Handle negative big.Int amounts, add tests of amounts parser

bchain/baseparser.go

@@ -65,18 +65,23 @@ func (p *BaseParser) AmountToBigInt(n json.Number) (big.Int, error) {
 
 // AmountToDecimalString converts amount in big.Int to string with decimal point in the correct place
 func (p *BaseParser) AmountToDecimalString(a *big.Int) string {
-	s := a.String()
-	if len(s) <= p.AmountDecimalPoint {
-		s = zeros[:p.AmountDecimalPoint-len(s)+1] + s
+	n := a.String()
+	var s string
+	if n[0] == '-' {
+		n = n[1:]
+		s = "-"
 	}
-	i := len(s) - p.AmountDecimalPoint
-	ad := strings.TrimRight(s[i:], "0")
+	if len(n) <= p.AmountDecimalPoint {
+		n = zeros[:p.AmountDecimalPoint-len(n)+1] + n
+	}
+	i := len(n) - p.AmountDecimalPoint
+	ad := strings.TrimRight(n[i:], "0")
 	if len(ad) > 0 {
-		s = s[:i] + "." + ad
+		n = n[:i] + "." + ad
 	} else {
-		s = s[:i]
+		n = n[:i]
 	}
-	return s
+	return s + n
 }
 
 // ParseTxFromJson parses JSON message containing transaction and returns Tx struct

bchain/baseparser_test.go

@@ -0,0 +1,56 @@
+package bchain
+
+import (
+	"encoding/json"
+	"math/big"
+	"testing"
+)
+
+func NewBaseParser(adp int) *BaseParser {
+	return &BaseParser{
+		AmountDecimalPoint: adp,
+	}
+}
+
+var amounts = []struct {
+	a           *big.Int
+	s           string
+	adp         int
+	alternative string
+}{
+	{big.NewInt(123456789), "1.23456789", 8, "!"},
+	{big.NewInt(2), "0.00000002", 8, "!"},
+	{big.NewInt(300000000), "3", 8, "!"},
+	{big.NewInt(498700000), "4.987", 8, "!"},
+	{big.NewInt(567890), "0.00000000000056789", 18, "!"},
+	{big.NewInt(-100000000), "-1", 8, "!"},
+	{big.NewInt(-8), "-0.00000008", 8, "!"},
+	{big.NewInt(-89012345678), "-890.12345678", 8, "!"},
+	{big.NewInt(-12345), "-0.00012345", 8, "!"},
+	{big.NewInt(12345678), "0.123456789012", 8, "0.12345678"}, // test of truncation of too many decimal places
+}
+
+func TestBaseParser_AmountToDecimalString(t *testing.T) {
+	for _, tt := range amounts {
+		t.Run(tt.s, func(t *testing.T) {
+			if got := NewBaseParser(tt.adp).AmountToDecimalString(tt.a); got != tt.s && got != tt.alternative {
+				t.Errorf("BaseParser.AmountToDecimalString() = %v, want %v", got, tt.s)
+			}
+		})
+	}
+}
+
+func TestBaseParser_AmountToBigInt(t *testing.T) {
+	for _, tt := range amounts {
+		t.Run(tt.s, func(t *testing.T) {
+			got, err := NewBaseParser(tt.adp).AmountToBigInt(json.Number(tt.s))
+			if err != nil {
+				t.Errorf("BaseParser.AmountToBigInt() error = %v", err)
+				return
+			}
+			if got.Cmp(tt.a) != 0 {
+				t.Errorf("BaseParser.AmountToBigInt() = %v, want %v", got, tt.a)
+			}
+		})
+	}
+}