/**
 * ExerciseViewer — Problem display with KaTeX, step-by-step solution reveal, interactive attempt
 */
const ExerciseViewer = (() => {
  let container = null;
  let currentExercise = null;
  let revealedSteps = 0;
  let ac = null; // AbortController for event listener cleanup

  function escapeHtml(str) {
    return (str || '').replace(/&/g, '&amp;').replace(/</g, '&lt;').replace(/>/g, '&gt;');
  }

  async function findExercise(id) {
    await ExerciseBrowser.loadExerciseData();
    const exercises = ExerciseBrowser.getExercises();
    return exercises.find(ex => ex.id === id);
  }

  function renderProblem(ex) {
    const diffLabel = { basic: 'Básico', intermediate: 'Intermedio', advanced: 'Avanzado' };
    const topicLabels = {
      'vector-ops': 'Vectores',
      'line-eq': 'Rectas',
      'plane-eq': 'Planos',
      'matrix-ops': 'Matrices',
      'determinants': 'Determinantes',
      'matrix-inverse': 'Inversa',
      'systems': 'Sistemas'
    };
    return `
      <div class="exercise-viewer__problem">
        <div class="exercise-viewer__problem-header">
          <span class="exercise-viewer__problem-id">${ex.id}</span>
          <span class="exercise-viewer__problem-topic">${topicLabels[ex.topic] || ex.topic} — ${diffLabel[ex.difficulty] || ex.difficulty}</span>
        </div>
        <div class="exercise-viewer__statement" id="exercise-statement"></div>
        ${ex.hint ? `<button class="exercise-viewer__hint-btn" id="hintBtn">💡 Ver pista</button>
        <div class="exercise-viewer__hint" id="hintBox">${escapeHtml(ex.hint)}</div>` : ''}
        ${ex.theoryKey ? `<button class="exercise-viewer__theory-btn" id="theoryBtn">📖 Ver teoría</button>
        <div class="exercise-viewer__theory theory-panel" id="theoryBox"></div>` : ''}
      </div>

      <div class="exercise-viewer__attempt">
        <h3>Tu respuesta</h3>
        <div class="attempt-input">
          <input type="text" class="attempt-input__field" id="attemptInput" placeholder="Ingresá tu respuesta...">
          <button class="attempt-input__submit" id="attemptSubmit">Verificar</button>
        </div>
        <div class="attempt-feedback" id="attemptFeedback" role="status" aria-live="polite"></div>
      </div>

      <div class="exercise-viewer__solution">
        <h3>Solución paso a paso</h3>
        <ol class="solution-steps" id="solutionSteps"></ol>
        <button class="reveal-btn" id="revealBtn">Mostrar siguiente paso ▼</button>
        <div class="solution-answer" id="solutionAnswer">
          <div class="solution-answer__label">Respuesta final</div>
          <div id="answerContent"></div>
        </div>
      </div>
    `;
  }

  let theoryCache = {};

  function renderStatement(ex) {
    const el = document.getElementById('exercise-statement');
    if (!el) return;
    const latex = ex.statement;
    if (!latex) {
      el.textContent = '';
      return;
    }
    if (typeof KatexRenderer !== 'undefined' && KatexRenderer.renderInline) {
      try {
        KatexRenderer.renderInline(el, latex);
      } catch (e) {
        console.warn('[ExerciseViewer] KaTeX render error, falling back to text:', e);
        el.textContent = latex;
      }
    } else {
      el.textContent = latex;
    }
  }

  async function loadTheory(chapter, theoryKey) {
    const cacheKey = `${chapter}-${theoryKey}`;
    if (theoryCache[cacheKey]) return theoryCache[cacheKey];

    try {
      const resp = await fetch(`data/theory-cap0${chapter}.json`);
      const data = await resp.json();
      theoryCache[cacheKey] = data[theoryKey] || null;
      return theoryCache[cacheKey];
    } catch (e) {
      console.warn('[ExerciseViewer] Failed to load theory:', e);
      return null;
    }
  }

