gui-cs.Terminal.Gui/Terminal.Gui/Views/Menu/ContextMenu.cs

using System;

namespace Terminal.Gui;

/// <summary>
/// ContextMenu provides a pop-up menu that can be positioned anywhere within a <see cref="View"/>. 
/// ContextMenu is analogous to <see cref="MenuBar"/> and, once activated, works like a sub-menu 
/// of a <see cref="MenuBarItem"/> (but can be positioned anywhere).
/// <para>
/// By default, a ContextMenu with sub-menus is displayed in a cascading manner, where each sub-menu pops out of the ContextMenu frame
/// (either to the right or left, depending on where the ContextMenu is relative to the edge of the screen). By setting
/// <see cref="UseSubMenusSingleFrame"/> to <see langword="true"/>, this behavior can be changed such that all sub-menus are
/// drawn within the ContextMenu frame.
/// </para>
/// <para>
/// ContextMenus can be activated using the Shift-F10 key (by default; use the <see cref="Key"/> to change to another key).
/// </para>
/// <para>
/// Callers can cause the ContextMenu to be activated on a right-mouse click (or other interaction) by calling <see cref="Show()"/>.
/// </para>
/// <para>
/// ContextMenus are located using screen using screen coordinates and appear above all other Views.
/// </para>
/// </summary>
public sealed class ContextMenu : IDisposable {
	/// <summary>
	/// The default shortcut key for activating the context menu.
	/// </summary>
	[SerializableConfigurationProperty (Scope = typeof (SettingsScope))]
	public static Key DefaultKey { get; set; } = Key.F10.WithShift;

	static MenuBar _menuBar;
	Key _key = DefaultKey;
	MouseFlags _mouseFlags = MouseFlags.Button3Clicked;
	Toplevel _container;

	/// <summary>
	/// Initializes a context menu with no menu items.
	/// </summary>
	public ContextMenu () : this (0, 0, new MenuBarItem ()) { }

	/// <summary>
	/// Initializes a context menu, with a <see cref="View"/> specifying the parent/host of the menu.
	/// </summary>
	/// <param name="host">The host view.</param>
	/// <param name="menuItems">The menu items for the context menu.</param>
	public ContextMenu (View host, MenuBarItem menuItems) :
		this (host.Frame.X, host.Frame.Y, menuItems)
	{
		Host = host;
	}

	/// <summary>
	/// Initializes a context menu with menu items at a specific screen location.
	/// </summary>
	/// <param name="x">The left position (screen relative).</param>
	/// <param name="y">The top position (screen relative).</param>
	/// <param name="menuItems">The menu items.</param>
	public ContextMenu (int x, int y, MenuBarItem menuItems)
	{
		if (IsShow) {
			if (_menuBar.SuperView != null) {
				Hide ();
			}
			IsShow = false;
		}
		MenuItems = menuItems;
		Position = new Point (x, y);
	}

	void MenuBar_MenuAllClosed (object sender, EventArgs e)
	{
		Dispose ();
	}

	/// <summary>
	/// Disposes the context menu object.
	/// </summary>
	public void Dispose ()
	{
		if (IsShow) {
			_menuBar.MenuAllClosed -= MenuBar_MenuAllClosed;
			_menuBar.Dispose ();
			_menuBar = null;
			IsShow = false;
		}
		if (_container != null) {
			_container.Closing -= Container_Closing;
		}
	}

