Allow negative values to invert transaction

Solves #228

bot/transactionBuilder.go

@@ -67,10 +67,6 @@ func HandleFloat(m *tb.Message) (string, error) {
 		if err != nil {
 			return "", fmt.Errorf("parsing failed at value '%s': %s", value, err.Error())
 		}
-		if v < 0 {
-			c.LogLocalf(INFO, nil, "Got negative value. Inverting.")
-			v *= -1
-		}
 		c.LogLocalf(TRACE, nil, "Handled float: '%s' -> %f", amount, v)
 		values = append(values, v)
 	}

bot/transactionBuilder_test.go

@@ -193,6 +193,35 @@ func TestTransactionBuilding(t *testing.T) {
 `, "Templated string should be filled with variables as expected.")
 }
 
+func TestTransactionBuildingWithNegativeAmount(t *testing.T) {
+	const twoWayTemplate = `${date} * "${description}"${tag}
+	${account:from:the money came *from*} ${-amount}
+	${account:to:the money went *to*} ${amount}`
+
+	tx, err := bot.CreateSimpleTx("", twoWayTemplate)
+	if err != nil {
+		t.Errorf("Error creating simple tx: %s", err.Error())
+	}
+	tx.Input(&tb.Message{Text: "-34"})                        // amount
+	tx.Input(&tb.Message{Text: "Birthday gift from grandma"}) // description
+	tx.Input(&tb.Message{Text: "Assets:Wallet"})              // from
+	tx.Input(&tb.Message{Text: "Income:Gifts"})               // to
+
+	if !tx.IsDone() {
+		t.Errorf("With given input transaction data should be complete for SimpleTx")
+	}
+
+	templated, err := tx.FillTemplate("USD", "", 0)
+	if err != nil {
+		t.Errorf("There should be no error raised during templating: %s", err.Error())
+	}
+	today := time.Now().Format(helpers.BEANCOUNT_DATE_FORMAT)
+	helpers.TestExpect(t, templated, today+` * "Birthday gift from grandma"
+  Assets:Wallet                                34.00 USD
+  Income:Gifts                                -34.00 USD
+`, "Templated string should be filled with variables as expected.")
+}
+
 func TestTransactionBuildingCustomCurrencyInAmount(t *testing.T) {
 	tx, err := bot.CreateSimpleTx("", bot.TEMPLATE_SIMPLE_DEFAULT)
 	if err != nil {