/*
The MIT License (MIT)

Copyright (c) 2012-2017 Syoyo Fujita and many contributors.

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in
all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
THE SOFTWARE.
*/

//
// version 1.0.8 : Fix parsing `g` tag just after `usemtl`(#138)
// version 1.0.7 : Support multiple tex options(#126)
// version 1.0.6 : Add TINYOBJLOADER_USE_DOUBLE option(#124)
// version 1.0.5 : Ignore `Tr` when `d` exists in MTL(#43)
// version 1.0.4 : Support multiple filenames for 'mtllib'(#112)
// version 1.0.3 : Support parsing texture options(#85)
// version 1.0.2 : Improve parsing speed by about a factor of 2 for large
// files(#105)
// version 1.0.1 : Fixes a shape is lost if obj ends with a 'usemtl'(#104)
// version 1.0.0 : Change data structure. Change license from BSD to MIT.
//

//
// Use this in *one* .cc
//   #define TINYOBJLOADER_IMPLEMENTATION
//   #include "tiny_obj_loader.h"
//

#ifndef TINY_OBJ_LOADER_H_
#define TINY_OBJ_LOADER_H_

#include <map>
#include <string>
#include <vector>

namespace tinyobj {

// https://en.wikipedia.org/wiki/Wavefront_.obj_file says ...
//
//  -blendu on | off                       # set horizontal texture blending
//  (default on)
//  -blendv on | off                       # set vertical texture blending
//  (default on)
//  -boost real_value                      # boost mip-map sharpness
//  -mm base_value gain_value              # modify texture map values (default
//  0 1)
//                                         #     base_value = brightness,
//                                         gain_value = contrast
//  -o u [v [w]]                           # Origin offset             (default
//  0 0 0)
//  -s u [v [w]]                           # Scale                     (default
//  1 1 1)
//  -t u [v [w]]                           # Turbulence                (default
//  0 0 0)
//  -texres resolution                     # texture resolution to create
//  -clamp on | off                        # only render texels in the clamped
//  0-1 range (default off)
//                                         #   When unclamped, textures are
//                                         repeated across a surface,
//                                         #   when clamped, only texels which
//                                         fall within the 0-1
//                                         #   range are rendered.
//  -bm mult_value                         # bump multiplier (for bump maps
//  only)
//
//  -imfchan r | g | b | m | l | z         # specifies which channel of the file
//  is used to
//                                         # create a scalar or bump texture.
//                                         r:red, g:green,
//                                         # b:blue, m:matte, l:luminance,
//                                         z:z-depth..
//                                         # (the default for bump is 'l' and
//                                         for decal is 'm')
//  bump -imfchan r bumpmap.tga            # says to use the red channel of
//  bumpmap.tga as the bumpmap
//
// For reflection maps...
//
//   -type sphere                           # specifies a sphere for a "refl"
//   reflection map
//   -type cube_top    | cube_bottom |      # when using a cube map, the texture
//   file for each
//         cube_front  | cube_back   |      # side of the cube is specified
//         separately
//         cube_left   | cube_right

#ifdef TINYOBJLOADER_USE_DOUBLE
  //#pragma message "using double"
  typedef double real_t;
#else
  //#pragma message "using float"
  typedef float real_t;
#endif

typedef enum {
  TEXTURE_TYPE_NONE,  // default
  TEXTURE_TYPE_SPHERE,
  TEXTURE_TYPE_CUBE_TOP,
  TEXTURE_TYPE_CUBE_BOTTOM,
  TEXTURE_TYPE_CUBE_FRONT,
  TEXTURE_TYPE_CUBE_BACK,
  TEXTURE_TYPE_CUBE_LEFT,
  TEXTURE_TYPE_CUBE_RIGHT
} texture_type_t;

typedef struct {
  texture_type_t type;     // -type (default TEXTURE_TYPE_NONE)
  real_t sharpness;         // -boost (default 1.0?)
  real_t brightness;        // base_value in -mm option (default 0)
  real_t contrast;          // gain_value in -mm option (default 1)
  real_t origin_offset[3];  // -o u [v [w]] (default 0 0 0)
  real_t scale[3];          // -s u [v [w]] (default 1 1 1)
  real_t turbulence[3];     // -t u [v [w]] (default 0 0 0)
  // int   texture_resolution; // -texres resolution (default = ?) TODO
  bool clamp;    // -clamp (default false)
  char imfchan;  // -imfchan (the default for bump is 'l' and for decal is 'm')
  bool blendu;   // -blendu (default on)
  bool blendv;   // -blendv (default on)
  real_t bump_multiplier;  // -bm (for bump maps only, default 1.0)
} texture_option_t;

typedef struct {
  std::string name;

  real_t ambient[3];
  real_t diffuse[3];
  real_t specular[3];
  real_t transmittance[3];
  real_t emission[3];
  real_t shininess;
  real_t ior;       // index of refraction
  real_t dissolve;  // 1 == opaque; 0 == fully transparent
  // illumination model (see http://www.fileformat.info/format/material/)
  int illum;

  int dummy;  // Suppress padding warning.

  std::string ambient_texname;             // map_Ka
  std::string diffuse_texname;             // map_Kd
  std::string specular_texname;            // map_Ks
  std::string specular_highlight_texname;  // map_Ns
  std::string bump_texname;                // map_bump, map_Bump, bump
  std::string displacement_texname;        // disp
  std::string alpha_texname;               // map_d
  std::string reflection_texname;          // refl

  texture_option_t ambient_texopt;
  texture_option_t diffuse_texopt;
  texture_option_t specular_texopt;
  texture_option_t specular_highlight_texopt;
  texture_option_t bump_texopt;
  texture_option_t displacement_texopt;
  texture_option_t alpha_texopt;
  texture_option_t reflection_texopt;

  // PBR extension
  // http://exocortex.com/blog/extending_wavefront_mtl_to_support_pbr
  real_t roughness;            // [0, 1] default 0
  real_t metallic;             // [0, 1] default 0
  real_t sheen;                // [0, 1] default 0
  real_t clearcoat_thickness;  // [0, 1] default 0
  real_t clearcoat_roughness;  // [0, 1] default 0
  real_t anisotropy;           // aniso. [0, 1] default 0
  real_t anisotropy_rotation;  // anisor. [0, 1] default 0
  real_t pad0;
  std::string roughness_texname;  // map_Pr
  std::string metallic_texname;   // map_Pm
  std::string sheen_texname;      // map_Ps
  std::string emissive_texname;   // map_Ke
  std::string normal_texname;     // norm. For normal mapping.

  texture_option_t roughness_texopt;
  texture_option_t metallic_texopt;
  texture_option_t sheen_texopt;
  texture_option_t emissive_texopt;
  texture_option_t normal_texopt;

  int pad2;

  std::map<std::string, std::string> unknown_parameter;
} material_t;

typedef struct {
  std::string name;

  std::vector<int> intValues;
  std::vector<real_t> floatValues;
  std::vector<std::string> stringValues;
} tag_t;

// Index struct to support different indices for vtx/normal/texcoord.
// -1 means not used.
typedef struct {
  int vertex_index;
  int normal_index;
  int texcoord_index;
} index_t;

typedef struct {
  std::vector<index_t> indices;
  std::vector<unsigned char> num_face_vertices;  // The number of vertices per
                                                 // face. 3 = polygon, 4 = quad,
                                                 // ... Up to 255.
  std::vector<int> material_ids;                 // per-face material ID
  std::vector<tag_t> tags;                       // SubD tag
} mesh_t;

typedef struct {
  std::string name;
  mesh_t mesh;
} shape_t;

// Vertex attributes
typedef struct {
  std::vector<real_t> vertices;   // 'v'
  std::vector<real_t> normals;    // 'vn'
  std::vector<real_t> texcoords;  // 'vt'
} attrib_t;

typedef struct callback_t_ {
  // W is optional and set to 1 if there is no `w` item in `v` line
  void (*vertex_cb)(void *user_data, real_t x, real_t y, real_t z, real_t w);
  void (*normal_cb)(void *user_data, real_t x, real_t y, real_t z);

