RelayReducer.swift

/*
Usage:

Store(
  initialState: .init(),
  reducer: UserRecipesListReducer().relay { [unowned self] featureAction in
    // Handle action here
  }
)
*/

extension Reducer {
  @inlinable
  public func relay(_ callback: @escaping (Action) -> Void) -> _RelayReducer<Self> {
    _RelayReducer<Self>(base: self, callback: callback)
  }
}

public struct _RelayReducer<Base: Reducer>: Reducer {
  @usableFromInline
  let base: Base

  @usableFromInline
  let callback: (Base.Action) -> Void

  @usableFromInline
  init(base: Base, callback: @escaping (Base.Action) -> Void) {
    self.base = base
    self.callback = callback
  }

  @inlinable
  public func reduce(into state: inout Base.State, action: Base.Action) -> Effect<Base.Action> {
    callback(action)
    return self.base.reduce(into: &state, action: action)
  }
}