chore: add usage examples to the examples directory (#74)

* chore: add usage examples to the examples directory

* docs: add the `example` section

Author: ns-vasilev

Examples/Core/Content.playground/Contents.swift

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+//
+// Validator
+// Copyright © 2025 Space Code. All rights reserved.
+//
+
+import ValidatorCore
+
+// 1. LengthValidationRule - validates string length
+let lengthRule = LengthValidationRule(min: 3, max: 20, error: "Length must be 3-20 characters")
+
+let shortString = "ab"
+let validString = "Hello"
+let longString = "This is a very long string that exceeds the limit"
+
+print("LengthValidationRule:")
+print("'\(shortString)' is valid: \(lengthRule.validate(input: shortString))") // false
+print("'\(validString)' is valid: \(lengthRule.validate(input: validString))") // true
+print("'\(longString)' is valid: \(lengthRule.validate(input: longString))") // false
+print()
+
+// 2. NonEmptyValidationRule - checks if string is not empty
+let nonEmptyRule = NonEmptyValidationRule(error: "Field is required")
+
+let emptyString = ""
+let whitespaceString = "   "
+let filledString = "Content"
+
+print("NonEmptyValidationRule:")
+print("'\(emptyString)' is valid: \(nonEmptyRule.validate(input: emptyString))") // false
+print("'\(whitespaceString)' is valid: \(nonEmptyRule.validate(input: whitespaceString))") // false
+print("'\(filledString)' is valid: \(nonEmptyRule.validate(input: filledString))") // true
+print()
+
+// 3. PrefixValidationRule - validates string prefix
+let prefixRule = PrefixValidationRule(prefix: "https://", error: "URL must start with https://")
+
+let httpURL = "http://example.com"
+let httpsURL = "https://example.com"
+let noProtocol = "example.com"
+
+print("PrefixValidationRule:")
+print("'\(httpURL)' is valid: \(prefixRule.validate(input: httpURL))") // false
+print("'\(httpsURL)' is valid: \(prefixRule.validate(input: httpsURL))") // true
+print("'\(noProtocol)' is valid: \(prefixRule.validate(input: noProtocol))") // false
+print()
+
+// 4. SuffixValidationRule - validates string suffix
+let suffixRule = SuffixValidationRule(suffix: ".com", error: "Domain must end with .com")
+
+let comDomain = "example.com"
+let orgDomain = "example.org"
+let noDomain = "example"
+
+print("SuffixValidationRule:")
+print("'\(comDomain)' is valid: \(suffixRule.validate(input: comDomain))") // true
+print("'\(orgDomain)' is valid: \(suffixRule.validate(input: orgDomain))") // false
+print("'\(noDomain)' is valid: \(suffixRule.validate(input: noDomain))") // false
+print()
+
+// 5. RegexValidationRule - validates using regular expression
+let phoneRule = RegexValidationRule(pattern: "^\\d{3}-\\d{4}$", error: "Invalid phone format")
+
+let validPhone = "123-4567"
+let invalidPhone1 = "1234567"
+let invalidPhone2 = "123-456"
+
+print("RegexValidationRule:")
+print("'\(validPhone)' is valid: \(phoneRule.validate(input: validPhone))") // true
+print("'\(invalidPhone1)' is valid: \(phoneRule.validate(input: invalidPhone1))") // false
+print("'\(invalidPhone2)' is valid: \(phoneRule.validate(input: invalidPhone2))") // false
+print()
+
+// 6. URLValidationRule - validates URL format
+let urlRule = URLValidationRule(error: "Please enter a valid URL")
+
+let validURL = "https://www.apple.com"
+let invalidURL = "not a url"
+let localURL = "file:///path/to/file"
+
+print("URLValidationRule:")
+print("'\(validURL)' is valid: \(urlRule.validate(input: validURL))") // true
+print("'\(invalidURL)' is valid: \(urlRule.validate(input: invalidURL))") // false
+print("'\(localURL)' is valid: \(urlRule.validate(input: localURL))") // true
+print()
+
+// 7. CreditCardValidationRule - validates credit card number (Luhn algorithm)
+let cardRule = CreditCardValidationRule(error: "Invalid card number")
+
+let validCard = "4532015112830366" // Valid Visa test number
+let invalidCard = "1234567890123456"
+let shortCard = "4532"
+
+print("CreditCardValidationRule:")
+print("'\(validCard)' is valid: \(cardRule.validate(input: validCard))") // true
+print("'\(invalidCard)' is valid: \(cardRule.validate(input: invalidCard))") // false
+print("'\(shortCard)' is valid: \(cardRule.validate(input: shortCard))") // false
+print()
+
+// 8. EmailValidationRule - validates email format
+let emailRule = EmailValidationRule(error: "Please enter a valid email")
+
+let validEmail = "user@example.com"
+let invalidEmail1 = "user@"
+let invalidEmail2 = "user.example.com"
+
+print("EmailValidationRule:")
+print("'\(validEmail)' is valid: \(emailRule.validate(input: validEmail))") // true
+print("'\(invalidEmail1)' is valid: \(emailRule.validate(input: invalidEmail1))") // false
+print("'\(invalidEmail2)' is valid: \(emailRule.validate(input: invalidEmail2))") // false
+print()
+
+// 9. CharactersValidationRule - validates allowed characters
+let lettersRule = CharactersValidationRule(characterSet: .letters, error: "Invalid characters")
+
+let onlyLetters = "HelloWorld"
+let withNumbers = "Hello123"
+let withSpaces = "Hello World"
+
+print("CharactersValidationRule:")
+print("'\(onlyLetters)' is valid: \(lettersRule.validate(input: onlyLetters))") // true
+print("'\(withNumbers)' is valid: \(lettersRule.validate(input: withNumbers))") // false
+print("'\(withSpaces)' is valid: \(lettersRule.validate(input: withSpaces))") // false
+print()
+
+// 10. NilValidationRule - validates that value is nil
+let nilRule = NilValidationRule<String>(error: "Value must be nil")
+
+let nilValue: String? = nil
+let nonNilValue: String? = "Something"
+
+print("NilValidationRule:")
+print("nil value is valid: \(nilRule.validate(input: nilValue))") // true
+print("non-nil value is valid: \(nilRule.validate(input: nonNilValue))") // false
+print()
+
+// MARK: - Combining Rules
+
+print("=== Combining Multiple Rules ===")
+
+// Example: password validation with multiple rules
+let passwordLengthRule = LengthValidationRule(min: 8, max: 32, error: "Password must be 8-32 characters")
+let passwordNotEmptyRule = NonEmptyValidationRule(error: "Password is required")
+
+let passwords = ["", "123", "ValidPass123", "VeryLongPasswordThatExceedsMaximumLength"]
+
+for password in passwords {
+    let isLengthValid = passwordLengthRule.validate(input: password)
+    let isNotEmpty = passwordNotEmptyRule.validate(input: password)
+    let isValid = isLengthValid && isNotEmpty
+
+    print("Password '\(password)': \(isValid ? "✅" : "❌")")
+}

