/**
 * Table of Contents Component
 * Tractatus Framework - Phase 3: Interactive Documentation
 *
 * Creates sticky TOC sidebar on desktop, collapsible on mobile
 * Highlights current section on scroll
 * Smooth scroll to sections
 */

class TableOfContents {
  constructor(options = {}) {
    this.contentSelector = options.contentSelector || '#document-viewer';
    this.tocSelector = options.tocSelector || '#table-of-contents';
    this.headingSelector = options.headingSelector || 'h1, h2, h3';
    this.activeClass = 'toc-active';
    this.collapsedClass = 'toc-collapsed';

    this.headings = [];
    this.tocLinks = [];
    this.currentActiveIndex = -1;

    this.init();
  }

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

    console.log('[TOC] Initialized');
  }

  build() {
    const tocContainer = document.querySelector(this.tocSelector);
    if (!tocContainer) {
      console.warn('[TOC] TOC container not found:', this.tocSelector);
      return;
    }

    const content = document.querySelector(this.contentSelector);
    if (!content) {
      console.warn('[TOC] Content container not found:', this.contentSelector);
      return;
    }

    // Find all headings in content
    this.headings = Array.from(content.querySelectorAll(this.headingSelector));

    if (this.headings.length === 0) {
      console.log('[TOC] No headings found, hiding TOC');
      tocContainer.style.display = 'none';
      return;
    }

    console.log(`[TOC] Found ${this.headings.length} headings`);

    // Generate IDs for headings if they don't have them
    this.headings.forEach((heading, index) => {
      if (!heading.id) {
        heading.id = `toc-heading-${index}`;
      }
    });

    // Build TOC HTML
    const tocHTML = this.buildTOCHTML();
    tocContainer.innerHTML = tocHTML;

    // Store TOC links
    this.tocLinks = Array.from(tocContainer.querySelectorAll('a'));

    // Add scroll spy
    this.initScrollSpy();

    // Add smooth scroll
    this.initSmoothScroll();

    // Add mobile toggle functionality
    this.initMobileToggle();
  }

  buildTOCHTML() {
    let html = '<nav class="toc-nav" aria-label="Table of Contents">';
    html += '<div class="toc-header flex items-center justify-between mb-4 md:mb-6">';
    html += '<h2 class="text-sm font-semibold text-gray-900 uppercase">On This Page</h2>';
    html += '<button id="toc-toggle" class="md:hidden p-2 text-gray-600 hover:text-gray-900" aria-label="Toggle table of contents">';
    html += '<svg class="w-5 h-5" fill="none" stroke="currentColor" viewBox="0 0 24 24">';
    html += '<path stroke-linecap="round" stroke-linejoin="round" stroke-width="2" d="M19 9l-7 7-7-7"/>';
    html += '</svg>';
    html += '</button>';
    html += '</div>';
    html += '<ul class="toc-list space-y-2" id="toc-list">';

    this.headings.forEach((heading) => {
      const level = parseInt(heading.tagName.substring(1)); // h1 -> 1, h2 -> 2, etc.
      const text = heading.textContent.trim();
      const id = heading.id;

      // Different indentation for different levels
      const indent = level === 1 ? '' : level === 2 ? 'ml-3' : 'ml-6';
      const fontSize = level === 1 ? 'text-sm' : level === 2 ? 'text-sm' : 'text-xs';
      const fontWeight = level === 1 ? 'font-semibold' : level === 2 ? 'font-medium' : 'font-normal';

      html += `<li class="${indent}">`;
      html += `<a href="#${id}" class="toc-link block py-1 ${fontSize} ${fontWeight} text-gray-700 hover:text-blue-600 transition-colors border-l-2 border-transparent hover:border-blue-600 pl-2" data-target="${id}">`;
      html += text;
      html += '</a>';
      html += '</li>';
    });

    html += '</ul>';
    html += '</nav>';

    return html;
  }

  initScrollSpy() {
    // Use Intersection Observer for better performance
    const observerOptions = {
      rootMargin: '-20% 0px -35% 0px',
      threshold: 0
    };

    const observer = new IntersectionObserver((entries) => {
      entries.forEach(entry => {
        if (entry.isIntersecting) {
          const id = entry.target.id;
          this.setActiveLink(id);
        }
      });
    }, observerOptions);

    // Observe all headings
    this.headings.forEach(heading => {
      observer.observe(heading);
    });

    console.log('[TOC] Scroll spy initialized');
  }

  setActiveLink(targetId) {
    // Remove active class from all links
    this.tocLinks.forEach(link => {
      link.classList.remove(this.activeClass);
      link.classList.remove('border-blue-600', 'text-blue-600', 'font-semibold');
      link.classList.add('border-transparent', 'text-gray-700');
    });

    // Add active class to current link
    const activeLink = this.tocLinks.find(link => link.dataset.target === targetId);
    if (activeLink) {
      activeLink.classList.add(this.activeClass);
      activeLink.classList.remove('border-transparent', 'text-gray-700');
      activeLink.classList.add('border-blue-600', 'text-blue-600', 'font-semibold');
    }
  }

  initSmoothScroll() {
    this.tocLinks.forEach(link => {
      link.addEventListener('click', (e) => {
        e.preventDefault();
        const targetId = link.dataset.target;
        const targetElement = document.getElementById(targetId);

        if (targetElement) {
          // Smooth scroll to target
          targetElement.scrollIntoView({
            behavior: 'smooth',
            block: 'start'
          });

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

          // On mobile, collapse TOC after clicking
          if (window.innerWidth < 768) {
            this.collapseTOC();
          }
        }
      });
    });

    console.log('[TOC] Smooth scroll initialized');
  }

  initMobileToggle() {
    const toggleButton = document.getElementById('toc-toggle');
    const tocList = document.getElementById('toc-list');

    if (!toggleButton || !tocList) return;

    toggleButton.addEventListener('click', () => {
      const isCollapsed = tocList.classList.contains('hidden');

      if (isCollapsed) {
        this.expandTOC();
      } else {
        this.collapseTOC();
      }
    });

    // Start collapsed on mobile
    if (window.innerWidth < 768) {
      this.collapseTOC();
    }

    console.log('[TOC] Mobile toggle initialized');
  }

  collapseTOC() {
    const tocList = document.getElementById('toc-list');
    const toggleButton = document.getElementById('toc-toggle');

    if (tocList) {
      tocList.classList.add('hidden');
    }

    if (toggleButton) {
      const svg = toggleButton.querySelector('svg');
      if (svg) {
        svg.style.transform = 'rotate(0deg)';
      }
    }
  }

  expandTOC() {
    const tocList = document.getElementById('toc-list');
    const toggleButton = document.getElementById('toc-toggle');

    if (tocList) {
      tocList.classList.remove('hidden');
    }

    if (toggleButton) {
      const svg = toggleButton.querySelector('svg');
      if (svg) {
        svg.style.transform = 'rotate(180deg)';
      }
    }
  }

  // Public method to rebuild TOC (useful for dynamically loaded content)
  rebuild() {
    this.build();
  }
}

// Auto-initialize when script loads (if TOC container exists)
if (typeof window !== 'undefined') {
  window.tocInstance = new TableOfContents();

  // Listen for custom event from document viewer for dynamic content
  document.addEventListener('documentLoaded', () => {
    console.log('[TOC] Document loaded, rebuilding TOC');
    window.tocInstance.rebuild();
  });
}

// Export for module usage
if (typeof module !== 'undefined' && module.exports) {
  module.exports = TableOfContents;
}