Nomenclature

// =============================================================================
// 1. DATA LOADER
// =============================================================================
flashcardData = {
  // Define the path to your JSON file.
  const jsonFilePath = "/files/json/nomenclature.json"; 
  
  // Fetch the data and handle potential errors.
  const response = await fetch(jsonFilePath);
  if (!response.ok) {
    throw new Error(`HTTP error! status: ${response.status} - Could not load ${jsonFilePath}`);
  }
  return await response.json();
}

// =============================================================================
// 2. HELPER FUNCTION
// =============================================================================
function shuffle(array) {
  const newArray = [...array];
  for (let i = newArray.length - 1; i > 0; i--) {
    const j = Math.floor(Math.random() * (i + 1));
    [newArray[i], newArray[j]] = [newArray[j], newArray[i]];
  }
  return newArray;
}

// =============================================================================
// 2. CSS STYLING (With Improved Box Shadow)
// =============================================================================
html`
<style>
  .flashcard-widget {
    max-width: 800px;
    margin: 2rem auto;
    padding: 1.5rem;
    font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
    background: linear-gradient(135deg, #f8fafc 0%, #ffffff 100%);
    border-radius: 16px;
    border: 1px solid #e2e8f0;
  }

  /* ... the rest of the CSS remains exactly the same ... */

  .setup-screen {
    display: flex;
    flex-direction: column;
    gap: 2rem;
  }

  .setup-section {
    background: white;
    padding: 1.5rem;
    border-radius: 12px;
    border: 1px solid #e2e8f0;
    box-shadow: 0 2px 8px rgba(0, 0, 0, 0.05);
  }

  .setup-section h3 {
    margin: 0 0 1.5rem 0;
    color: #1e293b;
    font-size: 1.25rem;
    font-weight: 600;
    display: flex;
    align-items: center;
    gap: 0.5rem;
  }

  .study-mode-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(200px, 1fr));
    gap: 1rem;
  }

  .study-mode-option {
    background: #ffffff;
    border: 2px solid #e2e8f0;
    border-radius: 10px;
    padding: 1.25rem;
    cursor: pointer;
    transition: all 0.3s ease;
    text-align: center;
    position: relative;
  }

  .study-mode-option:hover {
    border-color: #3b82f6;
    transform: translateY(-2px);
    box-shadow: 0 8px 20px rgba(59, 130, 246, 0.15);
  }

  .study-mode-option.selected {
    border-color: #3b82f6;
    background: linear-gradient(135deg, #eff6ff 0%, #dbeafe 100%);
    box-shadow: 0 8px 20px rgba(59, 130, 246, 0.2);
  }

  .study-mode-title {
    font-weight: 600;
    font-size: 1.1rem;
    color: #1e293b;
    margin-bottom: 0.5rem;
  }

  .study-mode-option.selected .study-mode-title {
    color: #1d4ed8;
  }

  .study-mode-desc {
    font-size: 0.9rem;
    color: #64748b;
    line-height: 1.4;
  }

  .study-mode-option.selected .study-mode-desc {
    color: #3730a3;
  }

  .category-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(250px, 1fr));
    gap: 1rem;
  }

  .category-option {
    background: #ffffff;
    border: 2px solid #e2e8f0;
    border-radius: 10px;
    padding: 1.25rem;
    cursor: pointer;
    transition: all 0.3s ease;
    text-align: center;
    position: relative;
  }

  .category-option:hover {
    border-color: #10b981;
    transform: translateY(-2px);
    box-shadow: 0 8px 20px rgba(16, 185, 129, 0.15);
  }

  .category-option.selected {
    border-color: #10b981;
    background: linear-gradient(135deg, #ecfdf5 0%, #d1fae5 100%);
    box-shadow: 0 8px 20px rgba(16, 185, 129, 0.2);
  }

  .category-title {
    font-weight: 600;
    font-size: 1.1rem;
    color: #1e293b;
    margin-bottom: 0.5rem;
  }

  .category-option.selected .category-title {
    color: #047857;
  }

  .category-desc {
    font-size: 0.9rem;
    color: #64748b;
    line-height: 1.4;
  }

