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

public class TestList : MonoBehaviour, IPointerClickHandler, IPointerDownHandler, IPointerUpHandler
{

    bool _isPress;
    Vector2 _curPos;

    // item列表
    List<Transform> _items;

    float _height;

    // 首尾位置
    float _start_y = 0f;
    float _end_y = 0f;

    // 移动总距离
    float _moveDis = 0;

    // 列表数据
    public List<int> _data;

    // 间距
    public float _interval = 5f;

    // Start is called before the first frame update
    void Start()
    {
        // 获取所有item，重复GetChild很浪费内存
        _items = new List<Transform>();
        for (int i = 0; i < transform.childCount; i++)
        {
            _items.Add(transform.GetChild(i));
        }

        // 自定义列表数据
        _data = new List<int>();
        for (int i = 0; i < 1000; i++)
        {
            _data.Add(i);
        }

        _height = _items[0].GetComponent<RectTransform>().sizeDelta.y;
        _start_y = _items[0].GetComponent<RectTransform>().localPosition.y;
        _end_y = _items[_items.Count - 1].GetComponent<RectTransform>().localPosition.y;

        _moveDis = _height * -1f;

        initList();
    }

    // Update is called once per frame
    void Update()
    {
        if (_isPress) moveItems();
    }

#if UNITY_EDITOR
    private void OnValidate()
    {
        if (_interval != transform.GetComponent<VerticalLayoutGroup>().spacing) resetInterval();
    }
#endif

    public void OnPointerClick(PointerEventData eventData)
    {
        _isPress = false;
    }

    public void OnPointerDown(PointerEventData eventData)
    {
        _isPress = true;
        _curPos = new Vector2(Input.mousePosition.x, Input.mousePosition.y);
    }

    public void OnPointerUp(PointerEventData eventData)
    {
        _isPress = false;
        _curPos = Vector2.zero;
    }

    // 编辑器状态下重置item之间的间隔
    void resetInterval()
    {
        transform.GetComponent<VerticalLayoutGroup>().enabled = true;
        transform.GetComponent<VerticalLayoutGroup>().spacing = _interval;
        transform.GetComponent<VerticalLayoutGroup>().enabled = false;
    }

    // 初始化列表数据
    void initList()
    {
        for (int i = 0; i < _items.Count; i++)
        {
            _items[i].GetChild(0).GetComponent<Text>().text = _data[i].ToString();
        }
    }

    void moveItems()
    {
        float _y = Input.mousePosition.y - _curPos.y;
        _curPos.y = Input.mousePosition.y;

        for (int i = 0; i < _items.Count; i++)
        {
            _items[i].localPosition = new Vector3(_items[i].localPosition.x, _items[i].localPosition.y + _y, 0);
        }

        // item位置移到最后
        if (_items[0].localPosition.y >= (_start_y + _height))
        {
            _items[0].localPosition = new Vector3(_items[_items.Count - 1].localPosition.x, _items[_items.Count - 1].localPosition.y - _height - _interval, 0);
            Transform item_temp = _items[0];
            _items.RemoveAt(0);
            _items.Add(item_temp);
        }
        // item位置移到最上
        if (_items[_items.Count - 1].localPosition.y <= _end_y)
        {
            _items[_items.Count - 1].localPosition = new Vector3(_items[0].localPosition.x, _items[0].localPosition.y + _height + _interval, 0);
            Transform item_temp = _items[_items.Count - 1];
            _items.RemoveAt(_items.Count - 1);
            _items.Insert(0, item_temp);
        }

        _moveDis += _y;
        refeshScroll();
    }

    int _index_data;
    void refeshScroll()
    {
        if (_moveDis >= (_height + _interval))
        {
            // 向上移动时
            _moveDis = 0f;
            _index_data++;
            if (_index_data > _data.Count - 1) _index_data = 0;
        }

        if (_moveDis <= (_height + _interval) * -1)
        {
            // 向下移动时
            _moveDis = 0f;
            _index_data--;
            if (_index_data < 0) _index_data = _data.Count - 1;
        }

        if (_moveDis == 0)
        {
            for (int i = 0; i < _items.Count; i++)
            {
                initItem(_items[i], _index_data + i);
            }
        }
    }

    // 刷新item中的数据
    void initItem(Transform item, int index)
    {
        if (index >= _data.Count) index -= _data.Count;
        if (index < 0) index += _data.Count;
        // Debug.Log("???" + index);
        item.GetChild(0).GetComponent<Text>().text = _data[index].ToString();
    }
}