/**
  racing module: implements the racing physics and logic.
*/

#ifndef _LCR_RACING_H
#define _LCR_RACING_H

typedef int32_t LCR_GameUnit;  ///< abstract game unit

#define LCR_GAME_UNIT 1024     ///< length of map square in LCR_GameUnits

#define LCR_RACING_INPUT_FORW     0x01
#define LCR_RACING_INPUT_RIGHT    0x02
#define LCR_RACING_INPUT_BACK     0x04
#define LCR_RACING_INPUT_LEFT     0x08

#define LCR_RACING_EVENT_CP_TAKEN    0x0001
#define LCR_RACING_EVENT_FINISHED    0x0002
#define LCR_RACING_EVENT_CRASH_SMALL 0x0004
#define LCR_RACING_EVENT_CRASH_BIG   0x0008

#define LCR_PHYSICS_UNIT       2048 ///< length of map square for physics engine
  
#define TPE_RESHAPE_TENSION_LIMIT 10
#define TPE_RESHAPE_ITERATIONS    5

#include "map.h"
#include "tinyphysicsengine.h"

// TODO: move some of this to constants?

#define LCR_GRAVITY (LCR_PHYSICS_UNIT / 140)
#define LCR_CAR_FORWARD_FRICTION (TPE_F / 9)
#define LCR_CAR_TURN_FRICTION (TPE_F)
#define LCR_CAR_ELASTICITY (TPE_F / 110)
#define LCR_CAR_ACCELERATION (LCR_PHYSICS_UNIT / 16)
#define LCR_CAR_TURN_SPEED (LCR_GAME_UNIT / 18)
#define LCR_CAR_TURN_MAX ((7 * LCR_GAME_UNIT) / 24)

#define LCR_CAR_FORWARD_FRICTION_ICE (TPE_F / 200)
#define LCR_CAR_TURN_FRICTION_ICE (TPE_F / 20)
#define LCR_CAR_ACCELERATION_ICE (LCR_PHYSICS_UNIT / 100)

#define LCR_CAR_FORWARD_FRICTION_DIRT (TPE_F / 7)
#define LCR_CAR_TURN_FRICTION_DIRT (TPE_F / 2)

#define LCR_CAR_TURN_FRICTION_GRASS (4 * (TPE_F / 5))
#define LCR_CAR_ACCELERATION_GRASS (LCR_PHYSICS_UNIT / 20)

#define LCR_CAR_JOINTS 5
#define LCR_CAR_CONNECTIONS 10

struct
{
  TPE_World physicsWorld;
  TPE_Body carBody;
  TPE_Joint carJoints[LCR_CAR_JOINTS];
  TPE_Connection carConnections[LCR_CAR_CONNECTIONS];
  uint32_t tick;
  uint8_t wheelCollisions;  /**< In individual bits records for each car wheel
                                 whether it's currently touching the ground.
                                 Lower bits record current collisions, higher
                                 bits the previous state (for averaging). */

  TPE_Vec3 carPositions[2]; ///* Current and previous position in game units.
  TPE_Vec3 carRotations[2]; ///* Current and previous rotation in game units.


TPE_Vec3 carOKPositions[LCR_CAR_JOINTS];
uint8_t carNotOKCount;


  LCR_GameUnit wheelRotation;
  LCR_GameUnit wheelSteer;
} LCR_racing;

TPE_Vec3 _LCR_TPE_vec3DividePlain(TPE_Vec3 v, TPE_Unit d)
{
  v.x /= d; v.y /= d; v.z /= d;
  return v;
}

TPE_Vec3 _LCR_racingBlockEnvFunc(TPE_Vec3 point, const uint8_t *block)
{
  TPE_Vec3 v, vBest;
  TPE_Unit d, dBest = TPE_INFINITY;

  uint8_t bx, by, bz;
  LCR_mapBlockGetCoords(block,&bx,&by,&bz);
 
  TPE_Vec3 blockOffset = TPE_vec3(
    (((int) bx) - LCR_MAP_SIZE_BLOCKS / 2) * LCR_PHYSICS_UNIT,
    (((int) by) - LCR_MAP_SIZE_BLOCKS / 2) * (LCR_PHYSICS_UNIT / 2),
    (((int) bz) - LCR_MAP_SIZE_BLOCKS / 2) * LCR_PHYSICS_UNIT);

  point = TPE_vec3Minus(point,blockOffset); // shift to origin

  uint8_t transform = 
    LCR_mapBlockOppositeTransform(LCR_mapBlockGetTransform(block));

