using DatReaderWriter;
using DatReaderWriter.DBObjs;

namespace AcDream.Core.World;

public static class LandblockLoader
{
    private const uint GfxObjMask = 0x01000000u;
    private const uint SetupMask  = 0x02000000u;
    private const uint TypeMask   = 0xFF000000u;

    /// <summary>
    /// Load a single landblock (heightmap + static objects) from the dats.
    /// </summary>
    /// <returns>Null if the landblock is missing from the cell dat.</returns>
    public static LoadedLandblock? Load(DatCollection dats, uint landblockId)
    {
        var block = dats.Get<LandBlock>(landblockId);
        if (block is null)
            return null;

        var info = dats.Get<LandBlockInfo>((landblockId & 0xFFFF0000u) | 0xFFFEu);
        var entities = info is null
            ? Array.Empty<WorldEntity>()
            : BuildEntitiesFromInfo(info);

        return new LoadedLandblock(landblockId, block, entities);
    }

    /// <summary>
    /// Pure mapping from a parsed LandBlockInfo to a list of WorldEntity.
    /// Each Stab and BuildingInfo becomes one entity. Unsupported id types
    /// (neither GfxObj 0x01xxxxxx nor Setup 0x02xxxxxx) are silently skipped.
    /// MeshRefs is left empty at this stage — Task 5 populates it.
    /// </summary>
    public static IReadOnlyList<WorldEntity> BuildEntitiesFromInfo(LandBlockInfo info)
    {
        var result = new List<WorldEntity>(info.Objects.Count + info.Buildings.Count);
        uint nextId = 1;

        foreach (var stab in info.Objects)
        {
            if (!IsSupported(stab.Id))
                continue;
            result.Add(new WorldEntity
            {
                Id = nextId++,
                SourceGfxObjOrSetupId = stab.Id,
                Position = stab.Frame.Origin,
                Rotation = stab.Frame.Orientation,
                MeshRefs = Array.Empty<MeshRef>(),
            });
        }

        foreach (var building in info.Buildings)
        {
            if (!IsSupported(building.ModelId))
                continue;
            result.Add(new WorldEntity
            {
                Id = nextId++,
                SourceGfxObjOrSetupId = building.ModelId,
                Position = building.Frame.Origin,
                Rotation = building.Frame.Orientation,
                MeshRefs = Array.Empty<MeshRef>(),
            });
        }

        return result;
    }

    private static bool IsSupported(uint id)
    {
        var type = id & TypeMask;
        return type == GfxObjMask || type == SetupMask;
    }
}