main.go

package main

import (
	"crypto/md5"
	"fmt"
	"log"
	"reflect"
	"strconv"
)

func main() {

}

//QR object
type QR struct {
	ID    string
	Value string
}

// MerchantToCode converts merchant struct tag to its equivalent EBS QR
var MerchantToCode = map[string]string{
	"ID":                     "00",
	"QRType":                 "01",
	"MerchantInfo":           "",
	"MerchantCode":           "",
	"TransactionCode":        "",
	"Amount":                 "",
	"TipIndicator":           "",
	"FixedTipIndicator":      "",
	"PercentageTipIndicator": "",
	"FixedTipVal":            "",
	"PerentageTip":           "",
	"CountryCode":            "",
	"Name":                   "",
	"City":                   "",
	"PostalCode":             "",
	"AdditionalData":         "",
	"CRC":                    "",
	"I18nMerchantInf":        "",
}

//Merchant qr struct
type Merchant struct {
	ID                     string
	QRType                 string
	IsMerchant             bool
	IsDynamic              bool
	MerchantInfo           string // length 99
	MerchantCode           string //0000 default, 9999 for governmental
	TransactionCode        int    // 938 for SDG
	Amount                 float32
	TipIndicator           bool // O
	FixedTipIndicator      bool
	PercentageTipIndicator bool
	FixedTipVal            float32
	PerentageTip           float32
	CountryCode            string
	Name                   string
	City                   string // max 15
	PostalCode             string //OOO 11111
	AdditionalData         string //O ~99 check table
	CRC                    int    // checksum for qr data
	I18nMerchantInfo       string
}

//Decode string to Merchant object
func (m *Merchant) Decode(s string) {
	if len(s) < 5 {
		return
	}

	log.Printf(s[:2])
	switch s[:2] {
	case "00":
		length := toInt(s[2:4])
		if s[4:4+length] == "01" {
			m.IsMerchant = true
		}
		s = s[4+length:] // VERY important

	case "01":
		length := toInt(s[2:4])
		if s[4:4+length] == "12" {
			m.IsDynamic = true
		}
		s = s[4+length:] // VERY important

	case "51":
		length := toInt(s[2:4])
		m.MerchantInfo = s[4:length]
		s = s[length+4:] // FIXME check this one

	case "52":
		m.MerchantCode = s[2:6] // 52 04 0000
		s = s[8:]

	case "53":
		m.TransactionCode = toInt(s[4 : 4+3]) // i was not sure 4 + 3 equals what
		// 5303938
		s = s[7:]

	case "54": // Transaction amount
		length := toInt(s[2:4])
		m.Amount = toFloat(s[4:length])
		s = s[2+2+length:]

	case "55": // there is a bug or inconsitency here
		if s[2:4] == "01" {
			m.TipIndicator = true
		} else if s[2:4] == "02" {
			m.FixedTipIndicator = true
		} else if s[2:4] == "03" {
			m.PercentageTipIndicator = true
		}
		s = s[4:]
	case "56":
		length := toInt(s[2:4])
		m.FixedTipVal = toFloat(s[4 : 4+length])
		s = s[2+2+length:]

	case "57":
		length := toInt(s[2:4])
		m.PerentageTip = toFloat(s[4 : 4+length])
		s = s[2+2+length:]

	case "58":
		m.CountryCode = s[4 : 4+2]
		s = s[6:]

	case "59": // merchant name
		length := toInt(s[2:4]) //59 16 MerchantName
		m.Name = s[4 : 4+length]
		s = s[4+length:]

	case "60": // city code
		length := toInt(s[2:4])

		m.City = s[4 : 4+length]
		s = s[2+2+length:]
	case "61":
		m.PostalCode = s[4 : 4+5] //FIXME
		s = s[9:]
	case "62":
		length := toInt(s[2:4])
		m.AdditionalData = s[4 : 4+length]
		s = s[4+length:]
	case "63": // FIXME this is a bug
		m.CRC = toInt(s[2 : 2+4])
		s = s[2+4:]
	}
	m.Decode(s)

}

//Encode a QR struct into a text. EBS compatible
func (m *Merchant) Encode() string {
	var s string

	fields := reflect.TypeOf(*m)
	values := reflect.ValueOf(*m)

	num := fields.NumField()

	for i := 0; i < num; i++ {
		field := fields.Field(i)
		value := values.Field(i)
		fmt.Print("Type:", field.Type, ",", field.Name, "=", value, "\n")
		k := MerchantToCode[field.Name]
		v := getValue(value)
		s += k
		s += v
		s += toString(value)
	}
	return s

}

func (m *Merchant) computeCrc() {
	/*
		The CRC (ID “63”) shall be calculated according to [ISO/IEC 13239] using the polynomial '1021' (hex) and
		initial value 'FFFF' (hex). The data over which the checksum is calculated shall cover all data objects,
		including their ID, Length and Value, to be included in the QR Code, in their respective order, as well as
		the ID and Length of the CRC itself (but excluding its Value). Following the calculation of the checksum,
		the resulting 2-byte hexadecimal value shall be encoded as a 4-character Alphanumeric Special value by
		converting each nibble to an Alphanumeric Special character. For example, a CRC with a two-byte
		hexadecimal value of '007B' is included in the QR Code as "6304007B".

		Example

		0002010102115138000310901020002090000000650408f8bfe0f85204000053039385802SD5912MerchantName6004City
		CRC: 5DD9
		6304


	*/
}

func (m *Merchant) checksum(data string) string {
	d := md5.Sum([]byte(data))
	return fmt.Sprintf("%x", d)
}

func toInt(s string) int {
	i, _ := strconv.ParseInt(s, 10, 64)
	return int(i)
}

func toFloat(s string) float32 {
	i, _ := strconv.ParseFloat(s, 10)
	return float32(i)
}

func toString(i interface{}) string {
	switch i := i.(type) {
	case int:
		return strconv.FormatInt(int64(i), 10)
	case float32:
		return strconv.FormatFloat(float64(i), 'b', -1, 32)
	case float64:
		log.Print(strconv.FormatFloat(i, 'f', -1, 32))
		return strconv.FormatFloat(i, 'f', -1, 32)
	case string:
		return i
	}
	return ""

}

func getValue(i interface{}) string {
	switch i := i.(type) {
	case string:
		return fmt.Sprintf("%02d", len(i))
	case int:
		return fmt.Sprintf("%02d", len(toString(i)))
	case float32:
		return fmt.Sprintf("%02d", len(toString(i)))
	case float64:
		return fmt.Sprintf("%02d", len(toString(i)))
	}
	return ""

}