  // y and z are optional and set to 0 if there is no `y` and/or `z` item(s) in
  // `vt` line.
  void (*texcoord_cb)(void *user_data, real_t x, real_t y, real_t z);

  // called per 'f' line. num_indices is the number of face indices(e.g. 3 for
  // triangle, 4 for quad)
  // 0 will be passed for undefined index in index_t members.
  void (*index_cb)(void *user_data, index_t *indices, int num_indices);
  // `name` material name, `material_id` = the array index of material_t[]. -1
  // if
  // a material not found in .mtl
  void (*usemtl_cb)(void *user_data, const char *name, int material_id);
  // `materials` = parsed material data.
  void (*mtllib_cb)(void *user_data, const material_t *materials,
                    int num_materials);
  // There may be multiple group names
  void (*group_cb)(void *user_data, const char **names, int num_names);
  void (*object_cb)(void *user_data, const char *name);

  callback_t_()
      : vertex_cb(NULL),
        normal_cb(NULL),
        texcoord_cb(NULL),
        index_cb(NULL),
        usemtl_cb(NULL),
        mtllib_cb(NULL),
        group_cb(NULL),
        object_cb(NULL) {}
} callback_t;

class MaterialReader {
 public:
  MaterialReader() {}
  virtual ~MaterialReader();

  virtual bool operator()(const std::string &matId,
                          std::vector<material_t> *materials,
                          std::map<std::string, int> *matMap,
                          std::string *err) = 0;
};

class MaterialFileReader : public MaterialReader {
 public:
  explicit MaterialFileReader(const std::string &mtl_basedir)
      : m_mtlBaseDir(mtl_basedir) {}
  virtual ~MaterialFileReader() {}
  virtual bool operator()(const std::string &matId,
                          std::vector<material_t> *materials,
                          std::map<std::string, int> *matMap, std::string *err);

 private:
  std::string m_mtlBaseDir;
};

class MaterialStreamReader : public MaterialReader {
 public:
  explicit MaterialStreamReader(std::istream &inStream)
      : m_inStream(inStream) {}
  virtual ~MaterialStreamReader() {}
  virtual bool operator()(const std::string &matId,
                          std::vector<material_t> *materials,
                          std::map<std::string, int> *matMap, std::string *err);

 private:
  std::istream &m_inStream;
};

/// Loads .obj from a file.
/// 'attrib', 'shapes' and 'materials' will be filled with parsed shape data
/// 'shapes' will be filled with parsed shape data
/// Returns true when loading .obj become success.
/// Returns warning and error message into `err`
/// 'mtl_basedir' is optional, and used for base directory for .mtl file.
/// In default(`NULL'), .mtl file is searched from an application's working
/// directory.
/// 'triangulate' is optional, and used whether triangulate polygon face in .obj
/// or not.
bool LoadObj(attrib_t *attrib, std::vector<shape_t> *shapes,
             std::vector<material_t> *materials, std::string *err,
             const char *filename, const char *mtl_basedir = NULL,
             bool triangulate = true);

/// Loads .obj from a file with custom user callback.
/// .mtl is loaded as usual and parsed material_t data will be passed to
/// `callback.mtllib_cb`.
/// Returns true when loading .obj/.mtl become success.
/// Returns warning and error message into `err`
/// See `examples/callback_api/` for how to use this function.
bool LoadObjWithCallback(std::istream &inStream, const callback_t &callback,
                         void *user_data = NULL,
                         MaterialReader *readMatFn = NULL,
                         std::string *err = NULL);

/// Loads object from a std::istream, uses GetMtlIStreamFn to retrieve
/// std::istream for materials.
/// Returns true when loading .obj become success.
/// Returns warning and error message into `err`
bool LoadObj(attrib_t *attrib, std::vector<shape_t> *shapes,
             std::vector<material_t> *materials, std::string *err,
             std::istream *inStream, MaterialReader *readMatFn = NULL,
             bool triangulate = true);

/// Loads materials into std::map
void LoadMtl(std::map<std::string, int> *material_map,
             std::vector<material_t> *materials, std::istream *inStream,
             std::string *warning);

}  // namespace tinyobj

#endif  // TINY_OBJ_LOADER_H_

#ifdef TINYOBJLOADER_IMPLEMENTATION
#include <cassert>
#include <cctype>
#include <cmath>
#include <cstddef>
#include <cstdlib>
#include <cstring>
#include <utility>

#include <fstream>
#include <sstream>

namespace tinyobj {

MaterialReader::~MaterialReader() {}


struct vertex_index {
  int v_idx, vt_idx, vn_idx;
  vertex_index() : v_idx(-1), vt_idx(-1), vn_idx(-1) {}
  explicit vertex_index(int idx) : v_idx(idx), vt_idx(idx), vn_idx(idx) {}
  vertex_index(int vidx, int vtidx, int vnidx)
      : v_idx(vidx), vt_idx(vtidx), vn_idx(vnidx) {}
};

struct tag_sizes {
  tag_sizes() : num_ints(0), num_reals(0), num_strings(0) {}
  int num_ints;
  int num_reals;
  int num_strings;
};

struct obj_shape {
  std::vector<real_t> v;
  std::vector<real_t> vn;
  std::vector<real_t> vt;
};

// See
// http://stackoverflow.com/questions/6089231/getting-std-ifstream-to-handle-lf-cr-and-crlf
static std::istream &safeGetline(std::istream &is, std::string &t) {
  t.clear();

  // The characters in the stream are read one-by-one using a std::streambuf.
  // That is faster than reading them one-by-one using the std::istream.
  // Code that uses streambuf this way must be guarded by a sentry object.
  // The sentry object performs various tasks,
  // such as thread synchronization and updating the stream state.

  std::istream::sentry se(is, true);
  std::streambuf *sb = is.rdbuf();

  if (se) {
    for (;;) {
      int c = sb->sbumpc();
      switch (c) {
        case '\n':
          return is;
        case '\r':
          if (sb->sgetc() == '\n') sb->sbumpc();
          return is;
        case EOF:
          // Also handle the case when the last line has no line ending
          if (t.empty()) is.setstate(std::ios::eofbit);
          return is;
        default:
          t += static_cast<char>(c);
      }
    }
  }

  return is;
}

#define IS_SPACE(x) (((x) == ' ') || ((x) == '\t'))
#define IS_DIGIT(x) \
  (static_cast<unsigned int>((x) - '0') < static_cast<unsigned int>(10))
#define IS_NEW_LINE(x) (((x) == '\r') || ((x) == '\n') || ((x) == '\0'))

// Make index zero-base, and also support relative index.
static inline int fixIndex(int idx, int n) {
  if (idx > 0) return idx - 1;
  if (idx == 0) return 0;
  return n + idx;  // negative value = relative
}

static inline std::string parseString(const char **token) {
  std::string s;
  (*token) += strspn((*token), " \t");
  size_t e = strcspn((*token), " \t\r");
  s = std::string((*token), &(*token)[e]);
  (*token) += e;
  return s;
}

static inline int parseInt(const char **token) {
  (*token) += strspn((*token), " \t");
  int i = atoi((*token));
  (*token) += strcspn((*token), " \t\r");
  return i;
}