	/// <summary>
	/// Shows (opens) the ContextMenu, displaying the <see cref="MenuItem"/>s it contains.
	/// </summary>
	public void Show ()
	{
		if (_menuBar != null) {
			Hide ();
		}
		_container = Application.Current;
		_container.Closing += Container_Closing;
		var frame = new Rect (0, 0, View.Driver.Cols, View.Driver.Rows);
		var position = Position;
		if (Host != null) {
			Host.BoundsToScreen (frame.X, frame.Y, out int x, out int y);
			var pos = new Point (x, y);
			pos.Y += Host.Frame.Height - 1;
			if (position != pos) {
				Position = position = pos;
			}
		}
		var rect = Menu.MakeFrame (position.X, position.Y, MenuItems.Children);
		if (rect.Right >= frame.Right) {
			if (frame.Right - rect.Width >= 0 || !ForceMinimumPosToZero) {
				position.X = frame.Right - rect.Width;
			} else if (ForceMinimumPosToZero) {
				position.X = 0;
			}
		} else if (ForceMinimumPosToZero && position.X < 0) {
			position.X = 0;
		}
		if (rect.Bottom >= frame.Bottom) {
			if (frame.Bottom - rect.Height - 1 >= 0 || !ForceMinimumPosToZero) {
				if (Host == null) {
					position.Y = frame.Bottom - rect.Height - 1;
				} else {
					Host.BoundsToScreen (frame.X, frame.Y, out int x, out int y);
					var pos = new Point (x, y);
					position.Y = pos.Y - rect.Height - 1;
				}
			} else if (ForceMinimumPosToZero) {
				position.Y = 0;
			}
		} else if (ForceMinimumPosToZero && position.Y < 0) {
			position.Y = 0;
		}

		_menuBar = new MenuBar (new [] { MenuItems }) {
			X = position.X,
			Y = position.Y,
			Width = 0,
			Height = 0,
			UseSubMenusSingleFrame = UseSubMenusSingleFrame,
			Key = Key
		};

		_menuBar._isContextMenuLoading = true;
		_menuBar.MenuAllClosed += MenuBar_MenuAllClosed;
		_menuBar.BeginInit ();
		_menuBar.EndInit ();
		IsShow = true;
		_menuBar.OpenMenu ();
	}

	void Container_Closing (object sender, ToplevelClosingEventArgs obj)
	{
		Hide ();
	}

	/// <summary>
	/// Hides (closes) the ContextMenu.
	/// </summary>
	public void Hide ()
	{
		_menuBar?.CleanUp ();
		Dispose ();
	}

	/// <summary>
	/// Event invoked when the <see cref="ContextMenu.Key"/> is changed.
	/// </summary>
	public event EventHandler<KeyChangedEventArgs> KeyChanged;

	/// <summary>
	/// Event invoked when the <see cref="ContextMenu.MouseFlags"/> is changed.
	/// </summary>
	public event EventHandler<MouseFlagsChangedEventArgs> MouseFlagsChanged;

	/// <summary>
	/// Gets or sets the menu position.
	/// </summary>
	public Point Position { get; set; }

	/// <summary>
	/// Gets or sets the menu items for this context menu.
	/// </summary>
	public MenuBarItem MenuItems { get; set; }

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

	/// <summary>
	/// <see cref="Gui.MouseFlags"/> specifies the mouse action used to activate the context menu by mouse.
	/// </summary>
	public MouseFlags MouseFlags {
		get => _mouseFlags;
		set {
			var oldFlags = _mouseFlags;
			_mouseFlags = value;
			MouseFlagsChanged?.Invoke (this, new MouseFlagsChangedEventArgs (oldFlags, value));
		}
	}

	/// <summary>
	/// Gets whether the ContextMenu is showing or not.
	/// </summary>
	public static bool IsShow { get; private set; }

	/// <summary>
	/// The host <see cref="View "/> which position will be used,
	/// otherwise if it's null the container will be used.
	/// </summary>
	public View Host { get; set; }

	/// <summary>
	/// Sets or gets whether the context menu be forced to the right, ensuring it is not clipped, if the x position 
	/// is less than zero. The default is <see langword="true"/> which means the context menu will be forced to the right.
	/// If set to <see langword="false"/>, the context menu will be clipped on the left if x is less than zero.
	/// </summary>
	public bool ForceMinimumPosToZero { get; set; } = true;

	/// <summary>
	/// Gets the <see cref="MenuBar"/> that is hosting this context menu.
	/// </summary>
	public MenuBar MenuBar => _menuBar;

	/// <summary>
	/// Gets or sets if sub-menus will be displayed using a "single frame" menu style. If <see langword="true"/>, the ContextMenu
	/// and any sub-menus that would normally cascade will be displayed within a single frame. If <see langword="false"/> (the default),
	/// sub-menus will cascade using separate frames for each level of the menu hierarchy.
	/// </summary>
	public bool UseSubMenusSingleFrame { get; set; }
}