/**
 * M2 Model Loader — Binary parser for WoW's M2 model format (WotLK 3.3.5a)
 *
 * M2 files contain skeletal-animated meshes used for characters, creatures,
 * and doodads. The format stores geometry, bones with animation tracks,
 * textures, and material batches. A companion .skin file holds the rendering
 * batches and submesh definitions.
 *
 * Key format details:
 *  - On-disk bone struct is 88 bytes (includes 3 animation track headers).
 *  - Animation tracks use an "array-of-arrays" indirection: the header points
 *    to N sub-array headers, each being {uint32 count, uint32 offset}.
 *  - Rotation tracks store compressed quaternions as int16[4], decoded with
 *    an offset mapping (not simple division).
 *  - Skin file indices use two-level indirection: triangle → vertex lookup
 *    table → global vertex index.
 *  - Skin batch struct is 24 bytes on disk — the geosetIndex field at offset 10
 *    is easily missed, causing a 2-byte alignment shift on all subsequent fields.
 *
 * Reference: https://wowdev.wiki/M2
 */
#include "pipeline/m2_loader.hpp"
#include "core/logger.hpp"
#include <cstring>
#include <algorithm>

namespace wowee {
namespace pipeline {

namespace {

// M2 file header structure (version 260+ for WotLK 3.3.5a)
struct M2Header {
    char magic[4];              // 'MD20'
    uint32_t version;
    uint32_t nameLength;
    uint32_t nameOffset;
    uint32_t globalFlags;

    uint32_t nGlobalSequences;
    uint32_t ofsGlobalSequences;
    uint32_t nAnimations;
    uint32_t ofsAnimations;
    uint32_t nAnimationLookup;
    uint32_t ofsAnimationLookup;

    uint32_t nBones;
    uint32_t ofsBones;
    uint32_t nKeyBoneLookup;
    uint32_t ofsKeyBoneLookup;

    uint32_t nVertices;
    uint32_t ofsVertices;
    uint32_t nViews;            // Number of skin files

    uint32_t nColors;
    uint32_t ofsColors;
    uint32_t nTextures;
    uint32_t ofsTextures;

    uint32_t nTransparency;
    uint32_t ofsTransparency;
    uint32_t nUVAnimation;
    uint32_t ofsUVAnimation;
    uint32_t nTexReplace;
    uint32_t ofsTexReplace;

    uint32_t nRenderFlags;
    uint32_t ofsRenderFlags;
    uint32_t nBoneLookupTable;
    uint32_t ofsBoneLookupTable;
    uint32_t nTexLookup;
    uint32_t ofsTexLookup;

    uint32_t nTexUnits;
    uint32_t ofsTexUnits;
    uint32_t nTransLookup;
    uint32_t ofsTransLookup;
    uint32_t nUVAnimLookup;
    uint32_t ofsUVAnimLookup;

    float vertexBox[6];         // Bounding box
    float vertexRadius;
    float boundingBox[6];
    float boundingRadius;

    uint32_t nBoundingTriangles;
    uint32_t ofsBoundingTriangles;
    uint32_t nBoundingVertices;
    uint32_t ofsBoundingVertices;
    uint32_t nBoundingNormals;
    uint32_t ofsBoundingNormals;

    uint32_t nAttachments;
    uint32_t ofsAttachments;
    uint32_t nAttachmentLookup;
    uint32_t ofsAttachmentLookup;
};

// M2 vertex structure (on-disk format)
struct M2VertexDisk {
    float pos[3];
    uint8_t boneWeights[4];
    uint8_t boneIndices[4];
    float normal[3];
    float texCoords[2][2];
};

// M2 animation track header (on-disk, 20 bytes)
struct M2TrackDisk {
    uint16_t interpolationType;
    int16_t globalSequence;
    uint32_t nTimestamps;
    uint32_t ofsTimestamps;
    uint32_t nKeys;
    uint32_t ofsKeys;
};

// Full M2 bone structure (on-disk, 88 bytes)
struct M2BoneDisk {
    int32_t keyBoneId;          // 4
    uint32_t flags;             // 4
    int16_t parentBone;         // 2
    uint16_t submeshId;         // 2
    uint32_t boneNameCRC;       // 4
    M2TrackDisk translation;    // 20
    M2TrackDisk rotation;       // 20
    M2TrackDisk scale;          // 20
    float pivot[3];             // 12
};                              // Total: 88

