#include <helianthus.h></helianthus.h>

#define COUNT     5

#define RADIUS    5

#define PRECISION 1e-5

double points[COUNT][2];

double *curPoint;

double curPointOffset[2];

double calcCurveValue(double *curve, int count, double x) {

  if (count <= 0) return 0;

  if (count == 1) return curve[1];

  if (x <= curve[0]) return curve[1];

  if (x >= curve[(count-1)*2]) return curve[(count-1)*2 + 1];

  int i = 0;

  while(i+1 < count && curve[(i+1)*2] < x)

    ++i;

  double *p1 = &curve[i*2];

  double *p0 = i   > 0     ? p1-2 : p1;

  double *p2 = i+1 < count ? p1+2 : p1;

  double *p3 = i+2 < count ? p2+2 : p2;

  double dx = p2[0] - p1[0];

  if (dx <= PRECISION) return p1[1];

  double a = p1[1];

  double b = p2[1];

  double ta = p2[0]-p0[0]; ta = ta > PRECISION ? (p2[1]-p0[1])/ta*dx : 0;

  double tb = p3[0]-p1[0]; tb = tb > PRECISION ? (p3[1]-p1[1])/tb*dx : 0;

  double l = (x - p1[0])/dx;

  return a + (ta + (3*(b-a)-ta-ta-tb + (2*(a-b)+ta+tb)*l)*l)*l;

}

void init() {

  for(int i = 0; i < COUNT; ++i)

    points[i][0] = points[i][1] = i/(COUNT - 1.0);

  calcCurveValue(points[0], COUNT, 0.3);

}

void draw() {

  double w = windowGetWidth();

  double h = windowGetHeight();

  saveState();

  translate(0, h);

  scale(1, -1);

  noFill();

  stroke(colorByRGBA(0.75, 0.75, 0.75, 1));

  strokeWidth(2);

  rect(0, 0, w, h);

  strokeWidth(2);

  line(0, 0, w, h);

  int m = mouseWentDown("left");

  double mx = mouseTransformedX();

  double my = mouseTransformedY();

  if (!mouseDown("left"))

    { m = FALSE; curPoint = 0; }

  if (curPoint) {

    curPoint[0] = (mx + curPointOffset[0])/w;

    curPoint[1] = (my + curPointOffset[1])/h;

  }

  stroke(COLOR_BLUE);

  fill(COLOR_WHITE);

  for(int i = 0; i < w+1; ++i)

    lineTo(i, calcCurveValue(points[0], COUNT, i/w)*h);

  strokePath();

  for(int i = 0; i < COUNT; ++i) {

    double x = points[i][0]*w, y = points[i][1]*h;

    circle(x, y, RADIUS);

    double dx = x-mx, dy = y-my;

    if (m && dx*dx + dy*dy <= RADIUS*RADIUS) {

      curPoint = points[i];

      curPointOffset[0] = dx;

      curPointOffset[1] = dy;

    }

  }

  restoreState();

}

int main() {

  windowSetVariableFrameRate();

  windowSetResizable(TRUE);

  windowSetInit(&init);

  windowSetDraw(&draw);

  windowRun();

  return 0;

}