// Tries to parse a floating point number located at s.
//
// s_end should be a location in the string where reading should absolutely
// stop. For example at the end of the string, to prevent buffer overflows.
//
// Parses the following EBNF grammar:
//   sign    = "+" | "-" ;
//   END     = ? anything not in digit ?
//   digit   = "0" | "1" | "2" | "3" | "4" | "5" | "6" | "7" | "8" | "9" ;
//   integer = [sign] , digit , {digit} ;
//   decimal = integer , ["." , integer] ;
//   float   = ( decimal , END ) | ( decimal , ("E" | "e") , integer , END ) ;
//
//  Valid strings are for example:
//   -0  +3.1417e+2  -0.0E-3  1.0324  -1.41   11e2
//
// If the parsing is a success, result is set to the parsed value and true
// is returned.
//
// The function is greedy and will parse until any of the following happens:
//  - a non-conforming character is encountered.
//  - s_end is reached.
//
// The following situations triggers a failure:
//  - s >= s_end.
//  - parse failure.
//
static bool tryParseDouble(const char *s, const char *s_end, double *result) {
  if (s >= s_end) {
    return false;
  }

  double mantissa = 0.0;
  // This exponent is base 2 rather than 10.
  // However the exponent we parse is supposed to be one of ten,
  // thus we must take care to convert the exponent/and or the
  // mantissa to a * 2^E, where a is the mantissa and E is the
  // exponent.
  // To get the final double we will use ldexp, it requires the
  // exponent to be in base 2.
  int exponent = 0;

  // NOTE: THESE MUST BE DECLARED HERE SINCE WE ARE NOT ALLOWED
  // TO JUMP OVER DEFINITIONS.
  char sign = '+';
  char exp_sign = '+';
  char const *curr = s;

  // How many characters were read in a loop.
  int read = 0;
  // Tells whether a loop terminated due to reaching s_end.
  bool end_not_reached = false;

  /*
          BEGIN PARSING.
  */

  // Find out what sign we've got.
  if (*curr == '+' || *curr == '-') {
    sign = *curr;
    curr++;
  } else if (IS_DIGIT(*curr)) { /* Pass through. */
  } else {
    goto fail;
  }

  // Read the integer part.
  end_not_reached = (curr != s_end);
  while (end_not_reached && IS_DIGIT(*curr)) {
    mantissa *= 10;
    mantissa += static_cast<int>(*curr - 0x30);
    curr++;
    read++;
    end_not_reached = (curr != s_end);
  }

  // We must make sure we actually got something.
  if (read == 0) goto fail;
  // We allow numbers of form "#", "###" etc.
  if (!end_not_reached) goto assemble;

  // Read the decimal part.
  if (*curr == '.') {
    curr++;
    read = 1;
    end_not_reached = (curr != s_end);
    while (end_not_reached && IS_DIGIT(*curr)) {
      static const double pow_lut[] = {
          1.0, 0.1, 0.01, 0.001, 0.0001, 0.00001, 0.000001, 0.0000001,
      };
      const int lut_entries = sizeof pow_lut / sizeof pow_lut[0];

      // NOTE: Don't use powf here, it will absolutely murder precision.
      mantissa += static_cast<int>(*curr - 0x30) *
                  (read < lut_entries ? pow_lut[read] : std::pow(10.0, -read));
      read++;
      curr++;
      end_not_reached = (curr != s_end);
    }
  } else if (*curr == 'e' || *curr == 'E') {
  } else {
    goto assemble;
  }

  if (!end_not_reached) goto assemble;

  // Read the exponent part.
  if (*curr == 'e' || *curr == 'E') {
    curr++;
    // Figure out if a sign is present and if it is.
    end_not_reached = (curr != s_end);
    if (end_not_reached && (*curr == '+' || *curr == '-')) {
      exp_sign = *curr;
      curr++;
    } else if (IS_DIGIT(*curr)) { /* Pass through. */
    } else {
      // Empty E is not allowed.
      goto fail;
    }

    read = 0;
    end_not_reached = (curr != s_end);
    while (end_not_reached && IS_DIGIT(*curr)) {
      exponent *= 10;
      exponent += static_cast<int>(*curr - 0x30);
      curr++;
      read++;
      end_not_reached = (curr != s_end);
    }
    exponent *= (exp_sign == '+' ? 1 : -1);
    if (read == 0) goto fail;
  }

assemble:
  *result =
      (sign == '+' ? 1 : -1) *
      (exponent ? std::ldexp(mantissa * std::pow(5.0, exponent), exponent) : mantissa);
  return true;
fail:
  return false;
}

static inline real_t parseReal(const char **token, double default_value = 0.0) {
  (*token) += strspn((*token), " \t");
  const char *end = (*token) + strcspn((*token), " \t\r");
  double val = default_value;
  tryParseDouble((*token), end, &val);
  real_t f = static_cast<real_t>(val);
  (*token) = end;
  return f;
}

static inline void parseReal2(real_t *x, real_t *y, const char **token,
                               const double default_x = 0.0,
                               const double default_y = 0.0) {
  (*x) = parseReal(token, default_x);
  (*y) = parseReal(token, default_y);
}

static inline void parseReal3(real_t *x, real_t *y, real_t *z, const char **token,
                               const double default_x = 0.0,
                               const double default_y = 0.0,
                               const double default_z = 0.0) {
  (*x) = parseReal(token, default_x);
  (*y) = parseReal(token, default_y);
  (*z) = parseReal(token, default_z);
}

static inline void parseV(real_t *x, real_t *y, real_t *z, real_t *w,
                          const char **token, const double default_x = 0.0,
                          const double default_y = 0.0,
                          const double default_z = 0.0,
                          const double default_w = 1.0) {
  (*x) = parseReal(token, default_x);
  (*y) = parseReal(token, default_y);
  (*z) = parseReal(token, default_z);
  (*w) = parseReal(token, default_w);
}

static inline bool parseOnOff(const char **token, bool default_value = true) {
  (*token) += strspn((*token), " \t");
  const char *end = (*token) + strcspn((*token), " \t\r");

  bool ret = default_value;
  if ((0 == strncmp((*token), "on", 2))) {
    ret = true;
  } else if ((0 == strncmp((*token), "off", 3))) {
    ret = false;
  }

  (*token) = end;
  return ret;
}

static inline texture_type_t parseTextureType(
    const char **token, texture_type_t default_value = TEXTURE_TYPE_NONE) {
  (*token) += strspn((*token), " \t");
  const char *end = (*token) + strcspn((*token), " \t\r");
  texture_type_t ty = default_value;

  if ((0 == strncmp((*token), "cube_top", strlen("cube_top")))) {
    ty = TEXTURE_TYPE_CUBE_TOP;
  } else if ((0 == strncmp((*token), "cube_bottom", strlen("cube_bottom")))) {
    ty = TEXTURE_TYPE_CUBE_BOTTOM;
  } else if ((0 == strncmp((*token), "cube_left", strlen("cube_left")))) {
    ty = TEXTURE_TYPE_CUBE_LEFT;
  } else if ((0 == strncmp((*token), "cube_right", strlen("cube_right")))) {
    ty = TEXTURE_TYPE_CUBE_RIGHT;
  } else if ((0 == strncmp((*token), "cube_front", strlen("cube_front")))) {
    ty = TEXTURE_TYPE_CUBE_FRONT;
  } else if ((0 == strncmp((*token), "cube_back", strlen("cube_back")))) {
    ty = TEXTURE_TYPE_CUBE_BACK;
  } else if ((0 == strncmp((*token), "sphere", strlen("sphere")))) {
    ty = TEXTURE_TYPE_SPHERE;
  }

  (*token) = end;
  return ty;
}

static tag_sizes parseTagTriple(const char **token) {
  tag_sizes ts;

  ts.num_ints = atoi((*token));
  (*token) += strcspn((*token), "/ \t\r");
  if ((*token)[0] != '/') {
    return ts;
  }
  (*token)++;

  ts.num_reals = atoi((*token));
  (*token) += strcspn((*token), "/ \t\r");
  if ((*token)[0] != '/') {
    return ts;
  }
  (*token)++;

  ts.num_strings = atoi((*token));
  (*token) += strcspn((*token), "/ \t\r") + 1;

  return ts;
}

// Parse triples with index offsets: i, i/j/k, i//k, i/j
static vertex_index parseTriple(const char **token, int vsize, int vnsize,
                                int vtsize) {
  vertex_index vi(-1);

  vi.v_idx = fixIndex(atoi((*token)), vsize);
  (*token) += strcspn((*token), "/ \t\r");
  if ((*token)[0] != '/') {
    return vi;
  }
  (*token)++;