  .category-option.selected .category-desc {
    color: #065f46;
  }

  .flashcard-screen {
    display: flex;
    flex-direction: column;
    gap: 1.5rem;
  }

  .progress-bar {
    background: #f1f5f9;
    border-radius: 20px;
    padding: 0.75rem 1.5rem;
    text-align: center;
    color: #475569;
    font-weight: 500;
    border: 1px solid #e2e8f0;
  }

  .flashcard {
    background: linear-gradient(135deg, #ffffff 0%, #f8fafc 100%);
    border: 2px solid #e2e8f0;
    border-radius: 12px;
    padding: 3rem 2rem;
    text-align: center;
    min-height: 150px;
    display: flex;
    align-items: center;
    justify-content: center;
    box-shadow: 0 4px 16px rgba(0, 0, 0, 0.08);
  }

  .flashcard-question {
    font-size: 2.5rem;
    font-weight: 600;
    color: #1e293b;
    line-height: 1.3;
  }

  .flashcard-answer {
    background: linear-gradient(135deg, #f0f9ff 0%, #e0f2fe 100%);
    border: 2px solid #0ea5e9;
    border-radius: 12px;
    padding: 0;
    overflow: hidden;
    opacity: 0;
    max-height: 0;
    transition: all 0.5s cubic-bezier(0.4, 0, 0.2, 1);
  }

  .flashcard-answer.visible {
    opacity: 1;
    max-height: 1200px;
    padding: 2rem;
  }

  .answer-section {
    margin-bottom: 1.5rem;
  }

  .answer-section:last-child {
    margin-bottom: 0;
  }

  .answer-label {
    font-weight: 600;
    color: #0c4a6e;
    margin-bottom: 0.5rem;
    font-size: 1rem;
  }

  .answer-content {
    color: #1e293b;
    line-height: 1.6;
    font-size: 1rem;
  }
  
  .answer-primary {
    font-size: 1.75rem;
    font-weight: 600;
    color: #0369a1;
    text-align: center;
  }
  
  .answer-details-separator {
    border: 0;
    height: 1px;
    background: #bae6fd;
    margin: 1.5rem 0;
  }

  .button-group {
    display: flex;
    justify-content: center;
    gap: 1rem;
    flex-wrap: wrap;
    margin-top: 1.5rem;
    padding-top: 1.5rem;
    border-top: 1px solid #e2e8f0;
  }

  .btn {
    padding: 0.875rem 1.75rem;
    font-size: 1rem;
    font-weight: 600;
    border: 2px solid transparent;
    border-radius: 10px;
    cursor: pointer;
    transition: all 0.2s ease;
    background: linear-gradient(135deg, #f8fafc 0%, #ffffff 100%);
    color: #4338ca;
    border-color: #c7d2fe;
  }

  .btn:hover {
    background: linear-gradient(135deg, #eef2ff 0%, #f8fafc 100%);
    border-color: #a5b4fc;
    transform: translateY(-1px);
  }

  .btn.primary {
    background: linear-gradient(135deg, #4338ca 0%, #3730a3 100%);
    color: white;
    border-color: #4338ca;
    box-shadow: 0 4px 12px rgba(67, 56, 202, 0.3);
  }

  .btn.primary:hover {
    background: linear-gradient(135deg, #3730a3 0%, #312e81 100%);
    border-color: #3730a3;
    transform: translateY(-2px);
    box-shadow: 0 8px 20px rgba(67, 56, 202, 0.4);
  }

  .error-message {
    padding: 1rem 1.5rem;
    background: linear-gradient(135deg, #fef2f2 0%, #fee2e2 100%);
    color: #dc2626;
    border: 2px solid #f87171;
    border-radius: 10px;
    text-align: center;
    font-weight: 500;
    margin-bottom: 1rem;
  }

  @media (max-width: 768px) {
    .flashcard-widget { margin: 1rem; padding: 1rem; }
    .flashcard-widget .flashcard-question { font-size: 1.8rem; }
    .flashcard-widget .study-mode-grid, .flashcard-widget .category-grid { grid-template-columns: 1fr; }
    .flashcard-widget .button-group { flex-direction: column; align-items: center; }
    .flashcard-widget .btn { width: 100%; max-width: 300px; }
  }
  @media (max-width: 480px) {
    .flashcard-widget .flashcard { padding: 2rem 1rem; }
    .flashcard-widget .flashcard-question { font-size: 1.5rem; }
  }
</style>
`

