// Email validation
func validateEmail(_ email: String) -> Bool {
    let emailRegex = "[A-Z0-9a-z._%+-]+@[A-Za-z0-9.-]+\\.[A-Za-z]{2,64}"
    let emailPredicate = NSPredicate(format: "SELF MATCHES %@", emailRegex)
    return emailPredicate.evaluate(with: email)
}

// Sanitize user input
func sanitizeInput(_ input: String) -> String {
    return input.trimmingCharacters(in: .whitespacesAndNewlines)
        .replacingOccurrences(of: "<", with: "&lt;")
        .replacingOccurrences(of: ">", with: "&gt;")
}

// Example usage
let userEmail = "user@example.com"
if validateEmail(userEmail) {
    print("Valid email")
} else {
    print("Invalid email")
}

import Security

func saveToKeychain(key: String, data: Data) -> Bool {
    let query: [String: Any] = [
        kSecClass as String: kSecClassGenericPassword,
        kSecAttrAccount as String: key,
        kSecValueData as String: data,
        kSecAttrAccessible as String: kSecAttrAccessibleWhenUnlockedThisDeviceOnly
    ]
    
    // Delete old value if exists
    SecItemDelete(query as CFDictionary)
    
    // Add new value
    let status = SecItemAdd(query as CFDictionary, nil)
    return status == errSecSuccess
}

func loadFromKeychain(key: String) -> Data? {
    let query: [String: Any] = [
        kSecClass as String: kSecClassGenericPassword,
        kSecAttrAccount as String: key,
        kSecReturnData as String: true,
        kSecMatchLimit as String: kSecMatchLimitOne
    ]
    
    var result: AnyObject?
    let status = SecItemCopyMatching(query as CFDictionary, &result)
    
    return status == errSecSuccess ? result as? Data : nil
}

// Example: Store authentication token
let token = "secret_auth_token"
if let tokenData = token.data(using: .utf8) {
    saveToKeychain(key: "authToken", data: tokenData)
}

// Load token
if let tokenData = loadFromKeychain(key: "authToken"),
   let token = String(data: tokenData, encoding: .utf8) {
    print("Token: \(token)")
}

import Foundation

class CertificatePinner: NSObject, URLSessionDelegate {
    
    func urlSession(_ session: URLSession,
                    didReceive challenge: URLAuthenticationChallenge,
                    completionHandler: @escaping (URLSession.AuthChallengeDisposition, URLCredential?) -> Void) {
        
        // Get server trust
        guard let serverTrust = challenge.protectionSpace.serverTrust,
              let certificate = SecTrustGetCertificateAtIndex(serverTrust, 0) else {
            completionHandler(.cancelAuthenticationChallenge, nil)
            return
        }
        
        // Get server certificate data
        let serverCertificateData = SecCertificateCopyData(certificate) as Data
        
        // Load pinned certificate from app bundle
        guard let pinnedCertPath = Bundle.main.path(forResource: "certificate", ofType: "cer"),
              let pinnedCertData = try? Data(contentsOf: URL(fileURLWithPath: pinnedCertPath)) else {
            completionHandler(.cancelAuthenticationChallenge, nil)
            return
        }
        
        // Compare certificates
        if serverCertificateData == pinnedCertData {
            let credential = URLCredential(trust: serverTrust)
            completionHandler(.useCredential, credential)
        } else {
            completionHandler(.cancelAuthenticationChallenge, nil)
        }
    }
}

// Usage
let session = URLSession(configuration: .default, delegate: CertificatePinner(), delegateQueue: nil)

func validatePublicKey(_ serverTrust: SecTrust) -> Bool {
    let policy = SecPolicyCreateBasicX509()
    SecTrustSetPolicies(serverTrust, policy)
    
    var result: SecTrustResultType = .invalid
    SecTrustEvaluate(serverTrust, &result)
    
    guard result == .unspecified || result == .proceed else {
        return false
    }
    
    guard let serverCertificate = SecTrustGetCertificateAtIndex(serverTrust, 0),
          let serverPublicKey = SecCertificateCopyKey(serverCertificate) else {
        return false
    }
    
