import Foundation
import Combine

final class ContentOverviewViewModel: ObservableObject {
    private let repository = ContentOverviewRepository()
    private var subscription = Set<AnyCancellable>()
    private let pageSize = 20
    private var latestRequestId = 0

    let type: ContentOverviewType

    @Published var items = [ContentOverviewItemResponse]()
    @Published var page = 0
    @Published var size = 20
    @Published var hasNext = false
    @Published var hasLoaded = false
    @Published var isLoading = false
    @Published var isLoadingNextPage = false
    @Published var errorMessage = ""
    @Published var isShowPopup = false

    var shouldShowEmptyState: Bool {
        hasLoaded && !isLoading && items.isEmpty
    }

    init(type: ContentOverviewType = .newAndHotAudio) {
        self.type = type
    }

    func fetchFirstPageIfNeeded() {
        guard !hasLoaded else { return }
        fetchFirstPage()
    }

    func fetchFirstPage() {
        fetchContents(page: 0, isNextPage: false)
    }

    func fetchNextPageIfNeeded(currentItem: ContentOverviewItemResponse) {
        guard items.last?.contentId == currentItem.contentId else { return }
        fetchNextPageIfPossible()
    }

    private func fetchNextPageIfPossible() {
        guard hasNext, isLoading == false, isLoadingNextPage == false else { return }
        fetchContents(page: page + 1, isNextPage: true)
    }

    private func fetchContents(page requestPage: Int, isNextPage: Bool) {
        latestRequestId += 1
        let requestId = latestRequestId

        if isNextPage {
            isLoadingNextPage = true
        } else {
            isLoading = true
        }

        repository.getContents(type: type, page: requestPage, size: pageSize)
            .sink { [weak self] result in
                guard let self else { return }
                guard requestId == self.latestRequestId else { return }

                switch result {
                case .finished:
                    DEBUG_LOG("finish")
                case .failure(let error):
                    ERROR_LOG(error.localizedDescription)
                    self.applyFailureState()
                }
            } receiveValue: { [weak self] response in
                guard let self else { return }
                guard requestId == self.latestRequestId else { return }

                do {
                    let jsonDecoder = JSONDecoder()
                    let decoded = try jsonDecoder.decode(ApiResponse<ContentOverviewPageResponse>.self, from: response.data)

                    if let data = decoded.data, decoded.success {
                        self.applySuccessState(data, isNextPage: isNextPage)
                    } else {
                        self.errorMessage = decoded.message ?? I18n.MainContentAll.loadFailedMessage
                        self.isShowPopup = true
                    }
                } catch {
                    ERROR_LOG(error.localizedDescription)
                    self.errorMessage = I18n.MainContentAll.loadFailedMessage
                    self.isShowPopup = true
                }

                self.hasLoaded = true
                self.isLoading = false
                self.isLoadingNextPage = false
            }
            .store(in: &subscription)
    }

    private func applySuccessState(_ data: ContentOverviewPageResponse, isNextPage: Bool) {
        page = data.page
        size = data.size
        hasNext = data.hasNext
        errorMessage = ""

        if isNextPage {
            items.append(contentsOf: data.items)
        } else {
            items = data.items
        }
    }

    private func applyFailureState() {
        errorMessage = I18n.MainContentAll.loadFailedMessage
        isShowPopup = true
        hasLoaded = true
        isLoading = false
        isLoadingNextPage = false
    }
}