#nullable enable
namespace Terminal.Gui;

/// <summary>
///     Provides a cascading menu that pops over all other content. Can be used as a context menu or a drop-down
///     all other content. Can be used as a context menu or a drop-down
///     menu as part of <see cref="MenuBar"/> as part of <see cref="MenuBar"/>.
/// </summary>
/// <remarks>
///     <para>
///         To use as a context menu, register the popover menu with <see cref="Application.Popover"/> and call
///         <see cref="MakeVisible"/>.
///     </para>
/// </remarks>
public class PopoverMenu : PopoverBaseImpl, IDesignable
{
    /// <summary>
    ///     Initializes a new instance of the <see cref="PopoverMenu"/> class.
    /// </summary>
    public PopoverMenu () : this ((Menuv2?)null) { }

    /// <inheritdoc/>
    public PopoverMenu (IEnumerable<View>? menuItems) : this (new Menuv2 (menuItems)) { }

    /// <inheritdoc/>
    public PopoverMenu (IEnumerable<MenuItemv2>? menuItems) : this (new Menuv2 (menuItems)) { }

    /// <summary>
    ///     Initializes a new instance of the <see cref="PopoverMenu"/> class with the specified root <see cref="Menuv2"/>.
    /// </summary>
    public PopoverMenu (Menuv2? root)
    {
        Key = DefaultKey;

        base.Visible = false;

        Root = root;

        AddCommand (Command.Right, MoveRight);
        KeyBindings.Add (Key.CursorRight, Command.Right);

        AddCommand (Command.Left, MoveLeft);
        KeyBindings.Add (Key.CursorLeft, Command.Left);

        // TODO: Remove; for debugging for now
        AddCommand (
                    Command.NotBound,
                    ctx =>
                    {
                        Logging.Trace ($"popoverMenu NotBound: {ctx}");

                        return false;
                    });

        KeyBindings.Add (Key, Command.Quit);
        KeyBindings.ReplaceCommands (Application.QuitKey, Command.Quit);

        AddCommand (
                    Command.Quit,
                    ctx =>
                    {
                        if (!Visible)
                        {
                            return false;
                        }

                        Visible = false;

                        return false;
                    });

        return;

        bool? MoveLeft (ICommandContext? ctx)
        {
            if (Focused == Root)
            {
                return false;
            }

            if (MostFocused is MenuItemv2 { SuperView: Menuv2 focusedMenu })
            {
                focusedMenu.SuperMenuItem?.SetFocus ();

                return true;
            }

            return AdvanceFocus (NavigationDirection.Backward, TabBehavior.TabStop);
        }

        bool? MoveRight (ICommandContext? ctx)
        {
            if (MostFocused is MenuItemv2 { SubMenu.Visible: true } focused)
            {
                focused.SubMenu.SetFocus ();

                return true;
            }

            return false; //AdvanceFocus (NavigationDirection.Forward, TabBehavior.TabStop);
        }
    }

    private Key _key = DefaultKey;

    /// <summary>Specifies the key that will activate the context menu.</summary>
    public Key Key
    {
        get => _key;
        set
        {
            Key oldKey = _key;
            _key = value;
            KeyChanged?.Invoke (this, new (oldKey, _key));
        }
    }

    /// <summary>Raised when <see cref="Key"/> is changed.</summary>
    public event EventHandler<KeyChangedEventArgs>? KeyChanged;

    /// <summary>The default key for activating popover menus.</summary>
    [SerializableConfigurationProperty (Scope = typeof (SettingsScope))]
    public static Key DefaultKey { get; set; } = Key.F10.WithShift;

    /// <summary>
    ///     The mouse flags that will cause the popover menu to be visible. The default is
    ///     <see cref="MouseFlags.Button3Clicked"/> which is typically the right mouse button.
    /// </summary>
    public MouseFlags MouseFlags { get; set; } = MouseFlags.Button3Clicked;

    /// <summary>
    ///     Makes the popover menu visible and locates it at <paramref name="idealScreenPosition"/>. The actual position of the
    ///     menu
    ///     will be adjusted to
    ///     ensure the menu fully fits on the screen, and the mouse cursor is over the first cell of the
    ///     first MenuItem.
    /// </summary>
    /// <param name="idealScreenPosition">If <see langword="null"/>, the current mouse position will be used.</param>
    public void MakeVisible (Point? idealScreenPosition = null)
    {
        UpdateKeyBindings ();
        SetPosition (idealScreenPosition);
        Application.Popover?.Show (this);
    }

