gui-cs.Terminal.Gui/Terminal.Gui/ViewBase/View.Mouse.cs

#nullable enable
using System.ComponentModel;

namespace Terminal.Gui.ViewBase;

public partial class View // Mouse APIs
{
    /// <summary>
    /// Handles <see cref="WantContinuousButtonPressed"/>, we have detected a button
    /// down in the view and have grabbed the mouse.
    /// </summary>
    public IMouseHeldDown? MouseHeldDown { get; set; }

    /// <summary>Gets the mouse bindings for this view.</summary>
    public MouseBindings MouseBindings { get; internal set; } = null!;

    private void SetupMouse ()
    {
        MouseHeldDown = new MouseHeldDown (this, Application.TimedEvents,Application.Mouse);
        MouseBindings = new ();

        // TODO: Should the default really work with any button or just button1?
        MouseBindings.Add (MouseFlags.Button1Clicked, Command.Select);
        MouseBindings.Add (MouseFlags.Button2Clicked, Command.Select);
        MouseBindings.Add (MouseFlags.Button3Clicked, Command.Select);
        MouseBindings.Add (MouseFlags.Button4Clicked, Command.Select);
        MouseBindings.Add (MouseFlags.Button1Clicked | MouseFlags.ButtonCtrl, Command.Select);
    }

    /// <summary>
    ///     Invokes the Commands bound to the MouseFlags specified by <paramref name="mouseEventArgs"/>.
    ///     <para>See <see href="../docs/mouse.md">for an overview of Terminal.Gui mouse APIs.</see></para>
    /// </summary>
    /// <param name="mouseEventArgs">The mouse event passed.</param>
    /// <returns>
    ///     <see langword="null"/> if no command was invoked; input processing should continue.
    ///     <see langword="false"/> if at least one command was invoked and was not handled (or cancelled); input processing
    ///     should continue.
    ///     <see langword="true"/> if at least one command was invoked and handled (or cancelled); input processing should
    ///     stop.
    /// </returns>
    protected bool? InvokeCommandsBoundToMouse (MouseEventArgs mouseEventArgs)
    {
        if (!MouseBindings.TryGet (mouseEventArgs.Flags, out MouseBinding binding))
        {
            return null;
        }

        binding.MouseEventArgs = mouseEventArgs;

        return InvokeCommands (binding.Commands, binding);
    }

    #region MouseEnterLeave

    /// <summary>
    ///     INTERNAL Called by <see cref="Application.RaiseMouseEvent"/> when the mouse moves over the View's
    ///     <see cref="Frame"/>.
    ///     <see cref="MouseLeave"/> will
    ///     be raised when the mouse is no longer over the <see cref="Frame"/>. If another View occludes this View, the
    ///     that View will also receive MouseEnter/Leave events.
    /// </summary>
    /// <param name="eventArgs"></param>
    /// <returns>
    ///     <see langword="true"/> if the event was canceled, <see langword="false"/> if not, <see langword="null"/> if the
    ///     view is not visible. Cancelling the event
    ///     prevents Views higher in the visible hierarchy from receiving Enter/Leave events.
    /// </returns>
    internal bool? NewMouseEnterEvent (CancelEventArgs eventArgs)
    {
        // Pre-conditions
        if (!CanBeVisible (this))
        {
            return null;
        }

        // Cancellable event
        if (OnMouseEnter (eventArgs))
        {
            return true;
        }

        MouseEnter?.Invoke (this, eventArgs);

        if (eventArgs.Cancel)
        {
            return true;
        }

        MouseState |= MouseState.In;

        if (HighlightStates != MouseState.None)
        {
            SetNeedsDraw ();
        }

