appstate.swift

public func change(_ state: AppState, _ change: [ AppState.Change ] ) -> AppState { state.alter(change) }

public struct AppState: Codable {
    public enum Change: Equatable {
        case by(_By); public enum _By: Equatable {
            case adding(_Add); public enum _Add: Equatable {
                case light(Light) }
            case replacing(_Replace); public enum _Replace: Equatable {
                case lights(with:[Light])
                case light (with:Light  )
                case rooms (with:[Room] )
            }
        }
    }
    public func alter(_ changes: [ Change ] ) -> AppState { changes.reduce(self) { $0.alter($1) } }
    
    private func alter (_ change:Change) -> Self {
        func sort  (_                    lights:[Light]) -> [Light] { lights.sorted(on:\.id, by:<)     }
        func remove(_ light: Light, from lights:[Light]) -> [Light] { lights.filter{$0.id != light.id} }
        switch change {
        case let .by(.adding   (.light (light ))): return .init(sort(lights                     + [light]), rooms)
        case let .by(.replacing(.lights(lights))): return .init(     lights                               , rooms)
        case let .by(.replacing(.light (light ))): return .init(sort(remove(light, from:lights) + [light]), rooms)
        case let .by(.replacing(.rooms (rooms ))): return .init(     lights                               , rooms)
        }
    }
    public init() {
        self.lights = []
        self.rooms = []
    }
    
    init(_ lights: [Light],_ rooms: [Room]) {
        self.lights = lights
        self.rooms = rooms
    }
    public let lights: [Light]
    public let rooms : [Room ]
}