import Foundation
import SwiftUI
import Combine

// MARK: - API Loading Manager

/// 全局 API 加载状态管理器
/// 
/// 该管理器负责：
/// - 跟踪多个并发的 API 调用状态
/// - 管理 loading 和错误信息的显示
/// - 自动清理过期的错误信息
/// - 提供线程安全的状态更新
@MainActor
class APILoadingManager: ObservableObject {
    // MARK: - Properties
    /// 单例实例
    static let shared = APILoadingManager()
    /// 当前活动的加载项
    @Published private(set) var loadingItems: [APILoadingItem] = []
    /// 错误清理任务
    private var errorCleanupTasks: [UUID: DispatchWorkItem] = [:]
    /// 私有初始化器，确保单例
    private init() {}
    // MARK: - Public Methods
    /// 开始显示 loading
    /// - Parameters:
    ///   - shouldShowLoading: 是否显示 loading 动画
    ///   - shouldShowError: 是否显示错误信息
    /// - Returns: 唯一的加载 ID，用于后续更新状态
    func startLoading(shouldShowLoading: Bool = true, shouldShowError: Bool = true) -> UUID {
        let loadingId = UUID()
        let loadingItem = APILoadingItem(
            id: loadingId,
            state: .loading,
            shouldShowError: shouldShowError,
            shouldShowLoading: shouldShowLoading
        )
        loadingItems.append(loadingItem)
        return loadingId
    }
    /// 更新 loading 状态为成功
    /// - Parameter id: 加载 ID
    func finishLoading(_ id: UUID) {
        removeLoading(id)
    }
    /// 更新 loading 状态为错误
    /// - Parameters:
    ///   - id: 加载 ID
    ///   - errorMessage: 错误信息
    func setError(_ id: UUID, errorMessage: String) {
        guard let index = loadingItems.firstIndex(where: { $0.id == id }) else { return }
        let currentItem = loadingItems[index]
        if currentItem.shouldShowError {
            let errorItem = APILoadingItem(
                id: id,
                state: .error(message: errorMessage),
                shouldShowError: true,
                shouldShowLoading: currentItem.shouldShowLoading
            )
            loadingItems[index] = errorItem
            setupErrorCleanup(for: id)
        } else {
            loadingItems.removeAll { $0.id == id }
        }
    }
    /// 手动移除特定的加载项
    /// - Parameter id: 加载 ID
    private func removeLoading(_ id: UUID) {
        cancelErrorCleanup(for: id)
        loadingItems.removeAll { $0.id == id }
    }
    /// 清空所有加载项（用于应急情况）
    func clearAll() {
        errorCleanupTasks.values.forEach { $0.cancel() }
        errorCleanupTasks.removeAll()
        loadingItems.removeAll()
    }
    // MARK: - Computed Properties
    /// 是否有正在显示的 loading
    var hasActiveLoading: Bool {
        loadingItems.contains { $0.state == .loading && $0.shouldDisplay }
    }
    /// 是否有正在显示的错误
    var hasActiveError: Bool {
        loadingItems.contains { $0.isError && $0.shouldDisplay }
    }
    // MARK: - Private Methods
    /// 设置错误信息自动清理
    /// - Parameter id: 加载 ID
    private func setupErrorCleanup(for id: UUID) {
        let workItem = DispatchWorkItem { [weak self] in
            self?.removeLoading(id)
        }
        errorCleanupTasks[id] = workItem
        DispatchQueue.main.asyncAfter(
            deadline: .now() + APILoadingConfiguration.errorDisplayDuration,
            execute: workItem
        )
    }
    /// 取消错误清理任务
    /// - Parameter id: 加载 ID
    private func cancelErrorCleanup(for id: UUID) {
        errorCleanupTasks[id]?.cancel()
        errorCleanupTasks.removeValue(forKey: id)
    }
}

// MARK: - Convenience Extensions

extension APILoadingManager {
    /// 便捷方法：执行带 loading 的异步操作
    /// - Parameters:
    ///   - shouldShowLoading: 是否显示 loading
    ///   - shouldShowError: 是否显示错误
    ///   - operation: 异步操作
    /// - Returns: 操作结果
    @MainActor
    func withLoading<T: Sendable>(
        shouldShowLoading: Bool = true,
        shouldShowError: Bool = true,
        operation: @escaping () async throws -> T
    ) async -> Result<T, Error> {
        let loadingId = startLoading(
            shouldShowLoading: shouldShowLoading,
            shouldShowError: shouldShowError
        )
        do {
            let result = try await operation()
            finishLoading(loadingId)
            return .success(result)
        } catch {
            setError(loadingId, errorMessage: error.localizedDescription)
            return .failure(error)
        }
    }
}