// M2 animation sequence structure
struct M2SequenceDisk {
    uint16_t id;
    uint16_t variationIndex;
    uint32_t duration;
    float movingSpeed;
    uint32_t flags;
    int16_t frequency;
    uint16_t padding;
    uint32_t replayMin;
    uint32_t replayMax;
    uint32_t blendTime;
    float bounds[6];
    float boundRadius;
    int16_t nextAnimation;
    uint16_t aliasNext;
};

// M2 texture definition
struct M2TextureDisk {
    uint32_t type;
    uint32_t flags;
    uint32_t nameLength;
    uint32_t nameOffset;
};

// Skin file header (contains rendering batches)
struct M2SkinHeader {
    char magic[4];              // 'SKIN'
    uint32_t nIndices;
    uint32_t ofsIndices;
    uint32_t nTriangles;
    uint32_t ofsTriangles;
    uint32_t nVertexProperties;
    uint32_t ofsVertexProperties;
    uint32_t nSubmeshes;
    uint32_t ofsSubmeshes;
    uint32_t nBatches;
    uint32_t ofsBatches;
    uint32_t nBones;
};

// Skin submesh structure (48 bytes for WotLK)
struct M2SkinSubmesh {
    uint16_t id;
    uint16_t level;
    uint16_t vertexStart;
    uint16_t vertexCount;
    uint16_t indexStart;
    uint16_t indexCount;
    uint16_t boneCount;
    uint16_t boneStart;
    uint16_t boneInfluences;
    uint16_t centerBoneIndex;
    float centerPosition[3];
    float sortCenterPosition[3];
    float sortRadius;
};

// Skin batch structure (24 bytes on disk)
struct M2BatchDisk {
    uint8_t flags;
    int8_t priorityPlane;
    uint16_t shader;
    uint16_t skinSectionIndex;
    uint16_t geosetIndex;           // Geoset index (not same as submesh ID)
    uint16_t colorIndex;
    uint16_t materialIndex;
    uint16_t materialLayer;
    uint16_t textureCount;
    uint16_t textureComboIndex;     // Index into texture lookup table
    uint16_t textureCoordIndex;     // Texture coordinate combo index
    uint16_t textureWeightIndex;    // Transparency lookup index
    uint16_t textureTransformIndex; // Texture animation lookup index
};

// Compressed quaternion (on-disk) for rotation tracks
struct CompressedQuat {
    int16_t x, y, z, w;
};

// M2 texture transform (on-disk, 3 × M2TrackDisk = 60 bytes)
struct M2TextureTransformDisk {
    M2TrackDisk translation;    // 20
    M2TrackDisk rotation;       // 20
    M2TrackDisk scaling;        // 20
};

// M2 attachment point (on-disk)
struct M2AttachmentDisk {
    uint32_t id;
    uint16_t bone;
    uint16_t unknown;
    float position[3];
    uint8_t trackData[20]; // M2Track<uint8_t> — skip
};

template<typename T>
T readValue(const std::vector<uint8_t>& data, uint32_t offset) {
    if (offset + sizeof(T) > data.size()) {
        return T{};
    }
    T value;
    std::memcpy(&value, &data[offset], sizeof(T));
    return value;
}

template<typename T>
std::vector<T> readArray(const std::vector<uint8_t>& data, uint32_t offset, uint32_t count) {
    std::vector<T> result;
    if (count == 0 || offset + count * sizeof(T) > data.size()) {
        return result;
    }

    result.resize(count);
    std::memcpy(result.data(), &data[offset], count * sizeof(T));
    return result;
}

std::string readString(const std::vector<uint8_t>& data, uint32_t offset, uint32_t length) {
    if (offset + length > data.size()) {
        return "";
    }

    // Strip trailing null bytes (M2 nameLength includes \0)
    while (length > 0 && data[offset + length - 1] == 0) {
        length--;
    }

    return std::string(reinterpret_cast<const char*>(&data[offset]), length);
}

enum class TrackType { VEC3, QUAT_COMPRESSED };

