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

namespace AcDream.App.Rendering;

/// <summary>
/// Splits a frame's landblock entities into the three draw buckets the per-cell
/// <see cref="InteriorRenderer"/> needs, using the SAME precedence as
/// <see cref="Wb.WbDrawDispatcher.ResolveEntitySlot"/>:
/// <list type="number">
/// <item><b>ServerGuid != 0</b> (player / NPCs / items / doors) ⇒ <see cref="Result.LiveDynamic"/>
///   — drawn unclipped (depth only). These have no <c>ParentCellId</c> so they MUST be tested first.</item>
/// <item><b>ParentCellId</b> in the visible set ⇒ <see cref="Result.ByCell"/>[cell] — per-cell, portal-clipped.</item>
/// <item><b>ParentCellId == null</b> (outdoor scenery / building shell) ⇒ <see cref="Result.Outdoor"/>
///   — drawn through the doorway, clipped to OutsideView.</item>
/// </list>
/// A static whose <c>ParentCellId</c> is NOT in <paramref name="visibleCells"/> is dropped (its cell
/// isn't drawn this frame). Entities with no <c>MeshRefs</c> are skipped. Pure; GL-free; unit-tested.
/// </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)            // live-dynamic — precedence first (no ParentCellId)
                {
                    result.LiveDynamic.Add(e);
                }
                else if (e.ParentCellId is uint cell)
                {
                    if (!visibleCells.Contains(cell)) continue;   // its cell isn't drawn this frame
                    if (!result.ByCell.TryGetValue(cell, out var list))
                        result.ByCell[cell] = list = new List<WorldEntity>();
                    list.Add(e);
                }
                else                              // outdoor scenery / building shell
                {
                    result.Outdoor.Add(e);
                }
            }
        }
        return result;
    }
}