tbd-station-14/Content.Shared/DragDrop/IDraggable.cs

using Robust.Shared.Map;

namespace Content.Shared.DragDrop
{
    /// <summary>
    ///     This interface allows a local client to initiate dragging of the component's
    ///     entity by mouse, for drag and drop interactions.
    /// </summary>
    [RequiresExplicitImplementation]
    public interface IDraggable
    {
        /// <summary>
        ///     Invoked when an user is attempting to initiate a drag with
        ///     this component's entity in range. It's fine to return true even if there
        ///     wouldn't be any valid targets - just return true if this entity is in a
        ///     "draggable" state.
        /// </summary>
        /// <param name="args">
        ///     The information about the drag, such as who is doing it.
        /// </param>
        /// <returns>True if the drag should be initiated, false otherwise.</returns>
        bool CanStartDrag(StartDragDropEvent args)
        {
            return true;
        }

        /// <summary>
        ///     Invoked on entities visible to the user to check if this component's
        ///     entity can be dropped on the indicated target entity.
        ///     No need to check range / reachability in here.
        ///     Returning true will cause the target entity to be highlighted as
        ///     a potential target and allow dropping when in range.
        /// </summary>
        /// <returns>
        ///     True if target is a valid target to be dropped on by this component's
        ///     entity, false otherwise.
        /// </returns>
        bool CanDrop(CanDropEvent args);

        /// <summary>
        ///     Invoked when this component's entity is being dropped on another.
        ///     Other drag and drop interactions may be attempted if this one fails.
        /// </summary>
        /// <param name="args">
        ///     The information about the drag, such as who is doing it.
        /// </param>
        /// <returns>
        ///     True if an interaction occurred and no further interaction should
        ///     be processed for this drop, false otherwise.
        /// </returns>
        bool Drop(DragDropEvent args)
        {
            return false;
        }
    }

    [Virtual]
    public class StartDragDropEvent : HandledEntityEventArgs
    {
        /// <summary>
        ///     Entity doing the drag and drop.
        /// </summary>
        public EntityUid User { get; }

        /// <summary>
        ///     Entity that is being dragged.
        /// </summary>
        public EntityUid Dragged { get; }

        /// <summary>
        ///     Creates a new instance of <see cref="StartDragDropEvent"/>.
        /// </summary>
        /// <param name="user">The entity doing the drag and drop.</param>
        /// <param name="dragged">The entity that is being dragged and dropped.</param>
        public StartDragDropEvent(EntityUid user, EntityUid dragged)
        {
            User = user;
            Dragged = dragged;
        }
    }

    [Virtual]
    public class CanDropEvent : StartDragDropEvent
    {
        /// <summary>
        ///     The entity uid that <see cref="StartDragDropEvent.Dragged"/>
        ///     is being dropped onto.
        /// </summary>
        public EntityUid Target { get; }

        /// <summary>
        ///     Creates a new instance of <see cref="CanDropEvent"/>.
        /// </summary>
        /// <param name="user">The entity doing the drag and drop.</param>
        /// <param name="dragged">The entity that is being dragged and dropped.</param>
        /// <param name="target">The entity that <see cref="dragged"/> is being dropped onto.</param>
        public CanDropEvent(EntityUid user, EntityUid dragged, EntityUid target) : base(user, dragged)
        {
            Target = target;
        }
    }

    [Virtual]
    public class DragDropEvent : CanDropEvent
    {
        /// <summary>
        ///     The location where <see cref="StartDragDropEvent.Dragged"/>
        ///     is being dropped.
        /// </summary>
        public EntityCoordinates DropLocation { get; }

        /// <summary>
        ///     Creates a new instance of <see cref="DragDropEvent"/>.
        /// </summary>
        /// <param name="user">The entity doing the drag and drop.</param>
        /// <param name="dropLocation">The location where <see cref="dropped"/> is being dropped.</param>
        /// <param name="dragged">The entity that is being dragged and dropped.</param>
        /// <param name="target">The entity that <see cref="dropped"/> is being dropped onto.</param>
        public DragDropEvent(EntityUid user, EntityCoordinates dropLocation, EntityUid dragged, EntityUid target) : base(user, dragged, target)
        {
            DropLocation = dropLocation;
        }
    }
}