[#708] morph/client: Add epoch block getter from netmap

Signed-off-by: Alex Vanin <alexey@nspcc.ru>

pkg/morph/client/netmap/epoch.go

@@ -22,6 +22,22 @@ func (e EpochValues) Number() int64 {
 	return e.num
 }
 
+// EpochBlockArgs groups the arguments of
+// get epoch block number test invoke call.
+type EpochBlockArgs struct {
+}
+
+// EpochBlockValues groups the stack parameters
+// returned by get epoch block number test invoke.
+type EpochBlockValues struct {
+	block int64
+}
+
+// Block return the block number of NeoFS epoch.
+func (e EpochBlockValues) Block() int64 {
+	return e.block
+}
+
 // Epoch performs the test invoke of get epoch number
 // method of NeoFS Netmap contract.
 func (c *Client) Epoch(_ EpochArgs) (*EpochValues, error) {
@@ -47,3 +63,28 @@ func (c *Client) Epoch(_ EpochArgs) (*EpochValues, error) {
 		num: num,
 	}, nil
 }
+
+// LastEpochBlock performs the test invoke of get epoch block number
+// method of NeoFS Netmap contract.
+func (c *Client) LastEpochBlock(_ EpochBlockArgs) (*EpochBlockValues, error) {
+	items, err := c.client.TestInvoke(c.epochBlockMethod)
+	if err != nil {
+		return nil, fmt.Errorf("could not perform test invocation (%s): %w",
+			c.epochBlockMethod, err)
+	}
+
+	if ln := len(items); ln != 1 {
+		return nil, fmt.Errorf("unexpected stack item count (%s): %d",
+			c.epochBlockMethod, ln)
+	}
+
+	block, err := client.IntFromStackItem(items[0])
+	if err != nil {
+		return nil, fmt.Errorf("could not get number from stack item (%s): %w",
+			c.epochBlockMethod, err)
+	}
+
+	return &EpochBlockValues{
+		block: block,
+	}, nil
+}