feat: add iban validation rule (#88)

Author: ns-vasilev

README.md

@@ -314,6 +314,7 @@ struct RegistrationView: View {
 | `ContainsValidationRule` | Validates that a string contains a specific substring | `ContainsValidationRule(substring: "@", error: "Must contain @")`
 | `EqualityValidationRule`| Validates that the input is equal to a given reference value | `EqualityValidationRule(compareTo: password, error: "Passwords do not match")`
 | `ComparisonValidationRule` | Validates that input against a comparison constraint | `ComparisonValidationRule(greaterThan: 0, error: "Must be greater than 0")`
+| `IBANValidationRule` | Validates that a string is a valid IBAN (International Bank Account Number) | `IBANValidationRule(error: "Invalid IBAN")`
 
 ## Custom Validators
 

Sources/ValidatorCore/Classes/Rules/IBANValidationRule.swift

@@ -0,0 +1,71 @@
+//
+// Validator
+// Copyright © 2025 Space Code. All rights reserved.
+//
+
+/// Validates that a string is a valid IBAN (International Bank Account Number).
+///
+/// Uses a simplified IBAN validation algorithm:
+/// 1. Checks length according to country code (2 letters + digits)
+/// 2. Moves first 4 characters to the end
+/// 3. Converts letters to numbers (A=10, B=11, ..., Z=35)
+/// 4. Checks if the resulting number mod 97 equals 1
+///
+/// # Example:
+/// ```swift
+/// let rule = IBANValidationRule(error: "Invalid IBAN")
+/// rule.validate(input: "GB82WEST12345698765432") // true
+/// rule.validate(input: "INVALIDIBAN")           // false
+/// ```
+public struct IBANValidationRule: IValidationRule {
+    // MARK: - Types
+
+    public typealias Input = String
+
+    // MARK: Properties
+
+    /// The validation error returned when validation fails.
+    public let error: IValidationError
+
+    // MARK: Initialization
+
+    /// Creates an IBAN validation rule.
+    ///
+    /// - Parameter error: The validation error returned if validation fails.
+    public init(error: IValidationError) {
+        self.error = error
+    }
+
+    // MARK: IValidationRule
+
+    public func validate(input: String) -> Bool {
+        let trimmed = input.replacingOccurrences(of: " ", with: "").uppercased()
+        guard trimmed.count >= 4 else { return false }
+
+        let rearranged = String(trimmed.dropFirst(4) + trimmed.prefix(4))
+
+        var numericString = ""
+        for char in rearranged {
+            if let digit = char.wholeNumberValue {
+                numericString.append(String(digit))
+            } else if let ascii = char.asciiValue, ascii >= 65, ascii <= 90 {
+                numericString.append(String(Int(ascii) - 55))
+            } else {
+                return false
+            }
+        }
+
+        var remainder = 0
+        var chunk = ""
+        for char in numericString {
+            chunk.append(char)
+            if let number = Int(chunk), number >= 97 {
+                remainder = number % 97
+                chunk = String(remainder)
+            }
+        }
+
+        remainder = (Int(chunk) ?? 0) % 97
+        return remainder == 1
+    }
+}

Sources/ValidatorCore/Validator.docc/Overview.md

@@ -37,6 +37,7 @@ ValidatorCore contains all core validation rules, utilities, and mechanisms for
 - ``ContainsValidationRule``
 - ``EqualityValidationRule``
 - ``ComparisonValidationRule``
+- ``IBANValidationRule``
 
 ### Articles
 

Tests/ValidatorCoreTests/UnitTests/Rules/IBANValidationRuleTests.swift

@@ -0,0 +1,72 @@
+//
+// Validator
+// Copyright © 2025 Space Code. All rights reserved.
+//
+
+@testable import ValidatorCore
+import XCTest
+
+// MARK: - IBANValidationRuleTests
+
+final class IBANValidationRuleTests: XCTestCase {
+    // MARK: Properties
+
+    private var sut: IBANValidationRule!
+
+    // MARK: XCTestCase
+
+    override func setUp() {
+        super.setUp()
+        sut = IBANValidationRule(error: String.error)
+    }
+
+    override func tearDown() {
+        sut = nil
+        super.tearDown()
+    }
+
+    // MARK: Tests
+
+    func test_thatValidationRuleSetsProperties() {
+        // then
+        XCTAssertEqual(sut.error.message, .error)
+    }
+
+    func test_thatIBANValidationRuleValidatesInput_whenInputIsCorrectValue() {
+        let validIBANs = [
+            "GB82 WEST 1234 5698 7654 32",
+            "DE89370400440532013000",
+            "FR1420041010050500013M02606",
+        ]
+
+        for iban in validIBANs {
+            XCTAssertTrue(sut.validate(input: iban))
+        }
+    }
+
+    func test_thatIBANValidationRuleValidatesInput_whenInputIsInCorrectValue() {
+        let invalidIBANs = [
+            "GB82WEST12345698765431",
+            "INVALIDIBAN",
+            "DE123",
+        ]
+
+        for iban in invalidIBANs {
+            XCTAssertFalse(sut.validate(input: iban))
+        }
+    }
+
+    func test_thatIBANValidationRuleValidatesInput_whenInputIsEmpty() {
+        XCTAssertFalse(sut.validate(input: ""))
+    }
+
+    func test_thatIBANValidationRuleValidatesInput_whenInputHasInvalidCharacters() {
+        XCTAssertFalse(sut.validate(input: "GB82WEST1234$5698765432"))
+    }
+}
+
+// MARK: Constants
+
+private extension String {
+    static let error = "Invalid IBAN"
+}