feat(services): EAN 13 generation

services/templater.go

@@ -2,13 +2,21 @@ package services
 
 import (
 	"bytes"
+	"encoding/base64"
+	"errors"
 	"html/template"
+	"image/png"
+	"math"
+	"strconv"
 
 	"git.odit.services/lfk/document-server/models"
+	"github.com/boombuler/barcode"
+	"github.com/boombuler/barcode/ean"
 )
 
 type Templater interface {
 	Execute(template *template.Template, data interface{}) (string, error)
+	StringToTemplate(templateString string) (*template.Template, error)
 }
 
 type DefaultTemplater struct {
@@ -23,10 +31,59 @@ type ContractTemplateOptions struct {
 	SponsoringHeader     string          `json:"base_url"`
 }
 
-func (t *DefaultTemplater) Execute(template *template.Template, data interface{}) (string, error) {
+func idToEan13(id int) (string, error) {
+	multiply := [2]int{1, 3}
+	idStr := strconv.Itoa(id)
+
+	if len(idStr) > 12 {
+		return "", errors.New("id too long")
+	}
+	for len(idStr) < 12 {
+		idStr = "0" + idStr
+	}
+
+	total := 0
+	for i, char := range idStr {
+		num, err := strconv.Atoi(string(char))
+		if err != nil {
+			return "", err
+		}
+		total += num * multiply[i%2]
+	}
+	checkSum := (int(math.Ceil(float64(total)/10)) * 10) - total
+	return idStr + strconv.Itoa(checkSum), nil
+}
+
+func (t *DefaultTemplater) GenerateBarcode(code int) (string, error) {
+	encodedEan, err := idToEan13(code)
+	eanCode, err := ean.Encode(encodedEan)
+	if err != nil {
+		return "", err
+	}
+	scaledCode, err := barcode.Scale(eanCode, 100, 50)
+	if err != nil {
+		return "", err
+	}
+
+	var buf bytes.Buffer
+	err = png.Encode(&buf, scaledCode)
+	if err != nil {
+		return "", err
+	}
+
+	return base64.StdEncoding.EncodeToString(buf.Bytes()), nil
+}
+
+func (t *DefaultTemplater) StringToTemplate(templateString string) (*template.Template, error) {
+	return template.New("template").Funcs(template.FuncMap{
+		"barcode": t.GenerateBarcode,
+	}).Parse(templateString)
+}
+
+func (t *DefaultTemplater) Execute(baseTemplate *template.Template, data interface{}) (string, error) {
 	resultBuffer := new(bytes.Buffer)
 
-	err := template.Execute(resultBuffer, data)
+	err := baseTemplate.Execute(resultBuffer, data)
 	if err != nil {
 		return "", err
 	}