Implement IBAN generation (#172)

* Add IBAN generation

* Move all IBAN related code inside iban.go

* Fix 'Unused method receiver RVV-B0013'

https://app.deepsource.com/gh/jaswdr/faker/run/a17100c5-d424-41ff-8b2f-3bc9f63de59a/go/RVV-B0013

* Fix 'Unused method receiver RVV-B0013'

https://app.deepsource.com/gh/jaswdr/faker/run/a17100c5-d424-41ff-8b2f-3bc9f63de59a/go/RVV-B0013?listindex=0

iban.go

@@ -0,0 +1,161 @@
+package faker
+
+import (
+	"fmt"
+	"strconv"
+	"strings"
+	"unicode"
+)
+
+// ibanFormats lists all IBAN formats, source: @link https://www.swift.com/swift-resource/9606/download
+// n: numeric, a: alphabetic, c: alphanumeric
+var ibanFormats = map[string]string{
+	"AD": format("n4", "n4", "c12"),
+	"AE": format("n3", "n16"),
+	"AL": format("n8", "c16"),
+	"AT": format("n5", "n11"),
+	"AZ": format("a4", "c20"),
+	"BA": format("n3", "n3", "n8", "n2"),
+	"BE": format("n3", "n7", "n2"),
+	"BG": format("a4", "n4", "n2", "c8"),
+	"BH": format("a4", "c14"),
+	"BR": format("n8", "n5", "n10", "a1", "c1"),
+	"CH": format("n5", "c12"),
+	"CR": format("n4", "n14"),
+	"CY": format("n3", "n5", "c16"),
+	"CZ": format("n4", "n6", "n10"),
+	"DE": format("n8", "n10"),
+	"DK": format("n4", "n9", "n1"),
+	"DO": format("c4", "n20"),
+	"EE": format("n2", "n2", "n11", "n1"),
+	"ES": format("n4", "n4", "n1", "n1", "n10"),
+	"FI": format("n6", "n7", "n1"),
+	"FR": format("n5", "n5", "c11", "n2"),
+	"GB": format("a4", "n6", "n8"),
+	"GE": format("a2", "n16"),
+	"GI": format("a4", "c15"),
+	"GR": format("n3", "n4", "c16"),
+	"GT": format("c4", "c20"),
+	"HR": format("n7", "n10"),
+	"HU": format("n3", "n4", "n1", "n15", "n1"),
+	"IE": format("a4", "n6", "n8"),
+	"IL": format("n3", "n3", "n13"),
+	"IS": format("n4", "n2", "n6", "n10"),
+	"IT": format("a1", "n5", "n5", "c12"),
+	"KW": format("a4", "n22"),
+	"KZ": format("n3", "c13"),
+	"LB": format("n4", "c20"),
+	"LI": format("n5", "c12"),
+	"LT": format("n5", "n11"),
+	"LU": format("n3", "c13"),
+	"LV": format("a4", "c13"),
+	"MC": format("n5", "n5", "c11", "n2"),
+	"MD": format("c2", "c18"),
+	"ME": format("n3", "n13", "n2"),
+	"MK": format("n3", "c10", "n2"),
+	"MR": format("n5", "n5", "n11", "n2"),
+	"MT": format("a4", "n5", "c18"),
+	"MU": format("a4", "n2", "n2", "n12", "n3", "a3"),
+	"NL": format("a4", "n10"),
+	"NO": format("n4", "n6", "n1"),
+	"PK": format("a4", "c16"),
+	"PL": format("n8", "n16"),
+	"PS": format("a4", "c21"),
+	"PT": format("n4", "n4", "n11", "n2"),
+	"RO": format("a4", "c16"),
+	"RS": format("n3", "n13", "n2"),
+	"SA": format("n2", "c18"),
+	"SE": format("n3", "n16", "n1"),
+	"SI": format("n5", "n8", "n2"),
+	"SK": format("n4", "n6", "n10"),
+	"SM": format("a1", "n5", "n5", "c12"),
+	"TN": format("n2", "n3", "n13", "n2"),
+	"TR": format("n5", "n1", "c16"),
+	"VG": format("a4", "n16"),
+}
+
+// format interprets the format of each section of the iban and returns a string with a specific format
+// Example: format("n5", "a2", "c1") => "nnnnnaac"
+func format(sections ...string) string {
+	var res string
+	for _, s := range sections {
+		if len(s) == 0 {
+			continue
+		}
+		if class := s[0]; unicode.IsLetter(rune(class)) {
+			size, _ := strconv.Atoi(s[1:])
+			res += strings.Repeat(string(class), size)
+		}
+	}
+	return res
+}
+
+// Iban returns a fake IBAN for Payment
+func (p Payment) Iban() string {
+	return p.ibanForCountry(p.Faker.RandomStringMapKey(ibanFormats))
+}
+
+// ibanForCountry returns a fake IBAN for a specific country
+// Returns an empty string if the country is not supported
+func (p Payment) ibanForCountry(countryCode string) string {
+	format, ok := ibanFormats[countryCode]
+	if !ok {
+		return ""
+	}
+
+	bban := strings.ToUpper(p.bban(format))
+	checksum := ibanChecksum(countryCode + "00" + bban)
+
+	return countryCode + checksum + bban
+}
+
+// bban generates a fake Basic Bank Account Number (BBAN) based on the format
+// the provided format must be a string only containing the following characters:
+// n: numeric, a: alphabetic, c: alphanumeric
+// which will be replaced by a random number or letter
+func (p Payment) bban(format string) string {
+	format = strings.ReplaceAll(format, "n", "#")
+	format = strings.ReplaceAll(format, "a", "?")
+	s := "?"
+	if p.Faker.Bool() {
+		s = "#"
+	}
+	format = strings.ReplaceAll(format, "c", s)
+
+	return p.Faker.Bothify(format)
+}
+
+func ibanChecksum(iban string) string {
+	iban = strings.ToUpper(strings.ReplaceAll(iban, " ", ""))
+
+	// Move first 4 characters to the end, and set checksum to 00
+	iban = iban[4:] + iban[:2] + "00"
+
+	// Replace letters with their respective numbers
+	var numericIBAN string
+	for _, char := range iban {
+		if char >= 'A' && char <= 'Z' {
+			numericIBAN += strconv.Itoa(int(char - 'A' + 10))
+		} else {
+			numericIBAN += string(char)
+		}
+	}
+
+	// Perform modulo 97 operation on the numeric IBAN
+	remainder := 0
+	for _, char := range numericIBAN {
+		digit := int(char - '0')
+		remainder = (remainder*10 + digit) % 97
+	}
+
+	// Calculate checksum
+	checksum := 98 - remainder
+	if checksum < 10 {
+		return fmt.Sprintf("0%d", checksum)
+	}
+	return fmt.Sprintf("%d", checksum)
+}
+
+func isIbanValid(iban string) bool {
+	return ibanChecksum(iban) == iban[2:4]
+}