    /// <summary>
    ///     Locates the popover menu at <paramref name="idealScreenPosition"/>. The actual position of the menu will be
    ///     adjusted to
    ///     ensure the menu fully fits on the screen, and the mouse cursor is over the first cell of the
    ///     first MenuItem (if possible).
    /// </summary>
    /// <param name="idealScreenPosition">If <see langword="null"/>, the current mouse position will be used.</param>
    public void SetPosition (Point? idealScreenPosition = null)
    {
        idealScreenPosition ??= Application.GetLastMousePosition ();

        if (idealScreenPosition is null || Root is null)
        {
            return;
        }

        Point pos = idealScreenPosition.Value;

        if (!Root.IsInitialized)
        {
            Root.BeginInit ();
            Root.EndInit ();
            Root.Layout ();
        }

        pos = GetMostVisibleLocationForSubMenu (Root, pos);

        Root.X = pos.X;
        Root.Y = pos.Y;
    }

    /// <inheritdoc/>
    protected override void OnVisibleChanged ()
    {
        base.OnVisibleChanged ();

        if (Visible)
        {
            AddAndShowSubMenu (_root);
        }
        else
        {
            HideAndRemoveSubMenu (_root);
            Application.Popover?.Hide (this);
        }
    }

    private Menuv2? _root;

    /// <summary>
    ///     Gets or sets the <see cref="Menuv2"/> that is the root of the Popover Menu.
    /// </summary>
    public Menuv2? Root
    {
        get => _root;
        set
        {
            if (_root == value)
            {
                return;
            }

            if (_root is { })
            {
                _root.Accepting -= MenuOnAccepting;
            }

            HideAndRemoveSubMenu (_root);

            _root = value;

            if (_root is { })
            {
                _root.Accepting += MenuOnAccepting;
            }

            // TODO: This needs to be done whenever any MenuItem in the menu tree changes to support dynamic menus
            // TODO: And it needs to clear the old bindings first
            UpdateKeyBindings ();

            // TODO: This needs to be done whenever any MenuItem in the menu tree changes to support dynamic menus
            IEnumerable<Menuv2> allMenus = GetAllSubMenus ();

            foreach (Menuv2 menu in allMenus)
            {
                menu.Accepting += MenuOnAccepting;
                menu.Accepted += MenuAccepted;
                menu.SelectedMenuItemChanged += MenuOnSelectedMenuItemChanged;
            }
        }
    }

    private void UpdateKeyBindings ()
    {
        IEnumerable<MenuItemv2> all = GetMenuItemsOfAllSubMenus ();

        foreach (MenuItemv2 menuItem in all.Where (mi => mi.Command != Command.NotBound))
        {
            Key? key;

            if (menuItem.TargetView is { })
            {
                // A TargetView implies HotKey
                key = menuItem.TargetView.HotKeyBindings.GetFirstFromCommands (menuItem.Command);
            }
            else
            {
                // No TargetView implies Application HotKey
                key = Application.KeyBindings.GetFirstFromCommands (menuItem.Command);
            }

            if (key is not { IsValid: true })
            {
                continue;
            }

            if (menuItem.Key.IsValid)
            {
                //Logging.Warning ("Do not specify a Key for MenuItems where a Command is specified. Key will be determined automatically.");
            }

            menuItem.Key = key;

