ViewModel.swift

import Republished
import SwiftUI

@MainActor
final class ViewModel: ObservableObject {

  // MARK: Lifecycle

  init(model: DomainModel) {
    _model = .init(wrappedValue: model)
  }

  // MARK: Internal

  var info: String {
    [
      model.isEven ? "even" : nil,
      model.isZero ? "zero" : nil,
      model.isNegative ? "negative" : nil,
      model.isPositive ? "positive" : nil,
      model.isMax ? "MAXINT" : nil,
      model.isMin ? "MININT" : nil,
      model.isPrime ? "prime" : nil,
    ]
    .compactMap { $0 }
    .sorted()
    .joined(separator: ", ")
  }

  var countString: String {
    "\(model.count)"
  }

  func increment() {
    model.set(count: model.count + 1)
  }

  func decrement() {
    model.set(count: model.count - 1)
  }

  func rand() {
    model.set(count: Int.random(in: Int.min ... Int.max))
  }

  func zero() {
    model.set(count: 0)
  }

  // MARK: Private

  // Here the @Republished property wrapper is used *instead* of
  // an @Published property wrapper and hold the nested ObservableObject.
  // (Note that there are no @Published wrappers in this file.)

  // @Republished listens to the inner ObservableObject's
  // change notifications and propagates them to the outer one.

  // SwiftUI views can use properties here derived from the inner object
  // just as they would use an @Published field.
  //
  // This outer object could also provide @Binding surfaces into
  // the inner object's data.

  @Republished private var model: DomainModel

}