[#404] morph/client: Add awaiting function

Awaiting function locks execution for N blocks.
Useful to wait for notary deposit.

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

pkg/morph/client/client.go

@@ -1,6 +1,9 @@
 package client
 
 import (
+	"context"
+	"time"
+
 	"github.com/nspcc-dev/neo-go/pkg/core/transaction"
 	"github.com/nspcc-dev/neo-go/pkg/encoding/fixedn"
 	"github.com/nspcc-dev/neo-go/pkg/rpc/client"
@@ -29,6 +32,8 @@ type Client struct {
 
 	gas util.Uint160 // native gas script-hash
 
+	waitInterval time.Duration
+
 	notary *notary
 }
 
@@ -136,6 +141,48 @@ func (c *Client) TransferGas(receiver util.Uint160, amount fixedn.Fixed8) error
 	return nil
 }
 
+// Wait function blocks routing execution until there
+// are `n` new blocks in the chain.
+func (c *Client) Wait(ctx context.Context, n uint32) {
+	var (
+		err               error
+		height, newHeight uint32
+	)
+
+	height, err = c.client.GetBlockCount()
+	if err != nil {
+		c.logger.Error("can't get blockchain height",
+			zap.String("error", err.Error()))
+		return
+	}
+
+	for {
+		select {
+		case <-ctx.Done():
+			return
+		default:
+		}
+
+		newHeight, err = c.client.GetBlockCount()
+		if err != nil {
+			c.logger.Error("can't get blockchain height",
+				zap.String("error", err.Error()))
+			return
+		}
+
+		if newHeight >= height+n {
+			return
+		}
+
+		time.Sleep(c.waitInterval)
+	}
+}
+
+// GasBalance returns GAS amount in the client's wallet.
+func (c *Client) GasBalance() (int64, error) {
+	return c.client.NEP17BalanceOf(c.gas, c.acc.PrivateKey().GetScriptHash())
+}
+
 func toStackParameter(value interface{}) (sc.Parameter, error) {
 	var result = sc.Parameter{
 		Value: value,