using System.Collections.Concurrent;
using System.Collections.Generic;
using System.Numerics;
using AcDream.Core.Physics;   // TerrainSurface

namespace AcDream.Core.World.Cells;

/// <summary>
/// The unified cell graph: the authoritative id-&gt;cell resolver and registry.
/// Built alongside the legacy render/physics cell systems in Stage 1 and consumed
/// by nobody (zero behavior change). Retail anchor: CObjCell::GetVisible (pseudo_c:308209).
/// Worker-thread populated; reads are concurrency-safe.
/// </summary>
public sealed class CellGraph
{
    private readonly ConcurrentDictionary<uint, EnvCell> _envCells = new();
    private readonly ConcurrentDictionary<uint, (TerrainSurface Terrain, Vector3 Origin)> _terrain = new();

    /// <summary>Player's current cell. Defined for Stage 2; INERT in Stage 1 (no writer).</summary>
    public ObjCell? CurrCell { get; internal set; }

    public bool Contains(uint envCellId) => _envCells.ContainsKey(envCellId);

    public void Add(EnvCell cell) => _envCells.TryAdd(cell.Id, cell);

    /// <param name="landblockPrefix">Any id in the cell's landblock; masked to (id &amp; 0xFFFF0000).</param>
    public void RegisterTerrain(uint landblockPrefix, TerrainSurface terrain, Vector3 worldOrigin)
        => _terrain[landblockPrefix & 0xFFFF0000u] = (terrain, worldOrigin);

    public void RemoveLandblock(uint landblockPrefix)
    {
        uint lb = landblockPrefix & 0xFFFF0000u;
        _terrain.TryRemove(lb, out _);
        foreach (var id in new List<uint>(_envCells.Keys))
            if ((id & 0xFFFF0000u) == lb) _envCells.TryRemove(id, out _);
    }

    /// <summary>The universal id-&gt;cell resolver (retail CObjCell::GetVisible).</summary>
    public ObjCell? GetVisible(uint id)
    {
        if (id == 0u) return null;
        if ((id & 0xFFFFu) >= 0x100u)
            return _envCells.TryGetValue(id, out var env) ? env : null;

        uint low = id & 0xFFFFu;
        if (low < 1u || low > 0x40u) return null;
        if (!_terrain.TryGetValue(id & 0xFFFF0000u, out var t)) return null;
        int idx = (int)(low - 1u);
        return LandCell.Synthesize(id, t.Terrain, t.Origin, idx / 8, idx % 8);
    }

    public ObjCell? Neighbor(ObjCell cell, in CellPortal portal) => GetVisible(portal.OtherCellId);
}