// ═══════════════════════════════════════════════════════
// Diff Checker
// ═══════════════════════════════════════════════════════
function computeDiff() {
  const a = document.getElementById('diffA').value.split('\n');
  const b = document.getElementById('diffB').value.split('\n');
  const max = Math.max(a.length, b.length);
  let html = '';
  for (let i = 0; i < max; i++) {
    const la = a[i] !== undefined ? a[i] : null;
    const lb = b[i] !== undefined ? b[i] : null;
    const esc = s => s.replace(/[<>&]/g, c => ({'<':'&lt;','>':'&gt;','&':'&amp;'}[c]));
    if (la === null) html += `<div class="diff-line diff-add">+ ${esc(lb)}</div>`;
    else if (lb === null) html += `<div class="diff-line diff-del">- ${esc(la)}</div>`;
    else if (la === lb) html += `<div class="diff-line diff-same">  ${esc(la)}</div>`;
    else {
      html += `<div class="diff-line diff-del">- ${esc(la)}</div>`;
      html += `<div class="diff-line diff-add">+ ${esc(lb)}</div>`;
    }
  }
  document.getElementById('diffOutput').innerHTML = html || '<span style="color:var(--text-muted);">Texts are identical.</span>';
}