Examples/Core/Content.playground/contents.xcplayground

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+<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
+<playground version='5.0' target-platform='macos' buildActiveScheme='true'>
+    <timeline fileName='timeline.xctimeline'/>
+</playground>

Examples/Core/PlaygroundDependencies/.gitignore

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+.DS_Store
+/.build
+/Packages
+xcuserdata/
+DerivedData/
+.swiftpm/configuration/registries.json
+.swiftpm/xcode/package.xcworkspace/contents.xcworkspacedata
+.netrc

Examples/Core/PlaygroundDependencies/Package.swift

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+// swift-tools-version: 6.2
+// The swift-tools-version declares the minimum version of Swift required to build this package.
+
+import PackageDescription
+
+let package = Package(
+    name: "PlaygroundDependencies",
+    products: [
+        .library(name: "PlaygroundDependencies", targets: ["PlaygroundDependencies"]),
+    ],
+    targets: [
+        .target(name: "PlaygroundDependencies"),
+        .testTarget(name: "PlaygroundDependenciesTests", dependencies: ["PlaygroundDependencies"]),
+    ]
+)
+
+package.dependencies = [
+    .package(path: "../../../"),
+]
+package.targets = [
+    .target(
+        name: "PlaygroundDependencies",
+        dependencies: [
+            .product(name: "ValidatorCore", package: "validator"),
+        ]
+    ),
+]
+package.platforms = [
+    .iOS("16.0"),
+    .macOS("13.0"),
+    .tvOS("16.0"),
+    .watchOS("9.0"),
+]

Examples/Core/PlaygroundDependencies/Sources/PlaygroundDependencies/PlaygroundDependencies.swift

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+//
+// Validator
+// Copyright © 2025 Space Code. All rights reserved.
+//
+
+// The Swift Programming Language
+// https://docs.swift.org/swift-book

Examples/Core/PlaygroundDependencies/Tests/PlaygroundDependenciesTests/PlaygroundDependenciesTests.swift

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+//
+// Validator
+// Copyright © 2025 Space Code. All rights reserved.
+//
+
+@testable import PlaygroundDependencies
+import Testing
+
+@Test func example() async throws {
+    // Write your test here and use APIs like `#expect(...)` to check expected conditions.
+}