#include <SDL2/SDL.h>
#include <SDL2/SDL_image.h>
#include <SDL2/SDL_ttf.h>
#include <stdio.h>
#include <sys/time.h>


#define SCREEN_WIDTH 1000
#define SCREEN_HEIGHT 600
#define IMAGE_FILE "Data/ghost-emoji-small.png"
#define FONT_NAME "Data/LiberationSans-Regular.ttf"
#define FONT_SIZE 16
#define BASIC_FPS 60
// Rozepsaná kalkulace vypadá takto: BASIC_STEP=2*M_PI/(4*BASIC_FPS)
#define BASIC_STEP 0.026179939f
#define RADIUS 170


SDL_Window *myWindow = NULL;
SDL_Renderer *myRenderer = NULL;
SDL_Surface *mySurf = NULL;
SDL_Texture *ghostTexture = NULL,
            *myMessage = NULL;
SDL_Rect drect;
SDL_Color textColor;
TTF_Font *myFont = NULL;
int sdl_init = 0,
    ttf_init = 0,
    iwidth,
    iheight,
    fps,
    keyblock,
    oldtime,
    quit;
unsigned int rfps,
             framecount;
struct timeval tv;
float angle,
      basic_frame,
      speed_ratio;
Uint32 time_a,
       time_b,
       time_c,
       time_d,
       overhead;
char unistring[1000];


void Finish(void)
{
  if(myFont!=NULL)
  {
    TTF_CloseFont(myFont);
  }
  if(ttf_init)
  {
    TTF_Quit();
  }
  if(ghostTexture!=NULL)
  {
    SDL_DestroyTexture(ghostTexture);
  }
  if(myRenderer!=NULL)
  {
    SDL_DestroyRenderer(myRenderer);
  }
  if(myWindow!=NULL)
  {
    SDL_DestroyWindow(myWindow);
  }
  if(sdl_init)
  {
    SDL_Quit();
  }
}


void Initialize(void)
{
  if( SDL_Init(SDL_INIT_VIDEO|SDL_INIT_TIMER) < 0 )
  {
    fprintf(stderr,"SDL could not initialize! SDL_Error: %s\n", SDL_GetError() );
    exit(EXIT_FAILURE);
  }
  sdl_init=1;


  if(TTF_Init()==-1)
  {
    fprintf(stderr,"SDL_ttf could not initialize! SDL_Error: %s\n", SDL_GetError() );
    Finish();
    exit(EXIT_FAILURE);
  }
  ttf_init=1;


  time_a=SDL_GetTicks();
  SDL_Delay(5);
  time_b=SDL_GetTicks();
  overhead=time_b-time_a-5;


  myWindow=SDL_CreateWindow("KeepAnimationSpeed",SDL_WINDOWPOS_CENTERED,SDL_WINDOWPOS_CENTERED,
    SCREEN_WIDTH,SCREEN_HEIGHT,SDL_WINDOW_SHOWN);
  if(myWindow==NULL)
  {
    fprintf(stderr,"Can't open a window!\n");
    Finish();
    exit(EXIT_FAILURE);
  }


  myRenderer=SDL_CreateRenderer(myWindow,-1,0);
  if(myRenderer==NULL)
  {
    fprintf(stderr,"Can't open a renderer!\n");
    Finish();
    exit(EXIT_FAILURE);
  }


  myFont=TTF_OpenFont(FONT_NAME,FONT_SIZE);
  if(myFont==NULL)
  {
    fprintf(stderr,"Cannot load TTF font!: %s\n",FONT_NAME);
    Finish();
    exit(EXIT_FAILURE);
  }


  textColor.r=0x00;
  textColor.g=0xFF;
  textColor.b=0x00;
  textColor.a=0xFF;


  mySurf=IMG_Load(IMAGE_FILE);
  if(mySurf==NULL)
  {
    fprintf(stderr,"Can't open image file!\n");
    Finish();
    exit(EXIT_FAILURE);
  }


  iwidth=mySurf->w;
  iheight=mySurf->h;
  ghostTexture=SDL_CreateTextureFromSurface(myRenderer,mySurf);
  SDL_FreeSurface(mySurf);
}


void ProcessEvents(void)
{
  SDL_Event event;


  while(SDL_PollEvent(&event))
  {
    if(event.type==SDL_QUIT)
    {
      quit=1;
    }
  }
}


void KeyboardInput(void)
{
  const Uint8 *keys;
  int kcount;


