using System.Collections.Generic;

/// <summary>
/// UI窗口可见性管理器（纯性能优化模块）
/// 
/// 核心理念：
/// - 只控制 GameObject.SetActive()，仅影响渲染层面
/// - 不触发 UIWindow 生命周期（不调用 CloseWindow/ShowWindow）
/// - 不改变窗口逻辑状态（_isShow 保持不变）
/// 
/// 优化目标：
/// - 当全屏窗口打开时，自动隐藏被遮挡的下层窗口，减少 Overdraw
/// - 当全屏窗口关闭时，自动恢复被遮挡的窗口渲染
/// - 节省 GPU 绘制开销和 CPU UI 遍历开销
/// </summary>
public class UIWindowVisibilityManager
{
    #region Singleton
    private static UIWindowVisibilityManager _instance;
    public static UIWindowVisibilityManager Instance
    {
        get
        {
            if (_instance == null)
            {
                _instance = new UIWindowVisibilityManager();
            }
            return _instance;
        }
    }
    
    private UIWindowVisibilityManager() { }
    #endregion

    #region Fields
    /// <summary>
    /// 复用的窗口列表，避免 GC
    /// </summary>
    private readonly List<UIWindow> _tempWindowList = new List<UIWindow>(32);
    #endregion

    #region Visibility Operations
    /// <summary>
    /// 处理窗口打开时的渲染优化
    /// HideBelow 策略：隐藏所有被遮挡的下层窗口
    /// 
    /// 性能优化：只控制 GameObject.SetActive(false)，不影响窗口逻辑状态
    /// </summary>
    /// <param name="newWindow">新打开的窗口</param>
    /// <param name="visibilityStrategy">可见性策略</param>
    public void HandleVisibilityOnOpen(UIWindow newWindow, UIVisibilityStrategy visibilityStrategy)
    {
        if (newWindow == null || visibilityStrategy == UIVisibilityStrategy.None)
            return;

        // HideBelow 策略：基于渲染层级隐藏
        if (visibilityStrategy == UIVisibilityStrategy.Occlusion)
        {
            var newWindowLayer = newWindow.uiWindowLayer;
            var newWindowSiblingIndex = newWindow.transform.GetSiblingIndex();
            var layerManager = UICanvasLayerManager.Instance;

            // 从底层到当前层，隐藏所有应该被遮挡的窗口（只控制 GameObject.active）
            for (int layer = 0; layer <= (int)newWindowLayer; layer++)
            {
                var windowList = layerManager.GetWindowsInLayer((UICanvasLayer)layer);
                foreach (var window in windowList)
                {
                    // 只隐藏逻辑上显示的窗口（预加载窗口不参与遮挡管理）
                    if (window != null && window != newWindow && window.IsShow() && window.gameObject.activeSelf)
                    {
                        bool shouldHide = false;
                        
                        if (layer < (int)newWindowLayer)
                        {
                            // 更低层：全部隐藏
                            shouldHide = true;
                        }
                        else // layer == (int)newWindowLayer
                        {
                            // 同层：只隐藏 SiblingIndex 更小（在下面）的窗口
                            var windowSiblingIndex = window.transform.GetSiblingIndex();
                            shouldHide = windowSiblingIndex < newWindowSiblingIndex;
                        }
                        
                        if (shouldHide)
                        {
                            window.gameObject.SetActive(false);
                        }
                    }
                }
            }
        }
    }

    /// <summary>
    /// 处理窗口关闭时的渲染恢复
    /// HideBelow 策略：恢复被遮挡窗口的渲染，直到遇到另一个 HideBelow 窗口
    /// 
    /// 性能优化：只控制 GameObject.SetActive(true)，不影响窗口逻辑状态
    /// </summary>
    /// <param name="closingWindow">正在关闭的窗口</param>
    /// <param name="visibilityStrategy">可见性策略</param>
    public void HandleVisibilityOnClose(UIWindow closingWindow, UIVisibilityStrategy visibilityStrategy)
    {
        if (closingWindow == null || visibilityStrategy == UIVisibilityStrategy.None)
            return;

        // HideBelow 策略：基于渲染层级显示
        if (visibilityStrategy == UIVisibilityStrategy.Occlusion)
        {
            var closingWindowLayer = closingWindow.uiWindowLayer;
            var closingWindowSiblingIndex = closingWindow.transform.GetSiblingIndex();
            var layerManager = UICanvasLayerManager.Instance;

            // 从当前层开始，向下遍历所有层级，直到遇到 HideBelow 窗口
            bool foundBlocker = false;

            for (int layer = (int)closingWindowLayer; layer >= 0; layer--)
            {
                var windowList = layerManager.GetWindowsInLayer((UICanvasLayer)layer);
                
                // 清空并复用列表，避免 GC
                _tempWindowList.Clear();
                
                // 收集需要检查的窗口（只收集逻辑上显示的窗口）
                foreach (var window in windowList)
                {
                    // ✅ 预加载的窗口（IsShow=false）不参与遮挡管理
                    if (window != null && window != closingWindow && window.IsShow())
                    {
                        // 同层：只检查在关闭窗口下面的窗口
                        if (layer == (int)closingWindowLayer)
                        {
                            var windowSiblingIndex = window.transform.GetSiblingIndex();
                            if (windowSiblingIndex < closingWindowSiblingIndex)
                            {
                                _tempWindowList.Add(window);
                            }
                        }
                        // 其他层：收集所有逻辑上显示的窗口
                        else
                        {
                            _tempWindowList.Add(window);
                        }
                    }
                }

                // 按 SiblingIndex 倒序排序（从上往下检查）
                _tempWindowList.Sort((a, b) => b.transform.GetSiblingIndex().CompareTo(a.transform.GetSiblingIndex()));

                // 遍历并处理窗口
                foreach (var window in _tempWindowList)
                {
                    var config = UIManager.Instance.GetWindowInfo(window.WindowName);
                    
                    // 显示被隐藏的窗口（只控制 GameObject.active）
                    if (!window.gameObject.activeSelf)
                    {
                        // // 🎯 如果窗口需要截图，在恢复前重新截图
                        // if (config.NeedScreenshot)
                        // {
                        //     ScreenshotManager.Instance.CaptureScreenshot();
                        //     
                        //     // 🎯 刷新模糊背景 texture
                        //     RefreshBlurBackground(window);
                        // }
                        // else
                        // {
                        //     ScreenshotManager.Instance.ResetScreenshot();
                        // }
                        
                        window.gameObject.SetActive(true);
                    }
                    
                    // 如果遇到另一个 HideBelow 窗口，停止继续向下恢复
                    // （因为这个窗口会负责隐藏它下面的窗口）
                    if (config.VisibilityStrategy == UIVisibilityStrategy.Occlusion)
                    {
                        foundBlocker = true;
                        break;
                    }
                }

                if (foundBlocker)
                {
                    break;
                }
            }
        }
    }

    #endregion
}