ISBN checker is added. Fixes #27 (#100)

# Describe Request

ISBN checker is added. 

Fixes #27

# Change Type

Checker added.

README.md

@@ -82,6 +82,7 @@ This package currently provides the following checkers:
 - [ip](doc/checkers/ip.md) checks if the given value is an IP address.
 - [ipv4](doc/checkers/ipv4.md) checks if the given value is an IPv4 address.
 - [ipv6](doc/checkers/ipv6.md) checks if the given value is an IPv6 address.
+- [isbn](doc/checkers/isbn.md) checks if the given value is a valid ISBN number.
 - [luhn](doc/checkers/luhn.md) checks if the given number is valid based on the Luhn algorithm.
 - [mac](doc/checkers/mac.md) checks if the given value is a valid an IEEE 802 MAC-48, EUI-48, EUI-64, or a 20-octet IP over InfiniBand link-layer address.
 - [max](doc/checkers/max.md) checks if the given value is less than the given maximum.

checker.go

@@ -41,6 +41,7 @@ var makers = map[string]MakeFunc{
 	CheckerIP:           makeIP,
 	CheckerIPV4:         makeIPV4,
 	CheckerIPV6:         makeIPV6,
+	CheckerISBN:         makeISBN,
 	CheckerLuhn:         makeLuhn,
 	CheckerMac:          makeMac,
 	CheckerMax:          makeMax,

doc/checkers/isbn.md

@@ -0,0 +1,52 @@
+# ISBN Checker
+
+An [ISBN (International Standard Book Number)](https://en.wikipedia.org/wiki/International_Standard_Book_Number) is a 10 or 13 digit number that is used to identify a book.
+
+The `isbn` checker checks if the given value is a valid ISBN. If the given value is not a valid ISBN, the checker will return the `NOT_ISBN` result. Here is an example:
+
+```golang
+type Book struct {
+  ISBN string `checkers:"isbn"`
+}
+
+book := &Book{
+  ISBN: "1430248270",
+}
+
+_, valid := checker.Check(book)
+if !valid {
+  // Send the mistakes back to the user
+}
+```
+
+The `isbn` checker can also be configured to check for a 10 digit or a 13 digit number. Here is an example:
+
+```golang
+type Book struct {
+  ISBN string `checkers:"isbn:13"`
+}
+
+book := &Book{
+  ISBN: "9781430248279",
+}
+
+_, valid := checker.Check(book)
+if !valid {
+  // Send the mistakes back to the user
+}
+```
+
+In your custom checkers, you can call the `isbn` checker functions below to validate the user input. 
+
+- [`IsISBN`](https://pkg.go.dev/github.com/cinar/checker#IsISBN) checks if the given value is a valid ISBN number.
+- [`IsISBN10`](https://pkg.go.dev/github.com/cinar/checker#IsISBN10) checks if the given value is a valid ISBN 10 number.
+- [`IsISBN13`](https://pkg.go.dev/github.com/cinar/checker#IsISBN13) checks if the given value is a valid ISBN 13 number.
+
+Here is an example:
+
+```golang
+result := checker.IsISBN("1430248270")
+if result != checker.ResultValid {
+  // Send the mistakes back to the user
+}
+```

doc/checkers/url.md

@@ -1,6 +1,6 @@
 # URL Checker
 
-The ```url``` checker checks if the given value is a valid URL. If the given value is not a valid URL, the checker will return the ```NOT_URL``` result. The checker uses [ParseRequestURI](https://pkg.go.dev/net/url#ParseRequestURI) function to parse the URL, and then checks if the schema or the host are both set.
+The `url` checker checks if the given value is a valid URL. If the given value is not a valid URL, the checker will return the `NOT_URL` result. The checker uses [ParseRequestURI](https://pkg.go.dev/net/url#ParseRequestURI) function to parse the URL, and then checks if the schema or the host are both set.
 
 Here is an example:
 
@@ -19,7 +19,7 @@ if !valid {
 }
 ```
 
-In your custom checkers, you can call the ```url``` checker function ```IsURL``` to validate the user input. Here is an example:
+In your custom checkers, you can call the `url` checker function [`IsURL`](https://pkg.go.dev/github.com/cinar/checker#IsURL) to validate the user input. Here is an example:
 
 ```golang
 result := checker.IsURL("https://zdo.com")