  LCR_TRANSFORM_COORDS(transform,point.x,point.y,point.z,LCR_PHYSICS_UNIT,
    (LCR_PHYSICS_UNIT / 2))

  point = TPE_vec3Minus(point,
    TPE_vec3(LCR_PHYSICS_UNIT / 2,LCR_PHYSICS_UNIT / 4,LCR_PHYSICS_UNIT / 2));

  switch (block[0])
  {
    case LCR_BLOCK_FULL:
    case LCR_BLOCK_BOTTOM:
    case LCR_BLOCK_LEFT:
    case LCR_BLOCK_BOTTOM_LEFT:
    case LCR_BLOCK_BOTTOM_LEFT_FRONT:
    case LCR_BLOCK_FULL_ACCEL:
    case LCR_BLOCK_FULL_FAN:
    {
      TPE_Vec3
        offset = TPE_vec3(0,0,0),
        size = TPE_vec3(LCR_PHYSICS_UNIT / 2,LCR_PHYSICS_UNIT / 4,
          LCR_PHYSICS_UNIT / 2);

      if (block[0] == LCR_BLOCK_BOTTOM ||
          block[0] == LCR_BLOCK_BOTTOM_LEFT ||
          block[0] == LCR_BLOCK_BOTTOM_LEFT_FRONT)
      {
        offset.y -= LCR_PHYSICS_UNIT / 8;
        size.y = LCR_PHYSICS_UNIT / 8;
      }

      if (block[0] == LCR_BLOCK_LEFT ||
          block[0] == LCR_BLOCK_BOTTOM_LEFT ||
          block[0] == LCR_BLOCK_BOTTOM_LEFT_FRONT)
      {
        offset.x -= LCR_PHYSICS_UNIT / 4;
        size.x = LCR_PHYSICS_UNIT / 4;
      }

      if (block[0] == LCR_BLOCK_BOTTOM_LEFT_FRONT)
      {
        offset.z -= LCR_PHYSICS_UNIT / 4;
        size.z = LCR_PHYSICS_UNIT / 4;
      }

      point = TPE_envAABox(point,offset,size);
      break;
    }

#define _CHECK_NEXT(check)\
  v = check;\
  d = TPE_dist(point,v);\
  if (d < dBest) {\
    vBest = v;\
    dBest = d;}\
  if (dBest == 0) {\
    point = vBest;\
    break;}

    case LCR_BLOCK_RAMP_CURVED_WALL:
      _CHECK_NEXT(TPE_envAABox(point,TPE_vec3(5 * LCR_PHYSICS_UNIT / 12,0,0),
        TPE_vec3(LCR_PHYSICS_UNIT / 12,LCR_PHYSICS_UNIT / 4,LCR_PHYSICS_UNIT
        / 2)));
      // fall through

    case LCR_BLOCK_RAMP_CURVED_PLAT:
      _CHECK_NEXT(TPE_envAABox(point,TPE_vec3(0,0,5 * LCR_PHYSICS_UNIT / 12),
      TPE_vec3(LCR_PHYSICS_UNIT / 2,LCR_PHYSICS_UNIT / 4,LCR_PHYSICS_UNIT / 12
      )));
      // fall through

    case LCR_BLOCK_RAMP_CURVED:
    {
      TPE_Unit sides[6];
      TPE_Unit rampShift = block[0] != LCR_BLOCK_RAMP_CURVED ?
        LCR_PHYSICS_UNIT / 6 : 0;

      sides[0] = LCR_PHYSICS_UNIT / 8 - rampShift;
      sides[1] = -1 * LCR_PHYSICS_UNIT / 4;
      sides[2] = LCR_PHYSICS_UNIT / 2 - rampShift;
      sides[3] = -1 * LCR_PHYSICS_UNIT / 4;
      sides[4] = LCR_PHYSICS_UNIT / 2 - rampShift;
      sides[5] = LCR_PHYSICS_UNIT / 4;

      _CHECK_NEXT(TPE_envAATriPrism(point,
        TPE_vec3(0,0,0),sides,LCR_PHYSICS_UNIT,2))

      sides[0] = -1 * LCR_PHYSICS_UNIT / 2;
      sides[1] = -1 * LCR_PHYSICS_UNIT / 4;
      sides[2] = LCR_PHYSICS_UNIT / 2 - rampShift;
      sides[3] = -1 * LCR_PHYSICS_UNIT / 4;
      sides[4] = LCR_PHYSICS_UNIT / 2 - rampShift;
      sides[5] = 0;

      _CHECK_NEXT(TPE_envAATriPrism(point,TPE_vec3(0,0,0),sides,LCR_PHYSICS_UNIT
        ,2));

      point = vBest;

      break;
    }

#undef _CHECK_NEXT

    case LCR_BLOCK_RAMP:
    case LCR_BLOCK_RAMP_34:
    case LCR_BLOCK_RAMP_12:
    case LCR_BLOCK_RAMP_14:
    case LCR_BLOCK_RAMP_STEEP:
    {
      uint8_t front, top;
      LCR_rampGetDimensions(block[0],&top,&front);
      front = 6 - front;