// Parse an M2 animation track from the binary data.
// The track uses an "array of arrays" layout: nTimestamps pairs of {count, offset}.
// sequenceFlags: per-sequence flags; sequences WITHOUT flag 0x20 store their keyframe
// data in external .anim files, so their sub-array offsets are .anim-relative and must
// be skipped when reading from the M2 file.
void parseAnimTrack(const std::vector<uint8_t>& data,
                    const M2TrackDisk& disk,
                    M2AnimationTrack& track,
                    TrackType type,
                    const std::vector<uint32_t>& sequenceFlags = {}) {
    track.interpolationType = disk.interpolationType;
    track.globalSequence = disk.globalSequence;

    if (disk.nTimestamps == 0 || disk.nKeys == 0) return;

    uint32_t numSubArrays = disk.nTimestamps;
    track.sequences.resize(numSubArrays);

    for (uint32_t i = 0; i < numSubArrays; i++) {
        // Sequences without flag 0x20 have their animation data in external .anim files.
        // Their sub-array offsets are .anim-file-relative, not M2-relative, so reading
        // from the M2 file would produce garbage data.
        if (i < sequenceFlags.size() && !(sequenceFlags[i] & 0x20)) continue;
        // Each sub-array header is {uint32_t count, uint32_t offset} = 8 bytes
        uint32_t tsHeaderOfs = disk.ofsTimestamps + i * 8;
        uint32_t keyHeaderOfs = disk.ofsKeys + i * 8;

        if (tsHeaderOfs + 8 > data.size() || keyHeaderOfs + 8 > data.size()) continue;

        uint32_t tsCount = readValue<uint32_t>(data, tsHeaderOfs);
        uint32_t tsOffset = readValue<uint32_t>(data, tsHeaderOfs + 4);
        uint32_t keyCount = readValue<uint32_t>(data, keyHeaderOfs);
        uint32_t keyOffset = readValue<uint32_t>(data, keyHeaderOfs + 4);

        if (tsCount == 0 || keyCount == 0) continue;

        // Validate offsets are within file data (external .anim files have out-of-range offsets)
        if (tsOffset + tsCount * sizeof(uint32_t) > data.size()) continue;

        // Read timestamps
        auto timestamps = readArray<uint32_t>(data, tsOffset, tsCount);
        track.sequences[i].timestamps = std::move(timestamps);

        // Validate key data offset
        size_t keyElementSize = (type == TrackType::VEC3) ? sizeof(float) * 3 : sizeof(int16_t) * 4;
        if (keyOffset + keyCount * keyElementSize > data.size()) {
            track.sequences[i].timestamps.clear();
            continue;
        }

        // Read key values
        if (type == TrackType::VEC3) {
            // Translation/scale: float[3] per key
            struct Vec3Disk { float x, y, z; };
            auto values = readArray<Vec3Disk>(data, keyOffset, keyCount);
            track.sequences[i].vec3Values.reserve(values.size());
            for (const auto& v : values) {
                track.sequences[i].vec3Values.emplace_back(v.x, v.y, v.z);
            }
        } else {
            // Rotation: compressed quaternion int16[4] per key
            auto compressed = readArray<CompressedQuat>(data, keyOffset, keyCount);
            track.sequences[i].quatValues.reserve(compressed.size());
            for (const auto& cq : compressed) {
                // M2 compressed quaternion: offset mapping, NOT simple division
                // int16 range [-32768..32767] maps to float [-1..1] with offset
                float fx = (cq.x < 0) ? (cq.x + 32768) / 32767.0f : (cq.x - 32767) / 32767.0f;
                float fy = (cq.y < 0) ? (cq.y + 32768) / 32767.0f : (cq.y - 32767) / 32767.0f;
                float fz = (cq.z < 0) ? (cq.z + 32768) / 32767.0f : (cq.z - 32767) / 32767.0f;
                float fw = (cq.w < 0) ? (cq.w + 32768) / 32767.0f : (cq.w - 32767) / 32767.0f;
                // M2 on-disk: (x,y,z,w), GLM quat constructor: (w,x,y,z)
                glm::quat q(fw, fx, fy, fz);
                float len = glm::length(q);
                if (len > 0.001f) {
                    q = q / len;
                } else {
                    q = glm::quat(1.0f, 0.0f, 0.0f, 0.0f); // identity
                }
                track.sequences[i].quatValues.push_back(q);
            }
        }
    }
}

