using System.Collections.Generic;
using System.Numerics;
using AcDream.Core.World;

namespace AcDream.App.Rendering;

/// <summary>
/// Splits a frame's landblock entities into the draw buckets used by the
/// retail-style DrawInside flood. Indoor ownership wins for live dynamics too:
/// a player, NPC, door, or item with a current indoor ParentCellId belongs to
/// that cell's portal-clipped object list, not a global overlay pass.
/// </summary>
public static class InteriorEntityPartition
{
    public sealed class Result
    {
        public Dictionary<uint, List<WorldEntity>> ByCell { get; } = new();
        public List<WorldEntity> Outdoor { get; } = new();
        public List<WorldEntity> LiveDynamic { get; } = new();
    }

    public static Result Partition(
        HashSet<uint> visibleCells,
        IEnumerable<(uint LandblockId, Vector3 AabbMin, Vector3 AabbMax,
                     IReadOnlyList<WorldEntity> Entities,
                     IReadOnlyDictionary<uint, WorldEntity>? AnimatedById)> landblockEntries)
    {
        var result = new Result();
        foreach (var entry in landblockEntries)
        {
            foreach (var e in entry.Entities)
            {
                if (e.MeshRefs.Count == 0) continue;

                if (e.ServerGuid != 0)
                {
                    if (e.ParentCellId is uint liveCell)
                        AddByCellOrOutdoor(e, liveCell, visibleCells, result);
                    else
                        result.LiveDynamic.Add(e);
                }
                else if (e.ParentCellId is uint cell)
                {
                    AddByCellOrOutdoor(e, cell, visibleCells, result);
                }
                else
                {
                    result.Outdoor.Add(e);
                }
            }
        }
        return result;
    }

    private static void AddByCellOrOutdoor(
        WorldEntity entity,
        uint cellId,
        HashSet<uint> visibleCells,
        Result result)
    {
        if (!IsIndoorCellId(cellId))
        {
            result.Outdoor.Add(entity);
            return;
        }

        if (!visibleCells.Contains(cellId))
            return;

        if (!result.ByCell.TryGetValue(cellId, out var list))
            result.ByCell[cellId] = list = new List<WorldEntity>();
        list.Add(entity);
    }

    private static bool IsIndoorCellId(uint cellId)
    {
        uint low = cellId & 0xFFFFu;
        return low >= 0x0100u && low != 0xFFFFu;
    }
}