using System.Collections.Generic;

/// <summary>
/// UI导航栈管理器
/// 负责管理窗口的入栈、出栈和返回历史
/// </summary>
public class UINavigationManager
{
    #region Singleton
    private static UINavigationManager _instance;
    public static UINavigationManager Instance
    {
        get
        {
            if (_instance == null)
            {
                _instance = new UINavigationManager();
            }
            return _instance;
        }
    }
    
    private UINavigationManager() { }
    #endregion

    #region Fields
    /// <summary>
    /// 导航栈：存储窗口的返回历史
    /// </summary>
    private List<UIWindow> _navigationStack = new List<UIWindow>(8);
    
    /// <summary>
    /// 对外只读访问（用于兼容旧代码）
    /// </summary>
    public List<UIWindow> NavigationStack => _navigationStack;
    
    /// <summary>
    /// 栈中窗口数量
    /// </summary>
    public int Count => _navigationStack.Count;
    #endregion

    #region Stack Operations
    /// <summary>
    /// 处理窗口入栈（根据配置）
    /// </summary>
    /// <param name="window">窗口实例</param>
    /// <param name="stackMode">栈管理模式</param>
    public void HandleWindowOpen(UIWindow window, UIStackMode stackMode)
    {
        if (window == null) return;

        switch (stackMode)
        {
            case UIStackMode.None:
                // 不入栈（如Tips、HUD）
                break;
                
            case UIStackMode.Stackable:
                // 普通入栈
                if (!_navigationStack.Contains(window))
                {
                    _navigationStack.Add(window);
                }
                break;
                
            case UIStackMode.Replace:
                // 替换栈顶
                if (_navigationStack.Count > 0)
                {
                    var top = _navigationStack[_navigationStack.Count - 1];
                    _navigationStack.RemoveAt(_navigationStack.Count - 1);
                }
                _navigationStack.Add(window);
                break;
                
            case UIStackMode.ClearAndPush:
                // 清空后入栈
                _navigationStack.Clear();
                _navigationStack.Add(window);
                break;
        }
    }

    /// <summary>
    /// 处理窗口关闭（出栈）
    /// </summary>
    /// <param name="window">窗口实例</param>
    public void HandleWindowClose(UIWindow window)
    {
        if (window != null && _navigationStack.Contains(window))
        {
            _navigationStack.Remove(window);
        }
    }

    /// <summary>
    /// 获取栈顶窗口
    /// </summary>
    public UIWindow GetTopWindow()
    {
        return _navigationStack.Count > 0 ? _navigationStack[_navigationStack.Count - 1] : null;
    }

    /// <summary>
    /// 检查窗口是否在栈中
    /// </summary>
    public bool IsWindowInStack(UIWindow window)
    {
        return _navigationStack.Contains(window);
    }

    /// <summary>
    /// 清空栈
    /// </summary>
    public void Clear()
    {
        _navigationStack.Clear();
    }
    #endregion
}