      TPE_Unit sides[6];
      sides[0] = 
        -1 * LCR_PHYSICS_UNIT / 2 + (LCR_PHYSICS_UNIT / 6) * ((int) front);

      sides[1] = -1 * LCR_PHYSICS_UNIT / 4;

      sides[2] = LCR_PHYSICS_UNIT / 2;
      sides[3] = -1 * LCR_PHYSICS_UNIT / 4;

      sides[4] = LCR_PHYSICS_UNIT / 2;
      sides[5] = -1 * LCR_PHYSICS_UNIT / 4 +
        ((int) top) * (LCR_PHYSICS_UNIT / 8);

      point = TPE_envAATriPrism(point,TPE_vec3(0,0,0),sides,LCR_PHYSICS_UNIT,2);
      break;
    }

    case LCR_BLOCK_CORNER:
    case LCR_BLOCK_CORNER_12:
    {
      TPE_Unit sides[6];
      sides[0] = -1 * LCR_PHYSICS_UNIT / 2;
      sides[1] = LCR_PHYSICS_UNIT / 2;
      sides[2] = -1 * LCR_PHYSICS_UNIT / 2;
      sides[3] = -1 * LCR_PHYSICS_UNIT / 2;
      sides[4] = block[0] == LCR_BLOCK_CORNER ? LCR_PHYSICS_UNIT / 2 : 0;
      sides[5] = LCR_PHYSICS_UNIT / 2;

      point = TPE_envAATriPrism(point,TPE_vec3(0,0,0),sides,
        LCR_PHYSICS_UNIT / 2,1);
      
      break;
    }

    default:
      point = TPE_vec3(0,0,LCR_MAP_SIZE_BLOCKS * LCR_PHYSICS_UNIT);
      break;
  }

  point = TPE_vec3Plus(point,
    TPE_vec3(LCR_PHYSICS_UNIT / 2,LCR_PHYSICS_UNIT / 4,LCR_PHYSICS_UNIT / 2));

  transform = LCR_mapBlockOppositeTransform(transform);

  LCR_TRANSFORM_COORDS(transform,point.x,point.y,point.z,LCR_PHYSICS_UNIT,
    (LCR_PHYSICS_UNIT / 2))

  point = TPE_vec3Plus(point,blockOffset); // shift back

  return point;
}

TPE_Vec3 _LCR_racingEnvironmentFunction(TPE_Vec3 point, TPE_Unit maxDist)
{
  // start with the map outside walls:
  TPE_ENV_START(TPE_envAABoxInside(point,TPE_vec3(0,0,0),TPE_vec3(
    LCR_PHYSICS_UNIT * LCR_MAP_SIZE_BLOCKS,
    (LCR_PHYSICS_UNIT * LCR_MAP_SIZE_BLOCKS) / 2,
    LCR_PHYSICS_UNIT * LCR_MAP_SIZE_BLOCKS)),point)

  // without this check we might try to get block outside the map 
  if (_pBest.x == point.x && _pBest.y == point.y && _pBest.z == point.z)
    return _pBest;

  if (maxDist <= LCR_PHYSICS_UNIT / 4) // considering half of square height
  {
    /* Here we only check the 8 closest blocks => relatively fast. */

    TPE_Vec3 pointShifted = TPE_vec3Plus(point,TPE_vec3(
        (LCR_MAP_SIZE_BLOCKS / 2) * LCR_PHYSICS_UNIT,
        (LCR_MAP_SIZE_BLOCKS / 4) * LCR_PHYSICS_UNIT,
        (LCR_MAP_SIZE_BLOCKS / 2) * LCR_PHYSICS_UNIT));

    uint8_t coords[6]; // x_low, x_high, y_low, y_high, z_low, z_high

    coords[0] = (pointShifted.x / LCR_PHYSICS_UNIT);
    coords[1] = (pointShifted.x % LCR_PHYSICS_UNIT < LCR_PHYSICS_UNIT / 2);

    coords[2] = (pointShifted.y / (LCR_PHYSICS_UNIT / 2));
    coords[3] =
      (pointShifted.y % (LCR_PHYSICS_UNIT / 2) < LCR_PHYSICS_UNIT / 4);

    coords[4] = (pointShifted.z / LCR_PHYSICS_UNIT);
    coords[5] = (pointShifted.z % LCR_PHYSICS_UNIT < LCR_PHYSICS_UNIT / 2);

    for (int i = 0; i < 6; i += 2)
      if (coords[i + 1])
      {
        coords[i + 1] = coords[i];
        coords[i] = coords[i] > 0 ? coords[i] - 1 : 0;
      }
      else
        coords[i + 1] = coords[i] < 63 ? coords[i] + 1 : 63;

    int start = 0, end = LCR_currentMap.blockCount - 1;

    for (uint8_t i = 0; i < 8; ++i)
    {
      /* Black magic: here we make it so that we the lowest coord numbers
        (0,0,0), then the highest (1,1,1), then second lowest (1,0,0), then
        second highest (0,1,1) etc. This way we are narrowing the range (start,
        end) for the binary search. */

      int blockNum = LCR_mapGetBlockAtFast(
        coords[0] + ((i ^ (i >> 1)) & 0x01),
        coords[2] + ((i ^ (i >> 2)) & 0x01),
        coords[4] + (i & 0x01),start,end);

      if (blockNum >= 0) // is there a block at the coords?
      {
        TPE_ENV_NEXT(_LCR_racingBlockEnvFunc(point, // check it
          LCR_currentMap.blocks + blockNum * LCR_BLOCK_SIZE),point)

