[#1461] cli: Reorganize common functions

Make `ParseEpoch` and `GetCurrentEpoch` funcs public and move the first one
to the `common` package.

Signed-off-by: Pavel Karpy <carpawell@nspcc.ru>

cmd/neofs-cli/internal/client/sdk.go

@@ -1,9 +1,13 @@
 package internal
 
 import (
+	"context"
 	"crypto/ecdsa"
+	"crypto/elliptic"
+	"crypto/rand"
 	"errors"
 	"fmt"
+	"time"
 
 	"github.com/nspcc-dev/neofs-node/cmd/neofs-cli/internal/common"
 	"github.com/nspcc-dev/neofs-node/pkg/network"
@@ -54,3 +58,32 @@ func GetSDKClient(key *ecdsa.PrivateKey, addr network.Address) (*client.Client,
 
 	return &c, nil
 }
+
+// GetCurrentEpoch returns current epoch.
+func GetCurrentEpoch(endpoint string) (uint64, error) {
+	var addr network.Address
+
+	if err := addr.FromString(endpoint); err != nil {
+		return 0, fmt.Errorf("can't parse RPC endpoint: %w", err)
+	}
+
+	key, err := ecdsa.GenerateKey(elliptic.P256(), rand.Reader)
+	if err != nil {
+		return 0, fmt.Errorf("can't generate key to sign query: %w", err)
+	}
+
+	c, err := GetSDKClient(key, addr)
+	if err != nil {
+		return 0, err
+	}
+
+	ctx, cancel := context.WithTimeout(context.Background(), time.Second*30)
+	defer cancel()
+
+	ni, err := c.NetworkInfo(ctx, client.PrmNetworkInfo{})
+	if err != nil {
+		return 0, err
+	}
+
+	return ni.Info().CurrentEpoch(), nil
+}

cmd/neofs-cli/internal/common/epoch.go

@@ -0,0 +1,28 @@
+package common
+
+import (
+	"fmt"
+	"strconv"
+
+	"github.com/spf13/cobra"
+)
+
+// ParseEpoch parses epoch argument. Second return value is true if
+// the specified epoch is relative, and false otherwise.
+func ParseEpoch(cmd *cobra.Command, flag string) (uint64, bool, error) {
+	s, _ := cmd.Flags().GetString(flag)
+	if len(s) == 0 {
+		return 0, false, nil
+	}
+
+	relative := s[0] == '+'
+	if relative {
+		s = s[1:]
+	}
+
+	epoch, err := strconv.ParseUint(s, 10, 64)
+	if err != nil {
+		return 0, relative, fmt.Errorf("can't parse epoch for %s argument: %w", flag, err)
+	}
+	return epoch, relative, nil
+}