using UnityEngine;
using UnityEngine.Events;
using UnityEngine.EventSystems;
/// <summary>
/// 接受拖动操作的Ui底层组件，Unity原生接口需要额外处理一些释放的问题
/// </summary>
public class UiDragComponent : MonoBehaviour, IDragHandler, IPointerDownHandler, IPointerUpHandler
{
    /// <summary>
    /// 当前操作的手指Id
    /// </summary>
    public int? CurrentPointerId { get; private set; }
    /// <summary>
    /// 上次移动的缓存位置
    /// </summary>
    public Vector2 lastPoint { get; private set; }
    /// <summary>
    /// 手指从一点移动到下一点
    /// </summary>
    public event UnityAction<Vector2, Vector2> onDrag;
    /// <summary>
    /// 手指按下操作
    /// </summary>
    public event UnityAction<Vector2> onPress;
    /// <summary>
    /// 手指抬起操作
    /// </summary>
    public event UnityAction<Vector2> onUp;

    private void OnDisable()
    {
        Release();
    }

    private void OnApplicationFocus(bool hasFocus)
    {
        if (!hasFocus)
            Release();
    }

    public void OnPointerDown(PointerEventData eventData)
    {
        if (CurrentPointerId == null)
        {
            CurrentPointerId = eventData.pointerId;
            lastPoint = eventData.position;
            if (onPress != null)
                onPress(lastPoint);
        }
    }

    public void OnDrag(PointerEventData eventData)
    {
        if (CurrentPointerId == eventData.pointerId)
        {
            if (onDrag != null)
                onDrag(lastPoint, eventData.position);
            lastPoint = eventData.position;
        }
    }
    
    public void OnPointerUp(PointerEventData eventData)
    {
        if (CurrentPointerId == eventData.pointerId)
        {
            lastPoint = eventData.position;
            Release();
        }
    }

    public void Release()
    {
        var temp = CurrentPointerId;
        CurrentPointerId = null;
        if (temp != null)
        {
            if (onUp != null)
                onUp(lastPoint);
        }
    }
}