StateActionDemo.swift

final class DepotViewModel: BaseViewModel<DepotViewModel.State, DepotViewModel.Action> {
    struct State: Equatable, Copyable {
        var showSearch = false
    }

    enum Action {
        case .openSearch(let show):
            showSearch(show: show)
        }
    }

    func showSearch(show: Bool) {
        updateState(changing: \.showSearch, to: show)
    }

    // updateState and perform methods are still public unfortunately. A developer can access them directly without another proxy method, which could increase the complexity for readability.
}





struct DepotOverviewView: View {
    @ObservedObject var viewModel: DepotViewModel

    var body: View {
        SomeView
        .sheet(isPresented: createShowSearchBinding(viewModel.state)) {
                    SBNavigationView(path: .constant(Routing.financeRouter.path))  {
                        SearchView(viewModel: viewModel.searchViewModel){
                                viewModel.showSearch(show: false)
                            }
                    }
                }
    }


  // This is the biggest downside of using the <State, Action> type.
  // @Bindings are essential part of a SwiftUI based implementation and creating them with a custom getter-setter compared to using just '$viewmodel.published' notation is error prone and cumbersome.
  // We need to maintain custom getter and setter implementations each time.

    private func createShowSearchBinding(_ state: DepotViewModel.State) -> Binding<Bool> {
        Binding(
            get: { state.showSearch },
            set: { value in viewModel.perform(.openSearch(value)) }
        )
    }
}

















public protocol ViewModeling: ObservableObject {
    associatedtype State: Equatable
    associatedtype Action
    
    var uiState: State { get }
    func perform(_ action: Action)
}

open class BaseViewModel<State: Equatable, Action>: ViewModeling {
    public typealias State = State
    public typealias Action = Action

    public var uiState: State { internalState }

    public var state: State {
        didSet { internalState = state }
    }

    @Published var internalState: State

    public init(state: State) {
        self.internalState = state
        self.state = state
    }

    open func perform(_ action: Action) {
        assertionFailure("This function must be overriden by the subclass")
    }
}

extension BaseViewModel where State: Copyable {
    public func updateState<T>(changing path: WritableKeyPath<State, T>, to value: T) {
        state = state.copy(changing: path, to: value)
    }
}