  // i//k
  if ((*token)[0] == '/') {
    (*token)++;
    vi.vn_idx = fixIndex(atoi((*token)), vnsize);
    (*token) += strcspn((*token), "/ \t\r");
    return vi;
  }

  // i/j/k or i/j
  vi.vt_idx = fixIndex(atoi((*token)), vtsize);
  (*token) += strcspn((*token), "/ \t\r");
  if ((*token)[0] != '/') {
    return vi;
  }

  // i/j/k
  (*token)++;  // skip '/'
  vi.vn_idx = fixIndex(atoi((*token)), vnsize);
  (*token) += strcspn((*token), "/ \t\r");
  return vi;
}

// Parse raw triples: i, i/j/k, i//k, i/j
static vertex_index parseRawTriple(const char **token) {
  vertex_index vi(static_cast<int>(0));  // 0 is an invalid index in OBJ

  vi.v_idx = atoi((*token));
  (*token) += strcspn((*token), "/ \t\r");
  if ((*token)[0] != '/') {
    return vi;
  }
  (*token)++;

  // i//k
  if ((*token)[0] == '/') {
    (*token)++;
    vi.vn_idx = atoi((*token));
    (*token) += strcspn((*token), "/ \t\r");
    return vi;
  }

  // i/j/k or i/j
  vi.vt_idx = atoi((*token));
  (*token) += strcspn((*token), "/ \t\r");
  if ((*token)[0] != '/') {
    return vi;
  }

  // i/j/k
  (*token)++;  // skip '/'
  vi.vn_idx = atoi((*token));
  (*token) += strcspn((*token), "/ \t\r");
  return vi;
}

static bool ParseTextureNameAndOption(std::string *texname,
                                      texture_option_t *texopt,
                                      const char *linebuf, const bool is_bump) {
  // @todo { write more robust lexer and parser. }
  bool found_texname = false;
  std::string texture_name;

  // Fill with default value for texopt.
  if (is_bump) {
    texopt->imfchan = 'l';
  } else {
    texopt->imfchan = 'm';
  }
  texopt->bump_multiplier = 1.0f;
  texopt->clamp = false;
  texopt->blendu = true;
  texopt->blendv = true;
  texopt->sharpness = 1.0f;
  texopt->brightness = 0.0f;
  texopt->contrast = 1.0f;
  texopt->origin_offset[0] = 0.0f;
  texopt->origin_offset[1] = 0.0f;
  texopt->origin_offset[2] = 0.0f;
  texopt->scale[0] = 1.0f;
  texopt->scale[1] = 1.0f;
  texopt->scale[2] = 1.0f;
  texopt->turbulence[0] = 0.0f;
  texopt->turbulence[1] = 0.0f;
  texopt->turbulence[2] = 0.0f;
  texopt->type = TEXTURE_TYPE_NONE;

  const char *token = linebuf;  // Assume line ends with NULL

  while (!IS_NEW_LINE((*token))) {
    token += strspn(token, " \t");  // skip space
    if ((0 == strncmp(token, "-blendu", 7)) && IS_SPACE((token[7]))) {
      token += 8;
      texopt->blendu = parseOnOff(&token, /* default */ true);
    } else if ((0 == strncmp(token, "-blendv", 7)) && IS_SPACE((token[7]))) {
      token += 8;
      texopt->blendv = parseOnOff(&token, /* default */ true);
    } else if ((0 == strncmp(token, "-clamp", 6)) && IS_SPACE((token[6]))) {
      token += 7;
      texopt->clamp = parseOnOff(&token, /* default */ true);
    } else if ((0 == strncmp(token, "-boost", 6)) && IS_SPACE((token[6]))) {
      token += 7;
      texopt->sharpness = parseReal(&token, 1.0);
    } else if ((0 == strncmp(token, "-bm", 3)) && IS_SPACE((token[3]))) {
      token += 4;
      texopt->bump_multiplier = parseReal(&token, 1.0);
    } else if ((0 == strncmp(token, "-o", 2)) && IS_SPACE((token[2]))) {
      token += 3;
      parseReal3(&(texopt->origin_offset[0]), &(texopt->origin_offset[1]),
                  &(texopt->origin_offset[2]), &token);
    } else if ((0 == strncmp(token, "-s", 2)) && IS_SPACE((token[2]))) {
      token += 3;
      parseReal3(&(texopt->scale[0]), &(texopt->scale[1]), &(texopt->scale[2]),
                  &token, 1.0, 1.0, 1.0);
    } else if ((0 == strncmp(token, "-t", 2)) && IS_SPACE((token[2]))) {
      token += 3;
      parseReal3(&(texopt->turbulence[0]), &(texopt->turbulence[1]),
                  &(texopt->turbulence[2]), &token);
    } else if ((0 == strncmp(token, "-type", 5)) && IS_SPACE((token[5]))) {
      token += 5;
      texopt->type = parseTextureType((&token), TEXTURE_TYPE_NONE);
    } else if ((0 == strncmp(token, "-imfchan", 8)) && IS_SPACE((token[8]))) {
      token += 9;
      token += strspn(token, " \t");
      const char *end = token + strcspn(token, " \t\r");
      if ((end - token) == 1) {  // Assume one char for -imfchan
        texopt->imfchan = (*token);
      }
      token = end;
    } else if ((0 == strncmp(token, "-mm", 3)) && IS_SPACE((token[3]))) {
      token += 4;
      parseReal2(&(texopt->brightness), &(texopt->contrast), &token, 0.0, 1.0);
    } else {
      // Assume texture filename
      size_t len = strcspn(token, " \t\r");  // untile next space
      texture_name = std::string(token, token + len);
      token += len;

      token += strspn(token, " \t");  // skip space

      found_texname = true;
    }
  }

  if (found_texname) {
    (*texname) = texture_name;
    return true;
  } else {
    return false;
  }
}

static void InitMaterial(material_t *material) {
  material->name = "";
  material->ambient_texname = "";
  material->diffuse_texname = "";
  material->specular_texname = "";
  material->specular_highlight_texname = "";
  material->bump_texname = "";
  material->displacement_texname = "";
  material->reflection_texname = "";
  material->alpha_texname = "";
  for (int i = 0; i < 3; i++) {
    material->ambient[i] = 0.f;
    material->diffuse[i] = 0.f;
    material->specular[i] = 0.f;
    material->transmittance[i] = 0.f;
    material->emission[i] = 0.f;
  }
  material->illum = 0;
  material->dissolve = 1.f;
  material->shininess = 1.f;
  material->ior = 1.f;

  material->roughness = 0.f;
  material->metallic = 0.f;
  material->sheen = 0.f;
  material->clearcoat_thickness = 0.f;
  material->clearcoat_roughness = 0.f;
  material->anisotropy_rotation = 0.f;
  material->anisotropy = 0.f;
  material->roughness_texname = "";
  material->metallic_texname = "";
  material->sheen_texname = "";
  material->emissive_texname = "";
  material->normal_texname = "";

  material->unknown_parameter.clear();
}

static bool exportFaceGroupToShape(
    shape_t *shape, const std::vector<std::vector<vertex_index> > &faceGroup,
    const std::vector<tag_t> &tags, const int material_id,
    const std::string &name, bool triangulate) {
  if (faceGroup.empty()) {
    return false;
  }

