Biometrics

//
//  Biometrics.swift
//  Local Auth Demo
//
//  Created by Rayhan Nabi on 1/12/19.
//  Copyright © 2019 Rayhan Janam. All rights reserved.
//

import UIKit
import LocalAuthentication

enum BiometryType {
  case faceID
  case touchID
  case none
}

protocol BiometricAuthentication {
  func didAuthenticate()
  func didFailAuthentication(error: Error)
}

final class Biometrics {

  static func getInstance(usePasscode: Bool) -> GenericBiometrics {
    if #available(iOS 11.0, *) {
      return RegularBiometrics(usePasscode)
    } else {
      return FallbackBiometrics(usePasscode)
    }
  }

}

class GenericBiometrics {

  private var policy: LAPolicy

  let context: LAContext

  var isSensorAvailable: Bool {
    return context.canEvaluatePolicy(policy,
                                     error: nil)
  }

  var biometryType: BiometryType {
    return .none
  }

  var delegate: BiometricAuthentication?

  init(_ usePasscode: Bool) {
    context = LAContext()
    policy = usePasscode ? .deviceOwnerAuthentication : .deviceOwnerAuthenticationWithBiometrics
  }

  func authenticate(reason: String) {
    context.evaluatePolicy(policy, localizedReason: reason) { (result, error) in
      DispatchQueue.main.async {
        self.handleAuthState(result: result, error: error)
        self.context.invalidate()
      }
    }
  }

  private func handleAuthState(result: Bool, error: Error?) {
    if result {
      delegate?.didAuthenticate()
    } else {
      guard let error = error else { return }
      delegate?.didFailAuthentication(error: error)
    }
  }

}

@available(iOS 11.0, *)
final class RegularBiometrics: GenericBiometrics {

  override var biometryType: BiometryType {
    if isSensorAvailable {
      switch context.biometryType {
      case .faceID:
        return .faceID
      case .touchID:
        return .touchID
      case .none:
        return .none
      }
    }

    return .none
  }

}

final class FallbackBiometrics: GenericBiometrics {

  override var biometryType: BiometryType {
    if isSensorAvailable {
      return .touchID
    }

    return .none
  }

}