} // anonymous namespace

M2Model M2Loader::load(const std::vector<uint8_t>& m2Data) {
    M2Model model;

    if (m2Data.size() < sizeof(M2Header)) {
        core::Logger::getInstance().error("M2 data too small");
        return model;
    }

    // Read header
    M2Header header;
    std::memcpy(&header, m2Data.data(), sizeof(M2Header));

    // Verify magic
    if (std::strncmp(header.magic, "MD20", 4) != 0) {
        core::Logger::getInstance().error("Invalid M2 magic: expected MD20");
        return model;
    }

    core::Logger::getInstance().debug("Loading M2 model (version ", header.version, ")");

    // Read model name
    if (header.nameLength > 0 && header.nameOffset > 0) {
        model.name = readString(m2Data, header.nameOffset, header.nameLength);
    }

    model.version = header.version;
    model.globalFlags = header.globalFlags;

    // Bounding box
    model.boundMin = glm::vec3(header.boundingBox[0], header.boundingBox[1], header.boundingBox[2]);
    model.boundMax = glm::vec3(header.boundingBox[3], header.boundingBox[4], header.boundingBox[5]);
    model.boundRadius = header.boundingRadius;

    // Read vertices
    if (header.nVertices > 0 && header.ofsVertices > 0) {
        auto diskVerts = readArray<M2VertexDisk>(m2Data, header.ofsVertices, header.nVertices);
        model.vertices.reserve(diskVerts.size());

        for (const auto& dv : diskVerts) {
            M2Vertex v;
            v.position = glm::vec3(dv.pos[0], dv.pos[1], dv.pos[2]);
            std::memcpy(v.boneWeights, dv.boneWeights, 4);
            std::memcpy(v.boneIndices, dv.boneIndices, 4);
            v.normal = glm::vec3(dv.normal[0], dv.normal[1], dv.normal[2]);
            v.texCoords[0] = glm::vec2(dv.texCoords[0][0], dv.texCoords[0][1]);
            v.texCoords[1] = glm::vec2(dv.texCoords[1][0], dv.texCoords[1][1]);
            model.vertices.push_back(v);
        }

        core::Logger::getInstance().debug("  Vertices: ", model.vertices.size());
    }

    // Read animation sequences (needed before bones to know sequence count)
    if (header.nAnimations > 0 && header.ofsAnimations > 0) {
        auto diskSeqs = readArray<M2SequenceDisk>(m2Data, header.ofsAnimations, header.nAnimations);
        model.sequences.reserve(diskSeqs.size());

        for (const auto& ds : diskSeqs) {
            M2Sequence seq;
            seq.id = ds.id;
            seq.variationIndex = ds.variationIndex;
            seq.duration = ds.duration;
            seq.movingSpeed = ds.movingSpeed;
            seq.flags = ds.flags;
            seq.frequency = ds.frequency;
            seq.replayMin = ds.replayMin;
            seq.replayMax = ds.replayMax;
            seq.blendTime = ds.blendTime;
            seq.boundMin = glm::vec3(ds.bounds[0], ds.bounds[1], ds.bounds[2]);
            seq.boundMax = glm::vec3(ds.bounds[3], ds.bounds[4], ds.bounds[5]);
            seq.boundRadius = ds.boundRadius;
            seq.nextAnimation = ds.nextAnimation;
            seq.aliasNext = ds.aliasNext;

            model.sequences.push_back(seq);
        }

        core::Logger::getInstance().debug("  Animation sequences: ", model.sequences.size());
    }

    // Read global sequence durations (used by environmental animations: smoke, fire, etc.)
    if (header.nGlobalSequences > 0 && header.ofsGlobalSequences > 0) {
        model.globalSequenceDurations = readArray<uint32_t>(m2Data,
            header.ofsGlobalSequences, header.nGlobalSequences);
        core::Logger::getInstance().debug("  Global sequences: ", model.globalSequenceDurations.size());
    }

