using System.Buffers.Binary;
using NResLib;

namespace MshLib;

/// <summary>
/// MSH-компонент 0x01: таблица узлов модели.
/// Для обычного AniMesh node имеет size 0x26.
/// У ландшафта metadata/magic1 может иметь другой смысл, например grid_x_count.
/// </summary>
public static class Msh0x01
{
    public const int NormalElementSize = 0x26;
    public const int StateCount = 3;
    public const int MaxLodCount = 5;
    public const int SlotCount = StateCount * MaxLodCount;

    public static Msh0x01Component ReadComponent(FileStream mshFs, NResArchive archive)
    {
        var entry = archive.Files.FirstOrDefault(x => x.FileType == "01 00 00 00");

        if (entry is null)
        {
            throw new Exception("Archive doesn't contain node table component (0x01)");
        }

        if (entry.ElementSize <= 0)
        {
            throw new Exception("Node table component (0x01) has invalid element size");
        }

        if (entry.FileLength % entry.ElementSize != 0)
        {
            throw new Exception("Node table component (0x01) payload size is not divisible by element size");
        }

        if (entry.ElementSize < 8)
        {
            throw new Exception("Node table component (0x01) element size is too small");
        }

        var elementCount = entry.FileLength / entry.ElementSize;
        var data = new byte[entry.FileLength];

        mshFs.Seek(entry.OffsetInFile, SeekOrigin.Begin);
        mshFs.ReadExactly(data, 0, data.Length);

        var dataSpan = data.AsSpan();

        var nodes = new List<Node>(elementCount);

        for (var i = 0; i < elementCount; i++)
        {
            var baseOffset = i * entry.ElementSize;
            var elementSpan = dataSpan.Slice(baseOffset, entry.ElementSize);

            var slotIndices = new ushort[SlotCount];
            Array.Fill(slotIndices, ushort.MaxValue);

            var slotWordCount = Math.Min(
                slotIndices.Length,
                Math.Max(0, (entry.ElementSize - 8) / 2));

            for (var slotIndex = 0; slotIndex < slotWordCount; slotIndex++)
            {
                slotIndices[slotIndex] =
                    BinaryPrimitives.ReadUInt16LittleEndian(elementSpan.Slice(0x08 + slotIndex * 2, 2));
            }

            nodes.Add(new Node(
                Flags: (NodeFlags)BinaryPrimitives.ReadUInt16LittleEndian(elementSpan.Slice(0x00, 2)),
                ParentIndexOrLink: BinaryPrimitives.ReadUInt16LittleEndian(elementSpan.Slice(0x02, 2)),
                AnimMapStart0x13: BinaryPrimitives.ReadUInt16LittleEndian(elementSpan.Slice(0x04, 2)),
                FallbackKey0x08: BinaryPrimitives.ReadUInt16LittleEndian(elementSpan.Slice(0x06, 2)),
                Msh02SlotIndicesByStateAndLOD: slotIndices));
        }

        return new Msh0x01Component(entry.ElementSize, nodes);
    }

    /// <summary>Результат чтения MSH-компонента 0x01.</summary>
    /// <param name="ElementSize">Размер node entry из NRes metadata.</param>
    /// <param name="Nodes">Узлы компонента 0x01.</param>
    public sealed record Msh0x01Component(
        int ElementSize,
        List<Node> Nodes)
    {
        public bool IsNormalAniMeshNodeTable => ElementSize == NormalElementSize;
    }

