepath.Join(root, id.String()) + gameDataFileSuffix
+}