smartcontract: add Builder, method invocation helpers and doc

Move the last remaining script-related things out of the rpcclient.

pkg/smartcontract/doc_test.go

@@ -0,0 +1,49 @@
+package smartcontract_test
+
+import (
+	"context"
+	"encoding/hex"
+
+	"github.com/nspcc-dev/neo-go/pkg/core/transaction"
+	"github.com/nspcc-dev/neo-go/pkg/encoding/address"
+	"github.com/nspcc-dev/neo-go/pkg/rpcclient"
+	"github.com/nspcc-dev/neo-go/pkg/smartcontract"
+	"github.com/nspcc-dev/neo-go/pkg/util"
+	"github.com/nspcc-dev/neo-go/pkg/wallet"
+)
+
+func ExampleBuilder() {
+	// No error checking done at all, intentionally.
+	c, _ := rpcclient.New(context.Background(), "url", rpcclient.Options{})
+	neoHash, _ := c.GetNativeContractHash("NeoToken")
+
+	pKey, _ := hex.DecodeString("03d9e8b16bd9b22d3345d6d4cde31be1c3e1d161532e3d0ccecb95ece2eb58336e") // Public key.
+
+	b := smartcontract.NewBuilder()
+	// Single NEO "vote" call with a check
+	b.InvokeWithAssert(neoHash, "vote", pKey)
+	script, _ := b.Script()
+
+	// The script can then be used to create transaction or to invoke via RPC.
+	res, _ := c.InvokeScript(script, []transaction.Signer{{Account: util.Uint160{0x01, 0x02, 0x03}, Scopes: transaction.CalledByEntry}})
+	if res.State != "HALT" {
+		// The script failed
+	}
+
+	b.Reset() // Copy the old script above if you need it!
+
+	w, _ := wallet.NewWalletFromFile("somewhere")
+	// Assuming there is one Account inside
+	acc := w.Accounts[0]
+	from, _ := address.StringToUint160(acc.Address)
+
+	// Multiple transfers in a single script. If any of them fail whole script fails.
+	b.InvokeWithAssert(neoHash, "transfer", from, util.Uint160{0x70}, 1, nil)
+	b.InvokeWithAssert(neoHash, "transfer", from, util.Uint160{0x71}, 10, []byte("data"))
+	b.InvokeWithAssert(neoHash, "transfer", from, util.Uint160{0x72}, 1, nil)
+	script, _ = b.Script()
+
+	// The script can then be used to create transaction or to invoke via RPC.
+	txid, _ := c.SignAndPushInvocationTx(script, acc, -1, 0, nil)
+	_ = txid
+}