window.onload = function() {
  var gui = new dat.GUI({
    closed: false,
    remembered: {
      undefined: {
        "0": {},
      },
    },
    folders: {},
    load: JSON,
    width: 400,
    autoPlace: false,
  });

  gui.add(controls, "step_time", 200, 2000).name("step time (ms)").step(1);
  gui.add(controls, "fadeout", 0, 20).name("time to fade (0 to disable").step(1);
  gui.addColor(controls, "color").name("guy color");
  gui.add(controls, "restart_button").name("start again");

  var customContainer = document.getElementById("controls-container");
  customContainer.append(gui.domElement);
};

var controls = new(function() {
  this.step_time = 500;
  this.fadeout = 10;
  this.color = "#FFB000";

  this.restart_button = function() {
    ctx.clearRect(0, 0, canvas.width, canvas.height)
    init_walk();
  }
})()


// Define a new mod function that behaves different on negatives.
// now, (-1).mod(4) -> 3. not -1.
// taken from https://stackoverflow.com/a/4467559, which itself took from elsewhere
Number.prototype.mod = function (n) {
    "use strict";
    return ((this % n) + n) % n;
};

function init_walk() {
  // Create array of walkers with set parameters, start walkers in center of canvas
  walker_array = []
  for (var i = 0; i < 1; i++) {
    var walker = {
      x_position: canvas.width / 2,
      y_position: canvas.height / 2,
      line_width: 1,
      color: controls.color,
      speed: 5,
      angle: Math.random() * 360,
      halt: false,
    }
    walker.x_velocity = walker.speed * Math.cos(walker.angle)
    walker.y_velocity = walker.speed * Math.sin(walker.angle)
    walker_array.push(walker)
  }
  setInterval(paint_canvas, 20);
}



function degrees_to_radians(degrees) {
  var pi = Math.PI;
  return degrees * (pi / 180);
}

function radians_to_degrees(radians) {
  var pi = Math.PI;
  return radians * (180 / pi);
}


function gen_angle_list(number_of_groups) {
  /* Generate array of possible angles from limitation

     For example, if the limitation of angles is 4, then 360 / 4 = 90, and resulting array will be angle_list = [0,90,180,270,360]
     Including 0 & 360 is to give the walker equal chance to turn around and stay in the canvas
     */
  var angle_list = []

  var initial_angle = 360 / number_of_groups;

  for (var i = 0; i < number_of_groups + 1; i++) {
    angle_list.push(initial_angle * i);
  }
  return angle_list
}

function get_nearest_angle(goal, angle_list) {
  // Source: https://stackoverflow.com/questions/8584902/get-closest-number-out-of-array

  // Find nearest angle in possible direction array from new random angle

  var closest = angle_list.reduce(function(prev, curr) {
    return (Math.abs(curr - goal) < Math.abs(prev - goal) ? curr : prev);
  });
  return closest

}


var possible_directions = gen_angle_list(4);


function move_walker(walker, possible_directions) {
  // Update new random direction & update velocity of walker
  var new_angle = Math.random() * 360
  walker.x_position = (walker.x_position + walker.x_velocity).mod(canvas.width);
  walker.y_position = (walker.y_position + walker.y_velocity).mod(canvas.height);
  walker.angle = degrees_to_radians(get_nearest_angle(new_angle, possible_directions))
  walker.x_velocity = walker.speed * Math.cos(walker.angle)
  walker.y_velocity = walker.speed * Math.sin(walker.angle)
}

function paint_canvas() {
  // Regenerate possible angle list
  possible_directions = gen_angle_list(4)

  // Loop through all walkers, moving & painting accordingly
  for (var i = 0; i < walker_array.length; i++) {

    current_walker = walker_array[i];

    // If walker hasn't hit the walls yet
    if (!current_walker.halt) {
      var prev_x = current_walker.x_position
      var prev_y = current_walker.y_position
      ctx.beginPath()
      ctx.moveTo(prev_x, prev_y)
      move_walker(current_walker, possible_directions);
      ctx.strokeStyle = current_walker.color;
      ctx.lineWidth = current_walker.line_width;
      ctx.lineTo(current_walker.x_position, current_walker.y_position)
      ctx.stroke()

      ctx.closePath();
    }
  }
}


var canvas = document.getElementById("walker-canvas")
var ctx = canvas.getContext('2d')
ctx.canvas.width = document.getElementById("walker-canvas").clientWidth
ctx.canvas.height = document.getElementById("walker-canvas").clientHeight

var walker_array = []
init_walk();