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


public class PhotoScrollView : MonoBehaviour, IBeginDragHandler, IEndDragHandler, IDragHandler
{
    public ScrollRect smallScrollView;
    public ScrollRect largeScrollView;
    public TextMeshProUGUI pageIndicatorText;
    public float swipeThreshold = 150f; // 拖曳触发阈值
    public float snapSpeed = 10f;      // 吸附速度
    public float threshold = 20f;
    private Vector2 startDragPos;      // 拖曳开始位置
    private Vector2 endDragPos;        // 拖曳结束位置
    private bool isDragging = false;   // 是否正在拖曳
    private bool isVerticalDrag;

    private int currentPage = 0;
    private int totalPages = 0;

    private void Awake()
    {
        StartCoroutine(InitAfterMainScriptStarts());
    }

    public IEnumerator InitAfterMainScriptStarts()
    {
        yield return new WaitForEndOfFrame(); // 等待到當前幀結束
        // 在這裡進行 PhotoScrollView 的初始化
        totalPages = smallScrollView.content.childCount - 1;
        UpdatePageIndicator();
    }

    public void OnBeginDrag(PointerEventData eventData)
    {
        startDragPos = eventData.position;
        Vector2 dragDelta = eventData.delta.normalized; // 正規化的拖曳向量
        isVerticalDrag = Mathf.Abs(dragDelta.y) > Mathf.Abs(dragDelta.x); // 判断拖拽方向
        if (isVerticalDrag)
        {
            largeScrollView.OnBeginDrag(eventData);
            // 如果是垂直方向的拖拽，则禁用小的水平滚动视图
            smallScrollView.enabled = false;
        }
        else
        {
            // 如果是水平方向的拖拽，则禁用大的垂直滚动视图
            largeScrollView.enabled = false;
        }
        
    }

    public void OnDrag(PointerEventData eventData)
    {
        if (isVerticalDrag)
        {
            // 垂直方向的拖拽，传递事件给大的垂直滚动视图
            largeScrollView.OnDrag(eventData);
        }
        else
        {
            // 水平方向的拖拽
            if (Mathf.Abs(eventData.delta.y) > threshold)
            {
                // 如果超過閥值，則禁用小的水平滾動視圖
                smallScrollView.enabled = false;
            }
            else
            {
                // 如果沒有超過閥值，則啟用小的水平滾動視圖
                smallScrollView.enabled = true;
            }
        }
       
    }

    public void OnEndDrag(PointerEventData eventData)
    {
        if (isVerticalDrag)
        {
            largeScrollView.OnEndDrag(eventData);
            smallScrollView.enabled = true;
        }
        else
        {
            // 水平方向的拖拽，恢复大的垂直滚动视图
            largeScrollView.enabled = true;

            // 判断水平拖动的距离，根据情况显示上一页或下一页
            float dragDistance = Mathf.Abs(eventData.position.x - startDragPos.x);
            if (dragDistance > swipeThreshold)
            {
                if (eventData.position.x > startDragPos.x)
                {
                    ShowPreviousPage();
                }
                else
                {
                    ShowNextPage();
                }
            }
            else
            {
                SnapToNearestPage();
            }
        }
        
    }

    private void ShowPreviousPage()
    {
        if (currentPage > 0)
        {
            currentPage--;
            float normalizedPosition = (float)currentPage / (float)(totalPages-1 );
            StartCoroutine(SmoothScrollTo(normalizedPosition));
            UpdatePageIndicator();
        }
    }

    private void ShowNextPage()
    {
        if (currentPage < totalPages - 1)
        {
            currentPage++;
            float normalizedPosition = (float)currentPage / (float)(totalPages-1 );
            StartCoroutine(SmoothScrollTo(normalizedPosition));
            UpdatePageIndicator();
        }
    }

    private IEnumerator SmoothScrollTo(float targetNormalizedPosition)
    {
        while (Mathf.Abs(smallScrollView.horizontalNormalizedPosition - targetNormalizedPosition) > 0.01f)
        {
            smallScrollView.horizontalNormalizedPosition = Mathf.Lerp(smallScrollView.horizontalNormalizedPosition, targetNormalizedPosition, snapSpeed * Time.deltaTime);
            yield return null;
        }
        smallScrollView.horizontalNormalizedPosition = targetNormalizedPosition;
    }

    private void SnapToNearestPage()
    {
        float targetNormalizedPosition = (float)currentPage / (float)(totalPages-1);
        StartCoroutine(SmoothScrollTo(targetNormalizedPosition));
    }

    public void UpdatePageIndicator()
    {
        pageIndicatorText.text = string.Format("{0}/{1}", currentPage + 1, totalPages);
    }
}