    // Compare with pinned public key
    guard let pinnedPublicKey = loadPinnedPublicKey() else {
        return false
    }
    
    return serverPublicKey == pinnedPublicKey
}

func loadPinnedPublicKey() -> SecKey? {
    // Load pinned public key from bundle
    // Implementation depends on your certificate format
    return nil
}

import Foundation

// Save file with encryption
func saveSecureFile(data: Data, to url: URL) throws {
    try data.write(to: url, options: .completeFileProtection)
}

// Set protection on existing file
func setFileProtection(for url: URL) throws {
    try FileManager.default.setAttributes(
        [.protectionKey: FileProtectionType.complete],
        ofItemAtPath: url.path
    )
}

// Example
let sensitiveData = "Sensitive information".data(using: .utf8)!
let documentPath = FileManager.default.urls(for: .documentDirectory, in: .userDomainMask)[0]
let fileURL = documentPath.appendingPathComponent("secure_data.txt")

try? saveSecureFile(data: sensitiveData, to: fileURL)

class SecureNetworkManager {
    
    func configureSecureSession() -> URLSession {
        let configuration = URLSessionConfiguration.default
        
        // Disable caching for sensitive data
        configuration.urlCache = nil
        configuration.requestCachePolicy = .reloadIgnoringLocalCacheData
        
        // Enforce minimum TLS version
        configuration.tlsMinimumSupportedProtocolVersion = .TLSv12
        
        return URLSession(configuration: configuration, delegate: self, delegateQueue: nil)
    }
}

import LocalAuthentication

func authenticateUser(completion: @escaping (Bool) -> Void) {
    let context = LAContext()
    var error: NSError?
    
    // Check if biometric authentication is available
    if context.canEvaluatePolicy(.deviceOwnerAuthenticationWithBiometrics, error: &error) {
        let reason = "Authenticate to access your account"
        
        context.evaluatePolicy(.deviceOwnerAuthenticationWithBiometrics, localizedReason: reason) { success, error in
            DispatchQueue.main.async {
                completion(success)
            }
        }
    } else {
        completion(false)
    }
}

// Usage
authenticateUser { success in
    if success {
        print("Authentication successful")
    } else {
        print("Authentication failed")
    }
}

import UIKit

class SecureViewController: UIViewController {
    
    override func viewDidLoad() {
        super.viewDidLoad()
        preventScreenshots()
    }
    
    func preventScreenshots() {
        // Detect screenshot
        NotificationCenter.default.addObserver(
            forName: UIApplication.userDidTakeScreenshotNotification,
            object: nil,
            queue: .main
        ) { [weak self] _ in
            self?.handleUnauthorizedScreenshot()
        }
    }
    
    func handleUnauthorizedScreenshot() {
        // Log security event
        print("Unauthorized screenshot detected")
        
        // Take action: logout user, show warning, etc.
        showSecurityAlert()
    }
    
    func showSecurityAlert() {
        let alert = UIAlertController(
            title: "Security Warning",
            message: "Screenshots are not allowed for security reasons",
            preferredStyle: .alert
        )
        alert.addAction(UIAlertAction(title: "OK", style: .default))
        present(alert, animated: true)
    }
}

// Safe logging function
func log(_ message: String) {
    #if DEBUG
    print(message)
    #endif
}

// Sanitize sensitive data before logging
func logSanitized(_ message: String) {
    // Remove passwords
    let sanitized = message.replacingOccurrences(
        of: "password=\\w+",
        with: "password=***",
        options: .regularExpression
    )
    
    // Remove tokens
    let final = sanitized.replacingOccurrences(
        of: "token=\\w+",
        with: "token=***",
        options: .regularExpression
    )
    
    log(final)
}

// Example
logSanitized("Login: email=user@example.com password=secret123 token=abc123")
// Output in debug: "Login: email=user@example.com password=*** token=***"

// BAD: Hardcoded API key
let apiKey = "sk_live_1234567890abcdef"