// =============================================================================
// 3. REACTIVE STATE
// =============================================================================
mutable appState = ({
  screen: 'setup', // 'setup' or 'study'
  studyMode: 'formula_to_name', // 'formula_to_name', 'name_to_formula', 'mixed'
  selectedCategories: ['Ions and Ionic Compounds', 'Covalent Compounds'],
  deck: [],
  currentIndex: 0,
  showAnswer: false,
  cardsStudied: 0,
  error: null
})

// =============================================================================
// 4. MAIN APPLICATION RENDERER
// =============================================================================
{
  // --- Define Event Handler Functions ---
  const handleModeSelect = (mode) => {
    mutable appState = {...appState, studyMode: mode};
  };

  const handleCategoryToggle = (category) => {
    const cats = appState.selectedCategories;
    const newCats = cats.includes(category) 
      ? cats.filter(c => c !== category)
      : [...cats, category];
    mutable appState = {...appState, selectedCategories: newCats, error: null};
  };

  const handleStartSession = () => {
    if (appState.selectedCategories.length === 0) {
      mutable appState = {...appState, error: 'Please select at least one category to study.'};
      return;
    }
    const filteredData = flashcardData.filter(card => 
      appState.selectedCategories.includes(card.category)
    );
    if (filteredData.length === 0) {
      mutable appState = {...appState, error: 'No cards available for selected categories.'};
      return;
    }
    const newDeck = shuffle(filteredData).map(card => {
      const cardName = card.common_name || card.IUPAC_name;
      const cardFormula = html`${card.formula}`;
      let question, answer;
      const mode = appState.studyMode;
      if (mode === 'formula_to_name') {
        question = cardFormula;
        answer = cardName;
      } else if (mode === 'name_to_formula') {
        question = cardName;
        answer = cardFormula;
      } else {
        if (Math.random() < 0.5) {
          question = cardFormula;
          answer = cardName;
        } else {
          question = cardName;
          answer = cardFormula;
        }
      }
      return { question, answer, details: card };
    });
    mutable appState = {
      ...appState, screen: 'study', deck: newDeck,
      currentIndex: 0, showAnswer: false, cardsStudied: 0, error: null
    };
  };
  
  const handleShowAnswer = () => {
    mutable appState = {...appState, showAnswer: true};
  };

  const handleNextCard = () => {
    const totalCards = appState.deck.length;
    const newCardsStudied = appState.cardsStudied + 1;
    const nextIndex = (appState.currentIndex + 1) % totalCards;
    
    mutable appState = {
      ...appState, currentIndex: nextIndex, showAnswer: false,
      cardsStudied: (nextIndex === 0 && appState.currentIndex === totalCards - 1) ? totalCards : newCardsStudied
    };
  };

  const handleEndSession = () => {
    mutable appState = {
      ...appState, screen: 'setup', deck: [], currentIndex: 0,
      showAnswer: false, cardsStudied: 0, error: null
    };
  };

