/**
 * Scroll At-Bottom Handler
 * Adds 'at-bottom' class to buttons and footer when user scrolls to page bottom
 */

(function() {
    'use strict';

    // Wait for DOM to be ready
    if (document.readyState === 'loading') {
        document.addEventListener('DOMContentLoaded', init);
    } else {
        init();
    }

    function init() {
        const footer = document.querySelector('footer.no-print');
        if (!footer) return;

        // Get all fixed buttons that need 'at-bottom' state
        const buttons = document.querySelectorAll(
            '.download-btn, .print-friendly-btn, .shortcuts-btn, ' +
            '.info-button, .back-to-top, .color-theme-switcher'
        );

        if (buttons.length === 0) return;

        // Throttle scroll events for better performance
        let ticking = false;

        function checkIfAtBottom() {
            // Calculate if we're at the bottom of the page
            // Allow 50px tolerance for smoother experience
            const scrollPosition = window.pageYOffset || document.documentElement.scrollTop;
            const windowHeight = window.innerHeight;
            const documentHeight = document.documentElement.scrollHeight;
            const distanceFromBottom = documentHeight - (scrollPosition + windowHeight);

            const isAtBottom = distanceFromBottom <= 50;

            if (isAtBottom) {
                // Add 'at-bottom' class to all buttons and footer
                buttons.forEach(btn => btn.classList.add('at-bottom'));
                footer.classList.add('at-bottom');
            } else {
                // Remove 'at-bottom' class from all buttons and footer
                buttons.forEach(btn => btn.classList.remove('at-bottom'));
                footer.classList.remove('at-bottom');
            }
        }

        function onScroll() {
            if (!ticking) {
                window.requestAnimationFrame(() => {
                    checkIfAtBottom();
                    ticking = false;
                });
                ticking = true;
            }
        }

        // Check initial state
        checkIfAtBottom();

        // Listen to scroll events
        window.addEventListener('scroll', onScroll, { passive: true });

        // Also check on resize (mobile orientation changes, etc.)
        window.addEventListener('resize', () => {
            setTimeout(checkIfAtBottom, 100);
        });
    }
})();