        return false;
    }

    /// <summary>
    ///     Called when the mouse moves over the View's <see cref="Frame"/> and no other non-SubView occludes it.
    ///     <see cref="MouseLeave"/> will
    ///     be raised when the mouse is no longer over the <see cref="Frame"/>.
    /// </summary>
    /// <remarks>
    ///     <para>
    ///         A view must be visible to receive Enter events (Leave events are always received).
    ///     </para>
    ///     <para>
    ///         If the event is cancelled, the mouse event will not be propagated to other views and <see cref="MouseEnter"/>
    ///         will not be raised.
    ///     </para>
    ///     <para>
    ///         Adornments receive MouseEnter/Leave events when the mouse is over the Adornment's <see cref="Thickness"/>.
    ///     </para>
    ///     <para>
    ///         See <see cref="MouseState"/> for more information.
    ///     </para>
    /// </remarks>
    /// <param name="eventArgs"></param>
    /// <returns>
    ///     <see langword="true"/> if the event was canceled, <see langword="false"/> if not. Cancelling the event
    ///     prevents Views higher in the visible hierarchy from receiving Enter/Leave events.
    /// </returns>
    protected virtual bool OnMouseEnter (CancelEventArgs eventArgs) { return false; }

    /// <summary>
    ///     Raised when the mouse moves over the View's <see cref="Frame"/>. <see cref="MouseLeave"/> will
    ///     be raised when the mouse is no longer over the <see cref="Frame"/>. If another View occludes this View, the
    ///     that View will also receive MouseEnter/Leave events.
    /// </summary>
    /// <remarks>
    ///     <para>
    ///         A view must be visible to receive Enter events (Leave events are always received).
    ///     </para>
    ///     <para>
    ///         If the event is cancelled, the mouse event will not be propagated to other views.
    ///     </para>
    ///     <para>
    ///         Adornments receive MouseEnter/Leave events when the mouse is over the Adornment's <see cref="Thickness"/>.
    ///     </para>
    ///     <para>
    ///         Set <see cref="CancelEventArgs.Cancel"/> to <see langword="true"/> if the event was canceled,
    ///         <see langword="false"/> if not. Cancelling the event
    ///         prevents Views higher in the visible hierarchy from receiving Enter/Leave events.
    ///     </para>
    ///     <para>
    ///         See <see cref="MouseState"/> for more information.
    ///     </para>
    /// </remarks>
    public event EventHandler<CancelEventArgs>? MouseEnter;

    /// <summary>
    ///     INTERNAL Called by <see cref="Application.RaiseMouseEvent"/> when the mouse leaves <see cref="Frame"/>, or is
    ///     occluded
    ///     by another non-SubView.
    /// </summary>
    /// <remarks>
    ///     <para>
    ///         This method calls <see cref="OnMouseLeave"/> and raises the <see cref="MouseLeave"/> event.
    ///     </para>
    ///     <para>
    ///         Adornments receive MouseEnter/Leave events when the mouse is over the Adornment's <see cref="Thickness"/>.
    ///     </para>
    ///     <para>
    ///         See <see cref="MouseState"/> for more information.
    ///     </para>
    /// </remarks>
    internal void NewMouseLeaveEvent ()
    {
        // Pre-conditions

        // Non-cancellable event
        OnMouseLeave ();

        MouseLeave?.Invoke (this, EventArgs.Empty);

        MouseState &= ~MouseState.In;

        // TODO: Should we also MouseState &= ~MouseState.Pressed; ??

        if (HighlightStates != MouseState.None)
        {
            SetNeedsDraw ();
        }
    }

    /// <summary>
    ///     Called when the mouse moves outside View's <see cref="Frame"/>, or is occluded by another non-SubView.
    /// </summary>
    /// <remarks>
    ///     <para>
    ///         Adornments receive MouseEnter/Leave events when the mouse is over the Adornment's <see cref="Thickness"/>.
    ///     </para>
    ///     <para>
    ///         See <see cref="MouseState"/> for more information.
    ///     </para>
    /// </remarks>
    protected virtual void OnMouseLeave () { }

    /// <summary>
    ///     Raised when the mouse moves outside View's <see cref="Frame"/>, or is occluded by another non-SubView.
    /// </summary>
    /// <remarks>
    ///     <para>
    ///         Adornments receive MouseEnter/Leave events when the mouse is over the Adornment's <see cref="Thickness"/>.
    ///     </para>
    ///     <para>
    ///         See <see cref="MouseState"/> for more information.
    ///     </para>
    /// </remarks>
    public event EventHandler? MouseLeave;

