<canvas id="canvas"></canvas>
<textarea id="codeEditor" class="editor" spellcheck="false" autocorrect="off" autocapitalize="off" translate="no" oninput="render()"></textarea>
<pre id="error"></pre>
<div id="indicator"></div>
<div id="controls">
  <div class="controls">
    <input id="btnToggleView" class="icon" type="checkbox" name="toggleView" onclick="toggleView()">
    <input id="btnToggleResolution" class="icon" type="checkbox" name="toggleResolution" onchange="toggleResolution()">
    <input id="btnReset" class="icon" type="checkbox" name="reset" onclick="reset()">
  </div>
</div>
<script type="x-shader/x-fragment">#version 300 es
/*********
* made by Matthias Hurrle (@atzedent)
*/ 
precision highp float;
out vec4 O;
uniform float time;
uniform vec2 resolution;
uniform vec2 move;
#define FC gl_FragCoord.xy
#define R resolution
#define T (time+12.)
#define N normalize
#define S smoothstep
#define MN min(R.x,R.y)
#define rot(a) mat2(cos((a)-vec4(0,11,33,0)))
#define hue(a) (.25+.6*cos(6.3*(a)+vec3(0,83,21)))
#define lum(a) dot(vec3(.21,.71,.07),a)

float shape(vec3 p) {
	
	// See details at:
	// http://blog.hvidtfeldts.net/index.php/2011/08/distance-estimated-3d-fractals-iii-folding-space/
	
	float offset=1.2, n=5.;
	
	for (float i=.0; i++<n;) {
		if(p.x+p.y<.0) p.xy=-p.yx; // fold 1
		if(p.x+p.z<.0) p.xz=-p.zx; // fold 2
		if(p.y+p.z<.0) p.zy=-p.yz; // fold 3	
		p=2.*p-offset;
	}
	
	return length(p)*pow(2.,-n)-.052;
}

vec2 map(vec3 p) {
	vec3 q=p;
	//p.y+=.5;
	//p.yz*=rot(-.955);
	//p.xz*=rot(-.78);
	vec2
	a=vec2(shape(p),1),
	b=vec2(q.y+1.215,0);
	
	a=a.x<b.x?a:b;
	return a;
}

vec3 norm(vec3 p) {
	float h=1e-3; vec2 k=vec2(-1,1);
	return N(
		k.xyy*map(p+k.xyy*h).x+
		k.yxy*map(p+k.yxy*h).x+
		k.yyx*map(p+k.yyx*h).x+
		k.xxx*map(p+k.xxx*h).x
	);
}

float calcAO(vec3 p, vec3 n) {
	float o=.0, s=1.;
	for(float i=.0; i++<5.;) {
		float
		h=.01+.12*i/4.,
		d=map(p+h*n).x;
		o+=(h-d)*s;
		s*=.65;
		if(o>.5) break;
	}
	return clamp(1.-3.*o,.0,1.)*(.5+.5*n.y);
}

float shadow(vec3 p, vec3 lp) {
	float shd=1., maxd=length(lp-p);
	vec3 l=N(lp-p);
	for (float i=1e-3; i<maxd;) {
		float d=map(p+l*i).x;
		if (d<1e-3) {
			shd=.0;
			break;
		}
		shd=min(shd,48.*d/i);
		i+=d;
	}
	return shd;
}

void cam(inout vec3 p) {
	p.yz*=rot(-(sin(1.5707-move.y*6.3/MN)*.5-.5)+(cos(T*.1)*.5+.5));
	p.xz*=rot(-move.x*6.3/MN+(sin(T*.2)*.5));
}

float box(vec3 p) {
	p=abs(p);
	return max(max(p.x,p.y),p.z);
}

void main() {
	vec2 uv=(FC-.5*R)/MN;
	vec3 col=vec3(0),
	p=vec3(0,0,-10),
	rd=N(vec3(uv,3.-exp(-cos(T*.05)*.3)));
	cam(p); cam(rd);
	float dd=.0;
	for (float i=.0; i++<400.;) {
		vec2 d=map(p);
		if (abs(d.x)<1e-3) {
			vec3 n=norm(p), lp=vec3(-1,4,-5), l=N(lp-p);
			float
			shd=shadow(p+n*3e-3,lp),
			occ=calcAO(p+n*3e-3,n),
			diff=clamp(dot(l,n),.0,1.),
			ref=pow(dot(reflect(rd,n),l),64.);
			col+=.2+diff*shd*occ;
      // In the next line change box to either length or shape and see what happens
			col*=1.2*hue(box(p*(d.y>.0?.65:.1))+(d.y>.0?.6-T*.05:-T*.05));
			if (d.y>.0) col+=sqrt(max(.0,lum(col)));
			if (ref>.0 && d.y>.0) col+=ref;
			col/=1.+exp(-col);
			col=sqrt(col);
			break;
		}
		if (d.x>200.) break;
		p+=rd*d.x;
		dd+=d.x;
	}
	col=mix(vec3(0),col,exp(-125e-5*dd*dd));
  O=vec4(col,1);
}</script>

