using System.Collections.Generic;
using UnityEngine;

namespace AlicizaX.UI
{
    /// <summary>
    /// 提供和管理 ViewHolder
    /// 负责 ViewHolder 的创建、回收和复用
    /// </summary>
    public abstract class ViewProvider
    {
        private readonly List<ViewHolder> viewHolders = new();

        /// <summary>
        /// 获取或设置数据适配器
        /// </summary>
        public IAdapter Adapter { get; set; }

        /// <summary>
        /// 获取或设置布局管理器
        /// </summary>
        public LayoutManager LayoutManager { get; set; }

        /// <summary>
        /// 获取当前所有活动的 ViewHolder 列表
        /// </summary>
        public List<ViewHolder> ViewHolders => viewHolders;

        protected RecyclerView recyclerView;
        protected ViewHolder[] templates;

        /// <summary>
        /// 构造函数
        /// </summary>
        /// <param name="recyclerView">关联的 RecyclerView 实例</param>
        /// <param name="templates">ViewHolder 模板数组</param>
        public ViewProvider(RecyclerView recyclerView, ViewHolder[] templates)
        {
            this.recyclerView = recyclerView;
            this.templates = templates;
        }

        /// <summary>
        /// 根据视图名称获取对应的模板（抽象方法，由子类实现）
        /// </summary>
        /// <param name="viewName">视图名称</param>
        /// <returns>对应的 ViewHolder 模板</returns>
        public abstract ViewHolder GetTemplate(string viewName);

        /// <summary>
        /// 获取所有模板（抽象方法，由子类实现）
        /// </summary>
        /// <returns>所有 ViewHolder 模板数组</returns>
        public abstract ViewHolder[] GetTemplates();

        /// <summary>
        /// 从对象池中分配一个 ViewHolder（抽象方法，由子类实现）
        /// </summary>
        /// <param name="viewName">视图名称</param>
        /// <returns>分配的 ViewHolder 实例</returns>
        public abstract ViewHolder Allocate(string viewName);

        /// <summary>
        /// 将 ViewHolder 回收到对象池（抽象方法，由子类实现）
        /// </summary>
        /// <param name="viewName">视图名称</param>
        /// <param name="viewHolder">要回收的 ViewHolder</param>
        public abstract void Free(string viewName, ViewHolder viewHolder);

        /// <summary>
        /// 重置 ViewProvider 状态（抽象方法，由子类实现）
        /// </summary>
        public abstract void Reset();

        /// <summary>
        /// 创建指定索引的 ViewHolder
        /// 从对象池中获取或创建新的 ViewHolder，并进行布局和数据绑定
        /// </summary>
        /// <param name="index">数据索引</param>
        public void CreateViewHolder(int index)
        {
            for (int i = index; i < index + LayoutManager.Unit; i++)
            {
                if (i > Adapter.GetItemCount() - 1) break;

                string viewName = Adapter.GetViewName(i);
                var viewHolder = Allocate(viewName);
                viewHolder.Name = viewName;
                viewHolder.Index = i;
                viewHolders.Add(viewHolder);

                LayoutManager.Layout(viewHolder, i);
                Adapter.OnBindViewHolder(viewHolder, i);
            }
        }

        /// <summary>
        /// 移除指定索引的 ViewHolder
        /// 将 ViewHolder 从活动列表中移除并回收到对象池
        /// </summary>
        /// <param name="index">数据索引</param>
        public void RemoveViewHolder(int index)
        {
            for (int i = index; i < index + LayoutManager.Unit; i++)
            {
                if (i > Adapter.GetItemCount() - 1) break;

                int viewHolderIndex = GetViewHolderIndex(i);

                if (viewHolderIndex < 0 || viewHolderIndex >= viewHolders.Count) return;

                var viewHolder = viewHolders[viewHolderIndex];
                viewHolders.RemoveAt(viewHolderIndex);
                viewHolder.OnRecycled();
                Free(viewHolder.Name, viewHolder);
            }
        }

        /// <summary>
        /// 根据数据的下标获取对应的 ViewHolder
        /// </summary>
        /// <param name="index">数据的下标</param>
        /// <returns></returns>
        public ViewHolder GetViewHolder(int index)
        {
            foreach (var viewHolder in viewHolders)
            {
                if (viewHolder.Index == index)
                {
                    return viewHolder;
                }
            }

            return null;
        }

        /// <summary>
        /// 根据数据的下标获取 ViewHolder 的下标
        /// </summary>
        /// <param name="index">数据的下标</param>
        /// <returns></returns>
        public int GetViewHolderIndex(int index)
        {
            for (int i = 0; i < viewHolders.Count; i++)
            {
                if (viewHolders[i].Index == index)
                {
                    return i;
                }
            }

            return -1;
        }

        /// <summary>
        /// 清空所有 ViewHolder
        /// 将所有活动的 ViewHolder 回收到对象池并清空列表
        /// </summary>
        public void Clear()
        {
            foreach (var viewHolder in viewHolders)
            {
                Free(viewHolder.Name, viewHolder);
            }

            viewHolders.Clear();
        }

        /// <summary>
        /// 计算 ViewHolder 的尺寸
        /// </summary>
        /// <param name="index"></param>
        /// <returns></returns>
        public Vector2 CalculateViewSize(int index)
        {
            Vector2 size = GetTemplate(Adapter.GetViewName(index)).SizeDelta;
            return size;
        }

        /// <summary>
        /// 获取数据项总数
        /// </summary>
        /// <returns>数据项总数，如果没有适配器则返回 0</returns>
        public int GetItemCount()
        {
            return Adapter == null ? 0 : Adapter.GetItemCount();
        }
    }
}