Return a paged list of results from a repository

GetListUseCase.swift

import RxSwift

struct List {
    struct Item {
        let name: String
    }
    let items: [Item]
}

protocol GetListRepository {
    func get(uniqueId: String, startingAt offset: Int, limit: Int) -> Single<List>
}

struct GetListUseCase {
    enum Result {
        case success(List)
        case failure(Error, Int)
    }
    
    private let repository: GetListRepository
    private let pageSize = 24
    private let uniqueId: String
    
    init(uniqueId: String, repository: GetListRepository) {
        self.uniqueId = uniqueId
        self.repository = repository
    }
    
    func getList(with nextPageTrigger: Observable<Void>) -> Observable<Result> {
        return nextPageTrigger
            .scan(0) { $0.0 + self.pageSize }
            .startWith(0)
            .flatMap(getPageStartingAt)
    }
    
    private func pageIndex(at offset: Int) -> Int {
        return offset / pageSize
    }
    
    private func getPageStartingAt(_ offset: Int) -> Observable<Result> {
        let currentPageIndex = pageIndex(at: offset)
        return repository.get(uniqueId: uniqueId, startingAt: offset, limit: pageSize)
            .map(Result.success)
            .catchError { .just(Result.failure($0, currentPageIndex)) }
            .asObservable()
    }
}