  keys=SDL_GetKeyboardState(NULL);
  if(keys[SDL_SCANCODE_ESCAPE])
  {
    quit=1;
  }
  kcount=0;
  if(keys[SDL_SCANCODE_KP_PLUS])
  {
    if(!keyblock)
    {
      if((keys[SDL_SCANCODE_LSHIFT])||(keys[SDL_SCANCODE_RSHIFT]))
      {
        rfps=rfps+10;
      }
      else
      {
        rfps=rfps+1;
      }
      keyblock=1;
    }
  }
  else
  {
    kcount++;
  }
  if(keys[SDL_SCANCODE_KP_MINUS])
  {
    if(!keyblock)
    {
      if((keys[SDL_SCANCODE_LSHIFT])||(keys[SDL_SCANCODE_RSHIFT]))
      {
        if(rfps>10)
        {
          rfps=rfps-10;
        }
      }
      else
      {
        if(rfps>1)
        {
          rfps--;
        }
      }
      keyblock=1;
    }
  }
  else
  {
    kcount++;
  }
  if(kcount==2)
  {
    keyblock=0;
  }
}


void DisplayGhost(void)
{
  drect.x =  SCREEN_WIDTH/2 + 1.5f*RADIUS*cos(angle);
  drect.y = SCREEN_HEIGHT/2 +      RADIUS*sin(angle);
  drect.w = iwidth;
  drect.h = iheight;
  SDL_RenderCopy(myRenderer,ghostTexture,NULL,&drect);


  // TOHLE JE TA DŮLEŽITÁ CHVÍLE, KDY SE URČUJE VELIKOST POSUNU ANIMOVANÉHO OBJEKTU
  // VE VZTAHU K AKTUÁLNÍMU POČTU SNÍMKŮ ZA VTEŘINU
  speed_ratio=time_c/basic_frame;
  angle=angle+BASIC_STEP*speed_ratio;
  if(angle>(2*M_PI))
  {
    angle=angle-(2*M_PI);
  }
}


void SingleLine(int line)
{
  mySurf=TTF_RenderText_Solid(myFont,unistring,textColor);
  if(mySurf==NULL)
  {
    fprintf(stderr,"Cannot render text!\n");
    Finish();
    exit(EXIT_FAILURE);
  }
  myMessage=SDL_CreateTextureFromSurface(myRenderer,mySurf);
  drect.x=10;
  drect.y=10+line*((mySurf->h)+6);
  drect.w=mySurf->w;
  drect.h=mySurf->h;
  SDL_RenderCopy(myRenderer,myMessage,NULL,&drect);
  SDL_FreeSurface(mySurf);
  SDL_DestroyTexture(myMessage);
}


void TextInfo(void)
{
  sprintf(unistring,"Required FPS: %d",rfps);
  SingleLine(0);


  if(fps<0)
  {
    strcpy(unistring,"Achieved FPS: n/a");
  }
  else
  {
    sprintf(unistring,"Achieved FPS: %d",fps);
  }
  SingleLine(1);


  sprintf(unistring,"Overhead: %d ms",overhead);
  SingleLine(2);


  sprintf(unistring,"Basic frame time: %f ms",basic_frame);
  SingleLine(3);


  sprintf(unistring,"Last delay: %d ms",time_d);
  SingleLine(4);


  sprintf(unistring,"Last frame: %d ms",time_c);
  SingleLine(5);


  sprintf(unistring,"Speed ratio: %0.2f",speed_ratio);
  SingleLine(6);


  sprintf(unistring,"Angle: %f rad",angle);
  SingleLine(7);
}


void DetermineDelay(void)
{
  time_c=time_b;
  time_b=SDL_GetTicks();
  time_c=time_b-time_c;
  if(time_b-time_a+overhead<(1000/rfps))
  {
    time_d=(1000/rfps)-(time_b-time_a)-overhead;
    SDL_Delay(time_d);
  }
  else
  {
    time_d=0;
  }
  time_a=SDL_GetTicks();
}


void CountFPS(void)
{
  int newtime;


  framecount++;
  gettimeofday(&tv,NULL);
  newtime=tv.tv_usec;
  if(oldtime>newtime)
  {
    if(fps==-2)
    {
      fps=-1;
      framecount=0;
    }
    else
    {
      fps=framecount;
      framecount=0;
    }
  }
  oldtime=newtime;
}


int main( int argc, char* args[] )
{
  Initialize();


  rfps=BASIC_FPS;
  fps=-2;
  framecount=0;
  keyblock=0;
  angle=0.0f;
  quit=0;
  time_a=SDL_GetTicks();
  basic_frame=1000.0f/BASIC_FPS;
  time_c=basic_frame;
  time_d=0;
  gettimeofday(&tv,NULL);
  oldtime=tv.tv_usec;


  SDL_SetRenderDrawColor(myRenderer,0x00,0x00,0x00,SDL_ALPHA_OPAQUE);


  // HLAVNÍ SMYČKA
  do
  {
    SDL_RenderClear(myRenderer);
    DisplayGhost();
    TextInfo();
    SDL_RenderPresent(myRenderer);
    ProcessEvents();
    KeyboardInput();
    DetermineDelay();
    CountFPS();
  }
  while(!quit);


  Finish();
  exit(EXIT_SUCCESS);
}