feat: add comparison validation rule (#86)

Author: ns-vasilev

README.md

@@ -313,6 +313,7 @@ struct RegistrationView: View {
 | `NoWhitespaceValidationRule` | Validates that a string does not contain any whitespace characters | `NoWhitespaceValidationRule(error: "Spaces are not allowed")`
 | `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")`
 
 ## Custom Validators
 

Sources/ValidatorCore/Classes/Rules/ComparisonValidationRule.swift

@@ -0,0 +1,91 @@
+//
+// Validator
+// Copyright © 2025 Space Code. All rights reserved.
+//
+
+/// A validation rule that checks input against a comparison constraint.
+///
+/// Supports comparisons such as:
+/// - `>` (greater than)
+/// - `>=` (greater than or equal to)
+/// - `<` (less than)
+/// - `<=` (less than or equal to)
+///
+/// # Examples:
+/// ```swift
+/// let rule1 = ComparisonValidationRule(greaterThan: 0, error: "Must be greater than 0")
+/// rule1.validate(input: 5)   // true
+/// rule1.validate(input: -1)  // false
+///
+/// let rule2 = ComparisonValidationRule(lessThanOrEqual: 100, error: "Must be <= 100")
+/// rule2.validate(input: 100) // true
+/// rule2.validate(input: 150) // false
+/// ```
+public struct ComparisonValidationRule<T: Comparable>: IValidationRule {
+    // MARK: - Types
+
+    public typealias Input = T
+
+    /// Supported comparison operators.
+    public enum Condition {
+        case greaterThan(T)
+        case greaterThanOrEqual(T)
+        case lessThan(T)
+        case lessThanOrEqual(T)
+    }
+
+    // MARK: - Properties
+
+    /// The comparison condition to evaluate.
+    public let condition: Condition
+
+    /// The validation error returned when validation fails.
+    public let error: IValidationError
+
+    // MARK: - Initialization
+
+    /// Creates a comparison-based validation rule.
+    ///
+    /// - Parameters:
+    ///   - condition: The comparison condition.
+    ///   - error: The validation error returned if validation fails.
+    public init(condition: Condition, error: IValidationError) {
+        self.condition = condition
+        self.error = error
+    }
+
+    /// Convenience initializer for `greaterThan`.
+    public init(greaterThan value: T, error: IValidationError) {
+        self.init(condition: .greaterThan(value), error: error)
+    }
+
+    /// Convenience initializer for `greaterThanOrEqual`.
+    public init(greaterThanOrEqual value: T, error: IValidationError) {
+        self.init(condition: .greaterThanOrEqual(value), error: error)
+    }
+
+    /// Convenience initializer for `lessThan`.
+    public init(lessThan value: T, error: IValidationError) {
+        self.init(condition: .lessThan(value), error: error)
+    }
+
+    /// Convenience initializer for `lessThanOrEqual`.
+    public init(lessThanOrEqual value: T, error: IValidationError) {
+        self.init(condition: .lessThanOrEqual(value), error: error)
+    }
+
+    // MARK: - IValidationRule
+
+    public func validate(input: T) -> Bool {
+        switch condition {
+        case let .greaterThan(value):
+            input > value
+        case let .greaterThanOrEqual(value):
+            input >= value
+        case let .lessThan(value):
+            input < value
+        case let .lessThanOrEqual(value):
+            input <= value
+        }
+    }
+}

Sources/ValidatorCore/Validator.docc/Overview.md

@@ -36,6 +36,7 @@ ValidatorCore contains all core validation rules, utilities, and mechanisms for
 - ``NoWhitespaceValidationRuleTests``
 - ``ContainsValidationRule``
 - ``EqualityValidationRule``
+- ``ComparisonValidationRule``
 
 ### Articles
 

Tests/ValidatorCoreTests/UnitTests/Rules/ComparisonValidationRuleTests.swift

@@ -0,0 +1,50 @@
+//
+// Validator
+// Copyright © 2025 Space Code. All rights reserved.
+//
+
+@testable import ValidatorCore
+import XCTest
+
+// MARK: - ComparisonValidationRuleTests
+
+final class ComparisonValidationRuleTests: XCTestCase {
+    func test_greaterThanRule_passesForValidValue() {
+        let sut = ComparisonValidationRule(greaterThan: 10, error: String.error)
+        XCTAssertTrue(sut.validate(input: 20))
+    }
+
+    func test_greaterThanRule_failsForInvalidValue() {
+        let sut = ComparisonValidationRule(greaterThan: 10, error: String.error)
+        XCTAssertFalse(sut.validate(input: 10))
+    }
+
+    func test_greaterThanOrEqualRule_allowsEqualValue() {
+        let sut = ComparisonValidationRule(greaterThanOrEqual: 10, error: String.error)
+        XCTAssertTrue(sut.validate(input: 10))
+    }
+
+    func test_lessThanRule_passesForSmallerValues() {
+        let sut = ComparisonValidationRule(lessThan: 100, error: String.error)
+        XCTAssertTrue(sut.validate(input: 50))
+        XCTAssertFalse(sut.validate(input: 100))
+    }
+
+    func test_lessThanOrEqualRule_allowsEqualValue() {
+        let sut = ComparisonValidationRule(lessThanOrEqual: 100, error: String.error)
+        XCTAssertTrue(sut.validate(input: 100))
+        XCTAssertFalse(sut.validate(input: 101))
+    }
+
+    func test_ruleWorksWithStringComparable() {
+        let sut = ComparisonValidationRule(lessThan: "m", error: String.error)
+        XCTAssertTrue(sut.validate(input: "apple"))
+        XCTAssertFalse(sut.validate(input: "z"))
+    }
+}
+
+// MARK: Constants
+
+private extension String {
+    static let error = "Invalid characters"
+}