MovieCollection.swift

import Foundation
import Combine

final class MovieCollection: ObservableObject {
    @Published var movieResponse: MovieResponse? = nil

    ...
    
    func fetchMovies() -> [Movie] {
        let response: MovieResponse? = fetchPreviewData(previewFile: "movies.json", fetcher: fetchResponse)
        return response?.results ?? []
    }

    private func fetchResponse() -> MovieResponse? {
        if movieResponse != nil {
            return movieResponse
        }
        moviesFetchable?.fetchMovies()
            .replaceError(with: MovieResponse.empty())
            .sink(receiveValue: { [weak self] movieResponse in
                self?.movieResponse = movieResponse
            })
            .store(in: &disposables)
        return movieResponse
    }
}