#include "DisplaySDL.hpp"

#include <stdexcept>

DisplaySDL::DisplaySDL(int w, int h, uint32_t fgColor, uint32_t bgColor) {
  // Create SDL Window
  mpWindow = SDL_CreateWindow(
    "ChocoChip-8",
    SDL_WINDOWPOS_UNDEFINED, SDL_WINDOWPOS_UNDEFINED,
    w, h,
    0
  );
  if(mpWindow == NULL) {
    throw std::runtime_error(SDL_GetError());
  }

  // Convert our foreground/background colors to the format expected by SDL
  SDL_PixelFormat *fmt = SDL_AllocFormat(SDL_GetWindowPixelFormat(mpWindow));
  mFgColor = SDL_MapRGB(
      fmt,
      (fgColor & 0x00FF0000) >> 16,
      (fgColor & 0x0000FF00) >> 8,
      (fgColor & 0x000000FF)
  );
  mBgColor = SDL_MapRGB(
      fmt,
      (bgColor & 0x00FF0000) >> 16,
      (bgColor & 0x0000FF00) >> 8,
      (bgColor & 0x000000FF)
  );
  SDL_FreeFormat(fmt);
};

DisplaySDL::~DisplaySDL() {
  SDL_DestroyWindow(mpWindow);
}

void DisplaySDL::updateWindow() const {
  if(miTopDirtyScanline > miBottomDirtyScanline) {
    // No changes since the last update
    return;
  }

  SDL_Surface *pSurface = SDL_GetWindowSurface(mpWindow);
  SDL_LockSurface(pSurface);

  int fx, fy; // ChocoChip8 Framebuffer coordinates
  int sx, sy; // SDL Surface coordinates
  int lx, ly; // Last-used ChocoChip8 Framebuffer coordinates
  Uint32 lc;  // Last-used SDL color
  
  // Fill the entire SDL surface, one pixel at a time
  lx = -1;
  ly = -1;
  for(sy = 0; sy < pSurface->h; sy++) {
    // Map SDL surface coordinates to Chocochip8 Framebuffer coordinates
    fy = sy * (double(chocochip8::gcHeight) / pSurface->h);
    if(fy < miTopDirtyScanline || miBottomDirtyScanline < fy) {
      // Skip scanlines that haven't changed since the last update
      continue;
    }

    for(sx = 0; sx < pSurface->w; sx++) {
      fx = sx * (double(chocochip8::gcWidth) / pSurface->w);

      // Reuse color if this screen pixel maps to the same ChocoChip8 pixel as the last
      if(fx != lx || fy != ly) {
        lx = fx;
        ly = ly;
        // Read Chocochip8 Framebuffer and choose appropriate color,
        // note that the MSB of an scanline's bitset is the leftmost pixel.
        lc = (mpFramebuffer->at(fy)[(chocochip8::gcWidth - 1) - fx] ? mFgColor : mBgColor);
      }

      // Convert (x, y) indexes into SDL Surface pixel array index
      Uint32 *pPixel = static_cast<Uint32*>(static_cast<void*>(
          static_cast<char*>(pSurface->pixels)
          + sy * pSurface->pitch
          + sx * pSurface->format->BytesPerPixel
      ));
      *pPixel = lc;
    }
  }

  miTopDirtyScanline = chocochip8::gcHeight - 1;
  miBottomDirtyScanline = 0;
  SDL_UnlockSurface(pSurface);
  SDL_UpdateWindowSurface(mpWindow);
}