StateMachine.swift

//
//  StateMachine.swift
//
//  Created by Ryoga Kitagawa on 5/6/16.
//

protocol StateMachineEvent {}
protocol StateMachineState {}

class StateMachine<S: StateMachineState, E: StateMachineEvent> {
    var routes: (event: E, from: S) -> S?
    var handler: ((event: E, from: S, to: S) -> ())?
    private(set) var state: S

    init(state: S, initClosure: ((StateMachine) -> ())? = nil) {
        self.state = state
        self.routes = { _ in state }
        initClosure?(self)
    }

    func fireEvent(event: E) {
        guard let nextState = self.routes(event: event, from: self.state) else {
            fatalError()
        }

        self.handler?(event: event, from: self.state, to: nextState)
        self.state = nextState
    }
}