isbn.go

@@ -0,0 +1,121 @@
+package checker
+
+import (
+	"reflect"
+	"strings"
+)
+
+// Program to check for ISBN
+// https://www.geeksforgeeks.org/program-check-isbn/
+
+// How to Verify an ISBN
+// https://www.instructables.com/How-to-verify-a-ISBN/
+
+// CheckerISBN is the name of the checker.
+const CheckerISBN = "isbn"
+
+// ResultNotISBN indicates that the given value is not a valid ISBN.
+const ResultNotISBN = "NOT_ISBN"
+
+// IsISBN10 checks if the given value is a valid ISBN-10 number.
+func IsISBN10(value string) Result {
+	value = strings.ReplaceAll(value, "-", "")
+
+	if len(value) != 10 {
+		return ResultNotISBN
+	}
+
+	digits := []rune(value)
+	sum := 0
+
+	for i, e := 0, len(digits); i < e; i++ {
+		n := isbnDigitToInt(digits[i])
+		sum += n * (e - i)
+	}
+
+	if sum%11 != 0 {
+		return ResultNotISBN
+	}
+
+	return ResultValid
+}
+
+// IsISBN13 checks if the given value is a valid ISBN-13 number.
+func IsISBN13(value string) Result {
+	value = strings.ReplaceAll(value, "-", "")
+
+	if len(value) != 13 {
+		return ResultNotISBN
+	}
+
+	digits := []rune(value)
+	sum := 0
+
+	for i, d := range digits {
+		n := isbnDigitToInt(d)
+		if i%2 != 0 {
+			n *= 3
+		}
+
+		sum += n
+	}
+
+	if sum%10 != 0 {
+		return ResultNotISBN
+	}
+
+	return ResultValid
+}
+
+// IsISBN checks if the given value is a valid ISBN number.
+func IsISBN(value string) Result {
+	value = strings.ReplaceAll(value, "-", "")
+
+	if len(value) == 10 {
+		return IsISBN10(value)
+	} else if len(value) == 13 {
+		return IsISBN13(value)
+	}
+
+	return ResultNotISBN
+}
+
+// isbnDigitToInt returns the integer value of given ISBN digit.
+func isbnDigitToInt(r rune) int {
+	if r == 'X' {
+		return 10
+	}
+
+	return int(r - '0')
+}
+
+// makeISBN makes a checker function for the URL checker.
+func makeISBN(config string) CheckFunc {
+	if config != "" && config != "10" && config != "13" {
+		panic("invalid format")
+	}
+
+	return func(value, parent reflect.Value) Result {
+		return checkISBN(value, parent, config)
+	}
+}
+
+// checkISBN checks if the given value is a valid ISBN number.
+func checkISBN(value, _ reflect.Value, mode string) Result {
+	if value.Kind() != reflect.String {
+		panic("string expected")
+	}
+
+	number := value.String()
+
+	switch mode {
+	case "10":
+		return IsISBN10(number)
+
+	case "13":
+		return IsISBN13(number)
+
+	default:
+		return IsISBN(number)
+	}
+}

isbn_test.go

@@ -0,0 +1,162 @@
+package checker_test
+
+import (
+	"testing"
+
+	"github.com/cinar/checker"
+)
+
+func TestIsISBN10Valid(t *testing.T) {
+	result := checker.IsISBN10("1430248270")
+	if result != checker.ResultValid {
+		t.Fail()
+	}
+}
+
+func TestIsISBN10ValidX(t *testing.T) {
+	result := checker.IsISBN10("007462542X")
+	if result != checker.ResultValid {
+		t.Fail()
+	}
+}
+
+func TestIsISBN10ValidWithDashes(t *testing.T) {
+	result := checker.IsISBN10("1-4302-4827-0")
+	if result != checker.ResultValid {
+		t.Fail()
+	}
+}
+
+func TestIsISBN10InvalidLength(t *testing.T) {
+	result := checker.IsISBN10("143024827")
+	if result != checker.ResultNotISBN {
+		t.Fail()
+	}
+}
+
+func TestIsISBN10InvalidCheck(t *testing.T) {
+	result := checker.IsISBN10("1430248272")
+	if result != checker.ResultNotISBN {
+		t.Fail()
+	}
+}
+
+func TestIsISBN13Valid(t *testing.T) {
+	result := checker.IsISBN13("9781430248279")
+	if result != checker.ResultValid {
+		t.Fail()
+	}
+}
+
+func TestIsISBN13ValidWithDashes(t *testing.T) {
+	result := checker.IsISBN13("978-1-4302-4827-9")
+	if result != checker.ResultValid {
+		t.Fail()
+	}
+}
+
+func TestIsISBN13InvalidLength(t *testing.T) {
+	result := checker.IsISBN13("978143024827")
+	if result != checker.ResultNotISBN {
+		t.Fail()
+	}
+}
+
+func TestIsISBN13InvalidCheck(t *testing.T) {
+	result := checker.IsISBN13("9781430248272")
+	if result != checker.ResultNotISBN {
+		t.Fail()
+	}
+}
+
+func TestIsISBNValid10(t *testing.T) {
+	result := checker.IsISBN("1430248270")
+	if result != checker.ResultValid {
+		t.Fail()
+	}
+}
+
+func TestIsISBNValid13(t *testing.T) {
+	result := checker.IsISBN("9781430248279")
+	if result != checker.ResultValid {
+		t.Fail()
+	}
+}
+
+func TestIsISBNInvalidLenght(t *testing.T) {
+	result := checker.IsISBN("978143024827")
+	if result != checker.ResultNotISBN {
+		t.Fail()
+	}
+}
+
+func TestCheckISBNNonString(t *testing.T) {
+	defer checker.FailIfNoPanic(t)
+
+	type Book struct {
+		ISBN int `checkers:"isbn"`
+	}
+
+	book := &Book{}
+
+	checker.Check(book)
+}
+
+func TestCheckISBNValid(t *testing.T) {
+	type Book struct {
+		ISBN string `checkers:"isbn"`
+	}
+
+	book := &Book{
+		ISBN: "1430248270",
+	}
+
+	_, valid := checker.Check(book)
+	if !valid {
+		t.Fail()
+	}
+}
+
+func TestCheckISBNInvalid(t *testing.T) {
+	defer checker.FailIfNoPanic(t)
+
+	type Book struct {
+		ISBN string `checkers:"isbn:20"`
+	}
+
+	book := &Book{
+		ISBN: "1430248270",
+	}
+
+	checker.Check(book)
+}
+
+func TestCheckISBNValid10(t *testing.T) {
+	type Book struct {
+		ISBN string `checkers:"isbn:10"`
+	}
+
+	book := &Book{
+		ISBN: "1430248270",
+	}
+
+	_, valid := checker.Check(book)
+	if !valid {
+		t.Fail()
+	}
+}
+
+func TestCheckISBNValid13(t *testing.T) {
+	type Book struct {
+		ISBN string `checkers:"isbn:13"`
+	}
+
+	book := &Book{
+		ISBN: "9781430248279",
+	}
+
+	_, valid := checker.Check(book)
+	if !valid {
+		t.Fail()
+	}
+}