    // Read bones with full animation track data
    if (header.nBones > 0 && header.ofsBones > 0) {
        // Verify we have enough data for the full bone structures
        uint32_t expectedBoneSize = header.nBones * sizeof(M2BoneDisk);
        if (header.ofsBones + expectedBoneSize > m2Data.size()) {
            core::Logger::getInstance().warning("M2 bone data extends beyond file, loading with fallback");
        }

        model.bones.reserve(header.nBones);
        int bonesWithKeyframes = 0;

        // Build per-sequence flags to skip external-data sequences during M2 parse
        std::vector<uint32_t> seqFlags;
        seqFlags.reserve(model.sequences.size());
        for (const auto& seq : model.sequences) {
            seqFlags.push_back(seq.flags);
        }

        for (uint32_t boneIdx = 0; boneIdx < header.nBones; boneIdx++) {
            uint32_t boneOffset = header.ofsBones + boneIdx * sizeof(M2BoneDisk);
            if (boneOffset + sizeof(M2BoneDisk) > m2Data.size()) {
                // Fallback: create identity bone
                M2Bone bone;
                bone.keyBoneId = -1;
                bone.flags = 0;
                bone.parentBone = -1;
                bone.submeshId = 0;
                bone.pivot = glm::vec3(0.0f);
                model.bones.push_back(bone);
                continue;
            }

            M2BoneDisk db = readValue<M2BoneDisk>(m2Data, boneOffset);

            M2Bone bone;
            bone.keyBoneId = db.keyBoneId;
            bone.flags = db.flags;
            bone.parentBone = db.parentBone;
            bone.submeshId = db.submeshId;
            bone.pivot = glm::vec3(db.pivot[0], db.pivot[1], db.pivot[2]);

            // Parse animation tracks (skip sequences with external .anim data)
            parseAnimTrack(m2Data, db.translation, bone.translation, TrackType::VEC3, seqFlags);
            parseAnimTrack(m2Data, db.rotation, bone.rotation, TrackType::QUAT_COMPRESSED, seqFlags);
            parseAnimTrack(m2Data, db.scale, bone.scale, TrackType::VEC3, seqFlags);

            if (bone.translation.hasData() || bone.rotation.hasData() || bone.scale.hasData()) {
                bonesWithKeyframes++;
            }

            model.bones.push_back(bone);
        }

        core::Logger::getInstance().debug("  Bones: ", model.bones.size(),
            " (", bonesWithKeyframes, " with keyframes)");
    }

    // Read textures
    if (header.nTextures > 0 && header.ofsTextures > 0) {
        auto diskTextures = readArray<M2TextureDisk>(m2Data, header.ofsTextures, header.nTextures);
        model.textures.reserve(diskTextures.size());

        for (const auto& dt : diskTextures) {
            M2Texture tex;
            tex.type = dt.type;
            tex.flags = dt.flags;

            if (dt.nameLength > 0 && dt.nameOffset > 0) {
                tex.filename = readString(m2Data, dt.nameOffset, dt.nameLength);
            }

            model.textures.push_back(tex);
        }

        core::Logger::getInstance().debug("  Textures: ", model.textures.size());
    }

    // Read texture lookup
    if (header.nTexLookup > 0 && header.ofsTexLookup > 0) {
        model.textureLookup = readArray<uint16_t>(m2Data, header.ofsTexLookup, header.nTexLookup);
    }

    // Read render flags / materials (blend modes)
    if (header.nRenderFlags > 0 && header.ofsRenderFlags > 0) {
        struct M2MaterialDisk { uint16_t flags; uint16_t blendMode; };
        auto diskMats = readArray<M2MaterialDisk>(m2Data, header.ofsRenderFlags, header.nRenderFlags);
        model.materials.reserve(diskMats.size());
        for (const auto& dm : diskMats) {
            M2Material mat;
            mat.flags = dm.flags;
            mat.blendMode = dm.blendMode;
            model.materials.push_back(mat);
        }
        core::Logger::getInstance().debug("  Materials: ", model.materials.size());
    }