  // Flatten vertices and indices
  for (size_t i = 0; i < faceGroup.size(); i++) {
    const std::vector<vertex_index> &face = faceGroup[i];

    vertex_index i0 = face[0];
    vertex_index i1(-1);
    vertex_index i2 = face[1];

    size_t npolys = face.size();

    if (triangulate) {
      // Polygon -> triangle fan conversion
      for (size_t k = 2; k < npolys; k++) {
        i1 = i2;
        i2 = face[k];

        index_t idx0, idx1, idx2;
        idx0.vertex_index = i0.v_idx;
        idx0.normal_index = i0.vn_idx;
        idx0.texcoord_index = i0.vt_idx;
        idx1.vertex_index = i1.v_idx;
        idx1.normal_index = i1.vn_idx;
        idx1.texcoord_index = i1.vt_idx;
        idx2.vertex_index = i2.v_idx;
        idx2.normal_index = i2.vn_idx;
        idx2.texcoord_index = i2.vt_idx;

        shape->mesh.indices.push_back(idx0);
        shape->mesh.indices.push_back(idx1);
        shape->mesh.indices.push_back(idx2);

        shape->mesh.num_face_vertices.push_back(3);
        shape->mesh.material_ids.push_back(material_id);
      }
    } else {
      for (size_t k = 0; k < npolys; k++) {
        index_t idx;
        idx.vertex_index = face[k].v_idx;
        idx.normal_index = face[k].vn_idx;
        idx.texcoord_index = face[k].vt_idx;
        shape->mesh.indices.push_back(idx);
      }

      shape->mesh.num_face_vertices.push_back(
          static_cast<unsigned char>(npolys));
      shape->mesh.material_ids.push_back(material_id);  // per face
    }
  }

  shape->name = name;
  shape->mesh.tags = tags;

  return true;
}

// Split a string with specified delimiter character.
// http://stackoverflow.com/questions/236129/split-a-string-in-c
static void SplitString(const std::string &s, char delim,
                        std::vector<std::string> &elems) {
  std::stringstream ss;
  ss.str(s);
  std::string item;
  while (std::getline(ss, item, delim)) {
    elems.push_back(item);
  }
}

void LoadMtl(std::map<std::string, int> *material_map,
             std::vector<material_t> *materials, std::istream *inStream,
             std::string *warning) {
  // Create a default material anyway.
  material_t material;
  InitMaterial(&material);

  // Issue 43. `d` wins against `Tr` since `Tr` is not in the MTL specification.
  bool has_d = false;
  bool has_tr = false;

  std::stringstream ss;

  std::string linebuf;
  while (inStream->peek() != -1) {
    safeGetline(*inStream, linebuf);

    // Trim trailing whitespace.
    if (linebuf.size() > 0) {
      linebuf = linebuf.substr(0, linebuf.find_last_not_of(" \t") + 1);
    }

    // Trim newline '\r\n' or '\n'
    if (linebuf.size() > 0) {
      if (linebuf[linebuf.size() - 1] == '\n')
        linebuf.erase(linebuf.size() - 1);
    }
    if (linebuf.size() > 0) {
      if (linebuf[linebuf.size() - 1] == '\r')
        linebuf.erase(linebuf.size() - 1);
    }

    // Skip if empty line.
    if (linebuf.empty()) {
      continue;
    }

    // Skip leading space.
    const char *token = linebuf.c_str();
    token += strspn(token, " \t");

    assert(token);
    if (token[0] == '\0') continue;  // empty line

    if (token[0] == '#') continue;  // comment line

    // new mtl
    if ((0 == strncmp(token, "newmtl", 6)) && IS_SPACE((token[6]))) {
      // flush previous material.
      if (!material.name.empty()) {
        material_map->insert(std::pair<std::string, int>(
            material.name, static_cast<int>(materials->size())));
        materials->push_back(material);
      }

      // initial temporary material
      InitMaterial(&material);

      has_d = false;
      has_tr = false;

      // set new mtl name
      token += 7;
      {
        std::stringstream sstr;
        sstr << token;
        material.name = sstr.str();
      }
      continue;
    }

    // ambient
    if (token[0] == 'K' && token[1] == 'a' && IS_SPACE((token[2]))) {
      token += 2;
      real_t r, g, b;
      parseReal3(&r, &g, &b, &token);
      material.ambient[0] = r;
      material.ambient[1] = g;
      material.ambient[2] = b;
      continue;
    }

    // diffuse
    if (token[0] == 'K' && token[1] == 'd' && IS_SPACE((token[2]))) {
      token += 2;
      real_t r, g, b;
      parseReal3(&r, &g, &b, &token);
      material.diffuse[0] = r;
      material.diffuse[1] = g;
      material.diffuse[2] = b;
      continue;
    }

    // specular
    if (token[0] == 'K' && token[1] == 's' && IS_SPACE((token[2]))) {
      token += 2;
      real_t r, g, b;
      parseReal3(&r, &g, &b, &token);
      material.specular[0] = r;
      material.specular[1] = g;
      material.specular[2] = b;
      continue;
    }

    // transmittance
    if ((token[0] == 'K' && token[1] == 't' && IS_SPACE((token[2]))) ||
        (token[0] == 'T' && token[1] == 'f' && IS_SPACE((token[2])))) {
      token += 2;
      real_t r, g, b;
      parseReal3(&r, &g, &b, &token);
      material.transmittance[0] = r;
      material.transmittance[1] = g;
      material.transmittance[2] = b;
      continue;
    }

    // ior(index of refraction)
    if (token[0] == 'N' && token[1] == 'i' && IS_SPACE((token[2]))) {
      token += 2;
      material.ior = parseReal(&token);
      continue;
    }

    // emission
    if (token[0] == 'K' && token[1] == 'e' && IS_SPACE(token[2])) {
      token += 2;
      real_t r, g, b;
      parseReal3(&r, &g, &b, &token);
      material.emission[0] = r;
      material.emission[1] = g;
      material.emission[2] = b;
      continue;
    }

    // shininess
    if (token[0] == 'N' && token[1] == 's' && IS_SPACE(token[2])) {
      token += 2;
      material.shininess = parseReal(&token);
      continue;
    }

    // illum model
    if (0 == strncmp(token, "illum", 5) && IS_SPACE(token[5])) {
      token += 6;
      material.illum = parseInt(&token);
      continue;
    }

    // dissolve
    if ((token[0] == 'd' && IS_SPACE(token[1]))) {
      token += 1;
      material.dissolve = parseReal(&token);

      if (has_tr) {
        ss << "WARN: Both `d` and `Tr` parameters defined for \""
           << material.name << "\". Use the value of `d` for dissolve."
           << std::endl;
      }
      has_d = true;
      continue;
    }
    if (token[0] == 'T' && token[1] == 'r' && IS_SPACE(token[2])) {
      token += 2;
      if (has_d) {
        // `d` wins. Ignore `Tr` value.
        ss << "WARN: Both `d` and `Tr` parameters defined for \""
           << material.name << "\". Use the value of `d` for dissolve."
           << std::endl;
      } else {
        // We invert value of Tr(assume Tr is in range [0, 1])
        // NOTE: Interpretation of Tr is application(exporter) dependent. For
        // some application(e.g. 3ds max obj exporter), Tr = d(Issue 43)
        material.dissolve = 1.0f - parseReal(&token);
      }
      has_tr = true;
      continue;
    }

    // PBR: roughness
    if (token[0] == 'P' && token[1] == 'r' && IS_SPACE(token[2])) {
      token += 2;
      material.roughness = parseReal(&token);
      continue;
    }

    // PBR: metallic
    if (token[0] == 'P' && token[1] == 'm' && IS_SPACE(token[2])) {
      token += 2;
      material.metallic = parseReal(&token);
      continue;
    }

    // PBR: sheen
    if (token[0] == 'P' && token[1] == 's' && IS_SPACE(token[2])) {
      token += 2;
      material.sheen = parseReal(&token);
      continue;
    }

