rpc: implement CalculateInputs for RPC client

Using getunspents RPC call.

pkg/rpc/client.go

@@ -11,7 +11,10 @@ import (
 	"sync"
 	"time"
 
+	"github.com/CityOfZion/neo-go/pkg/core"
+	"github.com/CityOfZion/neo-go/pkg/core/transaction"
 	"github.com/CityOfZion/neo-go/pkg/crypto/keys"
+	"github.com/CityOfZion/neo-go/pkg/util"
 	"github.com/pkg/errors"
 )
 
@@ -152,6 +155,29 @@ func (c *Client) SetClient(cli *http.Client) {
 	}
 }
 
+// CalculateInputs creates input transactions for the specified amount of given
+// asset belonging to specified address. This implementation uses GetUnspents
+// JSON-RPC call internally, so make sure your RPC server suppors that.
+func (c *Client) CalculateInputs(address string, asset util.Uint256, cost util.Fixed8) ([]transaction.Input, util.Fixed8, error) {
+	var utxos core.UnspentBalances
+
+	resp, err := c.GetUnspents(address)
+	if err != nil || resp.Error != nil {
+		if err == nil {
+			err = fmt.Errorf("remote returned %d: %s", resp.Error.Code, resp.Error.Message)
+		}
+		return nil, util.Fixed8(0), errors.Wrapf(err, "cannot get balance for address %v", address)
+	}
+	for _, ubi := range resp.Result.Balance {
+		if asset.Equals(ubi.AssetHash) {
+			utxos = ubi.Unspents
+			break
+		}
+	}
+	return unspentsToInputs(utxos, cost)
+
+}
+
 func (c *Client) performRequest(method string, p params, v interface{}) error {
 	var (
 		r = request{

pkg/rpc/neoScanBalanceGetter.go

@@ -6,6 +6,7 @@ import (
 	"net/http"
 	"sort"
 
+	"github.com/CityOfZion/neo-go/pkg/core"
 	"github.com/CityOfZion/neo-go/pkg/core/transaction"
 	"github.com/CityOfZion/neo-go/pkg/rpc/wrappers"
 	"github.com/CityOfZion/neo-go/pkg/util"
@@ -54,9 +55,6 @@ func filterSpecificAsset(asset string, balance []*Unspent, assetBalance *Unspent
 func (s NeoScanServer) CalculateInputs(address string, assetIDUint util.Uint256, cost util.Fixed8) ([]transaction.Input, util.Fixed8, error) {
 	var (
 		err          error
-		num, i       uint16
-		required     = cost
-		selected     = util.Fixed8(0)
 		us           []*Unspent
 		assetUnspent Unspent
 		assetID      = wrappers.GlobalAssets[assetIDUint.ReverseString()]
@@ -65,9 +63,19 @@ func (s NeoScanServer) CalculateInputs(address string, assetIDUint util.Uint256,
 		return nil, util.Fixed8(0), errs.Wrapf(err, "Cannot get balance for address %v", address)
 	}
 	filterSpecificAsset(assetID, us, &assetUnspent)
-	sort.Sort(assetUnspent.Unspent)
+	return unspentsToInputs(assetUnspent.Unspent, cost)
+}
 
-	for _, us := range assetUnspent.Unspent {
+// unspentsToInputs uses UnspentBalances to create a slice of inputs for a new
+// transcation containing the required amount of asset.
+func unspentsToInputs(utxos core.UnspentBalances, required util.Fixed8) ([]transaction.Input, util.Fixed8, error) {
+	var (
+		num, i   uint16
+		selected = util.Fixed8(0)
+	)
+	sort.Sort(utxos)
+
+	for _, us := range utxos {
 		if selected >= required {
 			break
 		}
@@ -81,8 +89,8 @@ func (s NeoScanServer) CalculateInputs(address string, assetIDUint util.Uint256,
 	inputs := make([]transaction.Input, 0, num)
 	for i = 0; i < num; i++ {
 		inputs = append(inputs, transaction.Input{
-			PrevHash:  assetUnspent.Unspent[i].Tx,
+			PrevHash:  utxos[i].Tx,
-			PrevIndex: assetUnspent.Unspent[i].Index,
+			PrevIndex: utxos[i].Index,
 		})
 	}