import React, { useState, useEffect, useRef, useCallback } from 'react';
import './App.css';
import Nav from './components/Nav';
import Hero from './components/Hero';
import LiveDemo from './components/LiveDemo';
import Benchmarks from './components/Benchmarks';
import Architecture from './components/Architecture';
import WhatBreaks from './components/WhatBreaks';
import TechStack from './components/TechStack';
import ResumeBullet from './components/ResumeBullet';
import Footer from './components/Footer';

const SECTIONS = ['hero', 'features', 'benchmarks', 'demo', 'failure-analysis', 'tech-stack'];

// Extract initial tab from URL hash (e.g. #demo/trigger)
function getInitialDemoTab() {
  const hash = window.location.hash.replace('#', '');
  const parts = hash.split('/');
  if (parts[0] === 'demo' && parts[1]) {
    return parts[1]; // nl2sql, trigger, search, dashboard
  }
  return null;
}

function App() {
  const [activeSection, setActiveSection] = useState('hero');
  const [initialDemoTab] = useState(getInitialDemoTab);
  const observerRef = useRef(null);

  const handleSectionInView = useCallback((sectionId) => {
    setActiveSection(sectionId);
  }, []);

  useEffect(() => {
    const observer = new IntersectionObserver(
      (entries) => {
        entries.forEach((entry) => {
          if (entry.isIntersecting) {
            handleSectionInView(entry.target.id);
          }
        });
      },
      { threshold: 0.3, rootMargin: '-80px 0px 0px 0px' }
    );
    observerRef.current = observer;

    SECTIONS.forEach((id) => {
      const el = document.getElementById(id);
      if (el) observer.observe(el);
    });

    return () => observer.disconnect();
  }, [handleSectionInView]);

  // Handle initial hash navigation on mount
  useEffect(() => {
    const hash = window.location.hash.replace('#', '');
    if (hash) {
      const sectionId = hash.split('/')[0];
      const timer = setTimeout(() => {
        const el = document.getElementById(sectionId);
        if (el) el.scrollIntoView({ behavior: 'smooth' });
      }, 500);
      return () => clearTimeout(timer);
    }
  }, []);

  const scrollToSection = (sectionId) => {
    const el = document.getElementById(sectionId);
    if (el) el.scrollIntoView({ behavior: 'smooth' });
    // Update hash without triggering a scroll
    window.history.replaceState(null, '', `#${sectionId}`);
  };

  return (
    <div style={{ background: 'var(--bg)', minHeight: '100vh' }}>
      <a href="#demo" className="skip-to-content" aria-label="Skip to main content">Skip to content</a>
      <Nav activeSection={activeSection} onNavigate={scrollToSection} />
      <main role="main" aria-label="NeuralVault application content">
        <section id="hero" aria-label="Hero introduction">
          <Hero onLaunchDemo={() => scrollToSection('demo')} onViewBenchmarks={() => scrollToSection('benchmarks')} />
        </section>
        <section id="features" aria-label="Architecture deep-dive">
          <Architecture />
        </section>
        <section id="benchmarks" aria-label="Performance benchmarks">
          <Benchmarks />
        </section>
        <section id="demo" aria-label="Live AI demos">
          <LiveDemo initialTab={initialDemoTab} />
        </section>
        <section id="failure-analysis" aria-label="Production failure analysis">
          <WhatBreaks />
        </section>
        <section id="tech-stack" aria-label="Technology stack and resume">
          <TechStack />
          <ResumeBullet />
        </section>
      </main>
      <Footer />
    </div>
  );
}

export default App;