/*
 * This file is part of the AzerothCore Project. See AUTHORS file for Copyright information
 *
 * This program is free software; you can redistribute it and/or modify it
 * under the terms of the GNU Affero General Public License as published by the
 * Free Software Foundation; either version 3 of the License, or (at your
 * option) any later version.
 *
 * This program is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU Affero General Public License for
 * more details.
 *
 * You should have received a copy of the GNU General Public License along
 * with this program. If not, see <http://www.gnu.org/licenses/>.
 */

#include "TerrainBuilder.h"
#include "PathCommon.h"
#include "MapBuilder.h"
#include "MapDefines.h"
#include "VMapMgr2.h"
#include "MapTree.h"
#include "ModelInstance.h"
#include <vector>

// ******************************************
// Map file format defines
// ******************************************
struct map_fileheader
{
    uint32 mapMagic;
    uint32 versionMagic;
    uint32 buildMagic;
    uint32 areaMapOffset;
    uint32 areaMapSize;
    uint32 heightMapOffset;
    uint32 heightMapSize;
    uint32 liquidMapOffset;
    uint32 liquidMapSize;
    uint32 holesOffset;
    uint32 holesSize;
};

#define MAP_HEIGHT_NO_HEIGHT  0x0001
#define MAP_HEIGHT_AS_INT16   0x0002
#define MAP_HEIGHT_AS_INT8    0x0004

struct map_heightHeader
{
    uint32 fourcc;
    uint32 flags;
    float  gridHeight;
    float  gridMaxHeight;
};

#define MAP_LIQUID_NO_TYPE    0x0001
#define MAP_LIQUID_NO_HEIGHT  0x0002

struct map_liquidHeader
{
    uint32 fourcc;
    uint16 flags;
    uint16 liquidType;
    uint8  offsetX;
    uint8  offsetY;
    uint8  width;
    uint8  height;
    float  liquidLevel;
};

#define MAP_LIQUID_TYPE_NO_WATER    0x00
#define MAP_LIQUID_TYPE_WATER       0x01
#define MAP_LIQUID_TYPE_OCEAN       0x02
#define MAP_LIQUID_TYPE_MAGMA       0x04
#define MAP_LIQUID_TYPE_SLIME       0x08
#define MAP_LIQUID_TYPE_DARK_WATER  0x10
#define MAP_LIQUID_TYPE_WMO_WATER   0x20

namespace MMAP
{

    uint32 const MAP_VERSION_MAGIC = 8;

    TerrainBuilder::TerrainBuilder(bool skipLiquid) : m_skipLiquid (skipLiquid) { }
    TerrainBuilder::~TerrainBuilder() = default;

    /**************************************************************************/
    void TerrainBuilder::getLoopVars(Spot portion, int& loopStart, int& loopEnd, int& loopInc)
    {
        switch (portion)
        {
            case ENTIRE:
                loopStart = 0;
                loopEnd = V8_SIZE_SQ;
                loopInc = 1;
                break;
            case TOP:
                loopStart = 0;
                loopEnd = V8_SIZE;
                loopInc = 1;
                break;
            case LEFT:
                loopStart = 0;
                loopEnd = V8_SIZE_SQ - V8_SIZE + 1;
                loopInc = V8_SIZE;
                break;
            case RIGHT:
                loopStart = V8_SIZE - 1;
                loopEnd = V8_SIZE_SQ;
                loopInc = V8_SIZE;
                break;
            case BOTTOM:
                loopStart = V8_SIZE_SQ - V8_SIZE;
                loopEnd = V8_SIZE_SQ;
                loopInc = 1;
                break;
        }
    }

    /**************************************************************************/
    void TerrainBuilder::loadMap(uint32 mapID, uint32 tileX, uint32 tileY, MeshData& meshData)
    {
        if (loadMap(mapID, tileX, tileY, meshData, ENTIRE))
        {
            loadMap(mapID, tileX + 1, tileY, meshData, LEFT);
            loadMap(mapID, tileX - 1, tileY, meshData, RIGHT);
            loadMap(mapID, tileX, tileY + 1, meshData, TOP);
            loadMap(mapID, tileX, tileY - 1, meshData, BOTTOM);
        }
    }

