compiler: implement GAS contract wrapper

pkg/interop/native/gas/gas.go

@@ -0,0 +1,35 @@
+package gas
+
+import (
+	"github.com/nspcc-dev/neo-go/pkg/interop"
+	"github.com/nspcc-dev/neo-go/pkg/interop/contract"
+)
+
+// Hash represents GAS contract hash.
+const Hash = "\x28\xb3\xad\xab\x72\x69\xf9\xc2\x18\x1d\xb3\xcb\x74\x1e\xbf\x55\x19\x30\xe2\x70"
+
+// Symbol represents `symbol` method of GAS native contract.
+func Symbol() string {
+	return contract.Call(interop.Hash160(Hash), "symbol", contract.NoneFlag).(string)
+}
+
+// Decimals represents `decimals` method of GAS native contract.
+func Decimals() int {
+	return contract.Call(interop.Hash160(Hash), "decimals", contract.NoneFlag).(int)
+}
+
+// TotalSupply represents `totalSupply` method of GAS native contract.
+func TotalSupply() int {
+	return contract.Call(interop.Hash160(Hash), "totalSupply", contract.ReadStates).(int)
+}
+
+// BalanceOf represents `balanceOf` method of GAS native contract.
+func BalanceOf(addr interop.Hash160) int {
+	return contract.Call(interop.Hash160(Hash), "balanceOf", contract.ReadStates, addr).(int)
+}
+
+// Transfer represents `transfer` method of GAS native contract.
+func Transfer(from, to interop.Hash160, amount int, data interface{}) bool {
+	return contract.Call(interop.Hash160(Hash), "transfer",
+		contract.WriteStates|contract.AllowCall|contract.AllowNotify, from, to, amount, data).(bool)
+}