Light.swift

struct Light:Codable, Equatable, Identifiable {
    enum Change {
        case renaming(_RenameIt); enum _RenameIt { case it     (to:String)    }
        case turning (_TurnIt  ); enum _TurnIt   { case it     (Turn)         }
        case adding  (_Add     ); enum _Add      { case mode   (Light.Mode)   }
        case toggling(_Toggle  ); enum _Toggle   { case display(to:Interface) }
        case setting (_Set     ); enum _Set      {
            case hue        (to:Double     )
            case saturation (to:Double     )
            case brightness (to:Double     )
            case temperature(to:Temperature)
        }
    }
    init(id:String, name:String) { self.init(id, name, .off, 0, 0, 0, 0, .slider, [], .unset) }

    enum Mode:Codable { case unset, hsb, ct }
    enum Temperature { case mirek(Int) }

    let id        : String
    let name      : String
    let isOn      : Turn

    let hue       : Double
    let saturation: Double
    let brightness: Double
    let ct        : Int

    let modes       : [Mode]
    let selectedMode: Mode
    let display     : Interface

    func alter(_ changes:Change...) -> Self { changes.reduce(self) { $0.alter($1) } }

    init(_ id:String,_ name:String,_ isOn:Turn,_ brightness:Double,_ saturation:Double,_ hue:Double,_ ct:Int,_ display:Interface,_ modes:[Mode],_ selectedMode:Mode) {
        self.id           = id
        self.name         = name
        self.isOn         = isOn
        self.hue          = hue
        self.saturation   = saturation
        self.brightness   = brightness
        self.ct           = checkCT(ct)
        self.modes        = modes
        self.selectedMode = selectedMode
        self.display      = display
    }
    private func alter(_ change:Change) -> Self {
        func __(_ x: Double) -> Double { min(max(x, 0.0), 1.0) }
        switch change {
        case let .renaming(         .it(to:name      )): return .init(id, name, isOn,   brightness,   saturation,   hue, ct,    display, modes,          selectedMode)
        case     .turning (         .it(.on          )): return .init(id, name, .on,    brightness,   saturation,   hue, ct,    display, modes,          selectedMode)
        case     .turning (         .it(.off         )): return .init(id, name, .off,   brightness,   saturation,   hue, ct,    display, modes,          selectedMode)
        case let .setting ( .brightness(to:brightness)): return .init(id, name, isOn,__(brightness),  saturation,   hue, ct,    display, modes,          selectedMode)
        case let .setting ( .saturation(to:saturation)): return .init(id, name, isOn,   brightness,__(saturation),  hue, ct,    display, modes,          .hsb        )
        case let .setting (        .hue(to:hue       )): return .init(id, name, isOn,   brightness,   saturation,__(hue),ct,    display, modes,          .hsb        )
        case let .setting (.temperature(to:.mirek(ct))): return .init(id, name, isOn,   brightness,   saturation,   hue, ct,    display, modes,          .ct         )
        case     .toggling(    .display(to:.slider   )): return .init(id, name, isOn,   brightness,   saturation,   hue, ct,    .slider, modes,          selectedMode)
        case     .toggling(    .display(to:.scrubbing)): return .init(id, name, isOn,   brightness,   saturation,   hue, ct, .scrubbing, modes,          selectedMode)
        case let .adding  (       .mode(mode         )): return .init(id, name, isOn,   brightness,   saturation,   hue, ct,    display, modes + [mode], selectedMode)
        }
    }
}