  // --- A. Render the Setup Screen ---
  if (appState.screen === 'setup') {
    const setupNode = html`
      <div class="flashcard-widget">
        <div class="setup-screen">
          ${appState.error ? html`<div class="error-message">${appState.error}</div>` : ''}
          <div class="setup-section">
            <h3>🧪 Study Mode</h3>
            <div class="study-mode-grid">
              <div class="study-mode-option ${appState.studyMode === 'formula_to_name' ? 'selected' : ''}" data-mode="formula_to_name">
                <div class="study-mode-title">Formula → Name</div>
                <div class="study-mode-desc">See chemical formulas, provide the names</div>
              </div>
              <div class="study-mode-option ${appState.studyMode === 'name_to_formula' ? 'selected' : ''}" data-mode="name_to_formula">
                <div class="study-mode-title">Name → Formula</div>
                <div class="study-mode-desc">See chemical names, provide the formulas</div>
              </div>
              <div class="study-mode-option ${appState.studyMode === 'mixed' ? 'selected' : ''}" data-mode="mixed">
                <div class="study-mode-title">Mixed Mode</div>
                <div class="study-mode-desc">Random combination of both directions</div>
              </div>
            </div>
          </div>
          <div class="setup-section">
            <h3>📚 Categories to Study</h3>
            <div class="category-grid">
              <div class="category-option ${appState.selectedCategories.includes('Ions and Ionic Compounds') ? 'selected' : ''}" data-category="Ions and Ionic Compounds">
                <div class="category-title">Ions and Ionic Compounds</div>
                <div class="category-desc">Monatomic ions, polyatomic ions, and ionic compounds</div>
              </div>
              <div class="category-option ${appState.selectedCategories.includes('Covalent Compounds') ? 'selected' : ''}" data-category="Covalent Compounds">
                <div class="category-title">Covalent Compounds</div>
                <div class="category-desc">Binary compounds, acids, and simple organic compounds</div>
              </div>
            </div>
          </div>
          <div class="button-group">
            <button class="btn primary" data-action="start">Start Studying</button>
          </div>
        </div>
      </div>
    `;
    
    setupNode.querySelectorAll('[data-mode]').forEach(el => el.addEventListener('click', () => handleModeSelect(el.dataset.mode)));
    setupNode.querySelectorAll('[data-category]').forEach(el => el.addEventListener('click', () => handleCategoryToggle(el.dataset.category)));
    setupNode.querySelector('[data-action="start"]').addEventListener('click', handleStartSession);
    
    return setupNode;
  }
  
  // --- B. Render the Study Screen ---
  const currentFlashcard = appState.deck[appState.currentIndex];
  const { question, answer, details: currentCard } = currentFlashcard;
  const totalCards = appState.deck.length;
  const cardName = currentCard.common_name || currentCard.IUPAC_name;
  
  const studyNode = html`
    <div class="flashcard-widget">
      <div class="flashcard-screen">
        <div class="progress-bar">Card ${appState.currentIndex + 1} of ${totalCards}</div>
        <div class="flashcard">
          <div class="flashcard-question">${question}</div>
        </div>
        <div class="flashcard-answer ${appState.showAnswer ? 'visible' : ''}">
          <div class="answer-primary">${answer}</div>
          <hr class="answer-details-separator">
          
          ${currentCard.common_name && currentCard.IUPAC_name && currentCard.common_name !== currentCard.IUPAC_name ? html`
            <div class="answer-section">
              <div class="answer-label">${cardName === currentCard.common_name ? "IUPAC Name:" : "Common Name:"}</div>
              <div class="answer-content">${cardName === currentCard.common_name ? currentCard.IUPAC_name : currentCard.common_name}</div>
            </div>
          ` : ''}
          <div class="answer-section">
            <div class="answer-label">Category:</div>
            <div class="answer-content">${currentCard.subcategory}</div>
          </div>
          ${currentCard.components ? html`<div class="answer-section"><div class="answer-label">Components:</div><div class="answer-content">${html`${currentCard.components.join(' + ')}`}</div></div>` : ''}
          ${currentCard.charge_balance ? html`<div class="answer-section"><div class="answer-label">Charge Balance:</div><div class="answer-content">${currentCard.charge_balance}</div></div>` : ''}
          ${currentCard.notes ? html`<div class="answer-section"><div class="answer-label">Notes:</div><div class="answer-content">${html`${currentCard.notes}`}</div></div>` : ''}
        </div>
        <div class="button-group">
          ${!appState.showAnswer ? `<button class="btn primary" data-action="show">Show Answer</button>` : ''}
          ${appState.showAnswer ? `<button class="btn primary" data-action="next">Next Card</button>` : ''}
          <button class="btn" data-action="end">End Session</button>
        </div>
      </div>
    </div>
  `;

  const showBtn = studyNode.querySelector('[data-action="show"]');
  if (showBtn) showBtn.addEventListener('click', handleShowAnswer);

  const nextBtn = studyNode.querySelector('[data-action="next"]');
  if (nextBtn) nextBtn.addEventListener('click', handleNextCard);
  
  studyNode.querySelector('[data-action="end"]').addEventListener('click', handleEndSession);

  return studyNode;
}