#include <sprstk/sprstk.h>

#include <simplexnoise1234.h>

#include <cmath>

namespace
{

constexpr int SIZE = 512;

double octaves(SimplexNoise1234& simplex, double x, double y, int layers, double persistence, double frequency)
{
  double ampl = 1;
  double maxval = 0;
  double val = 0;

  for (int i = 0; i < layers; i++)
  {
    val += simplex.noise(x * frequency, y * frequency) * ampl;

    maxval += ampl;

    ampl *= persistence;
    frequency *= 2;
  }

  return val / maxval;
}

uint8_t data[SIZE * SIZE];

double split_point = 0.5;

double ease_f(double n)
{
  return pow(n, 0.7);
}

double ease_g(double n)
{
  return pow(n, 2);
}

double prime(double (*fn)(double), double n)
{
  constexpr double DELTA = 0.001;

  return (fn(n + DELTA) - fn(n)) / DELTA;
}

double ease(double n)
{
  const double fprime = prime(ease_f, n);
  const double gprime = prime(ease_g, n);

  const double scale = (fprime / gprime) * (ease_g(1) - ease_g(split_point)) + ease_f(split_point);

  if (n < split_point) { return ease_f(n) / scale; }
  return (fprime / gprime * (ease_g(n) - ease_g(split_point)) + ease_f(split_point)) / scale;
}

uint32_t color(uint8_t r, uint8_t g, uint8_t b, uint8_t a)
{
  return (r << 0) | (g << 8) | (b << 16) | (a << 24);
}

uint32_t color(double r, double g, double b, double a)
{
  if (r < 0) { r = 0; }
  if (r > 1) { r = 1; }
  if (g < 0) { g = 0; }
  if (g > 1) { g = 1; }
  if (b < 0) { b = 0; }
  if (b > 1) { b = 1; }
  if (a < 0) { a = 0; }
  if (a > 1) { a = 1; }

  uint8_t r8 = r * 255.0;
  uint8_t g8 = g * 255.0;
  uint8_t b8 = b * 255.0;
  uint8_t a8 = a * 255.0;

  return color(r8, g8, b8, a8);
}

constexpr double ALPHA = 0.7;

const sprstk_palette* water_palette()
{
  static sprstk_palette pal;

  for (int i = 0; i < 32; i++)
  {
    pal.colors[i] = color(i / 32.0, i / 16.0, i / 8.0, ALPHA);
  }

  return &pal;
}

const sprstk_palette* sand_palette()
{
  static sprstk_palette pal;

  for (int i = 0; i < 32; i++)
  {
    pal.colors[i] = color(i / 20.0 + 0.3, i / 20.0 + 0.2, i / 20.0 + 0.1, ALPHA);
  }

  return &pal;
}

const sprstk_palette* land_palette()
{
  static sprstk_palette pal;

  for (int i = 0; i < 32; i++)
  {
    if (i <= 19)
    {
      pal.colors[i] = color(i / 24.0 + 0.1, i / 36.0 + 0.05, i / 48.0, ALPHA);
    }
    else
    {
      pal.colors[i] = color(i / 40.0 - 0.1, i / 40.0 + 0.1, 0.1, ALPHA);
    }
  }

  return &pal;
}

const sprstk_palette* stone_palette()
{
  static sprstk_palette pal;

  for (int i = 0; i < 32; i++)
  {
    const double offset = (i < 28 ? -0.2 : 0.2);
    pal.colors[i] = color(i / 35.2 + offset, i / 32.0 + offset, i / 29.0 + offset, ALPHA);
  }

  return &pal;
}

const sprstk_palette* shadow_palette()
{
  static sprstk_palette pal;

  for (int i = 0; i < 32; i++)
  {
    pal.colors[i] = color(0, 0, 0, 0.3);
  }

  return &pal;
}

int pick_pal(uint8_t height)
{
  if (height < 8) { return 0; } // water
  if (height < 13) { return 1; } // sand
  if (height < 24) { return 2; } // land
  return 3;
}

void init(sprstk* instance, void* userdata)
{
  sprstk_set_palette(instance, 0, water_palette());
  sprstk_set_palette(instance, 1, sand_palette());
  sprstk_set_palette(instance, 2, land_palette());
  sprstk_set_palette(instance, 3, stone_palette());
  sprstk_set_palette(instance, 4, shadow_palette());

  sprstk_set_scale(instance, 0.5);

  SimplexNoise1234 simplex;
  for (int i = 0; i < SIZE; i++)
  {
    for (int j = 0; j < SIZE; j++)
    {
      double value = octaves(simplex, i, j, 6, 0.4, 1.0 / 128.0);
      data[i + j * SIZE] = 30 * ease((value + 1) / 2) + 1;
    }
  }

  sprstk_clear(instance);
  for (int i = 0; i < SIZE; i++)
  {
    for (int j = 0; j < SIZE; j++)
    {
      sprstk_tile_info info = {};
      info.position = { i - SIZE / 2, j - SIZE / 2 };
      info.layers = data[i + SIZE * j];
      info.layer_modifiers = { 0, 15 };
      info.palette_index = pick_pal(data[i + SIZE * j]);
      info.layer_order_offset = 1;
      sprstk_put(instance, info);

      info.palette_index = 4;
      info.layer_modifiers = { 0.5, 15.5 };
      info.layer_order_offset = 0;
      sprstk_put(instance, info);
    }
  }
}

void update(sprstk* instance, float dt, float* userdata)
{
  *userdata += dt / 2;
  sprstk_set_angle(instance, *userdata);
}

}

int main()
{
  float data = 0;
  sprstk* instance = sprstk_new({.init = init, .update = (sprstk_update_fn)update}, &data);

  sprstk_run(instance);

  sprstk_del(instance);

  return 0;
}