using System;
using System.Collections;
using System.Collections.Generic;

using UnityEngine;
using UnityEngine.EventSystems;
using UnityEngine.UI;

public class VirtualScrollRectPlus : ScrollRect
{
    #region Config //上锁 解锁 对象池 需要外部实现

    public Action OnVerticalLessEqual0;
    public Action OnVerticalGreaterEqual1;
    public Action OnHorizontalLessEqual0;
    public Action OnHorizontalGreaterEqual1;

    public Func<int, VirtualScrollRectItem> GetNextItem;
    public Func<int, VirtualScrollRectItem> GetPreviousItem;
    public Action<int, VirtualScrollRectItem> OnSaveItem;

    public int FirstIndex;
    public int LastIndex;
    public bool Inited;
    public HorizontalOrVerticalLayoutGroup LayoutGroup;

    public int MaxRollAmount;
    public int MaxChildAmount;
    public bool NextPageLock;
    public bool PreviousPageLock;
    public List<VirtualScrollRectItem> Children = new List<VirtualScrollRectItem>();
    public Dictionary<VirtualScrollRectItem, int> ChildrenDataIndexDictionary = new Dictionary<VirtualScrollRectItem, int>();

    #endregion

    public override void OnDrag(PointerEventData eventData)
    {
        base.OnDrag(eventData);

        if (!Inited)
        {
            return;
        }

        if (horizontal && !vertical)
        {
            if (horizontalNormalizedPosition <= 0)
            {
                if (!PreviousPageLock)
                {
                    Vector2 widthAndHeight = PreviousPage();
                    Roll(new Vector2(-widthAndHeight.x, 0));
                }

                OnHorizontalGreaterEqual1.SafeInvoke();
            }

            if (horizontalNormalizedPosition >= 1)
            {
                if (!NextPageLock)
                {
                    Vector2 widthAndHeight = NextPage();
                    Roll(new Vector2(widthAndHeight.x, 0));
                }

                OnHorizontalLessEqual0.SafeInvoke();
            }
        }
        else if (!horizontal && vertical)
        {
            if (verticalNormalizedPosition >= 1)
            {
                if (!PreviousPageLock)
                {
                    Vector2 widthAndHeight = PreviousPage();
                    Roll(new Vector2(0, widthAndHeight.y));
                }

                OnVerticalGreaterEqual1.SafeInvoke();
            }

            if (verticalNormalizedPosition <= 0)
            {
                if (!NextPageLock)
                {
                    Vector2 widthAndHeight = NextPage();
                    Roll(new Vector2(0, -widthAndHeight.y));
                }

                OnVerticalLessEqual0.SafeInvoke();
            }
        }
    }


    public void Init(int maxRollAmount, int maxChildAmount, Func<int, VirtualScrollRectItem> getNextItem, Func<int, VirtualScrollRectItem> getPreviousItem, Action<int, VirtualScrollRectItem> onSaveItem)
    {
        Inited = true;
        MaxRollAmount = maxRollAmount;
        MaxChildAmount = maxChildAmount;
        LayoutGroup = content.GetComponent<HorizontalOrVerticalLayoutGroup>();
        GetNextItem = getNextItem;
        GetPreviousItem = getPreviousItem;
        OnSaveItem = onSaveItem;
    }

    public void SaveChild(VirtualScrollRectItem item)
    {
        int dataIndex = ChildrenDataIndexDictionary[item];
        OnSaveItem.Invoke(dataIndex, item);

        Children.Remove(item);
        ChildrenDataIndexDictionary.Remove(item);
        if (Children.Count > 0)
        {
            FirstIndex = ChildrenDataIndexDictionary[Children[0]];
            LastIndex = ChildrenDataIndexDictionary[Children.Back(0)];
        }
        else
        {
            FirstIndex = 0;
            LastIndex = 0;
        }
    }

    public void SaveFirstChild()
    {
        SaveChild(Children[0]);
    }

    public void SaveLastChild()
    {
        SaveChild(Children.Back(0));
    }

    public void InsertChild(int siblingIndex, int dataIndex, VirtualScrollRectItem item)
    {
        Children.Insert(siblingIndex, item);
        ChildrenDataIndexDictionary.Add(item, dataIndex);
        item.transform.SetSiblingIndex(siblingIndex);
        FirstIndex = ChildrenDataIndexDictionary[Children[0]];
        LastIndex = ChildrenDataIndexDictionary[Children.Back(0)];
    }

    public void InsertChildToFirst(int dataIndex, VirtualScrollRectItem item)
    {
        InsertChild(0, dataIndex, item);
    }

    public void InsertChildToLast(int dataIndex, VirtualScrollRectItem item)
    {
        InsertChild(Children.Count, dataIndex, item);
    }


    public Vector2 NextPage()
    {
        //Debug.LogWarning("NextPage");
        List<VirtualScrollRectItem> rolledItems = new List<VirtualScrollRectItem>();
        for (int i = 0; i < MaxRollAmount; i++)
        {
            int dataIndex = Children.Count == 0 ? 0 : LastIndex + 1;
            VirtualScrollRectItem item = GetNextItem.Invoke(dataIndex);
            if (item == null)
            {
                break;
            }
            else
            {
                if (Children.Count >= MaxChildAmount)
                {
                    SaveFirstChild();
                    rolledItems.Add(item);
                }
                InsertChildToLast(dataIndex, item);
            }
        }

        Vector2 widthAndHeight = new Vector2(rolledItems.MySum(item => item.RectTransform.rect.width), rolledItems.MySum(item => item.RectTransform.rect.height));
        widthAndHeight += new Vector2(LayoutGroup.spacing, LayoutGroup.spacing) * Mathf.Max(rolledItems.Count - 1, 0);
        return widthAndHeight;
    }

    public Vector2 PreviousPage()
    {
        //Debug.LogWarning("PreviousPage");
        List<VirtualScrollRectItem> rolledItems = new List<VirtualScrollRectItem>();
        for (int i = 0; i < MaxRollAmount; i++)
        {
            VirtualScrollRectItem item = GetPreviousItem.Invoke(FirstIndex-1);
            if (item == null)
            {
                break;
            }
            else
            {
                if (Children.Count >= MaxChildAmount)
                {
                    SaveLastChild();
                    rolledItems.Add(item);
                }
                InsertChildToFirst(FirstIndex-1, item);
            }
        }

        Vector2 widthAndHeight = new Vector2(rolledItems.MySum(item => item.RectTransform.rect.width), rolledItems.MySum(item => item.RectTransform.rect.height));
        widthAndHeight += new Vector2(LayoutGroup.spacing, LayoutGroup.spacing)*Mathf.Max(rolledItems.Count - 1, 0);
        return widthAndHeight;
    }


    public void Roll(Vector2 contentOffset)
    {
        m_ContentStartPosition += contentOffset;
    }
}