Mercari Atte and Automaton

Talk in Souzoh iOS 2017, English version.

Demo: https://github.com/orakaro/MonadicMealyMachine

Transcript

1. Mercari Atte and Automaton Vu Nhat Minh / @orakaro Souzoh iOS Talk
2. Mercari Atte Scala / Swift Engineer / @orakaro
3. Mercari Atte iOS development • Full RxSwift • Aggressive use of Driver • Define input/output type for ViewModel • Composition over Inheritance • Automaton
4. State Machine variations • Finite state machine • Transition function (s, a) -> s • Mealy Machine • Transition function (s, a) -> s • Output function (s, a) -> b • Moore Machine • Transition function (s, a) -> s • Output function s -> b
5. Finite State Machine • Finite state machine • Transition function (s, a) -> s • Mealy Machine • Transition function (s, a) -> s • Output function (s, a) -> b • Moore Machine • Transition function (s, a) -> s • Output function s -> b design pattern for state machines
6. Binary Gap A binary gap within a positive integer N is any maximal sequence of consecutive zeros that is surrounded by ones at both ends in the binary representation of N. Ex: 9 = 1001 → 2
7. A binary gap within a positive integer N is any maximal sequence of consecutive zeros that is surrounded by ones at both ends in the binary representation of N. Ex: 9 = 1001 → 2 Started Zero One Binary Gap
8. Visual Format Language class func constraints(withVisualFormat format: String, options opts: NSLayoutFormatOptions = [], metrics: [String : Any]?, views: [String : Any]) -> [NSLayoutConstraint] "H:|-15-[iconImageView(30)]-[appNameLabel]-[skipButton]-15-|"
9. Visual Format Language class func constraints(withVisualFormat format: String, options opts: NSLayoutFormatOptions = [], metrics: [String : Any]?, views: [String : Any]) -> [NSLayoutConstraint] "H:|-15-[iconImageView(30)]-[appNameLabel]-[skipButton]-15-|" Direction Start Line Number Label [ ] ( ) End
10. For a “healthy” codebase Try to avoid large if-else block Try to avoid global variables Try to write pure functions
11. Signup Flow ʁ ʁ ʁ ʁ ʁ
12. Signup Flow Signup by email Facebook login One click signup by second party app Reset Password Login by Email
13. Signup Flow
14. Signup condition
15. Facebook Login
16. Login by email
17. Signup Flow Graph Root Register Root Profile Register Start With Mercari AtteLogin Facebook Email Login Register With Mercari Confirm SMS Home PassCode Email SignUp Reset Password
18. Root Register Root Profile Register Start With Mercari AtteLogin Facebook Email Login Register With Mercari Confirm SMS Home PassCode Email SignUp Reset Password
19. Transitions is Domain knowledge and should be placed at Model layer MVC / MVP / MVVM
20. Each screen represents State
21. Transition by event Root Register Root Atte Login Start With Mercari Atte Resource Mercari Resource
22. RegistrationStateViewController protocol RegistrationStateViewController { var state: RegistrationState { get } func nextViewController(event: RegistrationEvent) -> UIViewController? } extension RegistrationStateViewController { func nextViewController(event: RegistrationEvent) -> UIViewController? { let machine = AutomatonManager.registrationMachine guard let state = machine.transition(from: state, by: event) else { return nil } switch state { //... } } Automaton
23. Define Transition struct Transition<S, E> { let from: S let to: S let by: E } from to by State State Event
24. Implement State Machine class Automaton<S: Hashable, E: Hashable> { var routes: [S: [E: S]] = [:] init(initialState: S, transitions: [Transition<S, E>]) { for t in transitions { addRoute(t) } } private func addRoute(_ t: Transition<S, E>) { var dict = routes[t.from] ?? [:] dict[t.by] = t.to routes[t.from] = dict } func transition(from: S, by: E) -> S? { guard let next = routes[from].flatMap({ $0[by] }) else { return nil } return next } }
25. Implement State Machine class Automaton<S: Hashable, E: Hashable> { var routes: [S: [E: S]] = [:] init(initialState: S, transitions: [Transition<S, E>]) { for t in transitions { addRoute(t) } } private func addRoute(_ t: Transition<S, E>) { var dict = routes[t.from] ?? [:] dict[t.by] = t.to routes[t.from] = dict } func transition(from: S, by: E) -> S? { guard let next = routes[from].flatMap({ $0[by] }) else { return nil } return next } } use dictionary for storing transitions
