function addLights(scene){
  scene.add(new THREE.AmbientLight(0x222222));

  const light1 = new THREE.PointLight(0xffffff, 1, 50);
  light1.position.set(15, 1, 40);
  scene.add(light1);

  const light2 = new THREE.PointLight(0xffffff, 1, 50);
  light2.position.set(-15, 0, 40);
  scene.add(light2);

  const light3 = new THREE.PointLight(0xffffff, 1, 50);
  light3.position.set(0, -1, 40);
  scene.add(light3);
}

/**
 * setup THREE JS Scene, Camera and Renderer
 */
function setup_scene(canvasSpace) {
  const scene = new THREE.Scene();
  const camera = new THREE.PerspectiveCamera(75, window.innerWidth / (window.innerHeight - canvasSpace), 0.1, 1000);
  const renderer = new THREE.WebGLRenderer();
  /** size canvas to leave some space for UI */
  renderer.setSize(window.innerWidth, window.innerHeight - canvasSpace);
  renderer.antialias = true;
  /** embed canvas in HTML */
  document.getElementById("threejscontainer").appendChild(renderer.domElement);

  /** add orbit controls */
  const controls = new THREE.OrbitControls(camera, renderer.domElement);
  controls.target.set(0, 0, 0);
  controls.update();

  /** add scene background */
  const loader = new THREE.TextureLoader();
  const texture = loader.load(
    'Textures/tears_of_steel_bridge_2k.jpg',
    () => {
      const rt = new THREE.WebGLCubeRenderTarget(texture.image.height);
      rt.fromEquirectangularTexture(renderer, texture);
      scene.background = rt;
    });

  /** add flag pole */
  const geometry = new THREE.CylinderGeometry(0.02, 0.02, 5, 32);
  const material = new THREE.MeshStandardMaterial({color: 0xffffff});
  const cylinder = new THREE.Mesh(geometry, material);
  cylinder.position.set(-0.5, -2.25, 0);
  scene.add(cylinder);

  /** add global light */
  const directionalLight = new THREE.DirectionalLight(0xffffff, 1);
  scene.add(directionalLight);

  /** position camera */
  camera.position.z = 2;
  addLights(scene);
  return [scene, camera, renderer];
}

/** call "init" when document is fully loaded */
document.body.onload = init;

function init() {
  let mousePos = new THREE.Vector2();
  
  /**
   * Space left empty under canvas
   * for UI elements
   */
  const canvasSpace = 200;

  /** Constant Frame Time */
  const frameTime = 1000.0 / 200.0;

  /** Setup scene */
  let [scene, camera, renderer] = setup_scene(canvasSpace);
  
  const loader = new THREE.TextureLoader();
  //Red color: 0xC70039

  const cloth = new Cloth(1, 0.5, 20, 20);
  const clothGeometry = cloth.generateGeometry();
  const clothMaterial = new THREE.MeshStandardMaterial({ map: loader.load('Textures/hsrm2.png'), color: {type: "c", value: new THREE.Color(0xffffff)}, side: THREE.DoubleSide, flatShading: false, transparent: true });
  //const clothMaterial = new THREE.MeshStandardMaterial({ color: 0xC70039, side: THREE.DoubleSide, flatShading: false });
  const clothMesh = new THREE.Mesh(clothGeometry, clothMaterial);
  scene.add(clothMesh);
  
  document.getElementById("windToggle").checked = options.wind;
  document.getElementById("windToggle").onchange = (e) => {
    options.wind = e.target.checked;
  };

  let raycaster = new THREE.Raycaster();
  let intersects;
  let windKeyDown = false;
  let dragKeyDown = false;
  let draggedIndex = -1;
  /**
   * function called every frame
   * @param {number} dt - time passed since last frame in ms
   */
  function animate(dt) {
    cloth.simulate(dt / 1000);

    cloth.updateGeometry(clothGeometry);
    
    raycaster.setFromCamera(new THREE.Vector2((mousePos.x / w) * 2 - 1, ((h - mousePos.y) / h) * 2 - 1), camera);

    intersects = raycaster.intersectObject(clothMesh);

    if (intersects.length > 0) {
      if (windKeyDown)
        cloth.blow(camera.position, intersects);
      if (dragKeyDown && draggedIndex == -1)
        draggedIndex = intersects[0].face.a;
    }
    if (dragKeyDown && draggedIndex != -1)
      cloth.drag(calculateMousePosToWorld(mousePos), draggedIndex);
    setTimeout(() => {
      animate(frameTime);
    }, frameTime);
    renderer.render(scene, camera);
  }


  /** add callback for window resize */
  let canvas = document.getElementsByTagName("canvas")[0];
  let w = window.innerWidth;
  let h = window.innerHeight - canvasSpace;
  let resize = function () {
    w = window.innerWidth;
    h = window.innerHeight - canvasSpace;
    canvas.width = w;
    canvas.height = h;
  }
  window.onresize = resize;
  resize();

  /**
   * if canvas has been successfully initialized
   * start rendering
   */
  if (canvas.getContext) {
    animate(frameTime);
  }

  

  /** add mouse move callback */
  canvas.onmousemove = (evt) => {
    mousePos.x = evt.clientX;
    mousePos.y = evt.clientY;
  };

  /**
   * Prevent context menu while blowing wind
   */
  canvas.addEventListener('contextmenu', function(evt) { 
    evt.preventDefault();
  }, false);

  document.onkeydown = (evt) => {
    if (evt.code === "KeyW")
      windKeyDown = true;
    if (evt.code === "KeyD")
      dragKeyDown = true;
  };

  document.onkeyup = (evt) => {
    if (evt.code === "KeyW")
      windKeyDown = false;
    if (evt.code === "KeyD") {
      dragKeyDown = false;
      draggedIndex = -1;
    }
  };

  function calculateMousePosToWorld(mousePos){
    var vec = new THREE.Vector3(); // create once and reuse
    var pos = new THREE.Vector3(); // create once and reuse

    vec.set(
      (mousePos.x / window.innerWidth) * 2 - 1,
    - (mousePos.y / window.innerHeight) * 2 + 1,
      0.5);

    vec.unproject(camera);

    vec.sub(camera.position).normalize();

    var distance = - camera.position.z / vec.z;

    pos.copy(camera.position).add(vec.multiplyScalar(distance));
    return pos;
  }
}