// GOOD: Load from secure storage
struct APIConfig {
    static var apiKey: String {
        return loadFromKeychain(key: "apiKey") ?? ""
    }
    
    private static func loadFromKeychain(key: String) -> String? {
        guard let data = KeychainHelper.load(key: key),
              let value = String(data: data, encoding: .utf8) else {
            return nil
        }
        return value
    }
}

// Keychain helper
class KeychainHelper {
    static func load(key: String) -> Data? {
        let query: [String: Any] = [
            kSecClass as String: kSecClassGenericPassword,
            kSecAttrAccount as String: key,
            kSecReturnData as String: true
        ]
        
        var result: AnyObject?
        let status = SecItemCopyMatching(query as CFDictionary, &result)
        
        return status == errSecSuccess ? result as? Data : nil
    }
}

class SecureAPIClient {
    private let session: URLSession
    
    init() {
        let config = URLSessionConfiguration.default
        config.tlsMinimumSupportedProtocolVersion = .TLSv12
        config.timeoutIntervalForRequest = 30
        
        session = URLSession(configuration: config)
    }
    
    func request(url: URL, headers: [String: String], completion: @escaping (Result<Data, Error>) -> Void) {
        var request = URLRequest(url: url)
        
        // Add security headers
        headers.forEach { request.setValue($1, forHTTPHeaderField: $0) }
        request.setValue("application/json", forHTTPHeaderField: "Content-Type")
        request.setValue("Bearer \(APIConfig.apiKey)", forHTTPHeaderField: "Authorization")
        
        session.dataTask(with: request) { data, response, error in
            if let error = error {
                completion(.failure(error))
                return
            }
            
            guard let data = data else {
                completion(.failure(NSError(domain: "No data", code: -1)))
                return
            }
            
            completion(.success(data))
        }.resume()
    }
}

// Use private access control
class SecurityManager {
    private static let instance = SecurityManager()
    
    private init() { }
    
    static func shared() -> SecurityManager {
        return instance
    }
    
    private func sensitiveOperation() {
        // Hidden implementation
    }
}

// Avoid string literals for sensitive values
enum SecurityKeys {
    private static let key1 = "k"
    private static let key2 = "e"
    private static let key3 = "y"
    
    static var apiKey: String {
        return key1 + key2 + key3
    }
}

func isJailbroken() -> Bool {
    // Check for common jailbreak files
    let jailbreakPaths = [
        "/Applications/Cydia.app",
        "/Library/MobileSubstrate/MobileSubstrate.dylib",
        "/bin/bash",
        "/usr/sbin/sshd",
        "/etc/apt",
        "/private/var/lib/apt/"
    ]
    
    for path in jailbreakPaths {
        if FileManager.default.fileExists(atPath: path) {
            return true
        }
    }
    
    // Check if can write outside sandbox
    let testPath = "/private/jailbreak.txt"
    do {
        try "test".write(toFile: testPath, atomically: true, encoding: .utf8)
        try FileManager.default.removeItem(atPath: testPath)
        return true
    } catch {
        return false
    }
}

// Prevent app usage on jailbroken devices
if isJailbroken() {
    showJailbreakAlert()
    exit(0)
}

import DeviceCheck

class AppAttestService {
    func generateKey(completion: @escaping (Result<String, Error>) -> Void) {
        DCAppAttestService.shared.generateKey { keyId, error in
            if let error = error {
                completion(.failure(error))
                return
            }
            
            guard let keyId = keyId else {
                completion(.failure(AppAttestError.noKeyId))
                return
            }
            
            // Save keyId for later use
            UserDefaults.standard.set(keyId, forKey: "appAttestKeyId")
            completion(.success(keyId))
        }
    }
    
    func attestKey(keyId: String, challenge: Data, completion: @escaping (Result<Data, Error>) -> Void) {
        DCAppAttestService.shared.attestKey(keyId, clientDataHash: challenge) { attestation, error in
            if let error = error {
                completion(.failure(error))
                return
            }
            
            guard let attestation = attestation else {
                completion(.failure(AppAttestError.noAttestation))
                return
            }
            
            // Send attestation to your server for validation
            completion(.success(attestation))
        }
    }
}

enum AppAttestError: Error {
    case noKeyId
    case noAttestation
}