<div id="card-container">
</div>
<div id="loader">
  <div class="skeleton-card"></div>
  <div class="skeleton-card"></div>
  <div class="skeleton-card"></div>
</div>
<div class="card-actions">
  <span>Showing 
    <span id="card-count"></span> of 
    <span id="card-total"></span> cards      
  </span>
</div>

body {
  font-family: "Roboto", sans-serif;
}

#card-container {
  display: flex;
  flex-wrap: wrap;
}

.card {
  height: 55vh;
  width: calc((100% / 3) - 16px);
  margin: 8px;
  border-radius: 3px;
  transition: all 200ms ease-in-out;
  display: flex;
  align-items: center;
  justify-content: center;
}

.card:hover {
  box-shadow: 0 4px 10px rgba(0, 0, 0, 0.2);
}

.card-actions {
  margin: 8px;
  padding: 16px 0;
  display: flex;
  justify-content: space-between;
  align-items: center;
}

#loader {
  display: flex;
}

.skeleton-card {
  height: 55vh;
  width: calc((100% / 3) - 16px);
  margin: 8px;
  border-radius: 3px;
  transition: all 200ms ease-in-out;
  position: relative;
  background-color: #eaeaea;
}

.skeleton-card::after {
  content: "";
  position: absolute;
  top: 0;
  right: 0;
  bottom: 0;
  left: 0;
  transform: translateX(-100%);
  background-image: linear-gradient(90deg, rgba(255, 255, 255, 0) 0, rgba(255, 255, 255, 0.2) 20%, rgba(255, 255, 255, 0.5) 60%, rgba(255, 255, 255, 0));
  animation: load 1s infinite;
}

@keyframes load {
  100% {
    transform: translateX(100%);
  }
}

@media screen and (prefers-reduced-motion: reduce) {
  .skeleton-card::after {
    animation: none;
  }
}

const cardContainer = document.getElementById("card-container");
const cardCountElem = document.getElementById("card-count");
const cardTotalElem = document.getElementById("card-total");
const loader = document.getElementById("loader");

const cardLimit = 99;
const cardIncrease = 9;
const pageCount = Math.ceil(cardLimit / cardIncrease);
let currentPage = 1;

cardTotalElem.innerHTML = cardLimit;

var throttleTimer;
const throttle = (callback, time) => {
  if (throttleTimer) return;

  throttleTimer = true;

  setTimeout(() => {
    callback();
    throttleTimer = false;
  }, time);
};

const getRandomColor = () => {
  const h = Math.floor(Math.random() * 360);

  return `hsl(${h}deg, 90%, 85%)`;
};

const createCard = (index) => {
  const card = document.createElement("div");
  card.className = "card";
  card.innerHTML = index;
  card.style.backgroundColor = getRandomColor();
  cardContainer.appendChild(card);
};

const addCards = (pageIndex) => {
  currentPage = pageIndex;

  const startRange = (pageIndex - 1) * cardIncrease;
  const endRange =
    currentPage == pageCount ? cardLimit : pageIndex * cardIncrease;

  cardCountElem.innerHTML = endRange;

  for (let i = startRange + 1; i <= endRange; i++) {
    createCard(i);
  }
};

const handleInfiniteScroll = () => {
  throttle(() => {
    const endOfPage =
      window.innerHeight + window.pageYOffset >= document.body.offsetHeight;

    if (endOfPage) {
      addCards(currentPage + 1);
    }

    if (currentPage === pageCount) {
      removeInfiniteScroll();
    }
  }, 1000);
};

const removeInfiniteScroll = () => {
  loader.remove();
  window.removeEventListener("scroll", handleInfiniteScroll);
};

window.onload = function () {
  addCards(currentPage);
};

window.addEventListener("scroll", handleInfiniteScroll);