cli: implement Fixed8Flag

Parsing gas from float value is not always a right idea as
a transform from float is not 1-to-1.
This commit implements Fixed8Flag which parses Fixed8 value from string.

cli/flags/fixed8.go

@@ -0,0 +1,75 @@
+package flags
+
+import (
+	"flag"
+	"strings"
+
+	"github.com/nspcc-dev/neo-go/pkg/util"
+	"github.com/urfave/cli"
+)
+
+// Fixed8 is a wrapper for Uint160 with flag.Value methods.
+type Fixed8 struct {
+	Value util.Fixed8
+}
+
+// Fixed8Flag is a flag with type string.
+type Fixed8Flag struct {
+	Name  string
+	Usage string
+	Value Fixed8
+}
+
+var (
+	_ flag.Value = (*Fixed8)(nil)
+	_ cli.Flag   = Fixed8Flag{}
+)
+
+// String implements fmt.Stringer interface.
+func (a Fixed8) String() string {
+	return a.Value.String()
+}
+
+// Set implements flag.Value interface.
+func (a *Fixed8) Set(s string) error {
+	f, err := util.Fixed8FromString(s)
+	if err != nil {
+		return cli.NewExitError(err, 1)
+	}
+	a.Value = f
+	return nil
+}
+
+// Fixed8 casts address to util.Fixed8.
+func (a *Fixed8) Fixed8() util.Fixed8 {
+	return a.Value
+}
+
+// String returns a readable representation of this value
+// (for usage defaults).
+func (f Fixed8Flag) String() string {
+	var names []string
+	eachName(f.Name, func(name string) {
+		names = append(names, getNameHelp(name))
+	})
+
+	return strings.Join(names, ", ") + "\t" + f.Usage
+}
+
+// GetName returns the name of the flag.
+func (f Fixed8Flag) GetName() string {
+	return f.Name
+}
+
+// Apply populates the flag given the flag set and environment
+// Ignores errors.
+func (f Fixed8Flag) Apply(set *flag.FlagSet) {
+	eachName(f.Name, func(name string) {
+		set.Var(&f.Value, name, f.Usage)
+	})
+}
+
+// Fixed8FromContext returns parsed util.Fixed8 value provided flag name.
+func Fixed8FromContext(ctx *cli.Context, name string) util.Fixed8 {
+	return ctx.Generic(name).(*Fixed8Flag).Value.Fixed8()
+}

cli/smartcontract/smart_contract.go

@@ -51,7 +51,7 @@ var (
 		Name:  "address, a",
 		Usage: "address to use as transaction signee (and gas source)",
 	}
-	gasFlag = cli.Float64Flag{
+	gasFlag = flags.Fixed8Flag{
 		Name:  "gas, g",
 		Usage: "gas to add to the transaction",
 	}
@@ -411,7 +411,7 @@ func invokeInternal(ctx *cli.Context, withMethod bool, signAndPush bool) error {
 	}
 
 	if signAndPush {
-		gas = util.Fixed8FromFloat(ctx.Float64("gas"))
+		gas = flags.Fixed8FromContext(ctx, "gas")
 		acc, err = getAccFromContext(ctx)
 		if err != nil {
 			return err
@@ -593,7 +593,7 @@ func contractDeploy(ctx *cli.Context) error {
 	if len(endpoint) == 0 {
 		return cli.NewExitError(errNoEndpoint, 1)
 	}
-	gas := util.Fixed8FromFloat(ctx.Float64("gas"))
+	gas := flags.Fixed8FromContext(ctx, "gas")
 
 	acc, err := getAccFromContext(ctx)
 	if err != nil {

cli/wallet/nep5.go

@@ -85,7 +85,7 @@ func newNEP5Commands() []cli.Command {
 					Name:  "amount",
 					Usage: "Amount of asset to send",
 				},
-				cli.StringFlag{
+				flags.Fixed8Flag{
 					Name:  "gas",
 					Usage: "Amount of GAS to attach to a tx",
 				},
@@ -309,14 +309,7 @@ func transferNEP5(ctx *cli.Context) error {
 	emit.AppCall(w.BinWriter, token.Hash, false)
 	emit.Opcode(w.BinWriter, opcode.THROWIFNOT)
 
-	var gas util.Fixed8
-	if gasString := ctx.String("gas"); gasString != "" {
-		gas, err = util.Fixed8FromString(gasString)
-		if err != nil {
-			return cli.NewExitError(fmt.Errorf("invalid GAS amount: %v", err), 1)
-		}
-	}
-
+	gas := flags.Fixed8FromContext(ctx, "gas")
 	tx := transaction.NewInvocationTX(w.Bytes(), gas)
 	tx.Attributes = append(tx.Attributes, transaction.Attribute{
 		Usage: transaction.Script,