    // Read texture transforms (UV animation data)
    if (header.nUVAnimation > 0 && header.ofsUVAnimation > 0) {
        // Build per-sequence flags for skipping external .anim data
        std::vector<uint32_t> seqFlags;
        seqFlags.reserve(model.sequences.size());
        for (const auto& seq : model.sequences) {
            seqFlags.push_back(seq.flags);
        }

        model.textureTransforms.reserve(header.nUVAnimation);
        for (uint32_t i = 0; i < header.nUVAnimation; i++) {
            uint32_t ofs = header.ofsUVAnimation + i * sizeof(M2TextureTransformDisk);
            if (ofs + sizeof(M2TextureTransformDisk) > m2Data.size()) break;

            M2TextureTransformDisk dt = readValue<M2TextureTransformDisk>(m2Data, ofs);
            M2TextureTransform tt;
            parseAnimTrack(m2Data, dt.translation, tt.translation, TrackType::VEC3, seqFlags);
            parseAnimTrack(m2Data, dt.rotation, tt.rotation, TrackType::QUAT_COMPRESSED, seqFlags);
            parseAnimTrack(m2Data, dt.scaling, tt.scale, TrackType::VEC3, seqFlags);
            model.textureTransforms.push_back(std::move(tt));
        }
        core::Logger::getInstance().debug("  Texture transforms: ", model.textureTransforms.size());
    }

    // Read texture transform lookup (nTransLookup)
    if (header.nTransLookup > 0 && header.ofsTransLookup > 0) {
        model.textureTransformLookup = readArray<uint16_t>(m2Data, header.ofsTransLookup, header.nTransLookup);
    }

    // Read attachment points
    if (header.nAttachments > 0 && header.ofsAttachments > 0) {
        auto diskAttachments = readArray<M2AttachmentDisk>(m2Data, header.ofsAttachments, header.nAttachments);
        model.attachments.reserve(diskAttachments.size());
        for (const auto& da : diskAttachments) {
            M2Attachment att;
            att.id = da.id;
            att.bone = da.bone;
            att.position = glm::vec3(da.position[0], da.position[1], da.position[2]);
            model.attachments.push_back(att);
        }
        core::Logger::getInstance().debug("  Attachments: ", model.attachments.size());
    }

    // Read attachment lookup
    if (header.nAttachmentLookup > 0 && header.ofsAttachmentLookup > 0) {
        model.attachmentLookup = readArray<uint16_t>(m2Data, header.ofsAttachmentLookup, header.nAttachmentLookup);
    }

    static int m2LoadLogBudget = 200;
    if (m2LoadLogBudget-- > 0) {
        core::Logger::getInstance().debug("M2 model loaded: ", model.name);
    }
    return model;
}

bool M2Loader::loadSkin(const std::vector<uint8_t>& skinData, M2Model& model) {
    if (skinData.size() < sizeof(M2SkinHeader)) {
        core::Logger::getInstance().error("Skin data too small");
        return false;
    }

    // Read skin header
    M2SkinHeader header;
    std::memcpy(&header, skinData.data(), sizeof(M2SkinHeader));

    // Verify magic
    if (std::strncmp(header.magic, "SKIN", 4) != 0) {
        core::Logger::getInstance().error("Invalid skin magic: expected SKIN");
        return false;
    }

    core::Logger::getInstance().debug("Loading M2 skin file");

    // Read vertex lookup table (maps skin-local indices to global vertex indices)
    std::vector<uint16_t> vertexLookup;
    if (header.nIndices > 0 && header.ofsIndices > 0) {
        vertexLookup = readArray<uint16_t>(skinData, header.ofsIndices, header.nIndices);
    }

    // Read triangle indices (indices into the vertex lookup table)
    std::vector<uint16_t> triangles;
    if (header.nTriangles > 0 && header.ofsTriangles > 0) {
        triangles = readArray<uint16_t>(skinData, header.ofsTriangles, header.nTriangles);
    }

