Ccy.Amt validation: %.2f to conform to spec

fixes https://github.com/stapelberg/qrbill/issues/8

qrbill.go

@@ -28,8 +28,11 @@ package qrbill
 
 import (
 	"bytes"
+	"fmt"
 	"image"
+	"log"
 	"regexp"
+	"strconv"
 	"strings"
 
 	"github.com/makiuchi-d/gozxing/qrcode/decoder"
@@ -128,11 +131,28 @@ func (a QRCHCcyAmt) Validate() QRCHCcyAmt {
 	c := a
 
 	if c.Amt != "" {
+		parsed, err := strconv.ParseFloat(c.Amt, 64)
+		if err != nil {
+			log.Printf("ParseFloat(%q): %v", c.Amt, err)
+		}
+
+		// The Swiss Payment Standards 2019 Swiss Implementation Guidelines
+		// QR-bill Version 2.3 explains:
+		//
+		// The amount element is to be entered without leading
+		// zeroes, including decimal separators and two decimal
+		// places.
+		// Decimal, maximum 12-digits permitted, including decimal
+		// separators. Only decimal points (".") are permitted as
+		// decimal separators. The amount must be between CHF/
+		// EUR 0.01 and 999,999,999.99
+		//
+		// (Notably, the validator is less strict and also permits values
+		// without decimal separators or with only one decimal place.)
+		//
 		// Some banking apps are picky regarding integer numbers (e.g. 50) and
 		// require a separator plus two digits (e.g. 50.00).
-		if !strings.Contains(c.Amt, ".") {
+		c.Amt = fmt.Sprintf("%.2f", parsed)
-			c.Amt += ".00"
-		}
 	}
 
 	return c

qrbill_test.go

@@ -0,0 +1,110 @@
+package qrbill_test
+
+import (
+	"testing"
+
+	"github.com/stapelberg/qrbill"
+)
+
+func TestAmountValidation(t *testing.T) {
+	for _, tt := range []struct {
+		amount     string
+		wantAmount string
+	}{
+		{
+			// ensure empty amount values are not modified
+			amount:     "",
+			wantAmount: "",
+		},
+
+		{
+			amount:     "50",
+			wantAmount: "50.00",
+		},
+
+		{
+			amount:     "50.3",
+			wantAmount: "50.30",
+		},
+
+		{
+			amount:     "50.32",
+			wantAmount: "50.32",
+		},
+
+		{
+			amount:     "50.32",
+			wantAmount: "50.32",
+		},
+
+		{
+			amount:     "50.000",
+			wantAmount: "50.00",
+		},
+
+		{
+			amount:     "50.-",
+			wantAmount: "0.00", // result of invalid input
+		},
+
+		{
+			amount:     ".30",
+			wantAmount: "0.30",
+		},
+
+		{
+			amount:     ".3",
+			wantAmount: "0.30",
+		},
+
+		{
+			// minimum amount mentioned in the Implementation Guidelines
+			amount:     "0.01",
+			wantAmount: "0.01",
+		},
+
+		{
+			// maximum amount mentioned in the Implementation Guidelines
+			amount:     "999999999.99",
+			wantAmount: "999999999.99",
+		},
+	} {
+		t.Run(tt.amount, func(t *testing.T) {
+			qrch := &qrbill.QRCH{
+				CdtrInf: qrbill.QRCHCdtrInf{
+					IBAN: "CH0209000000870913543",
+					Cdtr: qrbill.Address{
+						AdrTp:            qrbill.AddressTypeCombined,
+						Name:             "Legalize it",
+						StrtNmOrAdrLine1: "Quellenstrasse 25",
+						BldgNbOrAdrLine2: "8005 Zürich",
+						Ctry:             "CH",
+					},
+				},
+				CcyAmt: qrbill.QRCHCcyAmt{
+					Amt: tt.amount,
+					Ccy: "CHF",
+				},
+				UltmtDbtr: qrbill.Address{
+					AdrTp:            qrbill.AddressTypeCombined,
+					Name:             "Michael Stapelberg",
+					StrtNmOrAdrLine1: "Stauffacherstr 42",
+					BldgNbOrAdrLine2: "8004 Zürich",
+					Ctry:             "CH",
+				},
+				RmtInf: qrbill.QRCHRmtInf{
+					Tp:  "NON", // Reference type
+					Ref: "",    // Reference
+					AddInf: qrbill.QRCHRmtInfAddInf{
+						Ustrd: "test",
+					},
+				},
+			}
+
+			validated := qrch.Validate()
+			if got, want := validated.CcyAmt.Amt, tt.wantAmount; got != want {
+				t.Errorf("CcyAmt.Amt = %q, want %q", got, want)
+			}
+		})
+	}
+}