import CoreDomain
import CoreModel
import Observation

@MainActor
@Observable
public final class HomeViewModel {
    public private(set) var uiState: HomeUiState = .loading

    private let homeUseCase: HomeUseCase
    private let sessionUseCase: SessionUseCase
    private var loadTask: Task<Void, Never>?
    private var dataTask: Task<Void, Never>?

    public init(homeUseCase: HomeUseCase, sessionUseCase: SessionUseCase) {
        self.homeUseCase = homeUseCase
        self.sessionUseCase = sessionUseCase
    }

    public func load() {
        // flatMapLatest 的等价：登录态变化时重新订阅对应数据源。
        loadTask?.cancel()
        loadTask = Task { [weak self] in
            guard let self else { return }
            do {
                for try await isLoggedIn in self.sessionUseCase.observeIsLoggedIn() {
                    self.reload(isLoggedIn: isLoggedIn)
                }
            } catch is CancellationError {
            } catch {
                self.uiState = .error(error.localizedDescription)
            }
        }
    }

    private func reload(isLoggedIn: Bool) {
        dataTask?.cancel()
        uiState = .loading
        dataTask = Task { [weak self] in
            guard let self else { return }
            do {
                if isLoggedIn {
                    for try await data in self.homeUseCase.observeHome() {
                        self.uiState = .success(data, isGuest: false)
                    }
                } else {
                    for try await data in self.homeUseCase.observeGuestHome() {
                        self.uiState = .success(data, isGuest: true)
                    }
                }
            } catch is CancellationError {
            } catch {
                self.uiState = .error(error.localizedDescription)
            }
        }
    }
}