/**
 * This code is part of the Fungus library (http://fungusgames.com) maintained by Chris Gregan (http://twitter.com/gofungus).
 * It is released for free under the MIT open source license (https://github.com/snozbot/fungus/blob/master/LICENSE)
 */

using UnityEngine;
using UnityEngine.EventSystems;
using UnityEngine.Serialization;


namespace Fungus
{

	/**
	 * Detects drag and drop interactions on a Game Object, and sends events to all Flowchart event handlers in the scene.
	 * The Game Object must have Collider2D & RigidBody components attached. 
	 * The Collider2D must have the Is Trigger property set to true.
	 * The RigidBody would typically have the Is Kinematic property set to true, unless you want the object to move around using physics.
	 * Use in conjunction with the Drag Started, Drag Completed, Drag Cancelled, Drag Entered & Drag Exited event handlers.
	 */
    public class Draggable2D : MonoBehaviour, IBeginDragHandler, IDragHandler, IEndDragHandler
	{
		[Tooltip("Is object dragging enabled")]
		public bool dragEnabled = true;

		[Tooltip("Move object back to its starting position when drag is cancelled")]
		[FormerlySerializedAs("returnToStartPos")]
		public bool returnOnCancelled = true;

		[Tooltip("Move object back to its starting position when drag is completed")]
		public bool returnOnCompleted = true;

		[Tooltip("Time object takes to return to its starting position")]
		public float returnDuration = 1f;

		[Tooltip("Mouse texture to use when hovering mouse over object")]
		public Texture2D hoverCursor;

		protected Vector3 startingPosition;
		protected bool updatePosition = false;
		protected Vector3 newPosition;
        protected Vector3 delta = Vector3.zero;

        protected virtual void Start()
        {
            // If the main camera doesn't already have a Physics2DRaycaster then add one automatically to
            // use UI raycasts for hit detection. This allows UI to block clicks on objects behind.
            if (Camera.main == null)
                return;

            var raycast = Camera.main.GetComponent<Physics2DRaycaster>();
            if (raycast == null)
            {
                Camera.main.gameObject.AddComponent<Physics2DRaycaster>();
            }
        }

		protected virtual void LateUpdate()
		{
			// iTween will sometimes override the object position even if it should only be affecting the scale, rotation, etc.
			// To make sure this doesn't happen, we force the position change to happen in LateUpdate.
			if (updatePosition)
			{
				transform.position = newPosition;
				updatePosition = false;
			}
		}

		protected virtual void OnTriggerEnter2D(Collider2D other) 
		{
			if (!dragEnabled)
			{
				return;
			}

			foreach (DragEntered handler in GetHandlers<DragEntered>())
			{
				handler.OnDragEntered(this, other);
			}

			foreach (DragCompleted handler in GetHandlers<DragCompleted>())
			{
				handler.OnDragEntered(this, other);
			}
		}

		protected virtual void OnTriggerExit2D(Collider2D other) 
		{
			if (!dragEnabled)
			{
				return;
			}

			foreach (DragExited handler in GetHandlers<DragExited>())
			{
				handler.OnDragExited(this, other);
			}

			foreach (DragCompleted handler in GetHandlers<DragCompleted>())
			{
				handler.OnDragExited(this, other);
			}
		}

		protected virtual T[] GetHandlers<T>() where T : EventHandler
		{
			// TODO: Cache these object for faster lookup
			return GameObject.FindObjectsOfType<T>();
		}

		protected virtual void OnMouseEnter()
		{
			changeCursor(hoverCursor);
		}
		
		protected virtual void OnMouseExit()
		{
			SetMouseCursor.ResetMouseCursor();
		}
		
		protected virtual void changeCursor(Texture2D cursorTexture)
		{
			if (!dragEnabled)
			{
				return;
			}
			
			Cursor.SetCursor(cursorTexture, Vector2.zero, CursorMode.Auto);
		}

        #region IBeginDragHandler implementation
        public void OnBeginDrag(PointerEventData eventData)
        {
            // Offset the object so that the drag is anchored to the exact point where the user clicked it
            float x = Input.mousePosition.x;
            float y = Input.mousePosition.y;
            delta = Camera.main.ScreenToWorldPoint(new Vector3(x, y, 10f)) - transform.position;
            delta.z = 0f;

            startingPosition = transform.position;

            foreach (DragStarted handler in GetHandlers<DragStarted>())
            {
                handler.OnDragStarted(this);
            }
        }
        #endregion

        #region IDragHandler implementation
        public void OnDrag(PointerEventData eventData)
        {
            if (!dragEnabled)
            {
                return;
            }

            float x = Input.mousePosition.x;
            float y = Input.mousePosition.y;
            float z = transform.position.z;

            newPosition = Camera.main.ScreenToWorldPoint(new Vector3(x, y, 10f)) - delta;
            newPosition.z = z;
            updatePosition = true;
        }
        #endregion

        #region IEndHandler implementation
        public void OnEndDrag(PointerEventData eventData)
        {
            if (!dragEnabled)
            {
                return;
            }

            bool dragCompleted = false;

            DragCompleted[] handlers = GetHandlers<DragCompleted>();
            foreach (DragCompleted handler in handlers)
            {
                if (handler.draggableObject == this)
                {
                    if (handler.IsOverTarget())
                    {
                        handler.OnDragCompleted(this);
                        dragCompleted = true;

                        if (returnOnCompleted)
                        {
                            LeanTween.move(gameObject, startingPosition, returnDuration).setEase(LeanTweenType.easeOutExpo);
                        }
                    }
                }
            }

            if (!dragCompleted)
            {
                foreach (DragCancelled handler in GetHandlers<DragCancelled>())
                {
                    handler.OnDragCancelled(this);
                }

                if (returnOnCancelled)
                {
                    LeanTween.move(gameObject, startingPosition, returnDuration).setEase(LeanTweenType.easeOutExpo);
                }
            }
        }
        #endregion

	}

}