    /// <summary>Узел MSH 0x01.</summary>
    /// <param name="Flags">[0x00..0x02] Флаги узла.</param>
    /// <param name="ParentIndexOrLink">[0x02..0x04] Parent node index. 0xFFFF обычно значит root/no parent.</param>
    /// <param name="AnimMapStart0x13">[0x04..0x06] Начало блока в MSH 0x13 animation map или 0xFFFF.</param>
    /// <param name="FallbackKey0x08">[0x06..0x08] Fallback key / index в MSH 0x08.</param>
    /// <param name="Msh02SlotIndicesByStateAndLOD">
    /// [0x08..0x26] Индексы geometry slot в MSH 0x02.
    /// Формула индекса в этой таблице: index = state * MaxLodCount + lod.
    /// 0xFFFF значит, что для этой пары state/LOD геометрии нет.
    /// </param>
    public sealed record Node(
        NodeFlags Flags,
        ushort ParentIndexOrLink,
        ushort AnimMapStart0x13,
        ushort FallbackKey0x08,
        ushort[] Msh02SlotIndicesByStateAndLOD)
    {
        public ushort ResolveSlotIndex(int state, int lod = 0)
        {
            // State и LOD выбираются для конкретного узла/piece, не для всего файла сразу.
            // MODEL_STATE_DEFAULT	    -1
            // MODEL_STATE_REGULAR	    0
            // MODEL_STATE_COLLAPSED	1
            // _MODEL_STATE_UNKNOWN_2	2
            
            // LOD_LEVEL_MAX_0	    0
            // LOD_LEVEL_MINUS_1	1
            // LOD_LEVEL_MINUS_2	2
            // LOD_LEVEL_MINUS_3	3
            // LOD_LEVEL_MINUS_4	4
            
            var index = state * MaxLodCount + lod;

            return index >= 0 && index < Msh02SlotIndicesByStateAndLOD.Length
                ? Msh02SlotIndicesByStateAndLOD[index]
                : ushort.MaxValue;
        }
    }
}

[Flags]
public enum NodeFlags : ushort
{
    None = 0,

    /// <summary>
    /// Still uncertain. In recursive bounds/intersection paths this can suppress/alter child recursion.
    /// Seen as child_node.flags &amp; 0x04.
    /// </summary>
    MSH01_BOUNDS_MODE0_STOP = 0x0004,

    /// <summary>
    /// Stops recursive traversal into children for bounds/render/intersection helpers.
    /// </summary>
    MSH01_STOP_CHILD_BOUNDS_TRAVERSAL = 0x0010,

    /// <summary>
    /// Special lod-4 mode bit. In lod 4, selects alternate piece render mode.
    /// </summary>
    MSH01_HAS_SPECIAL_LOD_4 = 0x0020,

    /// <summary>
    /// Exclude from shadow / no shadow. CAniMesh tracks has_any_shadow_casting_piece when this bit is absent.
    /// </summary>
    MSH01_NO_SHADOW = 0x0040,

    /// <summary>
    /// If this MSH01 flag is set, depletion/restore of this NDP slot should not
    /// participate in central-piece state updates. In practice it maps to
    /// CONTROL_NDP_REF_FLAG_NO_CENTRAL_STATE_UPDATE and probably prevents this piece
    /// from changing the "central" damage/mobility accounting.
    /// </summary>
    MSH01_NO_CENTRAL_STATE_UPDATE = 0x0100,
    
    /// <summary>
    /// If this MSH01 flag is set, the matching ControlNdpRef becomes fatal/critical.
    /// When that NDP slot is depleted, higher-level life logic likely treats the owning
    /// object as destroyed or forces a kill/failure path.
    /// </summary>
    MSH01_NDP_FATAL_ON_DEPLETION = 0x0200,

    /// <summary>
    /// If this MSH01 flag is set, this NDP slot derives or clamps its life ratio
    /// from the parent piece/NDP slot. It maps to
    /// CONTROL_NDP_REF_FLAG_INHERIT_PARENT_LIFE_RATIO and is likely used for
    /// child/helper damage parts that should visually follow parent damage state.
    /// </summary>
    MSH01_NDP_INHERIT_PARENT_LIFE_RATIO = 0x0400,

    /// <summary>
    /// Used during attached MSH load: if parent/root description contains "central", piece gets hidden/excluded flag.
    /// Exact semantic name still provisional.
    /// </summary>
    MSH01_CHECK_PARENT_DESCRIPTION_CENTRAL = 0x0800,
}