// Turtletoy is a community for creative coding. We believe the joy 
// is in the craft. I love the joy :), but OGT AI helping ;)
// API Reference: https://turtletoy.net/syntax

// ToDo: Project on sphere and rotate

Canvas.setpenopacity(1);

const turtle = new Turtle();
turtle.penup();

const R = 100;        // min=50, max=100, step=1 // radius of the outer circle
const Ri = 1.5;       // min=-1, max=50, step=1 // radius of the inner circle
const waves = 12;     // number of sinus waves around
const amp = 10;       // wave amplitude
const steps = 720;    // smoothness
const rings = 12;     // min=3, max=20, step=1

// -------------------------
// mesh (latitude lines)
// -------------------------

/*for (let j = 1; j < rings; j++) {
  const rr = R * j / rings;
  const rr2 = R * (j + 1) / rings;
  turtle.goto(rr, 0);
  turtle.pendown();

  for (let i = 0; i <= steps; i++) {
    const a = i * 2 * Math.PI / steps;

    const r =
      rr +
      amp * Math.sin(waves * a) * (rr / R);

    const x = r * Math.cos(a);
    const y = r * Math.sin(a);

    turtle.goto(x, y);
  }
  
  for (let i = 0; i <= steps; i++) {
    const a = i * 2 * Math.PI / steps;

    const r =
      rr + amp * Math.cos(waves * a + Math.PI/2)
      * (rr / R)
      ;

    const x = r * Math.cos(a);
    const y = r * Math.sin(a);

    turtle.goto(x, y);
  }

  turtle.penup();
}*/


const dr = R / rings;

for (let j = 1; j < rings; j++) {

  const rr = dr * j + Ri;

  // half-distance rule
  const A_out = dr / 2;
  const A_in  = dr / 2;

  turtle.penup();
  turtle.goto(rr, 0);
  turtle.pendown();

  // primary wave
  for (let i = 0; i <= steps; i++) {
    const a = i * 2 * Math.PI / steps;
    const s = Math.sin(waves * a);

    const r =
      rr
      + A_out * Math.max(0,  s)
      - A_in  * Math.max(0, -s);

    turtle.goto(
      r * Math.cos(a),
      r * Math.sin(a)
    );
  }

  // phase-shifted wave (mesh)
  for (let i = 0; i <= steps; i++) {
    const a = i * 2 * Math.PI / steps;
    const s = Math.cos(waves * a + Math.PI/2);

    const r =
      rr
      + A_out * Math.max(0,  s)
      - A_in  * Math.max(0, -s);

    turtle.goto(
      r * Math.cos(a),
      r * Math.sin(a)
    );
  }

  turtle.penup();
}