    /**************************************************************************/
    bool TerrainBuilder::loadMap(uint32 mapID, uint32 tileX, uint32 tileY, MeshData& meshData, Spot portion)
    {
        char mapFileName[255];
        sprintf(mapFileName, "maps/%03u%02u%02u.map", mapID, tileY, tileX);

        FILE* mapFile = fopen(mapFileName, "rb");
        if (!mapFile)
            return false;

        map_fileheader fheader;
        if (fread(&fheader, sizeof(map_fileheader), 1, mapFile) != 1 ||
                fheader.versionMagic != MAP_VERSION_MAGIC)
        {
            fclose(mapFile);
            printf("%s is the wrong version, please extract new .map files\n", mapFileName);
            return false;
        }

        map_heightHeader hheader;
        fseek(mapFile, fheader.heightMapOffset, SEEK_SET);

        bool haveTerrain = false;
        bool haveLiquid = false;
        if (fread(&hheader, sizeof(map_heightHeader), 1, mapFile) == 1)
        {
            haveTerrain = !(hheader.flags & MAP_HEIGHT_NO_HEIGHT);
            haveLiquid = fheader.liquidMapOffset && !m_skipLiquid;
        }

        // no data in this map file
        if (!haveTerrain && !haveLiquid)
        {
            fclose(mapFile);
            return false;
        }

        // data used later
        uint16 holes[16][16];
        memset(holes, 0, sizeof(holes));
        uint8 liquid_type[16][16];
        memset(liquid_type, 0, sizeof(liquid_type));
        G3D::Array<int> ltriangles;
        G3D::Array<int> ttriangles;

        // terrain data
        if (haveTerrain)
        {
            float heightMultiplier;
            float V9[V9_SIZE_SQ], V8[V8_SIZE_SQ];
            int expected = V9_SIZE_SQ + V8_SIZE_SQ;

            if (hheader.flags & MAP_HEIGHT_AS_INT8)
            {
                uint8 v9[V9_SIZE_SQ];
                uint8 v8[V8_SIZE_SQ];
                int count = 0;
                count += fread(v9, sizeof(uint8), V9_SIZE_SQ, mapFile);
                count += fread(v8, sizeof(uint8), V8_SIZE_SQ, mapFile);
                if (count != expected)
                    printf("TerrainBuilder::loadMap: Failed to read some data expected %d, read %d\n", expected, count);

                heightMultiplier = (hheader.gridMaxHeight - hheader.gridHeight) / 255;

                for (int i = 0; i < V9_SIZE_SQ; ++i)
                    V9[i] = (float)v9[i] * heightMultiplier + hheader.gridHeight;

                for (int i = 0; i < V8_SIZE_SQ; ++i)
                    V8[i] = (float)v8[i] * heightMultiplier + hheader.gridHeight;
            }
            else if (hheader.flags & MAP_HEIGHT_AS_INT16)
            {
                uint16 v9[V9_SIZE_SQ];
                uint16 v8[V8_SIZE_SQ];
                int count = 0;
                count += fread(v9, sizeof(uint16), V9_SIZE_SQ, mapFile);
                count += fread(v8, sizeof(uint16), V8_SIZE_SQ, mapFile);
                if (count != expected)
                    printf("TerrainBuilder::loadMap: Failed to read some data expected %d, read %d\n", expected, count);

                heightMultiplier = (hheader.gridMaxHeight - hheader.gridHeight) / 65535;

                for (int i = 0; i < V9_SIZE_SQ; ++i)
                    V9[i] = (float)v9[i] * heightMultiplier + hheader.gridHeight;

                for (int i = 0; i < V8_SIZE_SQ; ++i)
                    V8[i] = (float)v8[i] * heightMultiplier + hheader.gridHeight;
            }
            else
            {
                int count = 0;
                count += fread(V9, sizeof(float), V9_SIZE_SQ, mapFile);
                count += fread(V8, sizeof(float), V8_SIZE_SQ, mapFile);
                if (count != expected)
                    printf("TerrainBuilder::loadMap: Failed to read some data expected %d, read %d\n", expected, count);
            }