    // PBR: clearcoat thickness
    if (token[0] == 'P' && token[1] == 'c' && IS_SPACE(token[2])) {
      token += 2;
      material.clearcoat_thickness = parseReal(&token);
      continue;
    }

    // PBR: clearcoat roughness
    if ((0 == strncmp(token, "Pcr", 3)) && IS_SPACE(token[3])) {
      token += 4;
      material.clearcoat_roughness = parseReal(&token);
      continue;
    }

    // PBR: anisotropy
    if ((0 == strncmp(token, "aniso", 5)) && IS_SPACE(token[5])) {
      token += 6;
      material.anisotropy = parseReal(&token);
      continue;
    }

    // PBR: anisotropy rotation
    if ((0 == strncmp(token, "anisor", 6)) && IS_SPACE(token[6])) {
      token += 7;
      material.anisotropy_rotation = parseReal(&token);
      continue;
    }

    // ambient texture
    if ((0 == strncmp(token, "map_Ka", 6)) && IS_SPACE(token[6])) {
      token += 7;
      ParseTextureNameAndOption(&(material.ambient_texname),
                                &(material.ambient_texopt), token,
                                /* is_bump */ false);
      continue;
    }

    // diffuse texture
    if ((0 == strncmp(token, "map_Kd", 6)) && IS_SPACE(token[6])) {
      token += 7;
      ParseTextureNameAndOption(&(material.diffuse_texname),
                                &(material.diffuse_texopt), token,
                                /* is_bump */ false);
      continue;
    }

    // specular texture
    if ((0 == strncmp(token, "map_Ks", 6)) && IS_SPACE(token[6])) {
      token += 7;
      ParseTextureNameAndOption(&(material.specular_texname),
                                &(material.specular_texopt), token,
                                /* is_bump */ false);
      continue;
    }

    // specular highlight texture
    if ((0 == strncmp(token, "map_Ns", 6)) && IS_SPACE(token[6])) {
      token += 7;
      ParseTextureNameAndOption(&(material.specular_highlight_texname),
                                &(material.specular_highlight_texopt), token,
                                /* is_bump */ false);
      continue;
    }

    // bump texture
    if ((0 == strncmp(token, "map_bump", 8)) && IS_SPACE(token[8])) {
      token += 9;
      ParseTextureNameAndOption(&(material.bump_texname),
                                &(material.bump_texopt), token,
                                /* is_bump */ true);
      continue;
    }

    // bump texture
    if ((0 == strncmp(token, "map_Bump", 8)) && IS_SPACE(token[8])) {
      token += 9;
      ParseTextureNameAndOption(&(material.bump_texname),
                                &(material.bump_texopt), token,
                                /* is_bump */ true);
      continue;
    }

    // bump texture
    if ((0 == strncmp(token, "bump", 4)) && IS_SPACE(token[4])) {
      token += 5;
      ParseTextureNameAndOption(&(material.bump_texname),
                                &(material.bump_texopt), token,
                                /* is_bump */ true);
      continue;
    }

    // alpha texture
    if ((0 == strncmp(token, "map_d", 5)) && IS_SPACE(token[5])) {
      token += 6;
      material.alpha_texname = token;
      ParseTextureNameAndOption(&(material.alpha_texname),
                                &(material.alpha_texopt), token,
                                /* is_bump */ false);
      continue;
    }

    // displacement texture
    if ((0 == strncmp(token, "disp", 4)) && IS_SPACE(token[4])) {
      token += 5;
      ParseTextureNameAndOption(&(material.displacement_texname),
                                &(material.displacement_texopt), token,
                                /* is_bump */ false);
      continue;
    }

    // reflection map
    if ((0 == strncmp(token, "refl", 4)) && IS_SPACE(token[4])) {
      token += 5;
      ParseTextureNameAndOption(&(material.reflection_texname),
                                &(material.reflection_texopt), token,
                                /* is_bump */ false);
      continue;
    }

    // PBR: roughness texture
    if ((0 == strncmp(token, "map_Pr", 6)) && IS_SPACE(token[6])) {
      token += 7;
      ParseTextureNameAndOption(&(material.roughness_texname),
                                &(material.roughness_texopt), token,
                                /* is_bump */ false);
      continue;
    }

    // PBR: metallic texture
    if ((0 == strncmp(token, "map_Pm", 6)) && IS_SPACE(token[6])) {
      token += 7;
      ParseTextureNameAndOption(&(material.metallic_texname),
                                &(material.metallic_texopt), token,
                                /* is_bump */ false);
      continue;
    }

    // PBR: sheen texture
    if ((0 == strncmp(token, "map_Ps", 6)) && IS_SPACE(token[6])) {
      token += 7;
      ParseTextureNameAndOption(&(material.sheen_texname),
                                &(material.sheen_texopt), token,
                                /* is_bump */ false);
      continue;
    }

    // PBR: emissive texture
    if ((0 == strncmp(token, "map_Ke", 6)) && IS_SPACE(token[6])) {
      token += 7;
      ParseTextureNameAndOption(&(material.emissive_texname),
                                &(material.emissive_texopt), token,
                                /* is_bump */ false);
      continue;
    }

    // PBR: normal map texture
    if ((0 == strncmp(token, "norm", 4)) && IS_SPACE(token[4])) {
      token += 5;
      ParseTextureNameAndOption(
          &(material.normal_texname), &(material.normal_texopt), token,
          /* is_bump */ false);  // @fixme { is_bump will be true? }
      continue;
    }

    // unknown parameter
    const char *_space = strchr(token, ' ');
    if (!_space) {
      _space = strchr(token, '\t');
    }
    if (_space) {
      std::ptrdiff_t len = _space - token;
      std::string key(token, static_cast<size_t>(len));
      std::string value = _space + 1;
      material.unknown_parameter.insert(
          std::pair<std::string, std::string>(key, value));
    }
  }
  // flush last material.
  material_map->insert(std::pair<std::string, int>(
      material.name, static_cast<int>(materials->size())));
  materials->push_back(material);

  if (warning) {
    (*warning) = ss.str();
  }
}

bool MaterialFileReader::operator()(const std::string &matId,
                                    std::vector<material_t> *materials,
                                    std::map<std::string, int> *matMap,
                                    std::string *err) {
  std::string filepath;

  if (!m_mtlBaseDir.empty()) {
    filepath = std::string(m_mtlBaseDir) + matId;
  } else {
    filepath = matId;
  }

  std::ifstream matIStream(filepath.c_str());
  if (!matIStream) {
    std::stringstream ss;
    ss << "WARN: Material file [ " << filepath << " ] not found." << std::endl;
    if (err) {
      (*err) += ss.str();
    }
    return false;
  }

  std::string warning;
  LoadMtl(matMap, materials, &matIStream, &warning);

  if (!warning.empty()) {
    if (err) {
      (*err) += warning;
    }
  }

  return true;
}

bool MaterialStreamReader::operator()(const std::string &matId,
                                      std::vector<material_t> *materials,
                                      std::map<std::string, int> *matMap,
                                      std::string *err) {
  (void)matId;
  if (!m_inStream) {
    std::stringstream ss;
    ss << "WARN: Material stream in error state. " << std::endl;
    if (err) {
      (*err) += ss.str();
    }
    return false;
  }

  std::string warning;
  LoadMtl(matMap, materials, &m_inStream, &warning);

  if (!warning.empty()) {
    if (err) {
      (*err) += warning;
    }
  }

  return true;
}

bool LoadObj(attrib_t *attrib, std::vector<shape_t> *shapes,
             std::vector<material_t> *materials, std::string *err,
             const char *filename, const char *mtl_basedir, bool trianglulate) {
  attrib->vertices.clear();
  attrib->normals.clear();
  attrib->texcoords.clear();
  shapes->clear();

  std::stringstream errss;

  std::ifstream ifs(filename);
  if (!ifs) {
    errss << "Cannot open file [" << filename << "]" << std::endl;
    if (err) {
      (*err) = errss.str();
    }
    return false;
  }

  std::string baseDir;
  if (mtl_basedir) {
    baseDir = mtl_basedir;
  }
  MaterialFileReader matFileReader(baseDir);

  return LoadObj(attrib, shapes, materials, err, &ifs, &matFileReader,
                 trianglulate);
}

bool LoadObj(attrib_t *attrib, std::vector<shape_t> *shapes,
             std::vector<material_t> *materials, std::string *err,
             std::istream *inStream, MaterialReader *readMatFn /*= NULL*/,
             bool triangulate) {
  std::stringstream errss;

  std::vector<real_t> v;
  std::vector<real_t> vn;
  std::vector<real_t> vt;
  std::vector<tag_t> tags;
  std::vector<std::vector<vertex_index> > faceGroup;
  std::string name;

