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

namespace AlicizaX.UI
{
    public abstract class ViewProvider
    {
        private readonly List<ViewHolder> viewHolders = new();
        private readonly Dictionary<int, ViewHolder> viewHoldersByIndex = new();
        private readonly Dictionary<int, List<ViewHolder>> viewHoldersByDataIndex = new();
        private readonly Dictionary<int, int> viewHolderPositions = new();

        public IAdapter Adapter { get; set; }

        public LayoutManager LayoutManager { get; set; }

        public IReadOnlyList<ViewHolder> ViewHolders => viewHolders;

        public abstract string PoolStats { get; }

        protected RecyclerView recyclerView;
        protected ViewHolder[] templates;

        public ViewProvider(RecyclerView recyclerView, ViewHolder[] templates)
        {
            this.recyclerView = recyclerView;
            this.templates = templates;
        }

        public abstract ViewHolder GetTemplate(string viewName);

        public abstract ViewHolder[] GetTemplates();

        public abstract ViewHolder Allocate(string viewName);

        public abstract void Free(string viewName, ViewHolder viewHolder);

        public abstract void Reset();

        public abstract void PreparePool();

        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;
                viewHolder.DataIndex = i;
                viewHolder.RecyclerView = recyclerView;
                viewHolders.Add(viewHolder);
                RegisterViewHolder(viewHolder);

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

        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];
                string viewName = viewHolder.Name;
                viewHolders.RemoveAt(viewHolderIndex);
                UnregisterViewHolder(viewHolder);
                RebuildViewHolderPositions(viewHolderIndex);
                Adapter?.OnRecycleViewHolder(viewHolder);
                viewHolder.OnRecycled();
                ClearSelectedState(viewHolder);
                Free(viewName, viewHolder);
            }
        }

        public ViewHolder GetViewHolder(int index)
        {
            return viewHoldersByIndex.TryGetValue(index, out ViewHolder viewHolder)
                ? viewHolder
                : null;
        }

        public ViewHolder GetViewHolderByDataIndex(int dataIndex)
        {
            return viewHoldersByDataIndex.TryGetValue(dataIndex, out List<ViewHolder> holders) &&
                   holders is { Count: > 0 }
                ? holders[0]
                : null;
        }

        public bool TryGetViewHoldersByDataIndex(int dataIndex, out IReadOnlyList<ViewHolder> holders)
        {
            if (viewHoldersByDataIndex.TryGetValue(dataIndex, out List<ViewHolder> list) && list.Count > 0)
            {
                holders = list;
                return true;
            }

            holders = null;
            return false;
        }

        public int GetViewHolderIndex(int index)
        {
            return viewHolderPositions.TryGetValue(index, out int viewHolderIndex)
                ? viewHolderIndex
                : -1;
        }

        public void Clear()
        {
            foreach (var viewHolder in viewHolders)
            {
                string viewName = viewHolder.Name;
                Adapter?.OnRecycleViewHolder(viewHolder);
                UnregisterViewHolder(viewHolder);
                viewHolder.OnRecycled();
                ClearSelectedState(viewHolder);
                Free(viewName, viewHolder);
            }

            viewHolders.Clear();
            viewHoldersByIndex.Clear();
            viewHoldersByDataIndex.Clear();
            viewHolderPositions.Clear();
        }

        public Vector2 CalculateViewSize(int index)
        {
            Vector2 size = GetTemplate(Adapter.GetViewName(index)).SizeDelta;
            return size;
        }

        public int GetItemCount()
        {
            return Adapter == null ? 0 : Adapter.GetItemCount();
        }

        protected int GetRecommendedWarmCount()
        {
            if (Adapter == null || LayoutManager == null)
            {
                return 0;
            }

            int itemCount = Adapter.GetItemCount();
            if (itemCount <= 0)
            {
                return 0;
            }

            int start = Mathf.Max(0, LayoutManager.GetStartIndex());
            int end = Mathf.Max(start, LayoutManager.GetEndIndex());
            int visibleCount = end - start + 1;
            int bufferCount = Mathf.Max(1, LayoutManager.Unit);
            return Mathf.Min(itemCount, visibleCount + bufferCount);
        }

        private void RegisterViewHolder(ViewHolder viewHolder)
        {
            if (viewHolder == null)
            {
                return;
            }

            viewHoldersByIndex[viewHolder.Index] = viewHolder;
            viewHolderPositions[viewHolder.Index] = viewHolders.Count - 1;

            if (!viewHoldersByDataIndex.TryGetValue(viewHolder.DataIndex, out List<ViewHolder> holders))
            {
                holders = new List<ViewHolder>();
                viewHoldersByDataIndex[viewHolder.DataIndex] = holders;
            }

            holders.Add(viewHolder);
        }

        private void UnregisterViewHolder(ViewHolder viewHolder)
        {
            if (viewHolder == null)
            {
                return;
            }

            viewHoldersByIndex.Remove(viewHolder.Index);
            viewHolderPositions.Remove(viewHolder.Index);

            if (!viewHoldersByDataIndex.TryGetValue(viewHolder.DataIndex, out List<ViewHolder> holders))
            {
                return;
            }

            holders.Remove(viewHolder);
            if (holders.Count == 0)
            {
                viewHoldersByDataIndex.Remove(viewHolder.DataIndex);
            }
        }

        private void RebuildViewHolderPositions(int startIndex)
        {
            for (int i = startIndex; i < viewHolders.Count; i++)
            {
                ViewHolder holder = viewHolders[i];
                if (holder != null)
                {
                    viewHolderPositions[holder.Index] = i;
                }
            }
        }

        private static void ClearSelectedState(ViewHolder viewHolder)
        {
            if (viewHolder == null)
            {
                return;
            }

            EventSystem eventSystem = EventSystem.current;
            if (eventSystem == null)
            {
                return;
            }

            GameObject selected = eventSystem.currentSelectedGameObject;
            if (selected != null && selected.transform.IsChildOf(viewHolder.transform))
            {
                eventSystem.SetSelectedGameObject(null);
            }
        }
    }
}