add NewFromFloat and NewFromString (#108)

money.go

@@ -5,6 +5,9 @@ import (
 	"encoding/json"
 	"errors"
 	"fmt"
+	"math"
+	"strconv"
+	"strings"
 )
 
 // Injection points for backward compatibility.
@@ -85,6 +88,33 @@ func New(amount int64, code string) *Money {
 	}
 }
 
+// NewFromFloat creates and returns new instance of Money from a float64.
+func NewFromFloat(amount float64, currency string) *Money {
+	currencyDecimals := math.Pow(10, float64(GetCurrency(currency).Fraction))
+	return New(int64(amount*currencyDecimals), currency)
+}
+
+// NewFromFloat creates and returns new instance of Money from a float64.
+func NewFromString(amount string, currency string) (*Money, error) {
+	amount = strings.Trim(amount, "0")
+
+	var exponent int
+	if pointIndex := strings.Index(amount, "."); pointIndex != -1 {
+		exponent = len(amount[pointIndex+1:])
+	}
+
+	intString := strings.ReplaceAll(amount, ".", "")
+	parsed, err := strconv.ParseInt(intString, 10, 64)
+	if err != nil {
+		return nil, fmt.Errorf("can't parse '%s' to money", amount)
+	}
+
+	currencyFraction := GetCurrency(currency).Fraction
+	parsed /= int64(math.Pow(10, float64(exponent-currencyFraction)))
+
+	return New(parsed, currency), nil
+}
+
 // Currency returns the currency used by Money.
 func (m *Money) Currency() *Currency {
 	return m.currency

money_test.go

@@ -629,6 +629,56 @@ func TestMoney_Amount(t *testing.T) {
 	}
 }
 
+func TestNewFromFloat(t *testing.T) {
+	m := NewFromFloat(12.34, EUR)
+
+	if m.amount.val != 1234 {
+		t.Errorf("Expected %d got %d", 1234, m.amount.val)
+	}
+
+	if m.currency.Code != EUR {
+		t.Errorf("Expected currency %s got %s", EUR, m.currency.Code)
+	}
+
+	m = NewFromFloat(-0.123, EUR)
+
+	if m.amount.val != -12 {
+		t.Errorf("Expected %d got %d", -12, m.amount.val)
+	}
+}
+
+func TestNewFromString(t *testing.T) {
+	m, err := NewFromString("12.34", EUR)
+
+	if err != nil {
+		t.Error(err)
+	}
+
+	if m.amount.val != 1234 {
+		t.Errorf("Expected %d got %d", 1234, m.amount.val)
+	}
+
+	if m.currency.Code != EUR {
+		t.Errorf("Expected currency %s got %s", EUR, m.currency.Code)
+	}
+
+	m, err = NewFromString("-1.12345", EUR)
+
+	if err != nil {
+		t.Error(err)
+	}
+
+	if m.amount.val != -112 {
+		t.Errorf("Expected %d got %d", -112, m.amount.val)
+	}
+
+	_, err = NewFromString("invalid_input", EUR)
+
+	if err.Error() != "can't parse 'invalid_input' to money" {
+		t.Error(err)
+	}
+}
+
 func TestDefaultMarshal(t *testing.T) {
 	given := New(12345, IQD)
 	expected := `{"amount":12345,"currency":"IQD"}`