            // hole data
            if (fheader.holesSize != 0)
            {
                memset(holes, 0, fheader.holesSize);
                fseek(mapFile, fheader.holesOffset, SEEK_SET);
                if (fread(holes, fheader.holesSize, 1, mapFile) != 1)
                    printf("TerrainBuilder::loadMap: Failed to read some data expected 1, read 0\n");
            }

            int count = meshData.solidVerts.size() / 3;
            float xoffset = (float(tileX) - 32) * GRID_SIZE;
            float yoffset = (float(tileY) - 32) * GRID_SIZE;

            float coord[3];

            for (int i = 0; i < V9_SIZE_SQ; ++i)
            {
                getHeightCoord(i, GRID_V9, xoffset, yoffset, coord, V9);
                meshData.solidVerts.append(coord[0]);
                meshData.solidVerts.append(coord[2]);
                meshData.solidVerts.append(coord[1]);
            }

            for (int i = 0; i < V8_SIZE_SQ; ++i)
            {
                getHeightCoord(i, GRID_V8, xoffset, yoffset, coord, V8);
                meshData.solidVerts.append(coord[0]);
                meshData.solidVerts.append(coord[2]);
                meshData.solidVerts.append(coord[1]);
            }

            int indices[] = { 0, 0, 0 };
            int loopStart = 0, loopEnd = 0, loopInc = 0;
            getLoopVars(portion, loopStart, loopEnd, loopInc);
            for (int i = loopStart; i < loopEnd; i += loopInc)
                for (int j = TOP; j <= BOTTOM; j += 1)
                {
                    getHeightTriangle(i, Spot(j), indices);
                    ttriangles.append(indices[2] + count);
                    ttriangles.append(indices[1] + count);
                    ttriangles.append(indices[0] + count);
                }
        }

        // liquid data
        if (haveLiquid)
        {
            map_liquidHeader lheader;
            fseek(mapFile, fheader.liquidMapOffset, SEEK_SET);
            if (fread(&lheader, sizeof(map_liquidHeader), 1, mapFile) != 1)
                printf("TerrainBuilder::loadMap: Failed to read some data expected 1, read 0\n");

            float* liquid_map = nullptr;

            if (!(lheader.flags & MAP_LIQUID_NO_TYPE))
                if (fread(liquid_type, sizeof(liquid_type), 1, mapFile) != 1)
                    printf("TerrainBuilder::loadMap: Failed to read some data expected 1, read 0\n");

            if (!(lheader.flags & MAP_LIQUID_NO_HEIGHT))
            {
                uint32 toRead = lheader.width * lheader.height;
                liquid_map = new float [toRead];
                if (fread(liquid_map, sizeof(float), toRead, mapFile) != toRead)
                    printf("TerrainBuilder::loadMap: Failed to read some data expected 1, read 0\n");
            }

            if (liquid_map)
            {
                int count = meshData.liquidVerts.size() / 3;
                float xoffset = (float(tileX) - 32) * GRID_SIZE;
                float yoffset = (float(tileY) - 32) * GRID_SIZE;

                float coord[3];
                int row, col;

                // generate coordinates
                if (!(lheader.flags & MAP_LIQUID_NO_HEIGHT))
                {
                    int j = 0;
                    for (int i = 0; i < V9_SIZE_SQ; ++i)
                    {
                        row = i / V9_SIZE;
                        col = i % V9_SIZE;

                        if (row < lheader.offsetY || row >= lheader.offsetY + lheader.height ||
                                col < lheader.offsetX || col >= lheader.offsetX + lheader.width)
                        {
                            // dummy vert using invalid height
                            meshData.liquidVerts.append((xoffset + col * GRID_PART_SIZE) * -1, INVALID_MAP_LIQ_HEIGHT, (yoffset + row * GRID_PART_SIZE) * -1);
                            continue;
                        }

                        getLiquidCoord(i, j, xoffset, yoffset, coord, liquid_map);
                        meshData.liquidVerts.append(coord[0]);
                        meshData.liquidVerts.append(coord[2]);
                        meshData.liquidVerts.append(coord[1]);
                        j++;
                    }
                }
                else
                {
                    for (int i = 0; i < V9_SIZE_SQ; ++i)
                    {
                        row = i / V9_SIZE;
                        col = i % V9_SIZE;
                        meshData.liquidVerts.append((xoffset + col * GRID_PART_SIZE) * -1, lheader.liquidLevel, (yoffset + row * GRID_PART_SIZE) * -1);
                    }
                }

                delete [] liquid_map;

                int indices[] = { 0, 0, 0 };
                int loopStart = 0, loopEnd = 0, loopInc = 0, triInc = BOTTOM - TOP;
                getLoopVars(portion, loopStart, loopEnd, loopInc);

