const MOTION_QUERY = '(prefers-reduced-motion: reduce)';

function prefersReducedMotion() {
    return window.matchMedia(MOTION_QUERY).matches;
}

function enableEnhancement() {
    if (prefersReducedMotion() || typeof IntersectionObserver !== 'function') {
        document.documentElement.removeAttribute('data-motion');
        return false;
    }

    document.documentElement.dataset.motion = 'enhance';
    return true;
}

function activatePageOpen(enhance) {
    document.querySelectorAll('[data-motion="page-open"]').forEach((node) => {
        if (!enhance) {
            node.classList.add('is-active');
            return;
        }

        requestAnimationFrame(() => {
            requestAnimationFrame(() => node.classList.add('is-active'));
        });
    });
}

function initializeMotionDelays() {
    const beatOrder = new Map([
        ['seal', 0],
        ['heading', 0],
        ['title', 1],
        ['media', 2],
        ['cta', 3],
    ]);

    document.querySelectorAll('[data-motion="page-open"]').forEach((page) => {
        page.querySelectorAll('[data-motion-beat]').forEach((beat, index) => {
            const namedIndex = beatOrder.get(beat.dataset.motionBeat);
            beat.style.setProperty('--motion-index', String(Math.min(namedIndex ?? index, 3)));
        });
    });

    document.querySelectorAll('[data-reveal-group]').forEach((group) => {
        const nodes = Array.from(group.querySelectorAll('[data-reveal]'))
            .filter((node) => node.closest('[data-reveal-group]') === group);

        nodes.forEach((node, index) => {
            node.style.setProperty('--motion-index', String(Math.min(index, 3)));
        });
    });
}

function observeReveals(enhance) {
    const nodes = Array.from(document.querySelectorAll('[data-reveal]'));
    if (nodes.length === 0) {
        return;
    }

    if (!enhance || typeof IntersectionObserver !== 'function') {
        nodes.forEach((node) => node.classList.add('is-revealed'));
        return;
    }

    const observer = new IntersectionObserver(
        (entries) => {
            entries.forEach((entry) => {
                if (!entry.isIntersecting) {
                    return;
                }

                entry.target.classList.add('is-revealed');
                observer.unobserve(entry.target);
            });
        },
        {
            rootMargin: '0px 0px -12% 0px',
            threshold: 0.2,
        },
    );

    nodes.forEach((node) => observer.observe(node));
}

function setupChapterIndex() {
    const index = document.querySelector('[data-chapter-index]');
    const progress = document.querySelector('[data-chapter-progress] span');
    const chapters = Array.from(document.querySelectorAll('[data-chapter]'));

    if (!index || chapters.length === 0) {
        return;
    }

    const links = Array.from(index.querySelectorAll('a[href^="#"]'));
    let framePending = false;

    const setActive = (id) => {
        links.forEach((link) => {
            const isCurrent = link.getAttribute('href') === `#${id}`;
            if (isCurrent) {
                link.setAttribute('aria-current', 'true');
            } else {
                link.removeAttribute('aria-current');
            }
        });
    };

    const updateProgress = (ratio) => {
        if (!progress) {
            return;
        }

        const clamped = Math.min(1, Math.max(0, ratio));
        progress.style.setProperty('--chapter-progress', `${(clamped * 100).toFixed(2)}%`);
    };

    const sync = () => {
        const marker = window.scrollY + Math.min(window.innerHeight * 0.35, 280);
        let current = chapters[0];

        chapters.forEach((chapter) => {
            if (chapter.offsetTop <= marker) {
                current = chapter;
            }
        });

        const heading = current.querySelector('[id$="-heading"]') || document.getElementById(`${current.dataset.chapter}-heading`);
        const headingId = heading?.id
            || current.getAttribute('aria-labelledby')
            || `${current.dataset.chapter}-heading`;

        setActive(headingId);

        const doc = document.documentElement;
        const max = Math.max(1, doc.scrollHeight - window.innerHeight);
        updateProgress(window.scrollY / max);
    };

    const scheduleSync = () => {
        if (framePending) {
            return;
        }

        framePending = true;
        requestAnimationFrame(() => {
            framePending = false;
            sync();
        });
    };

    setActive(chapters[0].getAttribute('aria-labelledby') || 'hero-heading');
    sync();

    window.addEventListener('scroll', scheduleSync, { passive: true });
    window.addEventListener('resize', scheduleSync);
}

function bootMotion() {
    initializeMotionDelays();
    const enhance = enableEnhancement();
    activatePageOpen(enhance);
    observeReveals(enhance);
    setupChapterIndex();

    window.matchMedia(MOTION_QUERY).addEventListener('change', (event) => {
        if (event.matches) {
            document.documentElement.removeAttribute('data-motion');
            document.querySelectorAll('[data-motion="page-open"]').forEach((node) => {
                node.classList.add('is-active');
            });
            document.querySelectorAll('[data-reveal]').forEach((node) => {
                node.classList.add('is-revealed');
            });
            return;
        }

        document.documentElement.dataset.motion = 'enhance';
    });
}

if (document.readyState === 'loading') {
    document.addEventListener('DOMContentLoaded', bootMotion, { once: true });
} else {
    bootMotion();
}