  // material
  std::map<std::string, int> material_map;
  int material = -1;

  shape_t shape;

  std::string linebuf;
  while (inStream->peek() != -1) {
    safeGetline(*inStream, linebuf);

    // Trim newline '\r\n' or '\n'
    if (linebuf.size() > 0) {
      if (linebuf[linebuf.size() - 1] == '\n')
        linebuf.erase(linebuf.size() - 1);
    }
    if (linebuf.size() > 0) {
      if (linebuf[linebuf.size() - 1] == '\r')
        linebuf.erase(linebuf.size() - 1);
    }

    // Skip if empty line.
    if (linebuf.empty()) {
      continue;
    }

    // Skip leading space.
    const char *token = linebuf.c_str();
    token += strspn(token, " \t");

    assert(token);
    if (token[0] == '\0') continue;  // empty line

    if (token[0] == '#') continue;  // comment line

    // vertex
    if (token[0] == 'v' && IS_SPACE((token[1]))) {
      token += 2;
      real_t x, y, z;
      parseReal3(&x, &y, &z, &token);
      v.push_back(x);
      v.push_back(y);
      v.push_back(z);
      continue;
    }

    // normal
    if (token[0] == 'v' && token[1] == 'n' && IS_SPACE((token[2]))) {
      token += 3;
      real_t x, y, z;
      parseReal3(&x, &y, &z, &token);
      vn.push_back(x);
      vn.push_back(y);
      vn.push_back(z);
      continue;
    }

    // texcoord
    if (token[0] == 'v' && token[1] == 't' && IS_SPACE((token[2]))) {
      token += 3;
      real_t x, y;
      parseReal2(&x, &y, &token);
      vt.push_back(x);
      vt.push_back(y);
      continue;
    }

    // face
    if (token[0] == 'f' && IS_SPACE((token[1]))) {
      token += 2;
      token += strspn(token, " \t");

      std::vector<vertex_index> face;
      face.reserve(3);

      while (!IS_NEW_LINE(token[0])) {
        vertex_index vi = parseTriple(&token, static_cast<int>(v.size() / 3),
                                      static_cast<int>(vn.size() / 3),
                                      static_cast<int>(vt.size() / 2));
        face.push_back(vi);
        size_t n = strspn(token, " \t\r");
        token += n;
      }

      // replace with emplace_back + std::move on C++11
      faceGroup.push_back(std::vector<vertex_index>());
      faceGroup[faceGroup.size() - 1].swap(face);

      continue;
    }

    // use mtl
    if ((0 == strncmp(token, "usemtl", 6)) && IS_SPACE((token[6]))) {
      token += 7;
      std::stringstream ss;
      ss << token;
      std::string namebuf = ss.str();

      int newMaterialId = -1;
      if (material_map.find(namebuf) != material_map.end()) {
        newMaterialId = material_map[namebuf];
      } else {
        // { error!! material not found }
      }

      if (newMaterialId != material) {
        // Create per-face material. Thus we don't add `shape` to `shapes` at
        // this time.
        // just clear `faceGroup` after `exportFaceGroupToShape()` call.
        exportFaceGroupToShape(&shape, faceGroup, tags, material, name,
                               triangulate);
        faceGroup.clear();
        material = newMaterialId;
      }

      continue;
    }

    // load mtl
    if ((0 == strncmp(token, "mtllib", 6)) && IS_SPACE((token[6]))) {
      if (readMatFn) {
        token += 7;

        std::vector<std::string> filenames;
        SplitString(std::string(token), ' ', filenames);

        if (filenames.empty()) {
          if (err) {
            (*err) +=
                "WARN: Looks like empty filename for mtllib. Use default "
                "material. \n";
          }
        } else {
          bool found = false;
          for (size_t s = 0; s < filenames.size(); s++) {
            std::string err_mtl;
            bool ok = (*readMatFn)(filenames[s].c_str(), materials,
                                   &material_map, &err_mtl);
            if (err && (!err_mtl.empty())) {
              (*err) += err_mtl;  // This should be warn message.
            }

            if (ok) {
              found = true;
              break;
            }
          }

          if (!found) {
            if (err) {
              (*err) +=
                  "WARN: Failed to load material file(s). Use default "
                  "material.\n";
            }
          }
        }
      }

      continue;
    }

    // group name
    if (token[0] == 'g' && IS_SPACE((token[1]))) {
      // flush previous face group.
      bool ret = exportFaceGroupToShape(&shape, faceGroup, tags, material, name,
                                        triangulate);
      (void)ret; // return value not used.

      if (shape.mesh.indices.size() > 0) {
        shapes->push_back(shape);
      }

      shape = shape_t();

      // material = -1;
      faceGroup.clear();

      std::vector<std::string> names;
      names.reserve(2);

      while (!IS_NEW_LINE(token[0])) {
        std::string str = parseString(&token);
        names.push_back(str);
        token += strspn(token, " \t\r");  // skip tag
      }

      assert(names.size() > 0);

      // names[0] must be 'g', so skip the 0th element.
      if (names.size() > 1) {
        name = names[1];
      } else {
        name = "";
      }

      continue;
    }

    // object name
    if (token[0] == 'o' && IS_SPACE((token[1]))) {
      // flush previous face group.
      bool ret = exportFaceGroupToShape(&shape, faceGroup, tags, material, name,
                                        triangulate);
      if (ret) {
        shapes->push_back(shape);
      }

      // material = -1;
      faceGroup.clear();
      shape = shape_t();

      // @todo { multiple object name? }
      token += 2;
      std::stringstream ss;
      ss << token;
      name = ss.str();

      continue;
    }

    if (token[0] == 't' && IS_SPACE(token[1])) {
      tag_t tag;

      token += 2;
      std::stringstream ss;
      ss << token;
      tag.name = ss.str();

      token += tag.name.size() + 1;

      tag_sizes ts = parseTagTriple(&token);

      tag.intValues.resize(static_cast<size_t>(ts.num_ints));

      for (size_t i = 0; i < static_cast<size_t>(ts.num_ints); ++i) {
        tag.intValues[i] = atoi(token);
        token += strcspn(token, "/ \t\r") + 1;
      }

      tag.floatValues.resize(static_cast<size_t>(ts.num_reals));
      for (size_t i = 0; i < static_cast<size_t>(ts.num_reals); ++i) {
        tag.floatValues[i] = parseReal(&token);
        token += strcspn(token, "/ \t\r") + 1;
      }

      tag.stringValues.resize(static_cast<size_t>(ts.num_strings));
      for (size_t i = 0; i < static_cast<size_t>(ts.num_strings); ++i) {
        std::stringstream sstr;
        sstr << token;
        tag.stringValues[i] = sstr.str();
        token += tag.stringValues[i].size() + 1;
      }

      tags.push_back(tag);
    }

    // Ignore unknown command.
  }

  bool ret = exportFaceGroupToShape(&shape, faceGroup, tags, material, name,
                                    triangulate);
  // exportFaceGroupToShape return false when `usemtl` is called in the last
  // line.
  // we also add `shape` to `shapes` when `shape.mesh` has already some
  // faces(indices)
  if (ret || shape.mesh.indices.size()) {
    shapes->push_back(shape);
  }
  faceGroup.clear();  // for safety

  if (err) {
    (*err) += errss.str();
  }

  attrib->vertices.swap(v);
  attrib->normals.swap(vn);
  attrib->texcoords.swap(vt);

  return true;
}

bool LoadObjWithCallback(std::istream &inStream, const callback_t &callback,
                         void *user_data /*= NULL*/,
                         MaterialReader *readMatFn /*= NULL*/,
                         std::string *err /*= NULL*/) {
  std::stringstream errss;