                // generate triangles
                for (int i = loopStart; i < loopEnd; i += loopInc)
                    for (int j = TOP; j <= BOTTOM; j += triInc)
                    {
                        getHeightTriangle(i, Spot(j), indices, true);
                        ltriangles.append(indices[2] + count);
                        ltriangles.append(indices[1] + count);
                        ltriangles.append(indices[0] + count);
                    }
            }
        }

        fclose(mapFile);

        // now that we have gathered the data, we can figure out which parts to keep:
        // liquid above ground, ground above liquid
        int loopStart = 0, loopEnd = 0, loopInc = 0, tTriCount = 4;
        bool useTerrain, useLiquid;

        float* lverts = meshData.liquidVerts.getCArray();
        int* ltris = ltriangles.getCArray();

        float* tverts = meshData.solidVerts.getCArray();
        int* ttris = ttriangles.getCArray();

        if ((ltriangles.size() + ttriangles.size()) == 0)
            return false;

        // make a copy of liquid vertices
        // used to pad right-bottom frame due to lost vertex data at extraction
        float* lverts_copy = nullptr;
        if (meshData.liquidVerts.size())
        {
            lverts_copy = new float[meshData.liquidVerts.size()];
            memcpy(lverts_copy, lverts, sizeof(float)*meshData.liquidVerts.size());
        }

        getLoopVars(portion, loopStart, loopEnd, loopInc);
        for (int i = loopStart; i < loopEnd; i += loopInc)
        {
            for (int j = 0; j < 2; ++j)
            {
                // default is true, will change to false if needed
                useTerrain = true;
                useLiquid = true;
                uint8 liquidType = MAP_LIQUID_TYPE_NO_WATER;
                // FIXME: "warning: the address of ‘liquid_type’ will always evaluate as ‘true’"

                // if there is no liquid, don't use liquid
                if (!meshData.liquidVerts.size() || !ltriangles.size())
                    useLiquid = false;
                else
                {
                    liquidType = getLiquidType(i, liquid_type);
                    switch (liquidType)
                    {
                        default:
                            useLiquid = false;
                            break;
                        case MAP_LIQUID_TYPE_WATER:
                        case MAP_LIQUID_TYPE_OCEAN:
                            // merge different types of water
                            liquidType = NAV_WATER;
                            break;
                        case MAP_LIQUID_TYPE_MAGMA:
                            liquidType = NAV_MAGMA;
                            break;
                        case MAP_LIQUID_TYPE_SLIME:
                            liquidType = NAV_SLIME;
                            break;
                        case MAP_LIQUID_TYPE_DARK_WATER:
                            // players should not be here, so logically neither should creatures
                            useTerrain = false;
                            useLiquid = false;
                            break;
                    }
                }

                // if there is no terrain, don't use terrain
                if (!ttriangles.size())
                    useTerrain = false;

                // while extracting ADT data we are losing right-bottom vertices
                // this code adds fair approximation of lost data
                if (useLiquid)
                {
                    float quadHeight = 0;
                    uint32 validCount = 0;
                    for (uint32 idx = 0; idx < 3; idx++)
                    {
                        float h = lverts_copy[ltris[idx] * 3 + 1];
                        if (h != INVALID_MAP_LIQ_HEIGHT && h < INVALID_MAP_LIQ_HEIGHT_MAX)
                        {
                            quadHeight += h;
                            validCount++;
                        }
                    }

                    // update vertex height data
                    if (validCount > 0 && validCount < 3)
                    {
                        quadHeight /= validCount;
                        for (uint32 idx = 0; idx < 3; idx++)
                        {
                            float h = lverts[ltris[idx] * 3 + 1];
                            if (h == INVALID_MAP_LIQ_HEIGHT || h > INVALID_MAP_LIQ_HEIGHT_MAX)
                                lverts[ltris[idx] * 3 + 1] = quadHeight;
                        }
                    }

                    // no valid vertexes - don't use this poly at all
                    if (validCount == 0)
                        useLiquid = false;
                }