        // narrow the search range:
        if (i % 2 == 0 && blockNum > start)
          start = blockNum;

        if (i % 2 && blockNum < end)
          end = blockNum;
      }
    }
  }
  else
  {
    LCR_LOG1("collision checking all blocks (shouldn't happen often!)");

    const uint8_t *block = LCR_currentMap.blocks;

    /* Full check of all map blocks, slow, shouldn't happen often! */
    for (int j = 0; j < LCR_currentMap.blockCount; ++j)
    {
      TPE_ENV_NEXT(_LCR_racingBlockEnvFunc(point,block),point)
      block += LCR_BLOCK_SIZE;
    }
  }

  TPE_ENV_END
}

LCR_GameUnit LCR_racingGetCarSpeed(void)
{
  return (TPE_vec3Len(TPE_vec3(
    LCR_racing.carBody.joints[4].velocity[0],
    LCR_racing.carBody.joints[4].velocity[1],
    LCR_racing.carBody.joints[4].velocity[2])) * LCR_GAME_UNIT)
    / LCR_PHYSICS_UNIT;
}

uint8_t _LCR_racingCollisionHandler(uint16_t b1, uint16_t j1, uint16_t b2,
  uint16_t j2, TPE_Vec3 p)
{
  // check which wheels are touching the ground.

  if (j1 < 4) // wheel joint?
    LCR_racing.wheelCollisions |= 0x01 << j1;

  return 1;
}

LCR_GameUnit _LCR_racingSmoothRot(LCR_GameUnit angleNew, LCR_GameUnit angleOld)
{
  /* We'll smooth small rotations by averaging the last two angles; bigger
     rotations won't be smoothed -- firstly this removes lag for fast rotations
     and also deals with the issue of averaging e.g. 1 and 359 degrees. */

  LCR_GameUnit diff = angleNew - angleOld;

  if (diff > LCR_GAME_UNIT / 8 || diff < -1 * LCR_GAME_UNIT / 8)
    return angleNew;

  return angleOld + diff / 2;
}

/**
  Initializes new run.
*/
void LCR_racingRestart(void)
{
  LCR_LOG0("restarting race");

  LCR_racing.tick = 0;

  TPE_bodyActivate(&(LCR_racing.carBody));
  LCR_racing.wheelCollisions = 0;

  LCR_racing.wheelRotation = 0;
  LCR_racing.wheelSteer = 0;

  LCR_racing.carPositions[0] = TPE_vec3(0,0,0);
  LCR_racing.carPositions[1] = LCR_racing.carPositions[0];

  LCR_racing.carRotations[0] = TPE_vec3(0,0,0);
  LCR_racing.carRotations[1] = LCR_racing.carRotations[0];
    
TPE_bodyMoveTo(&(LCR_racing.carBody),
  TPE_vec3(
    (((TPE_Unit) LCR_currentMap.startPos[0]) - LCR_MAP_SIZE_BLOCKS / 2)
      * LCR_PHYSICS_UNIT + LCR_PHYSICS_UNIT / 2,
    (((TPE_Unit) LCR_currentMap.startPos[1]) - LCR_MAP_SIZE_BLOCKS / 2)
      * LCR_PHYSICS_UNIT / 2 + LCR_PHYSICS_UNIT / 4,
    (((TPE_Unit) LCR_currentMap.startPos[2]) - LCR_MAP_SIZE_BLOCKS / 2)
      * LCR_PHYSICS_UNIT + LCR_PHYSICS_UNIT / 2));

// TODO: allow also flipping the car upside down on start?
if (LCR_currentMap.startPos[3])
  TPE_bodyRotateByAxis(&(LCR_racing.carBody),
    TPE_vec3(0,
      LCR_currentMap.startPos[3] == LCR_BLOCK_TRANSFORM_ROT_90 ? 3 * TPE_F / 4 :
        (LCR_currentMap.startPos[3] == LCR_BLOCK_TRANSFORM_ROT_180 ? TPE_F / 2 :
          (TPE_F / 4)),0));

for (int i = 0; i < LCR_CAR_JOINTS; ++i)
  LCR_racing.carOKPositions[i] = TPE_vec3(0,0,0);

LCR_racing.carNotOKCount = 0;


  // TODO
}





/**
  Initializes the racing module, only call once.
*/
void LCR_racingInit(void)
{
  LCR_LOG0("initializing racing engine");

  // make the car body:
  TPE_makeCenterRectFull(LCR_racing.carJoints,
    LCR_racing.carConnections,
    LCR_PHYSICS_UNIT / 2,
    (LCR_PHYSICS_UNIT * 3) / 4,
    LCR_PHYSICS_UNIT / 8);

  LCR_racing.carJoints[4].position.y += LCR_PHYSICS_UNIT / 6;
  LCR_racing.carJoints[4].sizeDivided *= 3;
  LCR_racing.carJoints[4].sizeDivided /= 2;