    #endregion MouseEnterLeave

    #region Low Level Mouse Events

    /// <summary>
    ///     Gets or sets whether the <see cref="View"/> wants continuous button pressed events. When set to
    ///     <see langword="true"/>,
    ///     and the user presses and holds the mouse button, <see cref="NewMouseEvent"/> will be
    ///     repeatedly called with the same <see cref="MouseFlags"/> for as long as the mouse button remains pressed.
    /// </summary>
    public bool WantContinuousButtonPressed { get; set; }

    /// <summary>Gets or sets whether the <see cref="View"/> wants mouse position reports.</summary>
    /// <value><see langword="true"/> if mouse position reports are wanted; otherwise, <see langword="false"/>.</value>
    public bool WantMousePositionReports { get; set; }

    /// <summary>
    ///     Processes a new <see cref="MouseEvent"/>. This method is called by <see cref="Application.RaiseMouseEvent"/> when a
    ///     mouse
    ///     event occurs.
    /// </summary>
    /// <remarks>
    ///     <para>
    ///         A view must be both enabled and visible to receive mouse events.
    ///     </para>
    ///     <para>
    ///         This method raises <see cref="RaiseMouseEvent"/>/<see cref="MouseEvent"/>; if not handled, and one of the
    ///         mouse buttons was clicked, the <see cref="RaiseMouseClickEvent"/>/<see cref="MouseClick"/> event will be raised
    ///     </para>
    ///     <para>
    ///         If <see cref="WantContinuousButtonPressed"/> is <see langword="true"/>, and the user presses and holds the
    ///         mouse button, <see cref="NewMouseEvent"/> will be repeatedly called with the same <see cref="MouseFlags"/> for
    ///         as long as the mouse button remains pressed.
    ///     </para>
    /// </remarks>
    /// <param name="mouseEvent"></param>
    /// <returns><see langword="true"/> if the event was handled, <see langword="false"/> otherwise.</returns>
    public bool? NewMouseEvent (MouseEventArgs mouseEvent)
    {
        // Pre-conditions
        if (!Enabled)
        {
            // A disabled view should not eat mouse events
            return false;
        }

        if (!CanBeVisible (this))
        {
            return false;
        }

        if (!WantMousePositionReports && mouseEvent.Flags == MouseFlags.ReportMousePosition)
        {
            return false;
        }

        // Cancellable event
        if (RaiseMouseEvent (mouseEvent) || mouseEvent.Handled)
        {
            return true;
        }

        // Post-Conditions
        if (HighlightStates != MouseState.None || WantContinuousButtonPressed)
        {
            if (WhenGrabbedHandlePressed (mouseEvent))
            {
                return mouseEvent.Handled;
            }

            if (WhenGrabbedHandleReleased (mouseEvent))
            {
                return mouseEvent.Handled;
            }

            if (WhenGrabbedHandleClicked (mouseEvent))
            {
                return mouseEvent.Handled;
            }
        }

        // We get here if the view did not handle the mouse event via OnMouseEvent/MouseEvent, and
        // it did not handle the press/release/clicked events via HandlePress/HandleRelease/HandleClicked
        if (mouseEvent.IsSingleDoubleOrTripleClicked)
        {
            return RaiseMouseClickEvent (mouseEvent);
        }

        if (mouseEvent.IsWheel)
        {
            return RaiseMouseWheelEvent (mouseEvent);
        }

        return false;
    }

    /// <summary>
    ///     Raises the <see cref="RaiseMouseEvent"/>/<see cref="MouseEvent"/> event.
    /// </summary>
    /// <param name="mouseEvent"></param>
    /// <returns><see langword="true"/>, if the event was handled, <see langword="false"/> otherwise.</returns>
    public bool RaiseMouseEvent (MouseEventArgs mouseEvent)
    {
        // TODO: probably this should be moved elsewhere, please advise
        if (WantContinuousButtonPressed && MouseHeldDown != null)
        {
            if (mouseEvent.IsPressed)
            {
                MouseHeldDown.Start ();
            }
            else
            {
                MouseHeldDown.Stop ();
            }
        }

        if (OnMouseEvent (mouseEvent) || mouseEvent.Handled)
        {
            return true;
        }