                // if there is a hole here, don't use the terrain
                if (useTerrain && fheader.holesSize != 0)
                    useTerrain = !isHole(i, holes);

                // we use only one terrain kind per quad - pick higher one
                if (useTerrain && useLiquid)
                {
                    float minLLevel = INVALID_MAP_LIQ_HEIGHT_MAX;
                    float maxLLevel = INVALID_MAP_LIQ_HEIGHT;
                    for (uint32 x = 0; x < 3; x++)
                    {
                        float h = lverts[ltris[x] * 3 + 1];
                        if (minLLevel > h)
                            minLLevel = h;

                        if (maxLLevel < h)
                            maxLLevel = h;
                    }

                    float maxTLevel = INVALID_MAP_LIQ_HEIGHT;
                    float minTLevel = INVALID_MAP_LIQ_HEIGHT_MAX;
                    for (uint32 x = 0; x < 6; x++)
                    {
                        float h = tverts[ttris[x] * 3 + 1];
                        if (maxTLevel < h)
                            maxTLevel = h;

                        if (minTLevel > h)
                            minTLevel = h;
                    }

                    // terrain under the liquid?
                    if (minLLevel > maxTLevel)
                        useTerrain = false;

                    //liquid under the terrain?
                    if (minTLevel > maxLLevel)
                        useLiquid = false;
                }

                // store the result
                if (useLiquid)
                {
                    meshData.liquidType.append(liquidType);
                    for (int k = 0; k < 3; ++k)
                        meshData.liquidTris.append(ltris[k]);
                }

                if (useTerrain)
                    for (int k = 0; k < 3 * tTriCount / 2; ++k)
                        meshData.solidTris.append(ttris[k]);

                // advance to next set of triangles
                ltris += 3;
                ttris += 3 * tTriCount / 2;
            }
        }

        if (lverts_copy)
            delete [] lverts_copy;

        return meshData.solidTris.size() || meshData.liquidTris.size();
    }

    /**************************************************************************/
    void TerrainBuilder::getHeightCoord(int index, Grid grid, float xOffset, float yOffset, float* coord, float* v)
    {
        // wow coords: x, y, height
        // coord is mirroed about the horizontal axes
        switch (grid)
        {
            case GRID_V9:
                coord[0] = (xOffset + index % (V9_SIZE) * GRID_PART_SIZE) * -1.f;
                coord[1] = (yOffset + (int)(index / (V9_SIZE)) * GRID_PART_SIZE) * -1.f;
                coord[2] = v[index];
                break;
            case GRID_V8:
                coord[0] = (xOffset + index % (V8_SIZE) * GRID_PART_SIZE + GRID_PART_SIZE / 2.f) * -1.f;
                coord[1] = (yOffset + (int)(index / (V8_SIZE)) * GRID_PART_SIZE + GRID_PART_SIZE / 2.f) * -1.f;
                coord[2] = v[index];
                break;
        }
    }

    /**************************************************************************/
    void TerrainBuilder::getHeightTriangle(int square, Spot triangle, int* indices, bool liquid/* = false*/)
    {
        int rowOffset = square / V8_SIZE;
        if (!liquid)
            switch (triangle)
            {
                case TOP:
                    indices[0] = square + rowOffset;                //           0-----1 .... 128
                    indices[1] = square + 1 + rowOffset;            //           |\ T /|
                    indices[2] = (V9_SIZE_SQ) + square;             //           | \ / |
                    break;                                          //           |L 0 R| .. 127
                case LEFT:                                          //           | / \ |
                    indices[0] = square + rowOffset;                //           |/ B \|
                    indices[1] = (V9_SIZE_SQ) + square;             //          129---130 ... 386
                    indices[2] = square + V9_SIZE + rowOffset;      //           |\   /|
                    break;                                          //           | \ / |
                case RIGHT:                                         //           | 128 | .. 255
                    indices[0] = square + 1 + rowOffset;            //           | / \ |
                    indices[1] = square + V9_SIZE + 1 + rowOffset;  //           |/   \|
                    indices[2] = (V9_SIZE_SQ) + square;             //          258---259 ... 515
                    break;
                case BOTTOM:
                    indices[0] = (V9_SIZE_SQ) + square;
                    indices[1] = square + V9_SIZE + 1 + rowOffset;
                    indices[2] = square + V9_SIZE + rowOffset;
                    break;
                default:
                    break;
            }
        else
            switch (triangle)
            {
                case TOP:
                    indices[0] = square + rowOffset;
                    indices[1] = square + 1 + rowOffset;
                    indices[2] = square + V9_SIZE + 1 + rowOffset;
                    break;
                case BOTTOM:
                    indices[0] = square + rowOffset;
                    indices[1] = square + V9_SIZE + 1 + rowOffset;
                    indices[2] = square + V9_SIZE + rowOffset;
                    break;
                default:
                    break;
            }