  TPE_bodyInit(&(LCR_racing.carBody),LCR_racing.carJoints,LCR_CAR_JOINTS,
    LCR_racing.carConnections,LCR_CAR_CONNECTIONS,TPE_F);

  TPE_worldInit(&(LCR_racing.physicsWorld),
  &(LCR_racing.carBody),1,_LCR_racingEnvironmentFunction);

  LCR_racing.physicsWorld.collisionCallback = _LCR_racingCollisionHandler;

  LCR_racing.carBody.friction = LCR_CAR_FORWARD_FRICTION;
  LCR_racing.carBody.elasticity = LCR_CAR_ELASTICITY;
  LCR_racing.carBody.flags |= TPE_BODY_FLAG_ALWAYS_ACTIVE;

  /* We disable bounding sphere checks because that would lead to calling env.
    function with large min. distance which would lead to slow iteration over
    all map blocks. */
  LCR_racing.carBody.flags |= TPE_BODY_FLAG_NO_BSPHERE;

  LCR_racingRestart();
}

/**
  Gets current car transformation intended for rendering, i.e. potentially with
  smoothing and interpolation applied to the underlying internal state in the
  physics engine.
*/
void LCR_racingGetCarTransform(LCR_GameUnit position[3],
  LCR_GameUnit rotation[3], LCR_GameUnit interpolationParam)
{
  LCR_LOG2("getting car transform");  

  TPE_Vec3 v;

#if LCR_SETTING_SMOOTH_ANIMATIONS
  v = TPE_vec3Plus(LCR_racing.carPositions[1], // LERP previous and current pos
    _LCR_TPE_vec3DividePlain(
      TPE_vec3TimesPlain(TPE_vec3Minus(
        LCR_racing.carPositions[0],LCR_racing.carPositions[1]),
          interpolationParam),LCR_GAME_UNIT));

  position[0] = v.x;
  position[1] = v.y;
  position[2] = v.z;

  rotation[0] = _LCR_racingSmoothRot(LCR_racing.carRotations[0].x,
      LCR_racing.carRotations[1].x);
  rotation[1] = _LCR_racingSmoothRot(LCR_racing.carRotations[0].y,
      LCR_racing.carRotations[1].y);
  rotation[2] = _LCR_racingSmoothRot(LCR_racing.carRotations[0].z,
      LCR_racing.carRotations[1].z);
#else
  position[0] = LCR_racing.carPositions[0].x;
  position[1] = LCR_racing.carPositions[0].y;
  position[2] = LCR_racing.carPositions[0].z;

  rotation[0] = LCR_racing.carRotations[0].x;
  rotation[1] = LCR_racing.carRotations[0].y;
  rotation[2] = LCR_racing.carRotations[0].z;
#endif
}

void _LCR_drawPhysicsDebugPixel(uint16_t x, uint16_t y, uint8_t color)
{
  if (x > 1 && x < LCR_EFFECTIVE_RESOLUTION_X - 2 &&
      y > 1 && y < LCR_EFFECTIVE_RESOLUTION_Y - 2)
  {
    uint16_t c = 0x8101 | (0x8f1f << (2 * color));

    for (int j = -1; j <= 2; ++j)
      for (int i = -1; i <= 2; ++i)
        LCR_drawPixelXYUnsafe(x + i,y + j,c);
  }
}

int LCR_racingCarWheelTouchesGround(int wheel)
{
  return ((LCR_racing.wheelCollisions & (LCR_racing.wheelCollisions >> 4))
    >> wheel) & 0x01;
}
      
LCR_GameUnit LCR_racingGetWheelRotation(void)
{
  return LCR_racing.wheelRotation;
}

LCR_GameUnit LCR_racingGetWheelSteer(void)
{
  return LCR_racing.wheelSteer;
}

void _LCR_racingWheelAccelerate(unsigned int wheel, TPE_Vec3 dir,
  uint8_t material)
{
  TPE_Unit acc =
    material == LCR_BLOCK_MATERIAL_ICE ?
      LCR_CAR_ACCELERATION_ICE :
      (material == LCR_BLOCK_MATERIAL_GRASS ?
         LCR_CAR_ACCELERATION_GRASS :
         LCR_CAR_ACCELERATION);

  LCR_racing.carBody.joints[wheel].velocity[0] +=
    (dir.x * acc) / TPE_F;
  LCR_racing.carBody.joints[wheel].velocity[1] +=
    (dir.y * acc) / TPE_F;
  LCR_racing.carBody.joints[wheel].velocity[2] +=
    (dir.z * acc) / TPE_F;
}

int _LCR_racingCarShapeOK(void)
{
  int r = 1;

  for (int i = 0; i < LCR_racing.carBody.jointCount; ++i)
    r &= TPE_connectionTension(TPE_dist(
        LCR_racing.carBody.joints[
          LCR_racing.carBody.connections[i].joint1].position,
        LCR_racing.carBody.joints[
          LCR_racing.carBody.connections[i].joint2].position),
      LCR_racing.carBody.connections[i].length) < TPE_F / 16; // TODO: const

