infinitePaging.swift

infinitePaging.swift.swift

import RxSwift
import RxRelay

protocol IssueListRepositoryProtocol {
    func fetch(page: Int) -> Single<[Issue]>
}

final class IssueListUseCase {
    private let fetchTrigger = PublishRelay<FetchMode>()
    private let issuePagesRelay = BehaviorRelay<[[Issue]]>(value: [])
    private let disposeBag = DisposeBag()
    let issues: Observable<[Issue]>

    init(repository: IssueListRepositoryProtocol) {
        fetchTrigger.filter { $0.isRefresh }
            .flatMapFirst { _ in repository.fetch(page: 1).map { [$0] } }
            .bind(to: issuePagesRelay)
            .disposed(by: disposeBag)

        fetchTrigger.filter { !$0.isRefresh }
            .withLatestFrom(issuePagesRelay) { $1 }
            .flatMapFirst { pagesOfIssues in
                repository.fetch(page: pagesOfIssues.count + 1)
                    .map { pagesOfIssues + [$0] }
            }
            .bind(to: issuePagesRelay)
            .disposed(by: disposeBag)

        issues = issuePagesRelay.skip(1).map { $0.flatMap { $0 } }
    }

    func fetch() {
        fetchTrigger.accept(.refresh)
    }

    func next() {
        fetchTrigger.accept(.next)
    }
}

extension IssueListUseCase {
    enum FetchMode {
        case refresh
        case next
        var isRefresh: Bool {
            switch self {
            case .refresh: return true
            case .next: return false
            }
        }
    }
}