let charges = [];

let sphere_mode = 'circles';
let sphere_radius = 200;

let physics = false;

function preload() {
  earth = loadImage("atlas1.jpg");
}

function setup() {
  createCanvas(600, 600, WEBGL);
}

function draw() {
  orbitControl();
  background(50);

  make_lights();
  if (physics) {
    move_charges();
  }
  draw_charges(sphere_radius);
  draw_sphere(sphere_radius, 25);
}

function move_charges() {
  for (charge of charges) {
    charge.acceleration.setMag(0);
  }
  for (let i = 0; i < charges.length; i += 1) {
    for (let j = 0; j < i; j += 1) {
      const displacement = p5.Vector.sub(
        charges[i].position,
        charges[j].position,
      );
      const acceleration_mag = 1 / displacement.mag() * 0.001;
      let ai = displacement.copy().normalize().mult(acceleration_mag);
      let aj = p5.Vector.mult(ai, -1);
      project_onto_plane(ai, charges[i].position);
      project_onto_plane(aj, charges[j].position);
      charges[i].acceleration.add(ai);
      charges[j].acceleration.add(aj);
    }
  }
  for (let i = 0; i < charges.length; i += 1) {
    let charge = charges[i];
    charge.velocity = charge.velocity.add(charge.acceleration);
    //project_onto_plane(charge.velocity, charge.position);
    charge.position = charge.position.add(charge.velocity);
    charge.position.normalize();
  }
}

function project_onto_unit_vector(v, unit_vector) {
  let size = p5.Vector.dot(v, unit_vector);
  return p5.Vector.mult(unit_vector, size);
}

/// Project `v` onto the plane normal to `unit_vector`
/// Mutates `v`
function project_onto_plane(v, unit_vector) {
  let v_proj = project_onto_unit_vector(v, unit_vector);
  v.sub(v_proj)
}

function make_charges(n) {
  charges = [];
  for (let i = 0; i < n; i += 1) {
    let position;
    if (i === 0) {
      position = createVector(0, -1, 0);
    } else {
      const lat = random(-TAU / 4, TAU / 4);
      const lon = random(0, TAU);
      position = createVector(
        cos(lat) * cos(lon),
        sin(lat),
        cos(lat) * sin(lon),
      );
    }
    charges.push({
      position: position,
      velocity: createVector(),
      acceleration: createVector(),
    });
  }
}

function draw_charges(radius) {
  push();
  noStroke();
  ambientMaterial(0xbf, 0x00, 0x00);
  for (let charge of charges.values()) {
    let position = charge.position.copy();
    position.mult(radius);
    push();
    translate(position.x, position.y, position.z);
    sphere(15);
    pop();
  }
  pop();
}

function draw_sphere(radius, n_axis_circles) {
  stroke(0x3f);
  noFill();

  push();
  rotateX(TAU / 4);
  draw_circles(
    radius,
    sphere_mode === 'earth' ? 2 : n_axis_circles,
    color(0x00, 0x9f, 0xff),
    color(0xff, 0x9f, 0x00),
  );
  pop();
  push();
  rotateY(TAU / 4);
  draw_circles(
    radius,
    sphere_mode === 'earth' ? 2 : n_axis_circles,
    color(0xff, 0x00, 0xff),
    color(0x00, 0xff, 0x00),
  );
  pop();

  if (sphere_mode === 'earth') {
    noStroke();
    noFill();
    tint(0xff, 0x9f);
    texture(earth);
    push();
    rotateY(TAU / 4);
    sphere(radius);
    pop();
  }
}

function draw_circles(radius, n_circles, pole_1_color, pole_2_color) {
  push();
  stroke(pole_1_color);
  translate(0, 0, -radius);
  point(0, 0);
  pop();
  for (let i = 1; i < n_circles; i += 1) {
    const angle = map(i, 0, n_circles - 1, -TAU / 4, TAU / 4);
    const circle_radius = radius * cos(angle);
    push();
    translate(0, 0, radius * sin(angle));
    circle(0, 0, circle_radius * 2);
    pop();
  }
  push();
  stroke(pole_2_color);
  translate(0, 0, radius);
  point(0, 0);
  pop();
}

function make_lights() {
  let light = createVector(0, 1, -1);
  light.normalize();
  directionalLight(0x1f, 0x1f, 0x1f, light);
  ambientLight(0xbf);
}

function keyPressed() {
  if (key == 'd') {
    sphere_mode = sphere_mode === 'earth' ? 'circles' : 'earth';
  } else if (key == ' ') {
    physics = !physics;
  } else if (key >= '0' && key <= '9') {
    make_charges(int(key));
  }
}