            //Logging.Trace ($"HotKey: {menuItem.Key}->{menuItem.Command}");
        }
    }

    /// <inheritdoc/>
    protected override bool OnKeyDownNotHandled (Key key)
    {
        // See if any of our MenuItems have this key as Key
        IEnumerable<MenuItemv2> all = GetMenuItemsOfAllSubMenus ();

        foreach (MenuItemv2 menuItem in all)
        {
            if (menuItem.Key == key)
            {
                return menuItem.NewKeyDownEvent (key);
            }
        }

        return base.OnKeyDownNotHandled (key);
    }

    /// <summary>
    ///     Gets all the submenus in the PopoverMenu.
    /// </summary>
    /// <returns></returns>
    internal IEnumerable<Menuv2> GetAllSubMenus ()
    {
        List<Menuv2> result = [];

        if (Root == null)
        {
            return result;
        }

        Stack<Menuv2> stack = new ();
        stack.Push (Root);

        while (stack.Count > 0)
        {
            Menuv2 currentMenu = stack.Pop ();
            result.Add (currentMenu);

            foreach (View subView in currentMenu.SubViews)
            {
                if (subView is MenuItemv2 menuItem && menuItem.SubMenu != null)
                {
                    stack.Push (menuItem.SubMenu);
                }
            }
        }

        return result;
    }

    /// <summary>
    ///     Gets all the MenuItems in the PopoverMenu.
    /// </summary>
    /// <returns></returns>
    internal IEnumerable<MenuItemv2> GetMenuItemsOfAllSubMenus ()
    {
        List<MenuItemv2> result = [];

        foreach (Menuv2 menu in GetAllSubMenus ())
        {
            foreach (View subView in menu.SubViews)
            {
                if (subView is MenuItemv2 menuItem)
                {
                    result.Add (menuItem);
                }
            }
        }

        return result;
    }

    /// <summary>
    ///     Pops up the submenu of the specified MenuItem, if there is one.
    /// </summary>
    /// <param name="menuItem"></param>
    internal void ShowSubMenu (MenuItemv2? menuItem)
    {
        var menu = menuItem?.SuperView as Menuv2;

        menu?.Layout ();

        // If there's a visible peer, remove / hide it
        if (menu?.SubViews.FirstOrDefault (v => v is MenuItemv2 { SubMenu.Visible: true }) is MenuItemv2 visiblePeer)
        {
            HideAndRemoveSubMenu (visiblePeer.SubMenu);
            visiblePeer.ForceFocusColors = false;
        }

        if (menuItem is { SubMenu: { Visible: false } })
        {
            AddAndShowSubMenu (menuItem.SubMenu);

            Point idealLocation = ScreenToViewport (
                                                    new (
                                                         menuItem.FrameToScreen ().Right - menuItem.SubMenu.GetAdornmentsThickness ().Left,
                                                         menuItem.FrameToScreen ().Top - menuItem.SubMenu.GetAdornmentsThickness ().Top));

            Point pos = GetMostVisibleLocationForSubMenu (menuItem.SubMenu, idealLocation);
            menuItem.SubMenu.X = pos.X;
            menuItem.SubMenu.Y = pos.Y;

            menuItem.ForceFocusColors = true;
        }
    }

    /// <summary>
    ///     Gets the most visible screen-relative location for <paramref name="menu"/>.
    /// </summary>
    /// <param name="menu">The menu to locate.</param>
    /// <param name="idealLocation">Ideal screen-relative location.</param>
    /// <returns></returns>
    internal Point GetMostVisibleLocationForSubMenu (Menuv2 menu, Point idealLocation)
    {
        var pos = Point.Empty;

        // Calculate the initial position to the right of the menu item
        GetLocationEnsuringFullVisibility (
                                           menu,
                                           idealLocation.X,
                                           idealLocation.Y,
                                           out int nx,
                                           out int ny);

        return new (nx, ny);
    }

    private void AddAndShowSubMenu (Menuv2? menu)
    {
        if (menu is { SuperView: null })
        {
            // TODO: Find the menu item below the mouse, if any, and select it

            // TODO: Enable No Border menu style
            menu.Border!.LineStyle = LineStyle.Single;
            menu.Border.Thickness = new (1);

            if (!menu.IsInitialized)
            {
                menu.BeginInit ();
                menu.EndInit ();
            }

            menu.ClearFocus ();
            base.Add (menu);