::-webkit-scrollbar {
  width: 0.625rem;
  height: 0.625rem;
}
::-webkit-scrollbar-thumb {
  background: #111;
  border-radius: 0.3125rem;
  box-shadow: inset 0.125rem 0.125rem 0.125rem rgba(255, 255, 255, 0.25),
    inset -0.125rem -0.125rem 0.125rem rgba(0, 0, 0, 0.25);
  cursor: default;
}
::-webkit-scrollbar-track {
  background: #333;
}
::selection {
  background: #fff;
  color: #333;
}
html,
body {
  height: 100vh;
  height: 100dvh;
  margin: 0;
  overflow: hidden;
}
body {
  display: grid;
  grid-template-rows: calc(100dvh - 4rem) 4rem;
  font-family: system-ui, sans-serif;
}
canvas,
.editor,
#controls {
  grid-row: 1;
  grid-column: 1;
}
canvas {
  width: 100%;
  height: auto;
  object-fit: contain;
  background: black;
  touch-action: none;
}
.editor,
.overlay,
#error {
  background: repeating-linear-gradient(0deg, #000a, #1119, #000a .25rem);
  padding: 1em;
}
.editor {
  color: #fefefe;
  tab-size: 2;
  border: none;
  resize: none;
}
.editor:focus {
  outline: none;
}
#error {
  grid-row: 2;
  grid-column: 1;
  margin: 0;
  padding-block: 0;
  padding-top: .5em;
  color: firebrick;
  overflow: auto;
  text-wrap: pretty;
}
#indicator {
  visibility: hidden;
  position: absolute;
  top: calc(var(--top, 0px) - var(--scroll-top, 0px));
  width: 0;
  height: 0;
  border-top: 10px solid transparent;
  border-bottom: 10px solid transparent;
  border-left: 10px solid firebrick;
  transform: translateY(-25%);
}
.overlay {
  position: absolute;
  top: 0;
  left: 0;
  right: 0;
  margin: 0;
}
.editor,
.overlay {
  font-size: 1rem;
  line-height: 1.2;
  white-space: pre;
}
#controls {
  position: fixed;
  top: 1em;
  right: 2em;
}
.controls {
  position: relative;
  display: flex;
  gap: 1.5em;
  padding: .5em 1.25em;
  background: #1111;
  border-radius: 4px;
}
.controls::before,
.controls::after {
  content: '';
  position: absolute;
  z-index: -1;
  inset: 0;
  transform: scale(.95);
  border-radius: inherit;
  opacity: 0;
}
.controls::before {
  background: #aef;
  animation: pulse 2s infinite;
}
.controls::after {
  background: #fefefe66;
  transition: transform 200ms ease-in-out;
}
.controls:hover::before,
.controls:hover::after {
  opacity: 1;
}
.controls:hover::before {
  transform: scale(.98);
  filter: blur(2px);
}
.controls:hover::after {
  transform: scale(1.025, 1.1);
}
.controls:hover {
  background: #111f;
}
@keyframes pulse {
  0% {
    transform: scale(1);
  }
  50% {
    transform: scale(1.0125);
  }
  100% {
    transform: scale(1);
  }
}
.hidden {
  display: none !important;
}
.opaque {
  opacity: 1 !important;
  background: #111 !important;
}
input {
  all: unset;
  opacity: .2;
  filter: saturate(0) invert(1);
  cursor: pointer;
  transition: opacity 200ms ease-in-out;
  padding: .25em .5em;
}
input:hover {
  opacity: 1;
}
.icon {
  text-align: center;
  line-height: 1;
}
#btnToggleView {
  width: 1.25em;
}
#btnToggleView::after {
  content: '👁';
}
#btnToggleView:checked::after {
  content: '✏️';
}
#btnToggleResolution::after {
  content: '1️⃣';
}
#btnToggleResolution:checked::after {
  content: '2️⃣';
}
#btnReset::after {
  content: '⏮️';
}

