moved checksum function to its own interface

its not needed that all barcodes have an integer checksum
so it should not be needed in every implementation.

aztec/azteccode.go

@@ -42,10 +42,6 @@ func (c *aztecCode) At(x, y int) color.Color {
 	return color.White
 }
 
-func (c *aztecCode) CheckSum() int {
-	return 0
-}
-
 func (c *aztecCode) set(x, y int) {
 	c.SetBit(x*c.size+y, true)
 }

barcode.go

@@ -17,5 +17,11 @@ type Barcode interface {
 	Metadata() Metadata
 	// the data that was encoded in this barcode
 	Content() string
+}
+
+// Additional interface that some barcodes might implement to provide
+// the value of its checksum.
+type BarcodeIntCS interface {
+	Barcode
 	CheckSum() int
 }

codabar/encoder.go

@@ -45,5 +45,5 @@ func Encode(content string) (barcode.Barcode, error) {
 		}
 		resBits.AddBit(encodingTable[r]...)
 	}
-	return utils.New1DCode("Codabar", content, resBits, 0), nil
+	return utils.New1DCode("Codabar", content, resBits), nil
 }

code128/encode.go

@@ -103,7 +103,7 @@ func getCodeIndexList(content []rune) *utils.BitList {
 }
 
 // Encode creates a Code 128 barcode for the given content
-func Encode(content string) (barcode.Barcode, error) {
+func Encode(content string) (barcode.BarcodeIntCS, error) {
 	contentRunes := strToRunes(content)
 	if len(contentRunes) <= 0 || len(contentRunes) > 80 {
 		return nil, fmt.Errorf("content length should be between 1 and 80 runes but got %d", len(contentRunes))
@@ -124,7 +124,8 @@ func Encode(content string) (barcode.Barcode, error) {
 		}
 		result.AddBit(encodingTable[idx]...)
 	}
-	result.AddBit(encodingTable[sum%103]...)
+	sum = sum % 103
+	result.AddBit(encodingTable[sum]...)
 	result.AddBit(encodingTable[stopSymbol]...)
-	return utils.New1DCode("Code 128", content, result, sum%103), nil
+	return utils.New1DCodeIntCheckSum("Code 128", content, result, sum), nil
 }

code39/encoder.go

@@ -113,7 +113,7 @@ func prepare(content string) (string, error) {
 
 // Encode returns a code39 barcode for the given content
 // if includeChecksum is set to true, a checksum character is calculated and added to the content
-func Encode(content string, includeChecksum bool, fullASCIIMode bool) (barcode.Barcode, error) {
+func Encode(content string, includeChecksum bool, fullASCIIMode bool) (barcode.BarcodeIntCS, error) {
 	if fullASCIIMode {
 		var err error
 		content, err = prepare(content)
@@ -148,5 +148,5 @@ func Encode(content string, includeChecksum bool, fullASCIIMode bool) (barcode.B
 	if err != nil {
 		checkSum = 0
 	}
-	return utils.New1DCode("Code 39", content, result, int(checkSum)), nil
+	return utils.New1DCodeIntCheckSum("Code 39", content, result, int(checkSum)), nil
 }

datamatrix/datamatrixcode.go

@@ -40,10 +40,6 @@ func (c *datamatrixCode) At(x, y int) color.Color {
 	return color.White
 }
 
-func (c *datamatrixCode) CheckSum() int {
-	return 0
-}
-
 func (c *datamatrixCode) get(x, y int) bool {
 	return c.GetBit(x*c.Rows + y)
 }

ean/encoder.go

@@ -158,7 +158,7 @@ func encodeEAN13(code string) *utils.BitList {
 }
 
 // Encode returns a EAN 8 or EAN 13 barcode for the given code
-func Encode(code string) (barcode.Barcode, error) {
+func Encode(code string) (barcode.BarcodeIntCS, error) {
 	var checkSum int
 	if len(code) == 7 || len(code) == 12 {
 		code += string(calcCheckNum(code))
@@ -175,12 +175,12 @@ func Encode(code string) (barcode.Barcode, error) {
 	if len(code) == 8 {
 		result := encodeEAN8(code)
 		if result != nil {
-			return utils.New1DCode("EAN 8", code, result, checkSum), nil
+			return utils.New1DCodeIntCheckSum("EAN 8", code, result, checkSum), nil
 		}
 	} else if len(code) == 13 {
 		result := encodeEAN13(code)
 		if result != nil {
-			return utils.New1DCode("EAN 13", code, result, checkSum), nil
+			return utils.New1DCodeIntCheckSum("EAN 13", code, result, checkSum), nil
 		}
 	}
 	return nil, errors.New("invalid ean code data")

qr/qrcode.go

@@ -46,10 +46,6 @@ func (qr *qrcode) Set(x, y int, val bool) {
 	qr.data.SetBit(x*qr.dimension+y, val)
 }
 