        MouseEvent?.Invoke (this, mouseEvent);

        return mouseEvent.Handled;
    }

    /// <summary>Called when a mouse event occurs within the view's <see cref="Viewport"/>.</summary>
    /// <remarks>
    ///     <para>
    ///         The coordinates are relative to <see cref="View.Viewport"/>.
    ///     </para>
    /// </remarks>
    /// <param name="mouseEvent"></param>
    /// <returns><see langword="true"/>, if the event was handled, <see langword="false"/> otherwise.</returns>
    protected virtual bool OnMouseEvent (MouseEventArgs mouseEvent) { return false; }

    /// <summary>Raised when a mouse event occurs.</summary>
    /// <remarks>
    ///     <para>
    ///         The coordinates are relative to <see cref="View.Viewport"/>.
    ///     </para>
    /// </remarks>
    public event EventHandler<MouseEventArgs>? MouseEvent;

    #endregion Low Level Mouse Events

    #region Mouse Pressed Events

    /// <summary>
    ///     INTERNAL For cases where the view is grabbed and the mouse is clicked, this method handles the released event
    ///     (typically
    ///     when <see cref="WantContinuousButtonPressed"/> or <see cref="HighlightStates"/> are set).
    /// </summary>
    /// <remarks>
    ///     Marked internal just to support unit tests
    /// </remarks>
    /// <param name="mouseEvent"></param>
    /// <returns><see langword="true"/>, if the event was handled, <see langword="false"/> otherwise.</returns>
    internal bool WhenGrabbedHandleReleased (MouseEventArgs mouseEvent)
    {
        mouseEvent.Handled = false;

        if (mouseEvent.IsReleased)
        {
            if (Application.Mouse.MouseGrabView == this)
            {
                //Logging.Debug ($"{Id} - {MouseState}");
                MouseState &= ~MouseState.Pressed;
                MouseState &= ~MouseState.PressedOutside;
            }

            return mouseEvent.Handled = true;
        }

        return false;
    }

    /// <summary>
    ///     INTERNAL For cases where the view is grabbed and the mouse is clicked, this method handles the released event
    ///     (typically
    ///     when <see cref="WantContinuousButtonPressed"/> or <see cref="HighlightStates"/> are set).
    /// </summary>
    /// <remarks>
    ///     <para>
    ///         Marked internal just to support unit tests
    ///     </para>
    /// </remarks>
    /// <param name="mouseEvent"></param>
    /// <returns><see langword="true"/>, if the event was handled, <see langword="false"/> otherwise.</returns>
    private bool WhenGrabbedHandlePressed (MouseEventArgs mouseEvent)
    {
        mouseEvent.Handled = false;

        if (mouseEvent.IsPressed)
        {
            // The first time we get pressed event, grab the mouse and set focus
            if (Application.Mouse.MouseGrabView != this)
            {
                Application.Mouse.GrabMouse (this);

                if (!HasFocus && CanFocus)
                {
                    // Set the focus, but don't invoke Accept
                    SetFocus ();
                }

                mouseEvent.Handled = true;
            }

            if (Viewport.Contains (mouseEvent.Position))
            {
                //Logging.Debug ($"{Id} - Inside Viewport: {MouseState}");
                // The mouse is inside.
                if (HighlightStates.HasFlag (MouseState.Pressed))
                {
                    MouseState |= MouseState.Pressed;
                }

                // Always clear PressedOutside when the mouse is pressed inside the Viewport
                MouseState &= ~MouseState.PressedOutside;
            }

            if (!Viewport.Contains (mouseEvent.Position))
            {
                // Logging.Debug ($"{Id} - Outside Viewport: {MouseState}");
                // The mouse is outside.
                // When WantContinuousButtonPressed is set we want to keep the mouse state as pressed (e.g. a repeating button).
                // This shows the user that the button is doing something, even if the mouse is outside the Viewport.
                if (HighlightStates.HasFlag (MouseState.PressedOutside) && !WantContinuousButtonPressed)
                {
                    MouseState |= MouseState.PressedOutside;
                }
            }