/*********
 * made by Matthias Hurrle (@atzedent)
 */
let editMode = false // set to false to hide the code editor on load
let resolution = .5 // set 1 for full resolution or to .5 to start with half resolution on load
let renderDelay = 1000 // delay in ms before rendering the shader after a change
let dpr = Math.max(1, resolution * window.devicePixelRatio)
let frm, source, editor, store, renderer, pointers
const shaderId = 'It Is All Just a Reflection'
window.onload = init

function resize() {
  const { innerWidth: width, innerHeight: height } = window

  canvas.width = width * dpr
  canvas.height = height * dpr

  if (renderer) {
    renderer.updateScale(dpr)
  }
}
function toggleView() {
  editor.hidden = btnToggleView.checked
}
function reset() {
  let shader = source
  editor.text = shader ? shader.textContent : renderer.defaultSource
  store.putShaderSource(shaderId, editor.text)
  renderThis()
}
function toggleResolution() {
  resolution = btnToggleResolution.checked ? .5 : 1
  dpr = Math.max(1, resolution * window.devicePixelRatio)
  pointers.updateScale(dpr)
  resize()
}
function loop(now) {
  renderer.updateMouse(pointers.first)
  renderer.updatePointerCount(pointers.count)
  renderer.updatePointerCoords(pointers.coords)
  renderer.updateMove(pointers.move)
  renderer.render(now)
  frm = requestAnimationFrame(loop)
}
function renderThis() {
  editor.clearError()
  store.putShaderSource(shaderId, editor.text)

  const result = renderer.test(editor.text)

  if (result) {
    editor.setError(result)
  } else {
    renderer.updateShader(editor.text)
  }
  cancelAnimationFrame(frm) // Always cancel the previous frame!
  loop(0)
}
const debounce = (fn, delay) => {
  let timerId
  return (...args) => {
    clearTimeout(timerId)
    timerId = setTimeout(() => fn.apply(this, args), delay)
  }
}
const render = debounce(renderThis, renderDelay)
function init() {
  source = document.querySelector("script[type='x-shader/x-fragment']")

  document.title = "🎢"

  renderer = new Renderer(canvas, dpr)
  pointers = new PointerHandler(canvas, dpr)
  store    = new Store(window.location)
  editor   = new Editor(codeEditor, error, indicator)
  editor.text = source.textContent
  renderer.setup()
  renderer.init()

  if (!editMode) {
    btnToggleView.checked = true
    toggleView()
  }
  if (resolution === .5) {
    btnToggleResolution.checked = true
    toggleResolution()
  }
  canvas.addEventListener('shader-error', e => editor.setError(e.detail))

  resize()

  if (renderer.test(source.textContent) === null) {
    renderer.updateShader(source.textContent)
  }
  loop(0)
  window.onresize = resize
  window.addEventListener("keydown", e => {
    if (e.key === "L" && e.ctrlKey) {
      e.preventDefault()
      btnToggleView.checked = !btnToggleView.checked
      toggleView()
    }
  })
}
class Renderer {
  #vertexSrc = "#version 300 es\nprecision highp float;\nin vec4 position;\nvoid main(){gl_Position=position;}"
  #fragmtSrc = "#version 300 es\nprecision highp float;\nout vec4 O;\nuniform float time;\nuniform vec2 resolution;\nvoid main() {\n\tvec2 uv=gl_FragCoord.xy/resolution;\n\tO=vec4(uv,sin(time)*.5+.5,1);\n}"
  #vertices = [-1, 1, -1, -1, 1, 1, 1, -1]
  constructor(canvas, scale) {
    this.canvas = canvas
    this.scale = scale
    this.gl = canvas.getContext("webgl2")
    this.gl.viewport(0, 0, canvas.width * scale, canvas.height * scale)
    this.shaderSource = this.#fragmtSrc
    this.mouseMove = [0, 0]
    this.mouseCoords = [0, 0]
    this.pointerCoords = [0, 0]
    this.nbrOfPointers = 0
  }
  get defaultSource() { return this.#fragmtSrc }
  updateShader(source) {
    this.reset()
    this.shaderSource = source
    this.setup()
    this.init()
  }
  updateMove(deltas) {
    this.mouseMove = deltas
  }
  updateMouse(coords) {
    this.mouseCoords = coords
  }
  updatePointerCoords(coords) {
    this.pointerCoords = coords
  }
  updatePointerCount(nbr) {
    this.nbrOfPointers = nbr
  }
  updateScale(scale) {
    this.scale = scale
    this.gl.viewport(0, 0, this.canvas.width * scale, this.canvas.height * scale)
  }
  compile(shader, source) {
    const gl = this.gl
    gl.shaderSource(shader, source)
    gl.compileShader(shader)