  return r;
}

/**
  Updates the racing physics world, call every LCR_RACING_TICK_MS milliseconds.
  Returns a set of events (logically ORed) that occured during this step.
*/
uint32_t LCR_racingStep(unsigned int input)
{
printf("---------\n");
  LCR_LOG2("racing step start");

  uint32_t result = 0;
  TPE_Vec3 carForw, carRight, carUp;
  uint8_t groundMat = LCR_BLOCK_MATERIAL_CONCRETE; // material under wheels
  int groundBlockIndex = -1;

  carForw = TPE_vec3Normalized(TPE_vec3Plus(
    TPE_vec3Minus(LCR_racing.carBody.joints[0].position,
                  LCR_racing.carBody.joints[2].position),
    TPE_vec3Minus(LCR_racing.carBody.joints[1].position,
                  LCR_racing.carBody.joints[3].position)));

  carRight = TPE_vec3Normalized(TPE_vec3Plus(
    TPE_vec3Minus(LCR_racing.carBody.joints[0].position,
                  LCR_racing.carBody.joints[1].position),
    TPE_vec3Minus(LCR_racing.carBody.joints[2].position,
                  LCR_racing.carBody.joints[3].position)));

  carUp = TPE_vec3Cross(carForw,carRight);

  if ((LCR_racing.wheelCollisions & 0x0f) != 0x0f) // EXPERIMENTAL: don't apply gravity with all wheels on ground
    TPE_bodyApplyGravity(&(LCR_racing.carBody),LCR_GRAVITY);

  if (LCR_racing.wheelCollisions) // at least one wheel on ground?
  {
    TPE_Unit upDot = TPE_vec3Dot(carUp,TPE_vec3(0,TPE_F,0));

    if (upDot > TPE_F / 8 || upDot < -1 * TPE_F / 8) // TODO: consts
    {
      uint8_t
        gx = (LCR_racing.carPositions[0].x + (LCR_MAP_SIZE_BLOCKS / 2) *
          LCR_GAME_UNIT) / LCR_GAME_UNIT,
        gy = (LCR_racing.carPositions[0].y + (LCR_MAP_SIZE_BLOCKS / 2) *
          (LCR_GAME_UNIT / 2)) / (LCR_GAME_UNIT / 2),
        gz = (LCR_racing.carPositions[0].z + (LCR_MAP_SIZE_BLOCKS / 2) *
          LCR_GAME_UNIT) / LCR_GAME_UNIT;

      TPE_Unit yMod = (LCR_racing.carPositions[0].y + LCR_MAP_SIZE_BLOCKS *
        LCR_GAME_UNIT / 2) % (LCR_GAME_UNIT / 2);

      if (upDot > 0 && yMod < LCR_GAME_UNIT / 2) // TODO: const
        groundBlockIndex = LCR_mapGetBlockAt(gx,gy - 1,gz);
      else if (upDot < 0 && yMod > LCR_GAME_UNIT / 2)
        groundBlockIndex = LCR_mapGetBlockAt(gx,gy + 1,gz);

      if (groundBlockIndex == -1)
        groundBlockIndex = LCR_mapGetBlockAt(gx,gy,gz);
    }

    if (groundBlockIndex != -1)
      groundMat = LCR_mapBlockGetMaterial(
        LCR_currentMap.blocks + groundBlockIndex * LCR_BLOCK_SIZE);
  }

  LCR_racing.carBody.friction =
    groundMat == LCR_BLOCK_MATERIAL_ICE ?
      LCR_CAR_FORWARD_FRICTION_ICE :
      (groundMat == LCR_BLOCK_MATERIAL_DIRT ?
        LCR_CAR_FORWARD_FRICTION_DIRT :
        LCR_CAR_FORWARD_FRICTION);

  if (input)
  {
    unsigned char steering = 0;

    // TODO: magic constants

    if (input & (LCR_RACING_INPUT_FORW | LCR_RACING_INPUT_BACK))
    {
      LCR_GameUnit rotateBy =
        (LCR_racing.wheelCollisions & 0x0f) ? // on ground slow down wheel rot.
        (LCR_racingGetCarSpeed() / 16) : LCR_GAME_UNIT / 32;

      if (!(input & LCR_RACING_INPUT_BACK))
        rotateBy *= -1;

      LCR_racing.wheelRotation =
        (LCR_racing.wheelRotation + rotateBy) % LCR_GAME_UNIT;

      if (LCR_racing.wheelRotation < 0)
        LCR_racing.wheelRotation += LCR_GAME_UNIT;
    }

    if (input & LCR_RACING_INPUT_RIGHT)
    {
      steering = 2;
      
      LCR_racing.wheelSteer = TPE_min(
        LCR_racing.wheelSteer + LCR_CAR_TURN_SPEED,
        LCR_CAR_TURN_MAX);
    }
    else if (input & LCR_RACING_INPUT_LEFT)
    {
      steering = 1;

