Add Inner Ring code

pkg/morph/client/balance/wrapper/wrapper.go

@@ -0,0 +1,43 @@
+package wrapper
+
+import (
+	"errors"
+
+	"github.com/nspcc-dev/neofs-node/pkg/morph/client/balance"
+)
+
+// Client represents the Balance contract client.
+//
+// It is a type alias of
+// github.com/nspcc-dev/neofs-node/pkg/morph/client/balance.Client.
+type Client = balance.Client
+
+// Wrapper is a wrapper over balance contract
+// client which implements:
+//  * tool for obtaining the amount of funds in the client's account;
+//  * tool for obtaining decimal precision of currency transactions.
+//
+// Working wrapper must be created via constructor New.
+// Using the Wrapper that has been created with new(Wrapper)
+// expression (or just declaring a Wrapper variable) is unsafe
+// and can lead to panic.
+type Wrapper struct {
+	client *Client
+}
+
+// ErrNilWrapper is returned by functions that expect
+// a non-nil Wrapper pointer, but received nil.
+var ErrNilWrapper = errors.New("balance contract client wrapper is nil")
+
+// New creates, initializes and returns the Wrapper instance.
+//
+// If Client is nil, balance.ErrNilClient is returned.
+func New(c *Client) (*Wrapper, error) {
+	if c == nil {
+		return nil, balance.ErrNilClient
+	}
+
+	return &Wrapper{
+		client: c,
+	}, nil
+}