        /*
            0-----1 .... 128
            |\    |
            | \ T |
            |  \  |
            | B \ |
            |    \|
            129---130 ... 386
            |\    |
            | \   |
            |  \  |
            |   \ |
            |    \|
            258---259 ... 515
        */
    }

    /**************************************************************************/
    void TerrainBuilder::getLiquidCoord(int index, int index2, float xOffset, float yOffset, float* coord, float* v)
    {
        // wow coords: x, y, height
        // coord is mirroed about the horizontal axes
        coord[0] = (xOffset + index % (V9_SIZE) * GRID_PART_SIZE) * -1.f;
        coord[1] = (yOffset + (int)(index / (V9_SIZE)) * GRID_PART_SIZE) * -1.f;
        coord[2] = v[index2];
    }

    static uint16 holetab_h[4] = {0x1111, 0x2222, 0x4444, 0x8888};
    static uint16 holetab_v[4] = {0x000F, 0x00F0, 0x0F00, 0xF000};

    /**************************************************************************/
    bool TerrainBuilder::isHole(int square, const uint16 holes[16][16])
    {
        int row = square / 128;
        int col = square % 128;
        int cellRow = row / 8;     // 8 squares per cell
        int cellCol = col / 8;
        int holeRow = row % 8 / 2;
        int holeCol = (square - (row * 128 + cellCol * 8)) / 2;

        uint16 hole = holes[cellRow][cellCol];

        return (hole & holetab_h[holeCol] & holetab_v[holeRow]) != 0;
    }

    /**************************************************************************/
    uint8 TerrainBuilder::getLiquidType(int square, const uint8 liquid_type[16][16])
    {
        int row = square / 128;
        int col = square % 128;
        int cellRow = row / 8;     // 8 squares per cell
        int cellCol = col / 8;

        return liquid_type[cellRow][cellCol];
    }

    /**************************************************************************/
    bool TerrainBuilder::loadVMap(uint32 mapID, uint32 tileX, uint32 tileY, MeshData& meshData)
    {
        IVMapMgr* vmapMgr = new VMapMgr2();
        int result = vmapMgr->loadMap("vmaps", mapID, tileX, tileY);
        bool retval = false;

        do
        {
            if (result == VMAP_LOAD_RESULT_ERROR)
                break;

            InstanceTreeMap instanceTrees;
            ((VMapMgr2*)vmapMgr)->GetInstanceMapTree(instanceTrees);

            if (!instanceTrees[mapID])
                break;

            ModelInstance* models = nullptr;
            uint32 count = 0;
            instanceTrees[mapID]->GetModelInstances(models, count);

            if (!models)
                break;

            for (uint32 i = 0; i < count; ++i)
            {
                ModelInstance instance = models[i];

                // model instances exist in tree even though there are instances of that model in this tile
                WorldModel* worldModel = instance.getWorldModel();
                if (!worldModel)
                    continue;

                // now we have a model to add to the meshdata
                retval = true;

                std::vector<GroupModel> groupModels;
                worldModel->GetGroupModels(groupModels);

                // all M2s need to have triangle indices reversed
                bool isM2 = instance.name.find(".m2") != std::string::npos || instance.name.find(".M2") != std::string::npos;

                // transform data
                float scale = instance.iScale;
                G3D::Matrix3 rotation = G3D::Matrix3::fromEulerAnglesXYZ(G3D::pi() * instance.iRot.z / -180.f, G3D::pi() * instance.iRot.x / -180.f, G3D::pi() * instance.iRot.y / -180.f);
                G3D::Vector3 position = instance.iPos;
                position.x -= 32 * GRID_SIZE;
                position.y -= 32 * GRID_SIZE;

                for (auto & groupModel : groupModels)
                {
                    std::vector<G3D::Vector3> tempVertices;
                    std::vector<G3D::Vector3> transformedVertices;
                    std::vector<MeshTriangle> tempTriangles;
                    WmoLiquid* liquid = nullptr;

                    groupModel.GetMeshData(tempVertices, tempTriangles, liquid);