      LCR_racing.wheelSteer = TPE_max(
        LCR_racing.wheelSteer - LCR_CAR_TURN_SPEED,
        -1 * LCR_CAR_TURN_MAX);
    }

    if ((LCR_racing.wheelCollisions & 0x0c)) // back wheel on ground?
    {
      if (input & LCR_RACING_INPUT_FORW)
      {
        _LCR_racingWheelAccelerate(0,carForw,groundMat);
        _LCR_racingWheelAccelerate(1,carForw,groundMat);
      }
      else if (input & LCR_RACING_INPUT_BACK)
      {
        _LCR_racingWheelAccelerate(0,TPE_vec3TimesPlain(carForw,-1),groundMat);
        _LCR_racingWheelAccelerate(1,TPE_vec3TimesPlain(carForw,-1),groundMat);
      }
    }

    for (int i = 0; i < 4; ++i)
      if (LCR_racing.wheelCollisions & (0x01 << i)) // wheel on ground?
      {
        TPE_Vec3 jv = TPE_vec3( // joint velocity 
          LCR_racing.carBody.joints[i].velocity[0],   
          LCR_racing.carBody.joints[i].velocity[1],   
          LCR_racing.carBody.joints[i].velocity[2]);   

        TPE_Vec3 ja = carRight; // wheel axis of rotation

        if (i >= 2 && steering)
        {
          // for front wheels with turning we tilt the wheel axis 45 degrees

          TPE_Unit steer =
            (LCR_racing.wheelSteer * TPE_F) / LCR_GAME_UNIT;
 
          ja = TPE_vec3Normalized(
            TPE_vec3Plus(TPE_vec3Times(carForw,steer),carRight));
        }

        /* friction is in the direction if the axis and its magnitude is
          determined by the dot product (angle) of the axis and velocity */
        TPE_Vec3 fric = TPE_vec3Times(ja,(TPE_vec3Dot(ja,jv) *
          (groundMat == LCR_BLOCK_MATERIAL_CONCRETE ?
          LCR_CAR_TURN_FRICTION :
            (groundMat == LCR_BLOCK_MATERIAL_DIRT ?
              LCR_CAR_TURN_FRICTION_DIRT :
              (
                groundMat == LCR_BLOCK_MATERIAL_GRASS ?
                LCR_CAR_TURN_FRICTION_GRASS :
                LCR_CAR_TURN_FRICTION_ICE)))
          ) / TPE_F);

        jv = TPE_vec3Minus(jv,fric); // subtract the friction

        LCR_racing.carBody.joints[i].velocity[0] = jv.x;
        LCR_racing.carBody.joints[i].velocity[1] = jv.y;
        LCR_racing.carBody.joints[i].velocity[2] = jv.z;
      }
  }

  if ((!(input & LCR_RACING_INPUT_LEFT)) &&
    (!(input & LCR_RACING_INPUT_RIGHT)))
    LCR_racing.wheelSteer /= 2;

  LCR_racing.wheelCollisions <<= 4;
  
  LCR_LOG2("gonna step physics engine");
  TPE_worldStep(&(LCR_racing.physicsWorld));
  LCR_LOG2("stepping physics engine done");

  TPE_Vec3 tmpVec = LCR_racing.carPositions[0];

  TPE_Vec3 wheelAverage = _LCR_TPE_vec3DividePlain(
    TPE_vec3Plus(
      TPE_vec3Plus(
        LCR_racing.carBody.joints[0].position,
        LCR_racing.carBody.joints[1].position),
      TPE_vec3Plus(
        LCR_racing.carBody.joints[2].position,
        LCR_racing.carBody.joints[3].position)),4);

  LCR_racing.carPositions[0] = _LCR_TPE_vec3DividePlain(
      TPE_vec3TimesPlain(wheelAverage,LCR_GAME_UNIT),LCR_PHYSICS_UNIT);

  LCR_racing.carPositions[0] = // smooth the position
    TPE_vec3KeepWithinBox(LCR_racing.carPositions[1],LCR_racing.carPositions[0],
        TPE_vec3(
          LCR_PHYSICS_UNIT / 64, // TODO: constant
          LCR_PHYSICS_UNIT / 64,
          LCR_PHYSICS_UNIT / 64));

  LCR_racing.carPositions[1] = tmpVec;

  tmpVec = _LCR_TPE_vec3DividePlain(TPE_vec3TimesPlain(TPE_bodyGetRotation(
    &(LCR_racing.carBody),0,2,1),LCR_GAME_UNIT),TPE_F);

  LCR_racing.carRotations[1] = LCR_racing.carRotations[0];
  LCR_racing.carRotations[0] = tmpVec;

  TPE_Unit angle = TPE_vec3Dot(carUp,TPE_vec3Normalized(TPE_vec3Minus(
    LCR_racing.carBody.joints[4].position,
    LCR_racing.carBody.joints[0].position)));

  if (angle < TPE_F / 4) // TODO: magic constant
  {
    LCR_LOG2("roof squeezed, applying anti force")

    tmpVec = TPE_vec3Times(carUp,LCR_PHYSICS_UNIT / 16); // TODO: 16 magic con.