-func (qr *qrcode) CheckSum() int {
-	return 0
-}
-
 func (qr *qrcode) calcPenalty() uint {
 	return qr.calcPenaltyRule1() + qr.calcPenaltyRule2() + qr.calcPenaltyRule3() + qr.calcPenaltyRule4()
 }

scaledbarcode.go

@@ -16,6 +16,10 @@ type scaledBarcode struct {
 	rect        image.Rectangle
 }
 
+type intCSscaledBC struct {
+	scaledBarcode
+}
+
 func (bc *scaledBarcode) Content() string {
 	return bc.wrapped.Content()
 }
@@ -36,8 +40,11 @@ func (bc *scaledBarcode) At(x, y int) color.Color {
 	return bc.wrapperFunc(x, y)
 }
 
-func (bc *scaledBarcode) CheckSum() int {
+func (bc *intCSscaledBC) CheckSum() int {
-	return bc.wrapped.CheckSum()
+	if cs, ok := bc.wrapped.(BarcodeIntCS); ok {
+		return cs.CheckSum()
+	}
+	return 0
 }
 
 // Scale returns a resized barcode with the given width and height.
@@ -52,6 +59,19 @@ func Scale(bc Barcode, width, height int) (Barcode, error) {
 	return nil, errors.New("unsupported barcode format")
 }
 
+func newScaledBC(wrapped Barcode, wrapperFunc wrapFunc, rect image.Rectangle) Barcode {
+	result := &scaledBarcode{
+		wrapped:     wrapped,
+		wrapperFunc: wrapperFunc,
+		rect:        rect,
+	}
+
+	if _, ok := wrapped.(BarcodeIntCS); ok {
+		return &intCSscaledBC{*result}
+	}
+	return result
+}
+
 func scale2DCode(bc Barcode, width, height int) (Barcode, error) {
 	orgBounds := bc.Bounds()
 	orgWidth := orgBounds.Max.X - orgBounds.Min.X
@@ -77,11 +97,11 @@ func scale2DCode(bc Barcode, width, height int) (Barcode, error) {
 		return bc.At(x, y)
 	}
 
-	return &scaledBarcode{
+	return newScaledBC(
 		bc,
 		wrap,
 		image.Rect(0, 0, width, height),
-	}, nil
+	), nil
 }
 
 func scale1DCode(bc Barcode, width, height int) (Barcode, error) {
@@ -106,10 +126,9 @@ func scale1DCode(bc Barcode, width, height int) (Barcode, error) {
 		return bc.At(x, 0)
 	}
 
-	return &scaledBarcode{
+	return newScaledBC(
 		bc,
 		wrap,
 		image.Rect(0, 0, width, height),
-	}, nil
+	), nil
-
 }

twooffive/encoder.go

@@ -134,5 +134,5 @@ func Encode(content string, interleaved bool) (barcode.Barcode, error) {
 	if interleaved {
 		kindTxt = " (interleaved)"
 	}
-	return utils.New1DCode("2 of 5"+kindTxt, content, resBits, -1), nil
+	return utils.New1DCode("2 of 5"+kindTxt, content, resBits), nil
 }

utils/base1dcode.go

@@ -12,6 +12,10 @@ type base1DCode struct {
 	*BitList
 	kind    string
 	content string
+}
+
+type base1DCodeIntCS struct {
+	base1DCode
 	checksum int
 }
 
@@ -38,11 +42,16 @@ func (c *base1DCode) At(x, y int) color.Color {
 	return color.White
 }
 
-func (c *base1DCode) CheckSum() int {
+func (c *base1DCodeIntCS) CheckSum() int {
 	return c.checksum
 }
 
 // New1DCode creates a new 1D barcode where the bars are represented by the bits in the bars BitList
-func New1DCode(codeKind, content string, bars *BitList, checksum int) barcode.Barcode {
+func New1DCodeIntCheckSum(codeKind, content string, bars *BitList, checksum int) barcode.BarcodeIntCS {
-	return &base1DCode{bars, codeKind, content, checksum}
+	return &base1DCodeIntCS{base1DCode{bars, codeKind, content}, checksum}
+}
+
+// New1DCode creates a new 1D barcode where the bars are represented by the bits in the bars BitList
+func New1DCode(codeKind, content string, bars *BitList) barcode.Barcode {
+	return &base1DCode{bars, codeKind, content}
 }