import Foundation
import Combine

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

    @Published var isLoading = false
    @Published var isLoadingNextPage = false
    @Published var response: CreatorChannelDonationTabResponse?
    @Published var rankings = [MemberDonationRankingResponse]()
    @Published var donations = [CreatorChannelDonationResponse]()
    @Published var page = 0
    @Published var size = 20
    @Published var hasNext = false
    @Published var hasLoaded = false
    @Published var errorMessage = ""
    @Published var isShowPopup = false

    var donationCount: Int {
        response?.donationCount ?? 0
    }

    func fetchFirstPage(creatorId: Int) {
        fetchDonations(creatorId: creatorId, page: 0, isNextPage: false)
    }

    func fetchNextPageIfNeeded(creatorId: Int, currentItem: CreatorChannelDonationResponse) {
        guard let lastDonation = donations.last else { return }
        guard lastDonation.createdAtUtc == currentItem.createdAtUtc,
              lastDonation.nickname == currentItem.nickname,
              lastDonation.can == currentItem.can else { return }
        guard hasNext, isLoadingNextPage == false, isLoading == false else { return }

        fetchDonations(creatorId: creatorId, page: page + 1, isNextPage: true)
    }

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

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

        repository.getDonations(creatorId: creatorId, 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")
                    self.isLoading = false
                    self.isLoadingNextPage = false
                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<CreatorChannelDonationTabResponse>.self, from: response.data)

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

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

    private func applySuccessState(_ data: CreatorChannelDonationTabResponse, isNextPage: Bool) {
        response = data
        rankings = data.rankings
        page = data.page
        size = data.size
        hasNext = data.hasNext

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

    private func applyFailureState() {
        errorMessage = I18n.Common.commonError
        isShowPopup = true
        isLoading = false
        isLoadingNextPage = false
    }
}