*, *::before, *::after {
  box-sizing: border-box;
}

body {
  font-family: system-ui, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
  margin: 0;
  background: #f8fafc;
  color: #0f172a;
  display: flex;
  justify-content: center;
  align-items: center;
  min-height: 100vh;
  padding: 20px;
}

.loader {
  position: fixed;
  top: 0;
  left: 0;
  right: 0;
  height: 3px;
  z-index: 100;
  opacity: 0;
  transition: opacity 0.4s ease;
  pointer-events: none;
}

.loader.active {
  opacity: 1;
}

.loader-bar {
  width: 0;
  height: 100%;
  background: #2563eb;
  box-shadow: 0 0 10px #3b82f6, 0 0 4px #3b82f6;
  transition: width 0.3s ease;
}

.demo {
  max-width: 440px;
  text-align: center;
}

.demo h1 {
  font-size: 1.5rem;
  margin: 0 0 10px;
}

.demo p {
  color: #475569;
  line-height: 1.6;
  margin: 0 0 24px;
}

.buttons {
  display: flex;
  justify-content: center;
  gap: 10px;
}

.buttons button {
  font: inherit;
  font-weight: 600;
  padding: 11px 20px;
  border: 0;
  border-radius: 10px;
  background: #0f172a;
  color: #ffffff;
  cursor: pointer;
  transition: background 0.15s ease;
}

.buttons button:hover {
  background: #1e293b;
}

.buttons button:disabled {
  opacity: 0.5;
  cursor: default;
}

.status {
  margin: 20px 0 0 !important;
  font-size: 0.875rem;
  font-weight: 500;
}

const loader = document.getElementById("loader");
const bar = document.getElementById("loader-bar");
const status = document.getElementById("status");
const buttons = document.querySelectorAll(".buttons button");

let progress = 0;
let trickle = null;
let fade = null;
let reset = null;

function set(value) {
  progress = Math.min(value, 99.4);
  bar.style.width = progress + "%";
}

function start() {
  clearInterval(trickle);
  clearTimeout(fade);
  clearTimeout(reset);
  bar.style.transition = "";
  loader.classList.add("active");
  loader.setAttribute("aria-hidden", "false");
  set(8);
  trickle = setInterval(function() {
    const step = (100 - progress) * 0.08 * Math.random();
    set(progress + step);
  }, 250);
}

function done() {
  clearInterval(trickle);
  bar.style.width = "100%";
  fade = setTimeout(function() {
    loader.classList.remove("active");
    loader.setAttribute("aria-hidden", "true");
    reset = setTimeout(function() {
      bar.style.transition = "none";
      bar.style.width = "0";
      bar.offsetWidth;
      bar.style.transition = "";
      progress = 0;
    }, 400);
  }, 300);
}

function simulate(duration, label) {
  buttons.forEach(function(b) { b.disabled = true; });
  status.textContent = "Loading " + label;
  start();
  setTimeout(function() {
    done();
    status.textContent = "Loaded in " + (duration / 1000).toFixed(1) + " seconds";
    buttons.forEach(function(b) { b.disabled = false; });
  }, duration);
}

document.getElementById("fast").addEventListener("click", function() {
  simulate(1200, "the dashboard");
});

document.getElementById("slow").addEventListener("click", function() {
  simulate(4500, "the full report");
});