using System.Collections;
using System.Collections.Generic;
using UnityEngine;
using UnityEngine.EventSystems;
using UnityEngine.UI;

[RequireComponent(typeof(ScrollRect))]
public class MouseScrollFix : MonoBehaviour, IPointerEnterHandler, IPointerExitHandler
{
    ScrollRect scrollRect;
    RectTransform content;
    float scrollSensitivity, step, viewportSize;
    bool isOver;

    private void Start()
    {
        scrollRect = GetComponent<ScrollRect>();
        content = scrollRect.content;
        scrollSensitivity = scrollRect.scrollSensitivity;
        viewportSize = scrollRect.viewport.rect.height;
        isOver = false;
    }

    private void Update()
    {
        if (isOver)
        {
            var d = Input.GetAxis("Mouse ScrollWheel");

            if (d > 0f)
            {
                step = Mathf.Abs(scrollSensitivity / (content.sizeDelta.y - viewportSize));
                scrollRect.verticalNormalizedPosition += step;

                if (scrollRect.verticalNormalizedPosition > 1)
                    scrollRect.verticalNormalizedPosition = 1;
            }
            else if (d < 0f)
            {
                step = Mathf.Abs(scrollSensitivity / (content.sizeDelta.y - viewportSize));
                scrollRect.verticalNormalizedPosition -= step;

                if (scrollRect.verticalNormalizedPosition < 0)
                    scrollRect.verticalNormalizedPosition = 0;
            }
        }
    }

    public void OnPointerEnter(PointerEventData eventData)
    {
        isOver = true;
    }

    public void OnPointerExit(PointerEventData eventData)
    {
        isOver = false;
    }
}