            return mouseEvent.Handled = true;
        }

        return false;
    }

    #endregion Mouse Pressed Events

    #region Mouse Click Events

    /// <summary>Raises the <see cref="OnMouseClick"/>/<see cref="MouseClick"/> event.</summary>
    /// <remarks>
    ///     <para>
    ///         Called when the mouse is either clicked or double-clicked.
    ///     </para>
    ///     <para>
    ///         If <see cref="WantContinuousButtonPressed"/> is <see langword="true"/>, will be invoked on every mouse event
    ///         where
    ///         the mouse button is pressed.
    ///     </para>
    /// </remarks>
    /// <returns><see langword="true"/>, if the event was handled, <see langword="false"/> otherwise.</returns>
    protected bool RaiseMouseClickEvent (MouseEventArgs args)
    {
        // Pre-conditions
        if (!Enabled)
        {
            // QUESTION: Is this right? Should a disabled view eat mouse clicks?
            return args.Handled = false;
        }

        // Cancellable event
        if (OnMouseClick (args) || args.Handled)
        {
            return args.Handled;
        }

        MouseClick?.Invoke (this, args);

        if (args.Handled)
        {
            return true;
        }

        // Post-conditions

        // By default, this will raise Selecting/OnSelecting - Subclasses can override this via AddCommand (Command.Select ...).
        args.Handled = InvokeCommandsBoundToMouse (args) == true;

        return args.Handled;
    }

    /// <summary>
    ///     Called when a mouse click occurs. Check <see cref="MouseEventArgs.Flags"/> to see which button was clicked.
    /// </summary>
    /// <remarks>
    ///     <para>
    ///         Called when the mouse is either clicked or double-clicked.
    ///     </para>
    ///     <para>
    ///         If <see cref="WantContinuousButtonPressed"/> is <see langword="true"/>, will be called on every mouse event
    ///         where
    ///         the mouse button is pressed.
    ///     </para>
    /// </remarks>
    /// <param name="args"></param>
    /// <returns><see langword="true"/>, if the event was handled, <see langword="false"/> otherwise.</returns>
    protected virtual bool OnMouseClick (MouseEventArgs args) { return false; }

    /// <summary>Raised when a mouse click occurs.</summary>
    /// <remarks>
    ///     <para>
    ///         Raised when the mouse is either clicked or double-clicked.
    ///     </para>
    ///     <para>
    ///         If <see cref="WantContinuousButtonPressed"/> is <see langword="true"/>, will be raised on every mouse event
    ///         where
    ///         the mouse button is pressed.
    ///     </para>
    /// </remarks>
    public event EventHandler<MouseEventArgs>? MouseClick;

    /// <summary>
    ///     INTERNAL For cases where the view is grabbed and the mouse is clicked, this method handles the click event
    ///     (typically
    ///     when <see cref="WantContinuousButtonPressed"/> or <see cref="HighlightStates"/> are set).
    /// </summary>
    /// <remarks>
    ///     Marked internal just to support unit tests
    /// </remarks>
    /// <param name="mouseEvent"></param>
    /// <returns><see langword="true"/>, if the event was handled, <see langword="false"/> otherwise.</returns>
    internal bool WhenGrabbedHandleClicked (MouseEventArgs mouseEvent)
    {
        mouseEvent.Handled = false;

        if (Application.Mouse.MouseGrabView == this && mouseEvent.IsSingleClicked)
        {
            // We're grabbed. Clicked event comes after the last Release. This is our signal to ungrab
            Application.Mouse.UngrabMouse ();

            // TODO: Prove we need to unset MouseState.Pressed and MouseState.PressedOutside here
            // TODO: There may be perf gains if we don't unset these flags here
            MouseState &= ~MouseState.Pressed;
            MouseState &= ~MouseState.PressedOutside;

            // If mouse is still in bounds, generate a click
            if (!WantMousePositionReports && Viewport.Contains (mouseEvent.Position))
            {
                return RaiseMouseClickEvent (mouseEvent);
            }

            return mouseEvent.Handled = true;
        }

        return false;
    }

    #endregion Mouse Clicked Events

    #region Mouse Wheel Events

    /// <summary>Raises the <see cref="OnMouseWheel"/>/<see cref="MouseWheel"/> event.</summary>
    /// <remarks>
    /// </remarks>
    /// <returns><see langword="true"/>, if the event was handled, <see langword="false"/> otherwise.</returns>
    protected bool RaiseMouseWheelEvent (MouseEventArgs args)
    {
        // Pre-conditions
        if (!Enabled)
        {
            // QUESTION: Is this right? Should a disabled view eat mouse?
            return args.Handled = false;
        }