    // Resolve two-level indirection: triangle index -> lookup table -> global vertex
    model.indices.clear();
    model.indices.reserve(triangles.size());
    uint32_t outOfBounds = 0;
    for (uint16_t triIdx : triangles) {
        if (triIdx < vertexLookup.size()) {
            uint16_t globalIdx = vertexLookup[triIdx];
            if (globalIdx < model.vertices.size()) {
                model.indices.push_back(globalIdx);
            } else {
                model.indices.push_back(0);
                outOfBounds++;
            }
        } else {
            model.indices.push_back(0);
            outOfBounds++;
        }
    }
    core::Logger::getInstance().debug("  Resolved ", model.indices.size(), " final indices");
    if (outOfBounds > 0) {
        core::Logger::getInstance().warning("  ", outOfBounds, " out-of-bounds indices clamped to 0");
    }

    // Read submeshes (proper vertex/index ranges)
    std::vector<M2SkinSubmesh> submeshes;
    if (header.nSubmeshes > 0 && header.ofsSubmeshes > 0) {
        submeshes = readArray<M2SkinSubmesh>(skinData, header.ofsSubmeshes, header.nSubmeshes);
        core::Logger::getInstance().debug("  Submeshes: ", submeshes.size());
        for (size_t i = 0; i < submeshes.size(); i++) {
            const auto& sm = submeshes[i];
            core::Logger::getInstance().info("  SkinSection[", i, "]: id=", sm.id,
                " level=", sm.level,
                " vtxStart=", sm.vertexStart, " vtxCount=", sm.vertexCount,
                " idxStart=", sm.indexStart, " idxCount=", sm.indexCount,
                " boneCount=", sm.boneCount, " boneStart=", sm.boneStart);
        }
    }

    // Read batches with proper submesh references
    if (header.nBatches > 0 && header.ofsBatches > 0) {
        auto diskBatches = readArray<M2BatchDisk>(skinData, header.ofsBatches, header.nBatches);
        model.batches.clear();
        model.batches.reserve(diskBatches.size());

        for (size_t i = 0; i < diskBatches.size(); i++) {
            const auto& db = diskBatches[i];
            M2Batch batch;

            batch.flags = db.flags;
            batch.priorityPlane = db.priorityPlane;
            batch.shader = db.shader;
            batch.skinSectionIndex = db.skinSectionIndex;
            batch.colorIndex = db.colorIndex;
            batch.materialIndex = db.materialIndex;
            batch.materialLayer = db.materialLayer;
            batch.textureCount = db.textureCount;
            batch.textureIndex = db.textureComboIndex;
            batch.textureUnit = db.textureCoordIndex;
            batch.transparencyIndex = db.textureWeightIndex;
            batch.textureAnimIndex = db.textureTransformIndex;

            // Look up proper vertex/index ranges from submesh
            if (db.skinSectionIndex < submeshes.size()) {
                const auto& sm = submeshes[db.skinSectionIndex];
                batch.indexStart = sm.indexStart;
                batch.indexCount = sm.indexCount;
                batch.vertexStart = sm.vertexStart;
                batch.vertexCount = sm.vertexCount;
                batch.submeshId = sm.id;
                batch.submeshLevel = sm.level;
            } else {
                // Fallback: render entire model as one batch
                batch.indexStart = 0;
                batch.indexCount = model.indices.size();
                batch.vertexStart = 0;
                batch.vertexCount = model.vertices.size();
            }

            model.batches.push_back(batch);
        }

        core::Logger::getInstance().debug("  Batches: ", model.batches.size());
    }

    return true;
}

void M2Loader::loadAnimFile(const std::vector<uint8_t>& m2Data,
                            const std::vector<uint8_t>& animData,
                            uint32_t sequenceIndex,
                            M2Model& model) {
    if (m2Data.size() < sizeof(M2Header) || animData.empty()) return;

    M2Header header;
    std::memcpy(&header, m2Data.data(), sizeof(M2Header));

    if (header.nBones == 0 || header.ofsBones == 0) return;
    if (sequenceIndex >= model.sequences.size()) return;

    int patchedTracks = 0;

    for (uint32_t boneIdx = 0; boneIdx < header.nBones && boneIdx < model.bones.size(); boneIdx++) {
        uint32_t boneOffset = header.ofsBones + boneIdx * sizeof(M2BoneDisk);
        if (boneOffset + sizeof(M2BoneDisk) > m2Data.size()) continue;

