apps/landing/static/js/main.js

let mouseOverEnabled = true;

function handleImageChange(imageURL, index, factTitle) {
    const factImage = document.getElementById("factImage");
    if (factImage.src.endsWith(imageURL)) {
        return;
    };
    highlightFact(index);
    factImage.classList.add("fade-out");
    setTimeout(() => {
        factImage.src = imageURL;
        factImage.alt = factTitle;
        factImage.classList.remove("fade-out");
    }, 300);
};

function highlightFact(index) {
    const facts = document.querySelectorAll(".facts");
    facts.forEach((fact, i) => {
        if (i === index) {
            fact.classList.add("active-fact");
        } else {
            fact.classList.remove("active-fact");
        };
    });
};

function handleMouseover(imageURL, index, factTitle) {
    if (!mouseOverEnabled) {
        return;
    };
    handleImageChange(imageURL, index, factTitle);
};

let scrollTimeout;
let mouseoverTimeout;

function delayScroll(func, delay) {
    return function (...args) {
        clearTimeout(scrollTimeout);
        scrollTimeout = setTimeout(() => {
            func.apply(this, args);
        }, delay);
    };
}

function delayMouseoverEnable(delay) {
    clearTimeout(mouseoverTimeout);
    mouseoverTimeout = setTimeout(() => {
        mouseOverEnabled = true;
    }, delay);
}

let lastScrollTop = 0;

function getFirstVisibleFact() {
    const facts = document.querySelectorAll(".facts");
    const factImage = document.getElementById("factImageBox");
    const imageBottom = factImage.getBoundingClientRect().bottom;

    const scrollTop = document.documentElement.scrollTop || document.body.scrollTop;
    const isScrollingDown = scrollTop > lastScrollTop;
    lastScrollTop = scrollTop;

    if (isScrollingDown) {
        for (let i = 0; i < facts.length; i++) {
            const rect = facts[i].getBoundingClientRect();
            if (rect.top < window.innerHeight && rect.top >= imageBottom) {
                return i;
            };
        };
        return 7;
    } else {
        for (let i = 0; i < facts.length; i++) {
            const rect = facts[i].getBoundingClientRect();
            if (rect.top >= 0 && rect.top >= imageBottom) {
                return i;
            };
        };
    };
    return 0;
};

document.addEventListener("DOMContentLoaded", function () {
    const gridContainer = document.querySelector(".grid-container");
    const facts = JSON.parse(gridContainer.dataset.facts);

    const handleScroll = () => {
        clearTimeout(scrollTimeout);
        mouseOverEnabled = false;
        scrollTimeout = setTimeout(() => {
            const currentSection = getFirstVisibleFact();
            handleImageChange(facts[currentSection].params.image, currentSection, facts[currentSection].params.title);
            delayMouseoverEnable(800);
        }, 300);
    };

    const checkAddRemoveScrollListener = () => {
        if (window.innerWidth <= 768) {
            window.addEventListener("scroll", handleScroll);
        } else {
            window.removeEventListener("scroll", handleScroll);
        }
    };

    checkAddRemoveScrollListener();

    window.addEventListener("resize", checkAddRemoveScrollListener);
});