26. Define State and Event enum RegistrationState { case root case registerRoot case profileRegister case startWithMercari case emailLogin case atteLogin case home } enum RegistrationEvent: Hashable { case showRegisterRoot(loginMode: RootViewController.LoginMode?) case registerWithFacebook(profile: FacebookProfile?) case startWithMercari(resource: MercariIdResource?, tokenPair: TokenPair?, showsCloseButton: Bool) case loginWithEmail(showsCancelButton: Bool) case loginWithAtte(resource: MercariIdResource?, tokenPair: TokenPair?) case loginAndShowHome(tokenPair: TokenPair?, userId: Int64, hasMercariItem: Bool) }
27. Define transition graph let registrationGraph: [Transition<RegistrationState, RegistrationEvent>] = [ Transition(from: .root, to: .registerRoot, by: DefaultEvent.showRegisterRoot), Transition(from: .registerRoot, to: .profileRegister, by: DefaultEvent.registerWithFacebook), Transition(from: .registerRoot, to: .startWithMercari, by: DefaultEvent.startWithMercari), Transition(from: .registerRoot, to: .emailLogin, by: DefaultEvent.loginWithEmail), Transition(from: .registerRoot, to: .atteLogin, by: DefaultEvent.loginWithAtte), Transition(from: .registerRoot, to: .home, by: DefaultEvent.loginAndShowHome), ] let registrationMachine = Automaton<RegistrationState, RegistrationEvent>( initialState: .root, transitions: registrationGraph )
28. Test for transition logic only describe("ΞϓϦىಈ࣌τʔΫϯ͕ଘࡏ͠ͳ͍") { it("ϝʔϧͰ৽نొ࿥͕Ͱ͖Δ") { self.tryRoute(events: [ DefaultEvent.showRegisterRoot, DefaultEvent.registerWithEmail, DefaultEvent.showProfileRegister, DefaultEvent.confirmSMS, DefaultEvent.loginAndShowHome ]) XCTAssert(self.currentState == .home) } } //... private func tryRoute(events: [RegistrationEvent]) { for event in events { self.currentState.map { state in self.currentState = self.machine.transition(from: state, by: event) } } }
30. still have problems
31. RegistrationStateViewController protocol RegistrationStateViewController { var state: RegistrationState { get } func nextViewController(event: RegistrationEvent) -> UIViewController? } extension RegistrationStateViewController { func nextViewController(event: RegistrationEvent) -> UIViewController? { let machine = AutomatonManager.registrationMachine guard let state = machine.transition(from: state, by: event) else { return nil } switch state { //... } } Should I create ViewController here?
32. RegistrationStateViewController switch state { case .root: return RootViewController.make(withDependency: ()) case .registerRoot: return RegisterRootViewController.make(withDependency: ()) case .profileRegister : switch event { case .registerWithFacebook(.some(let profile)): return ProfileRegisterViewController.make(withDependency: .init(facebookProfile: profile)) default: return nil } case .startWithMercari: switch event { case .startWithMercari(.some(let resource), .some(let token)): return StartWithMercariViewController.make(withDependency: .init(resource: resource, token: token)) default: return nil } case .emailLogin: return EmailLoginViewController.make(withDependency: ()) case .atteLogin: switch event { case .loginWithAtte(.some(let resource), .some(let token)): return AtteLoginViewController.make(withDependency: .init(resource: resource, token: token)) default: return nil } case .home: switch event { case .loginAndShowHome(.some(let token), let userId): return HomeViewController.make(withDependency: .init(token: token, userId: userId)) default: return nil } default: return nil } Not so much different from large if-else block
33. Define transition graph let registrationGraph: [Transition<RegistrationState, RegistrationEvent>] = [ Transition(from: .root, to: .registerRoot, by: DefaultEvent.showRegisterRoot), Transition(from: .registerRoot, to: .profileRegister, by: DefaultEvent.registerWithFacebook), Transition(from: .registerRoot, to: .startWithMercari, by: DefaultEvent.startWithMercari), Transition(from: .registerRoot, to: .emailLogin, by: DefaultEvent.loginWithEmail), Transition(from: .registerRoot, to: .atteLogin, by: DefaultEvent.loginWithAtte), Transition(from: .registerRoot, to: .home, by: DefaultEvent.loginAndShowHome), ] let registrationMachine = Automaton<RegistrationState, RegistrationEvent>( initialState: .root, transitions: registrationGraph ) DefaultEvent !?