        // Cancellable event

        if (OnMouseWheel (args) || args.Handled)
        {
            return args.Handled;
        }

        MouseWheel?.Invoke (this, args);

        if (args.Handled)
        {
            return true;
        }

        args.Handled = InvokeCommandsBoundToMouse (args) == true;

        return args.Handled;
    }

    /// <summary>
    ///     Called when a mouse wheel event occurs. Check <see cref="MouseEventArgs.Flags"/> to see which wheel was moved was
    ///     clicked.
    /// </summary>
    /// <remarks>
    /// </remarks>
    /// <param name="args"></param>
    /// <returns><see langword="true"/>, if the event was handled, <see langword="false"/> otherwise.</returns>
    protected virtual bool OnMouseWheel (MouseEventArgs args) { return false; }

    /// <summary>Raised when a mouse wheel event occurs.</summary>
    /// <remarks>
    /// </remarks>
    public event EventHandler<MouseEventArgs>? MouseWheel;

    #endregion Mouse Wheel Events

    #region MouseState Handling

    private MouseState _mouseState;

    /// <summary>
    ///     Gets the state of the mouse relative to the View. When changed, the <see cref="MouseStateChanged"/>/
    ///     <see cref="OnMouseStateChanged"/>
    ///     event will be raised.
    /// </summary>
    public MouseState MouseState
    {
        get => _mouseState;
        internal set
        {
            if (_mouseState == value)
            {
                return;
            }

            EventArgs<MouseState> args = new (value);

            RaiseMouseStateChanged (args);

            _mouseState = value;
        }
    }

    /// <summary>
    ///     Gets or sets which <see cref="MouseState"/> changes should cause the View to change its appearance.
    /// </summary>
    /// <remarks>
    ///     <para>
    ///         <see cref="MouseState.In"/> is set by default, which means the View will be highlighted when the
    ///         mouse is over it. The default behavior of <see cref="SetAttributeForRole"/>
    ///         is to use the <see cref="Drawing.VisualRole.Highlight"/> role for the highlight Attribute.
    ///     </para>
    ///     <para>
    ///         <see cref="MouseState.Pressed"/> means the View will be highlighted when the mouse is pressed over it.
    ///         <see cref="Border"/>'s default behavior is to use
    ///         the <see cref="VisualRole.Highlight"/> role when the Border is pressed for Arrangement.
    ///         <see cref="Margin"/>'s default behavior, when shadows are enabled, is to move the shadow providing
    ///         a pressed effect.
    ///     </para>
    ///     <para>
    ///         <see cref="MouseState.PressedOutside"/> means the View will be highlighted when the mouse was pressed
    ///         inside it and then moved outside of it, unless <see cref="WantContinuousButtonPressed"/> is set to
    ///         <see langword="true"/>, in which case the flag has no effect.
    ///     </para>
    /// </remarks>
    public MouseState HighlightStates { get; set; }

    /// <summary>
    ///     INTERNAL Raises the <see cref="MouseStateChanged"/> event.
    /// </summary>
    /// <param name="args"></param>
    private void RaiseMouseStateChanged (EventArgs<MouseState> args)
    {
        //Logging.Debug ($"{Id} - {args.Value} -> {args.Value}");

        OnMouseStateChanged (args);

        MouseStateChanged?.Invoke (this, args);
    }

    /// <summary>
    ///     Called when <see cref="MouseState"/> has changed, indicating the View should be highlighted or not. The <see cref="MouseState"/> passed in the event
    ///     indicates the highlight style that will be applied.
    /// </summary>
    protected virtual void OnMouseStateChanged (EventArgs<MouseState> args) { }

    /// <summary>
    ///     RaisedCalled when <see cref="MouseState"/> has changed, indicating the View should be highlighted or not. The <see cref="MouseState"/> passed in the event
    ///     indicates the highlight style that will be applied.
    /// </summary>
    public event EventHandler<EventArgs<MouseState>>? MouseStateChanged;

    #endregion MouseState Handling

    private void DisposeMouse () { }
}