  function renderTheoryPanel(theory) {
    const box = document.getElementById('theoryBox');
    if (!box) return;
    const title = escapeHtml(theory.title || '');
    const content = theory.content || '';
    box.innerHTML = `<div class="theory-panel"><h4>${title}</h4><div class="theory-content" id="theoryContent"></div></div>`;
    const contentEl = document.getElementById('theoryContent');
    if (contentEl && typeof KatexRenderer !== 'undefined') {
      contentEl.textContent = content;
      KatexRenderer.renderAll(contentEl);
    } else if (contentEl) {
      contentEl.textContent = content;
    }
  }

  function checkAnswer(userInput, exercise) {
    if (!exercise.answer) return { correct: false, message: 'No hay respuesta definida para este ejercicio.' };
    const ans = exercise.answer;
    const input = userInput.trim();

    if (exercise.answerType === 'numeric') {
      const num = parseFloat(input);
      if (isNaN(num)) return { correct: false, message: 'Ingresá un número válido.' };
      const correct = Math.abs(num - ans.value) < 0.01;
      return { correct, message: correct ? '¡Correcto! 🎉' : 'Incorrecto. Intentá de nuevo.' };
    }

    if (exercise.answerType === 'vector') {
      // Parse vector format: (1; 2; 3) or (1,2,3)
      const vecMatch = input.replace(/\s/g, '').match(/[\(-]?([-\d.]+)[;,]([-\d.]+)(?:[;,]([-\d.]+))?[;\)]?/);
      if (!vecMatch) return { correct: false, message: 'Formato: (1; 2; 3) o (1,2,3)' };
      const vals = vecMatch.slice(1).filter(v => v !== undefined).map(Number);
      const answerVals = ans.value;
      if (vals.length !== answerVals.length) return { correct: false, message: `Se esperan ${answerVals.length} componentes.` };
      const correct = vals.every((v, i) => Math.abs(v - answerVals[i]) < 0.01);
      return { correct, message: correct ? '¡Correcto! 🎉' : 'Incorrecto. Intentá de nuevo.' };
    }

    if (exercise.answerType === 'expression') {
      // Normalize and compare expression answers
      // Handle both text answers and LaTeX answers
      const normalizeText = (s) => {
        if (!s) return '';
        return s
          .trim()
          .toLowerCase()
          .replace(/\s+/g, ' ')
          .normalize('NFD')
          .replace(/[\u0300-\u036f]/g, ''); // Remove diacritics for accent-insensitive comparison
      };
      const normalizeLatex = (s) => {
        if (!s) return '';
        return s
          .trim()
          .replace(/\s+/g, ' ')
          .replace(/\\vec\{([^}]*)\}/g, '\\vec{$1}')
          .replace(/\\overrightarrow\{([^}]*)\}/g, '\\overrightarrow{$1}')
          .replace(/\\cdot/g, '\\cdot')
          .replace(/\\times/g, '\\times');
      };
      const normInput = normalizeText(input);
      const normAnswer = normalizeText(ans.value);
      if (!normAnswer) return { correct: false, message: 'Este ejercicio requiere verificación manual. Mirá la solución.' };
      const correct = normInput === normAnswer;
      return { correct, message: correct ? '¡Correcto! 🎉' : 'Incorrecto. Intentá de nuevo.' };
    }

    return { correct: false, message: 'Tipo de respuesta no soportado.' };
  }

  function revealNextStep() {
    if (!currentExercise || !currentExercise.solutionSteps) return;
    const steps = currentExercise.solutionSteps;
    const stepsEl = document.getElementById('solutionSteps');
    const revealBtn = document.getElementById('revealBtn');

    if (revealedSteps < steps.length) {
      const step = steps[revealedSteps];
      const li = document.createElement('li');
      li.className = 'solution-step';
      li.innerHTML = `
        <div class="solution-step__desc">${escapeHtml(step.desc)}</div>
        <div class="solution-step__expression" data-step="${revealedSteps}"></div>
      `;
      stepsEl.appendChild(li);

      // Render math
      const mathEl = li.querySelector('.solution-step__expression');
      if (mathEl && typeof KatexRenderer !== 'undefined') {
        KatexRenderer.renderDisplay(mathEl, step.expression);
      }

      revealedSteps++;