    if (angle <= 0)  
    {
      LCR_LOG1("roof flipped over, fixing")
      LCR_racing.carBody.joints[4].position = wheelAverage;
      angle = 0;
    }
    
    angle = TPE_F - 4 * angle; // 4 comes from above TPE_F / 4

    tmpVec = TPE_vec3Times(tmpVec,angle);

    // accelerate roof and wheels away from each other
    for (int i = 0; i < LCR_CAR_JOINTS; ++i)
    {
      LCR_racing.carBody.joints[i].velocity[0] += (i == 4 ? 1 : -1) * tmpVec.x;
      LCR_racing.carBody.joints[i].velocity[1] += (i == 4 ? 1 : -1) * tmpVec.y;
      LCR_racing.carBody.joints[i].velocity[2] += (i == 4 ? 1 : -1) * tmpVec.z;
    }
  }

  // now make a special test for a "pinch" front collision

  TPE_Vec3 frontWheelMiddle = TPE_vec3Plus(
    LCR_racing.carBody.joints[0].position,
    LCR_racing.carBody.joints[1].position);

  frontWheelMiddle.x /= 2;
  frontWheelMiddle.y /= 2;
  frontWheelMiddle.z /= 2;

  frontWheelMiddle = TPE_vec3Minus(frontWheelMiddle,
    _LCR_racingEnvironmentFunction(frontWheelMiddle,LCR_PHYSICS_UNIT / 4));

  uint8_t frontCollision = frontWheelMiddle.x == 0 && frontWheelMiddle.y == 0 &&
    frontWheelMiddle.z == 0;

  if (frontCollision)
  {
    // stop the car immediately
    LCR_LOG1("car front pierced");
    LCR_racing.carNotOKCount += (LCR_racing.carNotOKCount < 15 ? 32 : 0); // TODO: consts
  }

  if ((LCR_racing.carBody.flags & TPE_BODY_FLAG_UNRESOLVED) || frontCollision ||
    !_LCR_racingCarShapeOK())
  {
    // car not OK

    if (LCR_racing.carNotOKCount > 5) // TODO: constant
    {
      LCR_LOG1("car not OK (short), fixing");

      for (int i = 0; i < LCR_CAR_JOINTS; ++i)
      {
        if (LCR_racing.carNotOKCount < 50) // TODO: const
        {
          // for a while try to smoothly iterate towards previous OK position 
          LCR_racing.carBody.joints[i].position = 
            TPE_vec3Plus(LCR_racing.carBody.joints[i].position,
              LCR_racing.carOKPositions[i]);

          LCR_racing.carBody.joints[i].position.x /= 2;
          LCR_racing.carBody.joints[i].position.y /= 2;
          LCR_racing.carBody.joints[i].position.z /= 2;

          for (int j = 0; j < 3; ++j) // lower speed a bit
            LCR_racing.carBody.joints[i].velocity[j] = 
              (7 * ((int) LCR_racing.carBody.joints[i].velocity[j])) / 8;
        }
        else // hard set the pos (iteration may be infinite due to sim.)
        {
          LCR_LOG1("car not OK (long), teleporting");
          LCR_racing.carBody.joints[i].position = LCR_racing.carOKPositions[i];
        }
      }
    }

    LCR_racing.carNotOKCount += LCR_racing.carNotOKCount < 255 ? 1 : 0;
  }
  else
  {
    // car OK
    LCR_racing.carNotOKCount = 0;

    for (int i = 0; i < LCR_CAR_JOINTS; ++i)
      LCR_racing.carOKPositions[i] = LCR_racing.carBody.joints[i].position;
  }

  LCR_racing.tick++;

  LCR_LOG2("racing step end");

  return result;
}

void LCR_physicsDebugDraw(LCR_GameUnit camPos[3], LCR_GameUnit camRot[2],
  LCR_GameUnit camFov)
{
  LCR_LOG2("drawing physics debug overlay");

  TPE_Vec3 cPos, cRot, cView;

  cPos.x = (camPos[0] * LCR_PHYSICS_UNIT) / LCR_GAME_UNIT;
  cPos.y = (camPos[1] * LCR_PHYSICS_UNIT) / LCR_GAME_UNIT;
  cPos.z = (camPos[2] * LCR_PHYSICS_UNIT) / LCR_GAME_UNIT;

  cRot.x = (camRot[0] * TPE_F) / LCR_GAME_UNIT;
  cRot.y = (camRot[1] * TPE_F) / LCR_GAME_UNIT;
  cRot.z = 0; 

  cView.x = LCR_EFFECTIVE_RESOLUTION_X;
  cView.y = LCR_EFFECTIVE_RESOLUTION_Y;
  cView.z = (camFov * TPE_F) / LCR_GAME_UNIT;

  TPE_worldDebugDraw(&(LCR_racing.physicsWorld),_LCR_drawPhysicsDebugPixel,
    cPos,cRot,cView,16,LCR_PHYSICS_UNIT / 4,LCR_racing.tick * 4);
}

#endif // guard