/**
 * App — Hash router, component lifecycle, navigation, event bus
 */
const App = (() => {
  let currentComponent = null;
  let appEl = null;

  const routes = [
    { pattern: /^\/$/, handler: showHome },
    { pattern: /^\/exercises$/, handler: showExercises },
    { pattern: /^\/exercise\/(.+)$/, handler: showExercise },
    { pattern: /^\/workspace$/, handler: showWorkspace },
    { pattern: /^\/workspace\/matrix$/, handler: showMatrixBuilder },
    { pattern: /^\/workspace\/system$/, handler: showSystemSolver }
  ];

  // ── Event Bus ──
  const bus = {};
  function on(event, fn) {
    (bus[event] = bus[event] || []).push(fn);
  }
  function emit(event, data) {
    (bus[event] || []).forEach(fn => fn(data));
  }

  // ── Theme ──
  function initTheme() {
    const saved = localStorage.getItem('algebra-theme');
    if (saved === 'dark') {
      document.documentElement.setAttribute('data-theme', 'dark');
    }
  }

  function toggleTheme() {
    const isDark = document.documentElement.getAttribute('data-theme') === 'dark';
    if (isDark) {
      document.documentElement.removeAttribute('data-theme');
      localStorage.setItem('algebra-theme', 'light');
    } else {
      document.documentElement.setAttribute('data-theme', 'dark');
      localStorage.setItem('algebra-theme', 'dark');
    }
  }

  // ── Navigation ──
  function navigate(path) {
    window.location.hash = '#' + path;
  }

  function getHash() {
    return window.location.hash.slice(1) || '/';
  }

  function matchRoute(hash) {
    for (const route of routes) {
      const match = hash.match(route.pattern);
      if (match) {
        return { handler: route.handler, params: match.slice(1) };
      }
    }
    return { handler: showHome, params: [] };
  }

  function updateActiveNav() {
    const hash = getHash();
    document.querySelectorAll('.navbar__link').forEach(link => {
      const route = link.getAttribute('data-route');
      link.classList.remove('navbar__link--active');
      if (route === 'home' && (hash === '/' || hash === '')) {
        link.classList.add('navbar__link--active');
      } else if (route === 'exercises' && hash.startsWith('/exercise')) {
        link.classList.add('navbar__link--active');
      } else if (route === 'workspace' && hash.startsWith('/workspace')) {
        link.classList.add('navbar__link--active');
      }
    });
  }

  // ── Component Lifecycle ──
  function destroyCurrent() {
    if (currentComponent && typeof currentComponent.destroy === 'function') {
      currentComponent.destroy();
    }
    currentComponent = null;
    if (appEl) appEl.innerHTML = '';
  }

  function mountComponent(componentObj, initArgs) {
    destroyCurrent();
    currentComponent = componentObj;
    componentObj.init(appEl, initArgs);
  }

  // ── Page Handlers ──
  function showHome() {
    destroyCurrent();
    appEl.innerHTML = `
      <div class="home-page">
        <div class="home-page__hero">
          <h1>Álgebra Lineal Interactivo</h1>
          <p>Practicá los ejercicios de Vectores, Recta, Plano, Matrices, Determinantes y Sistemas de Ecuaciones. Paso a paso, con verificación automática.</p>
        </div>
        <div class="home-page__cards">
          <div class="home-card" data-nav="/exercises">
            <div class="home-card__icon">📚</div>
            <div class="home-card__title">Ejercicios</div>
            <div class="home-card__desc">68 ejercicios de los capítulos 1 a 3 con solución paso a paso</div>
          </div>
          <div class="home-card" data-nav="/workspace">
            <div class="home-card__icon">🧮</div>
            <div class="home-card__title">Taller</div>
            <div class="home-card__desc">Constructor de matrices y resolvedor de sistemas interactivos</div>
          </div>
        </div>
      </div>
    `;
    // Click handlers for home cards
    appEl.querySelectorAll('.home-card[data-nav]').forEach(card => {
      card.addEventListener('click', () => navigate(card.dataset.nav));
    });
  }

  function showExercises() {
    mountComponent(ExerciseBrowser);
  }

  function showExercise(params) {
    mountComponent(ExerciseViewer, { id: params[0] });
  }

  function showWorkspace() {
    destroyCurrent();
    appEl.innerHTML = `
      <div class="workspace">
        <div class="workspace__header">
          <h2>Taller de Cálculo</h2>
          <p>Operá con matrices y resolvé sistemas de ecuaciones</p>
        </div>
        <div class="workspace__tabs">
          <button class="workspace__tab workspace__tab--active" data-ws="matrix">Constructor de Matrices</button>
          <button class="workspace__tab" data-ws="system">Resolvedor de Sistemas</button>
        </div>
        <div class="workspace__content" id="workspaceContent"></div>
      </div>
    `;
    setupWorkspaceTabs();
    // Default to matrix
    const wsContent = document.getElementById('workspaceContent');
    MatrixBuilder.init(wsContent);
    currentComponent = MatrixBuilder;
  }

  function setupWorkspaceTabs() {
    const tabs = appEl.querySelectorAll('.workspace__tab');
    tabs.forEach(tab => {
      tab.addEventListener('click', () => {
        tabs.forEach(t => t.classList.remove('workspace__tab--active'));
        tab.classList.add('workspace__tab--active');
        const ws = tab.dataset.ws;
        const wsContent = document.getElementById('workspaceContent');
        if (!wsContent) return;

        if (currentComponent && typeof currentComponent.destroy === 'function') {
          currentComponent.destroy();
        }
        wsContent.innerHTML = '';

        if (ws === 'matrix') {
          MatrixBuilder.init(wsContent);
          currentComponent = MatrixBuilder;
        } else if (ws === 'system') {
          SystemSolver.init(wsContent);
          currentComponent = SystemSolver;
        }
      });
    });
  }

  function showMatrixBuilder() {
    navigate('/workspace');
  }

  function showSystemSolver() {
    navigate('/workspace');
  }

  // ── Router ──
  function handleRoute() {
    const hash = getHash();
    const { handler, params } = matchRoute(hash);
    updateActiveNav();

    // Fade out
    if (appEl) {
      appEl.style.opacity = '0';
      appEl.style.transition = 'opacity 150ms ease-out';
    }

    setTimeout(() => {
      handler(params);
      emit('routechange', hash);
      // Fade in
      if (appEl) {
        appEl.style.opacity = '1';
      }
    }, 150);
  }

  // ── Init ──
  function init() {
    appEl = document.getElementById('app');
    if (!appEl) {
      console.error('[App] #app element not found');
      return;
    }

    initTheme();

    // Init particles background
    if (typeof Particles !== 'undefined' && Particles.init) {
      Particles.init();
    }

    // Theme toggle
    const themeBtn = document.getElementById('themeToggle');
    if (themeBtn) {
      themeBtn.addEventListener('click', toggleTheme);
    }

    // Hash change listener
    window.addEventListener('hashchange', handleRoute);

    // Initial route
    handleRoute();
  }

  // Boot
  if (document.readyState === 'loading') {
    document.addEventListener('DOMContentLoaded', init);
  } else {
    init();
  }

  return {
    navigate,
    on,
    emit,
    getCurrentComponent: () => currentComponent
  };
})();