  // material
  std::map<std::string, int> material_map;
  int material_id = -1;  // -1 = invalid

  std::vector<index_t> indices;
  std::vector<material_t> materials;
  std::vector<std::string> names;
  names.reserve(2);
  std::string name;
  std::vector<const char *> names_out;

  std::string linebuf;
  while (inStream.peek() != -1) {
    safeGetline(inStream, linebuf);

    // Trim newline '\r\n' or '\n'
    if (linebuf.size() > 0) {
      if (linebuf[linebuf.size() - 1] == '\n')
        linebuf.erase(linebuf.size() - 1);
    }
    if (linebuf.size() > 0) {
      if (linebuf[linebuf.size() - 1] == '\r')
        linebuf.erase(linebuf.size() - 1);
    }

    // Skip if empty line.
    if (linebuf.empty()) {
      continue;
    }

    // Skip leading space.
    const char *token = linebuf.c_str();
    token += strspn(token, " \t");

    assert(token);
    if (token[0] == '\0') continue;  // empty line

    if (token[0] == '#') continue;  // comment line

    // vertex
    if (token[0] == 'v' && IS_SPACE((token[1]))) {
      token += 2;
      real_t x, y, z, w;  // w is optional. default = 1.0
      parseV(&x, &y, &z, &w, &token);
      if (callback.vertex_cb) {
        callback.vertex_cb(user_data, x, y, z, w);
      }
      continue;
    }

    // normal
    if (token[0] == 'v' && token[1] == 'n' && IS_SPACE((token[2]))) {
      token += 3;
      real_t x, y, z;
      parseReal3(&x, &y, &z, &token);
      if (callback.normal_cb) {
        callback.normal_cb(user_data, x, y, z);
      }
      continue;
    }

    // texcoord
    if (token[0] == 'v' && token[1] == 't' && IS_SPACE((token[2]))) {
      token += 3;
      real_t x, y, z;  // y and z are optional. default = 0.0
      parseReal3(&x, &y, &z, &token);
      if (callback.texcoord_cb) {
        callback.texcoord_cb(user_data, x, y, z);
      }
      continue;
    }

    // face
    if (token[0] == 'f' && IS_SPACE((token[1]))) {
      token += 2;
      token += strspn(token, " \t");

      indices.clear();
      while (!IS_NEW_LINE(token[0])) {
        vertex_index vi = parseRawTriple(&token);

        index_t idx;
        idx.vertex_index = vi.v_idx;
        idx.normal_index = vi.vn_idx;
        idx.texcoord_index = vi.vt_idx;

        indices.push_back(idx);
        size_t n = strspn(token, " \t\r");
        token += n;
      }

      if (callback.index_cb && indices.size() > 0) {
        callback.index_cb(user_data, &indices.at(0),
                          static_cast<int>(indices.size()));
      }

      continue;
    }

    // use mtl
    if ((0 == strncmp(token, "usemtl", 6)) && IS_SPACE((token[6]))) {
      token += 7;
      std::stringstream ss;
      ss << token;
      std::string namebuf = ss.str();

      int newMaterialId = -1;
      if (material_map.find(namebuf) != material_map.end()) {
        newMaterialId = material_map[namebuf];
      } else {
        // { error!! material not found }
      }

      if (newMaterialId != material_id) {
        material_id = newMaterialId;
      }

      if (callback.usemtl_cb) {
        callback.usemtl_cb(user_data, namebuf.c_str(), material_id);
      }

      continue;
    }

    // load mtl
    if ((0 == strncmp(token, "mtllib", 6)) && IS_SPACE((token[6]))) {
      if (readMatFn) {
        token += 7;

        std::vector<std::string> filenames;
        SplitString(std::string(token), ' ', filenames);

        if (filenames.empty()) {
          if (err) {
            (*err) +=
                "WARN: Looks like empty filename for mtllib. Use default "
                "material. \n";
          }
        } else {
          bool found = false;
          for (size_t s = 0; s < filenames.size(); s++) {
            std::string err_mtl;
            bool ok = (*readMatFn)(filenames[s].c_str(), &materials,
                                   &material_map, &err_mtl);
            if (err && (!err_mtl.empty())) {
              (*err) += err_mtl;  // This should be warn message.
            }

            if (ok) {
              found = true;
              break;
            }
          }

          if (!found) {
            if (err) {
              (*err) +=
                  "WARN: Failed to load material file(s). Use default "
                  "material.\n";
            }
          } else {
            if (callback.mtllib_cb) {
              callback.mtllib_cb(user_data, &materials.at(0),
                                 static_cast<int>(materials.size()));
            }
          }
        }
      }

      continue;
    }

    // group name
    if (token[0] == 'g' && IS_SPACE((token[1]))) {
      names.clear();

      while (!IS_NEW_LINE(token[0])) {
        std::string str = parseString(&token);
        names.push_back(str);
        token += strspn(token, " \t\r");  // skip tag
      }

      assert(names.size() > 0);

      // names[0] must be 'g', so skip the 0th element.
      if (names.size() > 1) {
        name = names[1];
      } else {
        name.clear();
      }

      if (callback.group_cb) {
        if (names.size() > 1) {
          // create const char* array.
          names_out.resize(names.size() - 1);
          for (size_t j = 0; j < names_out.size(); j++) {
            names_out[j] = names[j + 1].c_str();
          }
          callback.group_cb(user_data, &names_out.at(0),
                            static_cast<int>(names_out.size()));

        } else {
          callback.group_cb(user_data, NULL, 0);
        }
      }

      continue;
    }

    // object name
    if (token[0] == 'o' && IS_SPACE((token[1]))) {
      // @todo { multiple object name? }
      token += 2;

      std::stringstream ss;
      ss << token;
      std::string object_name = ss.str();

      if (callback.object_cb) {
        callback.object_cb(user_data, object_name.c_str());
      }

      continue;
    }

#if 0  // @todo
    if (token[0] == 't' && IS_SPACE(token[1])) {
      tag_t tag;

      token += 2;
      std::stringstream ss;
      ss << token;
      tag.name = ss.str();

      token += tag.name.size() + 1;

      tag_sizes ts = parseTagTriple(&token);

      tag.intValues.resize(static_cast<size_t>(ts.num_ints));

      for (size_t i = 0; i < static_cast<size_t>(ts.num_ints); ++i) {
        tag.intValues[i] = atoi(token);
        token += strcspn(token, "/ \t\r") + 1;
      }

      tag.floatValues.resize(static_cast<size_t>(ts.num_reals));
      for (size_t i = 0; i < static_cast<size_t>(ts.num_reals); ++i) {
        tag.floatValues[i] = parseReal(&token);
        token += strcspn(token, "/ \t\r") + 1;
      }

      tag.stringValues.resize(static_cast<size_t>(ts.num_strings));
      for (size_t i = 0; i < static_cast<size_t>(ts.num_strings); ++i) {
        std::stringstream ss;
        ss << token;
        tag.stringValues[i] = ss.str();
        token += tag.stringValues[i].size() + 1;
      }

      tags.push_back(tag);
    }
#endif

    // Ignore unknown command.
  }

  if (err) {
    (*err) += errss.str();
  }

  return true;
}
}  // namespace tinyobj

#endif