/**
 * Table of Contents JavaScript
 *
 * Provides smooth scrolling and active link highlighting for the TOC.
 * Pure vanilla JavaScript - no jQuery dependency.
 *
 * @package Apus_Theme
 * @since 1.0.0
 */

(function() {
    'use strict';

    /**
     * Initialize TOC functionality when DOM is ready
     */
    function initTOC() {
        const toc = document.querySelector('.apus-toc');
        if (!toc) {
            return; // No TOC on this page
        }

        initToggleButton();
        initSmoothScroll();
        initActiveHighlight();
    }

    /**
     * Initialize toggle button functionality
     */
    function initToggleButton() {
        const toggleButton = document.querySelector('.apus-toc-toggle');
        const tocList = document.querySelector('.apus-toc-list');

        if (!toggleButton || !tocList) {
            return;
        }

        toggleButton.addEventListener('click', function() {
            const isExpanded = this.getAttribute('aria-expanded') === 'true';
            this.setAttribute('aria-expanded', !isExpanded);

            // Save state to localStorage
            try {
                localStorage.setItem('apus-toc-collapsed', isExpanded ? 'true' : 'false');
            } catch (e) {
                // localStorage might not be available
            }
        });

        // Restore saved state
        try {
            const isCollapsed = localStorage.getItem('apus-toc-collapsed') === 'true';
            if (isCollapsed) {
                toggleButton.setAttribute('aria-expanded', 'false');
            }
        } catch (e) {
            // localStorage might not be available
        }
    }

    /**
     * Initialize smooth scrolling for TOC links
     * Respeta preferencia de movimiento reducido
     */
    function initSmoothScroll() {
        // Verificar si el usuario prefiere movimiento reducido
        const prefersReducedMotion = window.matchMedia('(prefers-reduced-motion: reduce)').matches;

        const tocLinks = document.querySelectorAll('.apus-toc-link');

        tocLinks.forEach(function(link) {
            link.addEventListener('click', function(e) {
                e.preventDefault();

                const targetId = this.getAttribute('href').substring(1);
                const targetElement = document.getElementById(targetId);

                if (!targetElement) {
                    return;
                }

                // Smooth scroll to target (o auto si prefiere movimiento reducido)
                targetElement.scrollIntoView({
                    behavior: prefersReducedMotion ? 'auto' : 'smooth',
                    block: 'start'
                });

                // Update URL without jumping
                if (history.pushState) {
                    history.pushState(null, null, '#' + targetId);
                } else {
                    window.location.hash = targetId;
                }

                // Update active state
                updateActiveLinkOnClick(this);

                // Focus the target heading for accessibility
                targetElement.setAttribute('tabindex', '-1');
                targetElement.focus();
            });
        });
    }

    /**
     * Initialize active link highlighting with IntersectionObserver
     * Issue #55 - ScrollSpy implementation
     */
    function initActiveHighlight() {
        const tocLinks = document.querySelectorAll('.apus-toc-link');
        const headings = Array.from(document.querySelectorAll('h2[id], h3[id]'));

        if (headings.length === 0) {
            return;
        }

        // Keep track of which headings are currently visible
        const visibleHeadings = new Set();

        // IntersectionObserver configuration with custom rootMargin
        // -20% top, -35% bottom for optimal detection
        const observerOptions = {
            root: null, // viewport
            rootMargin: '-20% 0px -35% 0px',
            threshold: 0
        };

        // Callback when heading visibility changes
        const observerCallback = function(entries) {
            entries.forEach(function(entry) {
                const headingId = entry.target.id;

                if (entry.isIntersecting) {
                    visibleHeadings.add(headingId);
                } else {
                    visibleHeadings.delete(headingId);
                }
            });

            // Update active link based on visible headings
            updateActiveLink(visibleHeadings, tocLinks, headings);
        };

        // Create observer
        const observer = new IntersectionObserver(observerCallback, observerOptions);

        // Observe all headings
        headings.forEach(function(heading) {
            observer.observe(heading);
        });
    }

    /**
     * Update active link based on visible headings
     *
     * @param {Set} visibleHeadings Set of currently visible heading IDs
     * @param {NodeList} tocLinks TOC link elements
     * @param {Array} headings Array of all heading elements
     */
    function updateActiveLink(visibleHeadings, tocLinks, headings) {
        // If no headings are visible, don't change anything
        if (visibleHeadings.size === 0) {
            return;
        }

        // Find the first visible heading (topmost in document order)
        let activeHeading = null;
        for (let i = 0; i < headings.length; i++) {
            if (visibleHeadings.has(headings[i].id)) {
                activeHeading = headings[i];
                break;
            }
        }

        // Update active class on TOC links
        tocLinks.forEach(function(link) {
            if (activeHeading && link.getAttribute('href') === '#' + activeHeading.id) {
                link.classList.add('active');
            } else {
                link.classList.remove('active');
            }
        });
    }

    /**
     * Update active link when clicked
     *
     * @param {Element} clickedLink The clicked TOC link
     */
    function updateActiveLinkOnClick(clickedLink) {
        const tocLinks = document.querySelectorAll('.apus-toc-link');
        tocLinks.forEach(function(link) {
            link.classList.remove('active');
        });
        clickedLink.classList.add('active');
    }

    /**
     * Handle hash navigation on page load
     */
    function handleHashOnLoad() {
        if (!window.location.hash) {
            return;
        }

        const targetId = window.location.hash.substring(1);
        const targetElement = document.getElementById(targetId);
        const tocLink = document.querySelector('.apus-toc-link[href="#' + targetId + '"]');

        if (targetElement && tocLink) {
            // Small delay to ensure page is fully loaded
            setTimeout(function() {
                targetElement.scrollIntoView({
                    behavior: 'smooth',
                    block: 'start'
                });
                updateActiveLinkOnClick(tocLink);
            }, 100);
        }
    }

    /**
     * Initialize when DOM is ready
     */
    if (document.readyState === 'loading') {
        document.addEventListener('DOMContentLoaded', function() {
            initTOC();
            handleHashOnLoad();
        });
    } else {
        // DOM is already ready
        initTOC();
        handleHashOnLoad();
    }

})();