Implement go version of the Bolivian invoice code algorithm

LICENSE

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+The MIT License (MIT)
+
+Copyright (c) 2020 Pablo Crivella.
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.

complicode.go

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+package complicode
+
+import (
+	"crypto/rc4"
+	"encoding/hex"
+	"math"
+	"strconv"
+	"strings"
+	"time"
+
+	"github.com/chtison/baseconverter"
+	"github.com/osamingo/checkdigit"
+)
+
+var verhoeff = checkdigit.NewVerhoeff()
+
+type Invoice struct {
+	Nit    int
+	Number int
+	Amount float64
+	Date   time.Time
+}
+
+type asciiSums struct {
+	total    int
+	partials []int
+}
+
+const base64 = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz+/"
+
+// Generate a code for the given authCode, key and invoice
+func Generate(authCode string, key string, inv Invoice) string {
+	seed1 := strconv.Itoa(inv.Number)
+	seed2 := strconv.Itoa(inv.Nit)
+	seed3 := inv.Date.Format("20060102")
+	seed4 := strconv.FormatFloat(math.Round(inv.Amount), 'f', -1, 64)
+
+	seeds := []string{seed1, seed2, seed3, seed4}
+	seeds = appendVerificationsDigits(seeds, 2)
+	digits := generateVerificationDigits(seeds)
+	partialKeys := generatePartialKeys(key, digits)
+
+	seeds = append([]string{authCode}, seeds...)
+	seeds = appendPartialKeys(seeds, partialKeys)
+
+	encryptionKey := key + digits
+	encryptedData := encrypt(strings.Join(seeds, ""), encryptionKey)
+	asciiSums := generateASCIISums(encryptedData, len(partialKeys))
+
+	sum := 0
+
+	for i, partialSum := range asciiSums.partials {
+		sum += (asciiSums.total * partialSum / len(partialKeys[i]))
+	}
+
+	data := changeBase(sum)
+	code := encrypt(data, encryptionKey)
+
+	return format(code)
+}
+
+func appendVerificationsDigits(seeds []string, count int) []string {
+	for index, seed := range seeds {
+		seeds[index] = appendVerificationDigits(seed, count)
+	}
+
+	return seeds
+}
+
+func appendVerificationDigits(seed string, count int) string {
+	for i := 1; i <= count; i++ {
+		digit, _ := verhoeff.Generate(seed)
+		seed += strconv.Itoa(digit)
+	}
+
+	return seed
+}
+
+func generateVerificationDigits(seeds []string) string {
+	sum := sumSeeds(seeds)
+	digits := appendVerificationDigits(strconv.Itoa(sum), 5)
+
+	return digits[len(digits)-5:]
+}
+
+func sumSeeds(seeds []string) int {
+	sum := 0
+
+	for _, seed := range seeds {
+		number, _ := strconv.Atoi(seed)
+		sum += number
+	}
+
+	return sum
+}
+
+func generatePartialKeys(key string, verificationDigits string) []string {
+	var partialKeySizes []int
+
+	for _, digit := range strings.Split(verificationDigits, "") {
+		size, _ := strconv.Atoi(digit)
+		partialKeySizes = append(partialKeySizes, size+1)
+	}
+
+	var partialKeys []string
+
+	start := 0
+	for _, size := range partialKeySizes {
+		end := start + size
+		pk := key[start:end]
+		partialKeys = append(partialKeys, pk)
+		start += size
+	}
+
+	return partialKeys
+}
+
+func appendPartialKeys(seeds []string, partialKeys []string) []string {
+	for index, seed := range seeds {
+		seeds[index] = seed + partialKeys[index]
+	}
+
+	return seeds
+}
+
+func encrypt(data string, key string) string {
+	cipher, _ := rc4.NewCipher([]byte(key))
+	encrypted := make([]byte, len(data))
+	cipher.XORKeyStream(encrypted, []byte(data))
+
+	return strings.ToUpper(hex.EncodeToString(encrypted))
+}
+
+func generateASCIISums(data string, partialsCount int) asciiSums {
+	sums := asciiSums{total: 0, partials: make([]int, partialsCount)}
+
+	for i, b := range []byte(data) {
+		sums.total += int(b)
+		sums.partials[i%partialsCount] += int(b)
+	}
+
+	return sums
+}
+
+func changeBase(number int) string {
+	result, _ := baseconverter.UInt64ToBase(uint64(number), base64)
+
+	return result
+}
+
+func format(code string) string {
+	formatted := ""
+
+	for i, char := range code {
+		if i != 0 && i%2 == 0 {
+			formatted += "-"
+		}
+		formatted += string(char)
+	}
+
+	return formatted
+}

complicode_test.go

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+package complicode
+
+import (
+	"testing"
+	"time"
+)
+
+func TestGenerate(t *testing.T) {
+	authCode := "29040011007"
+	key := "9rCB7Sv4X29d)5k7N%3ab89p-3(5[A"
+	date, _ := time.Parse("20060102", "20070702")
+	inv := Invoice{Number: 1503, Nit: 4189179011, Date: date, Amount: 2500}
+	code := Generate(authCode, key, inv)
+
+	expected := "6A-DC-53-05-14"
+
+	if code != expected {
+		t.Errorf("Generate() = %q, expected %q", code, expected)
+	}
+}

go.mod

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+module github.com/pablocrivella/complicode-go
+
+go 1.13
+
+require (
+	github.com/chtison/baseconverter v1.1.0
+	github.com/osamingo/checkdigit v1.0.0
+)

go.sum

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+github.com/chtison/baseconverter v1.1.0 h1:sQU2ajzqQ9SRL/Bu7pYO8WriYUaGhO2tkJ5mEYVZn2A=
+github.com/chtison/baseconverter v1.1.0/go.mod h1:5dP/UBFmWK2kow1iJj1N0HxArisokPO54a5WdI6b/PY=
+github.com/osamingo/checkdigit v1.0.0 h1:c5vj+swZrFKWtQEUqj9DbgzTGYa1UscZO5Rwz9L8RKU=
+github.com/osamingo/checkdigit v1.0.0/go.mod h1:1YyIqzN+gc5pRmqS39JtDY8Wz0CWY4+VOpR4dtQLUAY=