        M2BoneDisk db = readValue<M2BoneDisk>(m2Data, boneOffset);
        auto& bone = model.bones[boneIdx];

        // Helper to patch one track for this sequence index
        auto patchTrack = [&](const M2TrackDisk& disk, M2AnimationTrack& track, TrackType type) {
            if (disk.nTimestamps == 0 || disk.nKeys == 0) return;
            if (sequenceIndex >= disk.nTimestamps) return;

            // Ensure track.sequences is large enough
            if (track.sequences.size() <= sequenceIndex) {
                track.sequences.resize(sequenceIndex + 1);
            }

            auto& seqKeys = track.sequences[sequenceIndex];

            // Already has data (loaded from main M2 file)
            if (!seqKeys.timestamps.empty()) return;

            // Read sub-array header for this sequence from the M2 file
            uint32_t tsHeaderOfs = disk.ofsTimestamps + sequenceIndex * 8;
            uint32_t keyHeaderOfs = disk.ofsKeys + sequenceIndex * 8;
            if (tsHeaderOfs + 8 > m2Data.size() || keyHeaderOfs + 8 > m2Data.size()) return;

            uint32_t tsCount = readValue<uint32_t>(m2Data, tsHeaderOfs);
            uint32_t tsOffset = readValue<uint32_t>(m2Data, tsHeaderOfs + 4);
            uint32_t keyCount = readValue<uint32_t>(m2Data, keyHeaderOfs);
            uint32_t keyOffset = readValue<uint32_t>(m2Data, keyHeaderOfs + 4);

            if (tsCount == 0 || keyCount == 0) return;

            // These offsets point into the .anim file data
            if (tsOffset + tsCount * sizeof(uint32_t) > animData.size()) return;

            size_t keyElementSize = (type == TrackType::VEC3) ? sizeof(float) * 3 : sizeof(int16_t) * 4;
            if (keyOffset + keyCount * keyElementSize > animData.size()) return;

            // Read timestamps from .anim data
            auto timestamps = readArray<uint32_t>(animData, tsOffset, tsCount);
            seqKeys.timestamps = std::move(timestamps);

            // Read key values from .anim data
            if (type == TrackType::VEC3) {
                struct Vec3Disk { float x, y, z; };
                auto values = readArray<Vec3Disk>(animData, keyOffset, keyCount);
                seqKeys.vec3Values.reserve(values.size());
                for (const auto& v : values) {
                    seqKeys.vec3Values.emplace_back(v.x, v.y, v.z);
                }
            } else {
                auto compressed = readArray<CompressedQuat>(animData, keyOffset, keyCount);
                seqKeys.quatValues.reserve(compressed.size());
                for (const auto& cq : compressed) {
                    float fx = (cq.x < 0) ? (cq.x + 32768) / 32767.0f : (cq.x - 32767) / 32767.0f;
                    float fy = (cq.y < 0) ? (cq.y + 32768) / 32767.0f : (cq.y - 32767) / 32767.0f;
                    float fz = (cq.z < 0) ? (cq.z + 32768) / 32767.0f : (cq.z - 32767) / 32767.0f;
                    float fw = (cq.w < 0) ? (cq.w + 32768) / 32767.0f : (cq.w - 32767) / 32767.0f;
                    glm::quat q(fw, fx, fy, fz);
                    float len = glm::length(q);
                    if (len > 0.001f) {
                        q = q / len;
                    } else {
                        q = glm::quat(1.0f, 0.0f, 0.0f, 0.0f);
                    }
                    seqKeys.quatValues.push_back(q);
                }
            }
            patchedTracks++;
        };

        patchTrack(db.translation, bone.translation, TrackType::VEC3);
        patchTrack(db.rotation, bone.rotation, TrackType::QUAT_COMPRESSED);
        patchTrack(db.scale, bone.scale, TrackType::VEC3);
    }

    core::Logger::getInstance().info("Loaded .anim for sequence ", sequenceIndex,
        " (id=", model.sequences[sequenceIndex].id, "): patched ", patchedTracks, " bone tracks");
}

} // namespace pipeline
} // namespace wowee