    if (!gl.getShaderParameter(shader, gl.COMPILE_STATUS)) {
      console.error(gl.getShaderInfoLog(shader))
      this.canvas.dispatchEvent(new CustomEvent('shader-error', { detail: gl.getShaderInfoLog(shader) }))
    }
  }
  test(source) {
    let result = null
    const gl = this.gl
    const shader = gl.createShader(gl.FRAGMENT_SHADER)
    gl.shaderSource(shader, source)
    gl.compileShader(shader)

    if (!gl.getShaderParameter(shader, gl.COMPILE_STATUS)) {
      result = gl.getShaderInfoLog(shader)
    }
    if (gl.getShaderParameter(shader, gl.DELETE_STATUS)) {
      gl.deleteShader(shader)
    }
    return result
  }
  reset() {
    const { gl, program, vs, fs } = this
    if (!program || gl.getProgramParameter(program, gl.DELETE_STATUS)) return
    if (gl.getShaderParameter(vs, gl.DELETE_STATUS)) {
      gl.detachShader(program, vs)
      gl.deleteShader(vs)
    }
    if (gl.getShaderParameter(fs, gl.DELETE_STATUS)) {
      gl.detachShader(program, fs)
      gl.deleteShader(fs)
    }
    gl.deleteProgram(program)
  }
  setup() {
    const gl = this.gl
    this.vs = gl.createShader(gl.VERTEX_SHADER)
    this.fs = gl.createShader(gl.FRAGMENT_SHADER)
    this.compile(this.vs, this.#vertexSrc)
    this.compile(this.fs, this.shaderSource)
    this.program = gl.createProgram()
    gl.attachShader(this.program, this.vs)
    gl.attachShader(this.program, this.fs)
    gl.linkProgram(this.program)

    if (!gl.getProgramParameter(this.program, gl.LINK_STATUS)) {
      console.error(gl.getProgramInfoLog(this.program))
    }
  }
  init() {
    const { gl, program } = this
    this.buffer = gl.createBuffer()
    gl.bindBuffer(gl.ARRAY_BUFFER, this.buffer)
    gl.bufferData(gl.ARRAY_BUFFER, new Float32Array(this.#vertices), gl.STATIC_DRAW)

    const position = gl.getAttribLocation(program, "position")

    gl.enableVertexAttribArray(position)
    gl.vertexAttribPointer(position, 2, gl.FLOAT, false, 0, 0)

    program.resolution = gl.getUniformLocation(program, "resolution")
    program.time = gl.getUniformLocation(program, "time")
    program.move = gl.getUniformLocation(program, "move")
    program.touch = gl.getUniformLocation(program, "touch")
    program.pointerCount = gl.getUniformLocation(program, "pointerCount")
    program.pointers = gl.getUniformLocation(program, "pointers")
  }
  render(now = 0) {
    const { gl, program, buffer, canvas, mouseMove, mouseCoords, pointerCoords, nbrOfPointers } = this
    
    if (!program || gl.getProgramParameter(program, gl.DELETE_STATUS)) return

    gl.clearColor(0, 0, 0, 1)
    gl.clear(gl.COLOR_BUFFER_BIT)
    gl.useProgram(program)
    gl.bindBuffer(gl.ARRAY_BUFFER, buffer)
    gl.uniform2f(program.resolution, canvas.width, canvas.height)
    gl.uniform1f(program.time, now * 1e-3)
    gl.uniform2f(program.move, ...mouseMove)
    gl.uniform2f(program.touch, ...mouseCoords)
    gl.uniform1i(program.pointerCount, nbrOfPointers)
    gl.uniform2fv(program.pointers, pointerCoords)
    gl.drawArrays(gl.TRIANGLE_STRIP, 0, 4)
  }
}
class Store {
  constructor(key) {
    this.key = key
    this.store = window.localStorage
  }
  #ownShadersKey = 'ownShaders'
  #StorageType = Object.freeze({
    shader: 'fragmentSource',
    config: 'config'
  })
  #getKeyPrefix(type) {
    return `${type}${btoa(this.key)}`
  }
  #getKey(type, name) {
    return `${this.#getKeyPrefix(type)}${btoa(name)}`
  }
  putShaderSource(name, source) {
    const storageType = this.#StorageType.shader
    this.store.setItem(this.#getKey(storageType, name), source)
  }
  getShaderSource(name) {
    const storageType = this.#StorageType.shader
    return this.store.getItem(this.#getKey(storageType, name))
  }
  deleteShaderSource(name) {
    const storageType = this.#StorageType.shader
    this.store.removeItem(this.#getKey(storageType, name))
  }
  /** @returns {{title:string, uuid:string}[]} */
  getOwnShaders() {
    const storageType = this.#StorageType.config
    const result = this.store.getItem(this.#getKey(storageType, this.#ownShadersKey))
    