      // Hide button if all steps revealed
      if (revealedSteps >= steps.length) {
        revealBtn.textContent = 'Mostrar respuesta final ▼';
        revealBtn.onclick = revealAnswer;
      }
    }
  }

  function revealAnswer() {
    if (!currentExercise || !currentExercise.answer) return;
    const answerEl = document.getElementById('solutionAnswer');
    const contentEl = document.getElementById('answerContent');
    const revealBtn = document.getElementById('revealBtn');

    if (contentEl && typeof KatexRenderer !== 'undefined') {
      KatexRenderer.renderDisplay(contentEl, currentExercise.answer.latex);
    } else if (contentEl) {
      contentEl.textContent = currentExercise.answer.latex;
    }

    answerEl.classList.add('solution-answer--visible');
    revealBtn.style.display = 'none';
  }

  function setupEvents() {
    ac = new AbortController();

    // Back button
    const backBtn = container.querySelector('.exercise-viewer__back');
    if (backBtn) {
      backBtn.addEventListener('click', () => {
        if (typeof App !== 'undefined') App.navigate('/exercises');
      }, { signal: ac.signal });
    }

    // Hint button
    const hintBtn = document.getElementById('hintBtn');
    if (hintBtn) {
      hintBtn.addEventListener('click', () => {
        const hintBox = document.getElementById('hintBox');
        hintBox.classList.toggle('exercise-viewer__hint--visible');
        hintBtn.textContent = hintBox.classList.contains('exercise-viewer__hint--visible') ? '🙈 Ocultar pista' : '💡 Ver pista';
      }, { signal: ac.signal });
    }

    // Theory button
    const theoryBtn = document.getElementById('theoryBtn');
    if (theoryBtn && currentExercise && currentExercise.theoryKey) {
      theoryBtn.addEventListener('click', async () => {
        const theoryBox = document.getElementById('theoryBox');
        const isVisible = theoryBox.classList.contains('exercise-viewer__theory--visible');
        if (isVisible) {
          theoryBox.classList.remove('exercise-viewer__theory--visible');
          theoryBtn.textContent = '📖 Ver teoría';
        } else {
          const chapter = currentExercise.chapter || 1;
          const theory = await loadTheory(chapter, currentExercise.theoryKey);
          if (theory) {
            renderTheoryPanel(theory);
            theoryBox.classList.add('exercise-viewer__theory--visible');
            theoryBtn.textContent = '📕 Ocultar teoría';
          } else {
            theoryBox.innerHTML = '<p>Teoría no disponible.</p>';
            theoryBox.classList.add('exercise-viewer__theory--visible');
          }
        }
      }, { signal: ac.signal });
    }

    // Attempt
    const submitBtn = document.getElementById('attemptSubmit');
    const attemptInput = document.getElementById('attemptInput');
    const feedback = document.getElementById('attemptFeedback');

    if (submitBtn && currentExercise) {
      const doCheck = () => {
        const result = checkAnswer(attemptInput.value, currentExercise);
        feedback.className = 'attempt-feedback';
        feedback.classList.add(result.correct ? 'attempt-feedback--correct' : 'attempt-feedback--incorrect');
        feedback.textContent = result.message;
      };
      submitBtn.addEventListener('click', doCheck, { signal: ac.signal });
      attemptInput.addEventListener('keydown', (e) => {
        if (e.key === 'Enter') doCheck();
      }, { signal: ac.signal });
    }

    // Reveal steps
    const revealBtn = document.getElementById('revealBtn');
    if (revealBtn) {
      revealBtn.addEventListener('click', revealNextStep, { signal: ac.signal });
    }
  }

  async function init(el, params) {
    container = el;
    revealedSteps = 0;
    currentExercise = null;

    if (!params || !params.id) {
      container.innerHTML = '<p>Ejercicio no especificado.</p>';
      return;
    }

    const ex = await findExercise(params.id);
    if (!ex) {
      container.innerHTML = `<p>Ejercicio "${escapeHtml(params.id)}" no encontrado.</p>`;
      return;
    }

    currentExercise = ex;
    container.innerHTML = `
      <div class="exercise-viewer">
        <button class="exercise-viewer__back">← Volver a ejercicios</button>
        ${renderProblem(ex)}
      </div>
    `;

    renderStatement(ex);
    setupEvents();
  }

  function destroy() {
    if (ac) {
      ac.abort();
      ac = null;
    }
    if (container) container.innerHTML = '';
    container = null;
    currentExercise = null;
    revealedSteps = 0;
  }

  return { init, destroy };
})();