/******************************************************************************\
| OpenGL 4 Example Code.                                                       |
| Accompanies written series "Anton's OpenGL 4 Tutorials"                      |
| Email: anton at antongerdelan dot net                                        |
| First version 27 Jan 2014                                                    |
| Dr Anton Gerdelan, Trinity College Dublin, Ireland.                          |
| See individual libraries separate legal notices                              |
|******************************************************************************|
| This is just a file holding some commonly-used "utility" functions to keep   |
| the main file a bit easier to read. You can might build up something like    |
| this as learn more GL. Note that you don't need much code here to do good GL.|
| If you have a big object-oriented engine then maybe you can ask yourself if  |
| it is really making life easier.                                             |
\******************************************************************************/
#include "include/gl_utils.h"
#include <assert.h>
#include <stdio.h>
#include <string.h>
#include <time.h>
#define GL_LOG_FILE "gl.log"
#define MAX_SHADER_LENGTH 262144

/*--------------------------------LOG FUNCTIONS-------------------------------*/
bool restart_gl_log() {
  FILE* file = fopen( GL_LOG_FILE, "w" );
  if ( !file ) {
    fprintf( stderr, "ERROR: could not open GL_LOG_FILE log file %s for writing\n", GL_LOG_FILE );
    return false;
  }
  time_t now = time( NULL );
  char* date = ctime( &now );
  fprintf( file, "GL_LOG_FILE log. local time %s\n", date );
  fclose( file );
  return true;
}

bool gl_log( const char* message, ... ) {
  va_list argptr;
  FILE* file = fopen( GL_LOG_FILE, "a" );
  if ( !file ) {
    fprintf( stderr, "ERROR: could not open GL_LOG_FILE %s file for appending\n", GL_LOG_FILE );
    return false;
  }
  va_start( argptr, message );
  vfprintf( file, message, argptr );
  va_end( argptr );
  fclose( file );
  return true;
}

/* same as gl_log except also prints to stderr */
bool gl_log_err( const char* message, ... ) {
  va_list argptr;
  FILE* file = fopen( GL_LOG_FILE, "a" );
  if ( !file ) {
    fprintf( stderr, "ERROR: could not open GL_LOG_FILE %s file for appending\n", GL_LOG_FILE );
    return false;
  }
  va_start( argptr, message );
  vfprintf( file, message, argptr );
  va_end( argptr );
  va_start( argptr, message );
  vfprintf( stderr, message, argptr );
  va_end( argptr );
  fclose( file );
  return true;
}


void glfw_error_callback( int error, const char* description ) {
  fputs( description, stderr );
  gl_log_err( "%s\n", description );
}


void _update_fps_counter( GLFWwindow* window ) {
  static double previous_seconds = glfwGetTime();
  static int frame_count;
  double current_seconds = glfwGetTime();
  double elapsed_seconds = current_seconds - previous_seconds;
  if ( elapsed_seconds > 0.25 ) {
    previous_seconds = current_seconds;
    double fps       = (double)frame_count / elapsed_seconds;
    char tmp[128];
    sprintf( tmp, "opengl @ fps: %.2f", fps );
    glfwSetWindowTitle( window, tmp );
    frame_count = 0;
  }
  frame_count++;
}

/*-----------------------------------SHADERS----------------------------------*/
/* copy a shader from a plain text file into a character array */
bool parse_file_into_str( const char* file_name, char* shader_str, int max_len ) {
  FILE* file = fopen( file_name, "r" );
  if ( !file ) {
    gl_log_err( "ERROR: opening file for reading: %s\n", file_name );
    return false;
  }
  size_t cnt = fread( shader_str, 1, max_len - 1, file );
  if ( (int)cnt >= max_len - 1 ) { gl_log_err( "WARNING: file %s too big - truncated.\n", file_name ); }
  if ( ferror( file ) ) {
    gl_log_err( "ERROR: reading shader file %s\n", file_name );
    fclose( file );
    return false;
  }
  // append \0 to end of file string
  shader_str[cnt] = 0;
  fclose( file );
  return true;
}

void print_shader_info_log( GLuint shader_index ) {
  int max_length    = 2048;
  int actual_length = 0;
  char log[2048];
  glGetShaderInfoLog( shader_index, max_length, &actual_length, log );
  printf( "shader info log for GL index %i:\n%s\n", shader_index, log );
  gl_log( "shader info log for GL index %i:\n%s\n", shader_index, log );
}

bool create_shader( const char* file_name, GLuint* shader, GLenum type ) {
  gl_log( "creating shader from %s...\n", file_name );
  char shader_string[MAX_SHADER_LENGTH];
  parse_file_into_str( file_name, shader_string, MAX_SHADER_LENGTH );
  *shader         = glCreateShader( type );
  const GLchar* p = (const GLchar*)shader_string;
  glShaderSource( *shader, 1, &p, NULL );
  glCompileShader( *shader );
  // check for compile errors
  int params = -1;
  glGetShaderiv( *shader, GL_COMPILE_STATUS, &params );
  if ( GL_TRUE != params ) {
    gl_log_err( "ERROR: GL shader index %i did not compile\n", *shader );
    print_shader_info_log( *shader );
    return false; // or exit or something
  }
  gl_log( "shader compiled. index %i\n", *shader );
  return true;
}

void print_programme_info_log( GLuint sp ) {
  int max_length    = 2048;
  int actual_length = 0;
  char log[2048];
  glGetProgramInfoLog( sp, max_length, &actual_length, log );
  printf( "program info log for GL index %u:\n%s", sp, log );
  gl_log( "program info log for GL index %u:\n%s", sp, log );
}

bool is_programme_valid( GLuint sp ) {
  glValidateProgram( sp );
  GLint params = -1;
  glGetProgramiv( sp, GL_VALIDATE_STATUS, &params );
  if ( GL_TRUE != params ) {
    gl_log_err( "program %i GL_VALIDATE_STATUS = GL_FALSE\n", sp );
    print_programme_info_log( sp );
    return false;
  }
  gl_log( "program %i GL_VALIDATE_STATUS = GL_TRUE\n", sp );
  return true;
}

bool create_programme( GLuint vert, GLuint frag, GLuint* programme ) {
  *programme = glCreateProgram();
  gl_log( "created programme %u. attaching shaders %u and %u...\n", *programme, vert, frag );
  glAttachShader( *programme, vert );
  glAttachShader( *programme, frag );
  // link the shader programme. if binding input attributes do that before link
  glLinkProgram( *programme );
  GLint params = -1;
  glGetProgramiv( *programme, GL_LINK_STATUS, &params );
  if ( GL_TRUE != params ) {
    gl_log_err( "ERROR: could not link shader programme GL index %u\n", *programme );
    print_programme_info_log( *programme );
    return false;
  }
  ( is_programme_valid( *programme ) );
  // delete shaders here to free memory
  glDeleteShader( vert );
  glDeleteShader( frag );
  return true;
}

GLuint create_programme_from_files( const char* vert_file_name, const char* frag_file_name ) {
  GLuint vert, frag, programme;
  ( create_shader( vert_file_name, &vert, GL_VERTEX_SHADER ) );
  ( create_shader( frag_file_name, &frag, GL_FRAGMENT_SHADER ) );
  ( create_programme( vert, frag, &programme ) );
  return programme;
}