34. What is DefaultEvent? • In Swift 3 we still can not use default value for associated value in enum • Proposal: SE-0155 Accepted status but not included in Swift 4 struct DefaultEvent { static let showRegisterRoot: RegistrationEvent = .showRegisterRoot() static let registerWithFacebook: RegistrationEvent = .registerWithFacebook(profile: nil) static let startWithMercari: RegistrationEvent = .startWithMercari(resource: nil, token: nil) static let loginWithEmail: RegistrationEvent = .loginWithEmail() static let loginWithAtte: RegistrationEvent = .loginWithAtte(resource: nil, token: nil) static let loginAndShowHome: RegistrationEvent = .loginAndShowHome(token: nil, userId: 0) }
35. Optional type associated value enum RegistrationEvent: Hashable { case showRegisterRoot(loginMode: RootViewController.LoginMode?) case registerWithFacebook(profile: FacebookProfile?) case startWithMercari(resource: MercariIdResource?, tokenPair: TokenPair?, showsCloseButton: Bool) case loginWithEmail(showsCancelButton: Bool) case loginWithAtte(resource: MercariIdResource?, tokenPair: TokenPair?) case loginAndShowHome(tokenPair: TokenPair?, userId: Int64, hasMercariItem: Bool) } Optional
36. Automaton + FP
37. Transition function (aka Reducer) • Finite State Machine • Transition function (s, a) -> s • Mealy Machine • Transition function (s, a) -> s • Output function (s, a) -> b • Moore Machine • Transition function (s, a) -> s • Output function s -> b
38. Transition (s, a) -> s Output (s, a) -> b Mealy Machine / Moore Machine Reducer (s, a) -> (s, b) Transition (s, a) -> s Output s -> b Reducer s -> (a -> s, b)
39. Mealy Machine vs Elm Elm Architecture fun update(state: State, action: Action): Pair<State, Command> Transition (s, a) -> s Output (s, a) -> b Reducer (s, a) -> (s, b)
40. Mealy Machine Reducer a -> s -> (s, b) Transition (s, a) -> s Output (s, a) -> b Reducer (s, a) -> (s, b)
41. Mealy Machine Reducer a -> s -> (s, b) Transition (s, a) -> s Output (s, a) -> b Reducer (s, a) -> (s, b) Stateful Computation !!
42. Stateful Computation A stateful computation is a function that takes some state and returns a value along with some new state: s -> (s, a) class State<S, A> { private let run: (S) -> (S, A) init(f: @escaping (S) -> (S, A)) { self.run = f } func run(s: S) -> (S, A) { return self.run(s) } }
43. State Monad extension State { func map<B>(g: @escaping (A) -> B) -> State<S, B> { return State<S, B> { s in let (s1, val) = self.run(s: s) return (s1, g(val)) } } func flatMap<B>(g: @escaping (A) -> State<S, B>) -> State<S, B> { return State<S, B> { s in let (s1, val) = self.run(s: s) return g(val).run(s: s1) } } } A stateful computation is a function that takes some state and returns a value along with some new state: s -> (s, a)
44. Monad = flatmappable type Image credit: Functors, Applicatives, And Monads In Pictures
45. Swift Monads Maybe Monad Either Monad Reader Monad Observable Monad State Monad I/O Monad … Swift Optional antitypical/Result Statically typed Dependency Injection Signal / Observable Mealy Machine
46. Mealy Machine Reducer a -> s -> (s, b) Transition (s, a) -> s Output (s, a) -> b Reducer (s, a) -> (s, b) Reducer a -> State[s, b] State Monad
47. MonadicAutomaton class MonadicAutomaton<S, A, B> { typealias T = (A) -> State<S, B> private var f : T init(f: @escaping T) { self.f = f } func transition(from: S, by: A) -> (S, B) { return f(by).run(s: from) } } Reducer A -> State[S, B] A:InputɺB: Output A = Event enumɺB = UIViewController
48. Define States and Events enum RState { case any case root case registerRoot case profileRegister case startWithMercari case emailLogin case atteLogin case home } enum REvent { case showRegisterRoot case registerWithFacebook(profile: FacebookProfile) case startWithMercari(resource: MercariIdResource, token: String) case loginWithEmail case loginWithAtte(resource: MercariIdResource, token: String) case loginAndShowHome(token: String, userId: Int64) } custom type
49. Define transition graph let transitionFunc: (REvent) -> State<RState, UIViewController> = { event in switch event { case .registerWithFacebook(let profile): let vc = ProfileRegisterViewController.make(withDependency: .init(facebookProfile: profile)) return State<RState, UIViewController> { s in let s1: RState = s == .registerRoot ? .profileRegister : .any return (s1, vc) //... } } let registrationMachine = MonadicAutomaton<RState, REvent, UIViewController>(f : transitionFunc) A S B A S B
50. Automaton + FRP
51. Automaton + FRP • State Machine for UI inside one screen • Use stream to represent events • ReactiveSwift • inamiy/ReactiveAutomaton • RxSwift • kzaher/RxFeedback
52. Recap • State Machine • Finite State Machine • Mealy Machine • Moore Machine • Design pattern for state management • Can use FSM for simple transitions • Mealy Machine = State Monad
53. https://github.com/orakaro/MonadicMealyMachine Twitter / Github: @orakaro Q&A