    return result ? JSON.parse(result) : []
  }
  /** @param {{title:string, uuid:string}[]} shader */
  putOwnShader(shader) {
    const ownShaders = this.getOwnShaders()
    const storageType = this.#StorageType.config
    const index = ownShaders.findIndex((s) => s.uuid === shader.uuid)
    if (index === -1) {
      ownShaders.push(shader)
    } else {
      ownShaders[index] = shader
    }
    this.store.setItem(this.#getKey(storageType, this.#ownShadersKey), JSON.stringify(ownShaders))
  }
  deleteOwnShader(uuid) {
    const ownShaders = this.getOwnShaders()
    const storageType = this.#StorageType.config
    this.store.setItem(this.#getKey(storageType, this.#ownShadersKey), JSON.stringify(ownShaders.filter((s) => s.uuid !== uuid) ))
    this.deleteShaderSource(uuid)
  }
  /** @param {string[]} keep The names of the shaders to keep*/
  cleanup(keep=[]) {
    const storageType = this.#StorageType.shader
    const ownShaders = this.getOwnShaders().map((s) => this.#getKey(storageType, s.uuid))
    const premadeShaders = keep.map((name) => this.#getKey(storageType, name))
    const keysToKeep = [...ownShaders, ...premadeShaders]
    const result = []

    for (let i = 0; i < this.store.length; i++) {
      const key = this.store.key(i)

      if (key.startsWith(this.#getKeyPrefix(this.#StorageType.shader)) && !keysToKeep.includes(key)) {
        result.push(key)
      }
    }

    result.forEach((key) => this.store.removeItem(key))
  }
}
class PointerHandler {
  constructor(element, scale) {
    this.scale = scale
    this.active = false
    this.pointers = new Map()
    this.lastCoords = [0,0]
    this.moves = [0,0]
    const map = (element, scale, x, y) => [x * scale, element.height - y * scale]
    element.addEventListener("pointerdown", (e) => {
      this.active = true
      this.pointers.set(e.pointerId, map(element, this.getScale(), e.clientX, e.clientY))
    })
    element.addEventListener("pointerup", (e) => {
      if (this.count === 1) {
        this.lastCoords = this.first
      }
      this.pointers.delete(e.pointerId)
      this.active = this.pointers.size > 0
    })
    element.addEventListener("pointerleave", (e) => {
      if (this.count === 1) {
        this.lastCoords = this.first
      }
      this.pointers.delete(e.pointerId)
      this.active = this.pointers.size > 0
    })
    element.addEventListener("pointermove", (e) => {
      if (!this.active) return
      this.lastCoords = [e.clientX, e.clientY]
      this.pointers.set(e.pointerId, map(element, this.getScale(), e.clientX, e.clientY))
      this.moves = [this.moves[0]+e.movementX, this.moves[1]+e.movementY]
    })
  }
  getScale() {
    return this.scale
  }
  updateScale(scale) { this.scale = scale }
  reset() {
    this.pointers.clear()
    this.active = false
    this.moves = [0,0]
  }
  get count() {
    return this.pointers.size
  }
  get move() {
    return this.moves
  }
  get coords() {
    return this.pointers.size > 0 ? Array.from(this.pointers.values()).map((p) => [...p]).flat() : [0, 0]
  }
  get first() {
    return this.pointers.values().next().value || this.lastCoords
  }
}
class Editor {
  constructor(textarea, errorfield, errorindicator) {
    this.textarea = textarea
    this.errorfield = errorfield
    this.errorindicator = errorindicator
    textarea.addEventListener('keydown', this.handleKeydown.bind(this))
    textarea.addEventListener('scroll', this.handleScroll.bind(this))
  }
  get hidden() { return this.textarea.classList.contains('hidden') }
  set hidden(value) { value ? this.#hide() : this.#show() }
  get text() { return this.textarea.value }
  set text(value) { this.textarea.value = value }
  get scrollTop() { return this.textarea.scrollTop }
  set scrollTop(value) { this.textarea.scrollTop = value }
  setError(message) {
    this.errorfield.innerHTML = message
    this.errorfield.classList.add('opaque')
    const match = message.match(/ERROR: \d+:(\d+):/)
    const lineNumber = match ? parseInt(match[1]) : 0
    const overlay = document.createElement('pre')

