import Foundation
import Combine

final class GiftBoxListViewModel: ObservableObject {
    private let repository = GiftRepository()
    private let pageSize = 20
    private var subscription: AnyCancellable?
    private var page = 0
    private var isRequestInFlight = false

    @Published private(set) var items = [GiftListItemResponse]()
    @Published private(set) var totalCount = 0
    @Published private(set) var hasNext = false
    @Published private(set) var hasLoaded = false
    @Published private(set) var isLoading = false
    @Published private(set) var isLoadingMore = false
    @Published private(set) var isRefreshing = false
    @Published private(set) var errorMessage = ""
    @Published var isShowPopup = false

    func fetchInitialPage() {
        guard !hasLoaded else { return }
        fetch(page: 0)
    }

    func fetchNextPage(currentItem: GiftListItemResponse) {
        guard hasLoaded, hasNext,
              currentItem.applicationNo == items.last?.applicationNo else { return }
        fetch(page: page + 1)
    }

    @MainActor
    func refresh() async {
        await withCheckedContinuation { continuation in
            fetch(page: 0, isRefresh: true) {
                continuation.resume()
            }
        }
    }

    private func fetch(page requestedPage: Int, isRefresh: Bool = false, completion: (() -> Void)? = nil) {
        guard !isRequestInFlight else {
            completion?()
            return
        }

        isRequestInFlight = true
        isLoading = requestedPage == 0 && !isRefresh
        isLoadingMore = requestedPage > 0
        isRefreshing = isRefresh
        errorMessage = ""
        isShowPopup = false

        subscription = repository.getGifts(page: requestedPage, size: pageSize)
            .receive(on: DispatchQueue.main)
            .sink { [weak self] result in
                defer { completion?() }
                guard let self else { return }

                if case .failure(let error) = result {
                    self.showError(data: error.response?.data)
                }
                self.isLoading = false
                self.isLoadingMore = false
                self.isRefreshing = false
                self.isRequestInFlight = false
            } receiveValue: { [weak self] response in
                guard let self else { return }

                do {
                    let decoded = try JSONDecoder().decode(ApiResponse<GiftListResponse>.self, from: response.data)
                    guard decoded.success, let data = decoded.data else {
                        self.showError(data: response.data)
                        return
                    }

                    if requestedPage == 0 {
                        self.items = data.items
                    } else {
                        self.items.append(contentsOf: data.items)
                    }
                    self.page = data.page
                    self.totalCount = data.totalCount
                    self.hasNext = data.hasNext
                    self.hasLoaded = true
                } catch {
                    self.showError(data: response.data)
                }
            }
    }

    private func showError(data: Data?) {
        struct ErrorResponse: Decodable {
            let message: String?
        }

        let decoded = data.flatMap { try? JSONDecoder().decode(ErrorResponse.self, from: $0) }
        let message = decoded?.message?.trimmingCharacters(in: .whitespacesAndNewlines) ?? ""
        errorMessage = message.isEmpty ? I18n.Common.commonError : message
        isShowPopup = true
    }
}