                    // first handle collision mesh
                    transform(tempVertices, transformedVertices, scale, rotation, position);

                    int offset = meshData.solidVerts.size() / 3;

                    copyVertices(transformedVertices, meshData.solidVerts);
                    copyIndices(tempTriangles, meshData.solidTris, offset, isM2);

                    // now handle liquid data
                    if (liquid)
                    {
                        std::vector<G3D::Vector3> liqVerts;
                        std::vector<int> liqTris;
                        uint32 tilesX, tilesY, vertsX, vertsY;
                        G3D::Vector3 corner;
                        liquid->GetPosInfo(tilesX, tilesY, corner);
                        vertsX = tilesX + 1;
                        vertsY = tilesY + 1;
                        uint8* flags = liquid->GetFlagsStorage();
                        float* data = liquid->GetHeightStorage();
                        uint8 type = NAV_EMPTY;

                        // convert liquid type to NavTerrain
                        switch (liquid->GetType() & 3)
                        {
                            case 0:
                            case 1:
                                type = NAV_WATER;
                                break;
                            case 2:
                                type = NAV_MAGMA;
                                break;
                            case 3:
                                type = NAV_SLIME;
                                break;
                        }

                        // indexing is weird...
                        // after a lot of trial and error, this is what works:
                        // vertex = y*vertsX+x
                        // tile   = x*tilesY+y
                        // flag   = y*tilesY+x

                        G3D::Vector3 vert;
                        for (uint32 x = 0; x < vertsX; ++x)
                        {
                            for (uint32 y = 0; y < vertsY; ++y)
                            {
                                vert = G3D::Vector3(corner.x + x * GRID_PART_SIZE, corner.y + y * GRID_PART_SIZE, data[y * vertsX + x]);
                                vert = vert * rotation * scale + position;
                                vert.x *= -1.f;
                                vert.y *= -1.f;
                                liqVerts.push_back(vert);
                            }
                        }

                        int idx1, idx2, idx3, idx4;
                        uint32 square;
                        for (uint32 x = 0; x < tilesX; ++x)
                        {
                            for (uint32 y = 0; y < tilesY; ++y)
                            {
                                if ((flags[x + y * tilesX] & 0x0f) != 0x0f)
                                {
                                    square = x * tilesY + y;
                                    idx1 = square + x;
                                    idx2 = square + 1 + x;
                                    idx3 = square + tilesY + 1 + 1 + x;
                                    idx4 = square + tilesY + 1 + x;

                                    // top triangle
                                    liqTris.push_back(idx3);
                                    liqTris.push_back(idx2);
                                    liqTris.push_back(idx1);
                                    // bottom triangle
                                    liqTris.push_back(idx4);
                                    liqTris.push_back(idx3);
                                    liqTris.push_back(idx1);
                                }
                            }
                        }

                        uint32 liqOffset = meshData.liquidVerts.size() / 3;
                        for (auto & liqVert : liqVerts)
                        {
                            meshData.liquidVerts.append(liqVert.y, liqVert.z, liqVert.x);
                        }

                        for (uint32 j = 0; j < liqTris.size() / 3; ++j)
                        {
                            meshData.liquidTris.append(liqTris[j * 3 + 1] + liqOffset, liqTris[j * 3 + 2] + liqOffset, liqTris[j * 3] + liqOffset);
                            meshData.liquidType.append(type);
                        }
                    }
                }
            }
        } while (false);

        vmapMgr->unloadMap(mapID, tileX, tileY);
        delete vmapMgr;

        return retval;
    }

    /**************************************************************************/
    void TerrainBuilder::transform(std::vector<G3D::Vector3>& source, std::vector<G3D::Vector3>& transformedVertices, float scale, G3D::Matrix3& rotation, G3D::Vector3& position)
    {
        for (auto & it : source)
        {
            // apply tranform, then mirror along the horizontal axes
            G3D::Vector3 v(it * rotation * scale + position);
            v.x *= -1.f;
            v.y *= -1.f;
            transformedVertices.push_back(v);
        }
    }