    overlay.classList.add('overlay')
    overlay.textContent = '\n'.repeat(lineNumber)

    document.body.appendChild(overlay)

    const offsetTop = parseInt(getComputedStyle(overlay).height)

    this.errorindicator.style.setProperty('--top', offsetTop + 'px')
    this.errorindicator.style.visibility = 'visible'

    document.body.removeChild(overlay)
  }
  clearError() {
    this.errorfield.textContent = ''
    this.errorfield.classList.remove('opaque')
    this.errorfield.blur()
    this.errorindicator.style.visibility = 'hidden'
  }
  focus() {
    this.textarea.focus()
  }
  #hide() {
    for (const el of [this.errorindicator, this.errorfield, this.textarea]) {
      el.classList.add('hidden')
    }
  }
  #show() {
    for (const el of [this.errorindicator, this.errorfield, this.textarea]) {
      el.classList.remove('hidden')
    }
    this.focus()
  }
  handleScroll() {
    this.errorindicator.style.setProperty('--scroll-top', `${this.textarea.scrollTop}px`)
  }
  handleKeydown(event) {
    if (event.key === "Tab") {
      event.preventDefault()
      this.handleTabKey(event.shiftKey)
    } else if (event.key === "Enter") {
      event.preventDefault()
      this.handleEnterKey()
    }
  }
  handleTabKey(shiftPressed) {
    if (this.#getSelectedText() !== "") {
      if (shiftPressed) {
        this.#unindentSelectedText()
        return
      }
      this.#indentSelectedText()
    } else {
      this.#indentAtCursor()
    }
  }
  #getSelectedText() {
    const editor = this.textarea
    const start = editor.selectionStart
    const end = editor.selectionEnd
    return editor.value.substring(start, end)
  }
  #indentAtCursor() {
    const editor = this.textarea
    const cursorPos = editor.selectionStart

    document.execCommand('insertText', false, '\t')
    editor.selectionStart = editor.selectionEnd = cursorPos + 1
  }
  #indentSelectedText() {
    const editor = this.textarea
    const cursorPos = editor.selectionStart
    const selectedText = this.#getSelectedText()
    const lines = selectedText.split('\n')
    const indentedText = lines.map(line => '\t' + line).join('\n')

    document.execCommand('insertText', false, indentedText)
    editor.selectionStart = cursorPos
  }
  #unindentSelectedText() {
    const editor = this.textarea
    const cursorPos = editor.selectionStart
    const selectedText = this.#getSelectedText()
    const lines = selectedText.split('\n')
    const indentedText = lines.map(line => line.replace(/^\t/, '').replace(/^ /, '')).join('\n')

    document.execCommand('insertText', false, indentedText)
    editor.selectionStart = cursorPos
  }
  handleEnterKey() {
    const editor = this.textarea
    const visibleTop = editor.scrollTop
    const cursorPosition = editor.selectionStart

    let start = cursorPosition - 1
    while (start >= 0 && editor.value[start] !== '\n') {
      start--
    }

    let newLine = ''
    while (start < cursorPosition - 1 && (editor.value[start + 1] === ' ' || editor.value[start + 1] === '\t')) {
      newLine += editor.value[start + 1]
      start++
    }

    document.execCommand('insertText', false, '\n' + newLine)
    editor.selectionStart = editor.selectionEnd = cursorPosition + 1 + newLine.length
    editor.scrollTop = visibleTop // Prevent the editor from scrolling
    const lineHeight = editor.scrollHeight / editor.value.split('\n').length
    const line = editor.value.substring(0, cursorPosition).split('\n').length

    // Do the actual layout calculation in order to get the correct scroll position
    const visibleBottom = editor.scrollTop + editor.clientHeight
    const lineTop = lineHeight * (line - 1)
    const lineBottom = lineHeight * (line + 2)

    // If the cursor is outside the visible range, scroll the editor
    if (lineTop < visibleTop) editor.scrollTop = lineTop
    if (lineBottom > visibleBottom) editor.scrollTop = lineBottom - editor.clientHeight
  }
}