            // IMPORTANT: This must be done after adding the menu to the super view or Add will try
            // to set focus to it.
            menu.Visible = true;

            menu.Layout ();
        }
    }

    private void HideAndRemoveSubMenu (Menuv2? menu)
    {
        if (menu is { Visible: true })
        {
            // If there's a visible submenu, remove / hide it
            if (menu.SubViews.FirstOrDefault (v => v is MenuItemv2 { SubMenu.Visible: true }) is MenuItemv2 visiblePeer)
            {
                HideAndRemoveSubMenu (visiblePeer.SubMenu);
                visiblePeer.ForceFocusColors = false;
            }

            menu.Visible = false;
            menu.ClearFocus ();
            base.Remove (menu);

            if (menu == Root)
            {
                Visible = false;
            }
        }
    }

    private void MenuOnAccepting (object? sender, CommandEventArgs e)
    {
        var senderView = sender as View;
        Logging.Trace ($"Sender: {senderView?.GetType ().Name}, {e.Context?.Source?.Title}");

        if (e.Context?.Command != Command.HotKey)
        {
            Visible = false;
        }

        // This supports the case when a hotkey of a menuitem with a submenu is pressed
        //e.Cancel = true;
    }

    private void MenuAccepted (object? sender, CommandEventArgs e)
    {
        //Logging.Trace ($"{e.Context?.Source?.Title}");

        if (e.Context?.Source is MenuItemv2 { SubMenu: null })
        {
            HideAndRemoveSubMenu (_root);
            RaiseAccepted (e.Context);
        }
        else if (e.Context?.Source is MenuItemv2 { SubMenu: { } } menuItemWithSubMenu)
        {
            ShowSubMenu (menuItemWithSubMenu);
        }
    }

    /// <summary>
    ///     Raises the <see cref="OnAccepted"/>/<see cref="Accepted"/> event indicating a menu (or submenu)
    ///     was accepted and the Menus in the PopoverMenu were hidden. Use this to determine when to hide the PopoverMenu.
    /// </summary>
    /// <param name="ctx"></param>
    /// <returns></returns>
    protected bool? RaiseAccepted (ICommandContext? ctx)
    {
        //Logging.Trace ($"RaiseAccepted: {ctx}");
        CommandEventArgs args = new () { Context = ctx };

        OnAccepted (args);
        Accepted?.Invoke (this, args);

        return true;
    }

    /// <summary>
    ///     Called when the user has accepted an item in this menu (or submenu. This is used to determine when to hide the
    ///     menu.
    /// </summary>
    /// <remarks>
    /// </remarks>
    /// <param name="args"></param>
    protected virtual void OnAccepted (CommandEventArgs args) { }

    /// <summary>
    ///     Raised when the user has accepted an item in this menu (or submenu. This is used to determine when to hide the
    ///     menu.
    /// </summary>
    /// <remarks>
    ///     <para>
    ///         See <see cref="RaiseAccepted"/> for more information.
    ///     </para>
    /// </remarks>
    public event EventHandler<CommandEventArgs>? Accepted;

    private void MenuOnSelectedMenuItemChanged (object? sender, MenuItemv2? e)
    {
        Logging.Trace ($"e: {e?.Title}");
        ShowSubMenu (e);
    }

    /// <inheritdoc/>
    protected override void OnSubViewAdded (View view)
    {
        if (Root is null && (view is Menuv2 || view is MenuItemv2))
        {
            throw new InvalidOperationException ("Do not add MenuItems or Menus directly to a PopoverMenu. Use the Root property.");
        }

        base.OnSubViewAdded (view);
    }

    /// <inheritdoc/>
    protected override void Dispose (bool disposing)
    {
        if (disposing)
        {
            IEnumerable<Menuv2> allMenus = GetAllSubMenus ();

            foreach (Menuv2 menu in allMenus)
            {
                menu.Accepting -= MenuOnAccepting;
                menu.Accepted -= MenuAccepted;
                menu.SelectedMenuItemChanged -= MenuOnSelectedMenuItemChanged;
            }

            _root?.Dispose ();
            _root = null;
        }

        base.Dispose (disposing);
    }

    /// <inheritdoc/>
    public bool EnableForDesign<TContext> (ref readonly TContext context) where TContext : notnull
    {
        Root = new (
                    [
                        new MenuItemv2 (this, Command.Cut),
                        new MenuItemv2 (this, Command.Copy),
                        new MenuItemv2 (this, Command.Paste),
                        new Line (),
                        new MenuItemv2 (this, Command.SelectAll)
                    ]);

        Visible = true;

        return true;
    }
}