    /**************************************************************************/
    void TerrainBuilder::copyVertices(std::vector<G3D::Vector3>& source, G3D::Array<float>& dest)
    {
        for (auto & it : source)
        {
            dest.push_back(it.y);
            dest.push_back(it.z);
            dest.push_back(it.x);
        }
    }

    /**************************************************************************/
    void TerrainBuilder::copyIndices(std::vector<MeshTriangle>& source, G3D::Array<int>& dest, int offset, bool flip)
    {
        if (flip)
        {
            for (auto & it : source)
            {
                dest.push_back(it.idx2 + offset);
                dest.push_back(it.idx1 + offset);
                dest.push_back(it.idx0 + offset);
            }
        }
        else
        {
            for (auto & it : source)
            {
                dest.push_back(it.idx0 + offset);
                dest.push_back(it.idx1 + offset);
                dest.push_back(it.idx2 + offset);
            }
        }
    }

    /**************************************************************************/
    void TerrainBuilder::copyIndices(G3D::Array<int>& source, G3D::Array<int>& dest, int offset)
    {
        int* src = source.getCArray();
        for (int32 i = 0; i < source.size(); ++i)
            dest.append(src[i] + offset);
    }

    /**************************************************************************/
    void TerrainBuilder::cleanVertices(G3D::Array<float>& verts, G3D::Array<int>& tris)
    {
        std::map<int, int> vertMap;

        int* t = tris.getCArray();
        float* v = verts.getCArray();

        G3D::Array<float> cleanVerts;
        int index, count = 0;
        // collect all the vertex indices from triangle
        for (int i = 0; i < tris.size(); ++i)
        {
            if (vertMap.find(t[i]) != vertMap.end())
                continue;
            std::pair<int, int> val;
            val.first = t[i];

            index = val.first;
            val.second = count;

            vertMap.insert(val);
            cleanVerts.append(v[index * 3], v[index * 3 + 1], v[index * 3 + 2]);
            count++;
        }

        verts.fastClear();
        verts.append(cleanVerts);
        cleanVerts.clear();

        // update triangles to use new indices
        for (int i = 0; i < tris.size(); ++i)
        {
            std::map<int, int>::iterator it;
            if ((it = vertMap.find(t[i])) == vertMap.end())
                continue;

            t[i] = (*it).second;
        }

        vertMap.clear();
    }

    /**************************************************************************/
    void TerrainBuilder::loadOffMeshConnections(uint32 mapID, uint32 tileX, uint32 tileY, MeshData& meshData, const char* offMeshFilePath)
    {
        // no meshfile input given?
        if (offMeshFilePath == nullptr)
            return;

        FILE* fp = fopen(offMeshFilePath, "rb");
        if (!fp)
        {
            printf(" loadOffMeshConnections:: input file %s not found!\n", offMeshFilePath);
            return;
        }

        // pretty silly thing, as we parse entire file and load only the tile we need
        // but we don't expect this file to be too large
        char* buf = new char[512];
        while (fgets(buf, 512, fp))
        {
            float p0[3], p1[3];
            uint32 mid, tx, ty;
            float size;
            if (sscanf(buf, "%u %u,%u (%f %f %f) (%f %f %f) %f", &mid, &tx, &ty,
                       &p0[0], &p0[1], &p0[2], &p1[0], &p1[1], &p1[2], &size) != 10)
                continue;

            if (mapID == mid && tileX == tx && tileY == ty)
            {
                meshData.offMeshConnections.append(p0[1]);
                meshData.offMeshConnections.append(p0[2]);
                meshData.offMeshConnections.append(p0[0]);

                meshData.offMeshConnections.append(p1[1]);
                meshData.offMeshConnections.append(p1[2]);
                meshData.offMeshConnections.append(p1[0]);

                meshData.offMeshConnectionDirs.append(1);          // 1 - both direction, 0 - one sided
                meshData.offMeshConnectionRads.append(size);       // agent size equivalent
                // can be used same way as polygon flags
                meshData.offMeshConnectionsAreas.append((unsigned char)0xFF);
                meshData.offMeshConnectionsFlags.append((unsigned short)0xFF);  // all movement masks can make this path
            }
        }

        delete [] buf;
        fclose(fp);
    }
}