/**
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* Glossary Navigation Active State Manager
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* Handles highlighting active terms as they scroll into view
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* and syncing navigation with scroll position
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*/
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class GlossaryNavigator {
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constructor(glossarySelector = 'dl.glossary', navSelector = 'nav.glossary-index') {
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this.glossary = document.querySelector(glossarySelector);
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this.nav = document.querySelector(navSelector);
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if (!this.glossary || !this.nav) return;
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this.terms = this.glossary.querySelectorAll('dt[id]');
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this.navList = this.nav.querySelector('ul');
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this.activeClass = 'active';
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this.currentActive = null;
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this.init();
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this.setupResizeHandler();
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}
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init() {
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// Set up Intersection Observer with screen-size appropriate margins
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const observerOptions = {
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root: null, // viewport
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rootMargin: this.getRootMargin(),
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threshold: 0
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};
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this.observer = new IntersectionObserver(
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(entries) => this.handleIntersection(entries),
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observerOptions
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);
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// Observe all terms
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this.terms.forEach(term => this.observer.observe(term));
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// Also handle manual scroll for edge cases
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this.handleScroll = this.debounce(() => this.checkActiveTerm(), 100);
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window.addEventListener('scroll', this.handleScroll, { passive: true });
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}
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getRootMargin() {
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// On larger screens: centered (50% from top and bottom)
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return '-50% 0px -50% 0px';
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}
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setupResizeHandler() {
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let resizeTimer;
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window.addEventListener('resize', () => {
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clearTimeout(resizeTimer);
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resizeTimer = setTimeout(() => {
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// Reinitialize observer with new margins on resize
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this.reinitialize();
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}, 250);
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});
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}
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reinitialize() {
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// Disconnect old observer
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if (this.observer) {
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this.observer.disconnect();
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}
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// Create new observer with updated margins
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this.init();
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}
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handleIntersection(entries) {
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// Find the entry that's intersecting
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const intersecting = entries.find(entry => entry.isIntersecting);
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if (intersecting) {
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this.setActive(intersecting.target);
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}
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}
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checkActiveTerm() {
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// Fallback method to find which term is in the trigger zone
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const remInPixels = parseFloat(getComputedStyle(document.documentElement).fontSize);
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const margin = remInPixels * 4;
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let closestTerm = null;
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let closestDistance = Infinity;
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this.terms.forEach(term => {
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const rect = term.getBoundingClientRect();
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const isInZone = rect.top + rect.height / 2 >= 0 && rect.top + rect.height / 2 <= window.innerHeight;
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if (isInZone) {
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// Find closest to the trigger point
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const triggerPoint = window.innerHeight / 2;
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const distance = Math.abs(rect.top - triggerPoint);
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if (distance < closestDistance) {
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closestDistance = distance;
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closestTerm = term;
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}
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}
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});
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if (closestTerm) {
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this.setActive(closestTerm);
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}
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}
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setActive(term) {
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if (this.currentActive === term) return;
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// Remove active class from previous term
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if (this.currentActive) {
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this.currentActive.classList.remove(this.activeClass);
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}
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// Add active class to current term
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term.classList.add(this.activeClass);
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this.currentActive = term;
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// Update navigation
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this.updateNavigation(term.id);
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}
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updateNavigation(termId) {
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// Remove active from all nav links
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const navLinks = this.nav.querySelectorAll('a');
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navLinks.forEach(link => link.classList.remove(this.activeClass));
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// Find and activate corresponding nav link
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const activeLink = this.nav.querySelector(`a[href="#${termId}"]`);
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if (activeLink) {
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activeLink.classList.add(this.activeClass);
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// Scroll the nav list to center the active link
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this.centerNavItem(activeLink);
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}
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}
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centerNavItem(link) {
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const listRect = this.navList.getBoundingClientRect();
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const linkRect = link.getBoundingClientRect();
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// Calculate position to center the link in the nav container
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const scrollTop = this.navList.scrollTop;
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const linkOffset = linkRect.top - listRect.top;
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const centerOffset = (listRect.height / 2) - (linkRect.height / 2);
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this.navList.scrollTo({
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top: scrollTop + linkOffset - centerOffset,
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behavior: 'smooth'
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});
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}
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debounce(func, wait) {
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let timeout;
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return function executedFunction(...args) {
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const later = () => {
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clearTimeout(timeout);
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func(...args);
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};
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clearTimeout(timeout);
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timeout = setTimeout(later, wait);
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};
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}
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destroy() {
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if (this.observer) {
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this.observer.disconnect();
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}
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window.removeEventListener('scroll', this.handleScroll);
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}
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}
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// Initialize when DOM is ready
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if (document.readyState === 'loading') {
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document.addEventListener('DOMContentLoaded', () => {
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new GlossaryNavigator();
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});
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} else {
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new GlossaryNavigator();
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}
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