SwiftStateManagement

//: Playground - noun: a place where people can play

import UIKit

enum State {
    case initial
    case launched
    case launchingWithLocation
    case launchingWithoutLocation
    case running
    case backgrounded
    case fromBackground
    case fromBackgroundWithLocation
    case fromBackgroundWithoutLocation
}

class ViewController: UIViewController {
    
    private var state = State.initial {
        didSet {
            
            switch state {
                
            case .launched:
                // Do launch specific stuff, like attempt to get user's location
                break
                
            case .launchingWithLocation:
                // Yeah! We have location, do stuff like make API calls
                
                // We can also act depending on how we got to this state
                switch oldValue {
                    
                case .launched:
                    // Do launch with location specific stuff
                    break
                    
                case .fromBackground:
                    // Do from background with location specific stuff
                    break
                    
                default:
                    break
                }
                
            case .launchingWithoutLocation:
                // Sad, no location, but do some stuff anyway
                break
                
            case .running:
                // Woohoo, we are fully set up and running so do cool stuff here
                break
                
            case .backgrounded:
                // We are background, so do stuff like stop location updates
                break
                
            case .fromBackground:
                // We are coming from the background, so do stuff like re-start location updates
                break
                
            case .fromBackgroundWithLocation:
                // Yeah! We are back AND have location, do stuff like make API calls
                break
                
            default:
                break
            }
        }
    }
    
    override func viewDidLoad() {
        changeState()
    }
}

typealias StateManager = ViewController
extension StateManager {
    
    private func changeState(hasLocation: Bool = true, isBackgrounding: Bool = false) {
        let compositeState = (state, hasLocation, isBackgrounding)
        
        switch  compositeState {
  
        case (.launched, true, false):
            state = .launchingWithLocation
        case (.launched, false, false):
            state = .launchingWithoutLocation
        case (.launched, _, true):
            state = .fromBackground
            
        case (.launchingWithLocation, _, false):
            state = .running
            
        case (.running, _, true):
            state = .backgrounded
            
        case (.backgrounded, _, _):
            state = .fromBackground
            
        case (.fromBackground, true, _):
            state = .fromBackgroundWithLocation
        case (.fromBackground, false, _):
            state = .fromBackgroundWithoutLocation
        case (.fromBackgroundWithLocation, true, _):
            state = .running
            
        default:
            break
        }
    }
}