import Foundation
import Combine

final class MainChatViewModel: ObservableObject {
    private let repository = MainChatRepository()
    private var subscription = Set<AnyCancellable>()
    private var latestRequestId = 0

    @Published var rooms = [MainChatRoomItem]()
    @Published var selectedFilter: MainChatFilter = .all
    @Published var isLoading = false
    @Published var isLoadingNextPage = false
    @Published var hasMore = false
    @Published var nextCursor: String?
    @Published var hasLoaded = false
    @Published var errorMessage = ""
    @Published var isShowPopup = false

    var shouldShowEmptyState: Bool {
        hasLoaded && isLoading == false && rooms.isEmpty
    }

    func fetchFirstPageIfNeeded() {
        guard hasLoaded == false else { return }
        fetchFirstPage(filter: selectedFilter)
    }

    func fetchFirstPage(filter: MainChatFilter) {
        selectedFilter = filter
        clearRooms()
        fetchChatRooms(filter: filter, cursor: nil, isNextPage: false)
    }

    func applyFilter(_ filter: MainChatFilter) {
        guard selectedFilter != filter else { return }
        fetchFirstPage(filter: filter)
    }

    func fetchNextPageIfNeeded(currentItem: MainChatRoomItem) {
        guard rooms.last?.roomId == currentItem.roomId else { return }
        guard hasMore, let nextCursor, isLoading == false, isLoadingNextPage == false else { return }
        fetchChatRooms(filter: selectedFilter, cursor: nextCursor, isNextPage: true)
    }

    private func fetchChatRooms(filter: MainChatFilter, cursor: String?, isNextPage: Bool) {
        latestRequestId += 1
        let requestId = latestRequestId

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

        repository.getChatRooms(filter: filter.queryValue, cursor: cursor)
            .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<MainChatRoomsResponse>.self, from: response.data)

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

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

    private func applySuccessState(_ data: MainChatRoomsResponse, isNextPage: Bool) {
        hasMore = data.hasMore
        nextCursor = data.nextCursor

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

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

    private func clearRooms() {
        rooms = []
        hasMore = false
        nextCursor = nil
        hasLoaded = false
    }
}