async function loadManifest() {
  const res = await fetch('../data/manifest.json');
  if (!res.ok) throw new Error('Failed to load manifest.json');
  return res.json();
}

function parseCSV(text) {
  const lines = text.trim().split(/\r?\n/);
  if (!lines.length) return { headers: [], rows: [] };
  const headers = lines[0].split(',').map(h => h.trim());
  const rows = lines.slice(1).map(line => {
    const cols = [];
    let current = '';
    let inQuotes = false;
    for (let i = 0; i < line.length; i++) {
      const ch = line[i];
      if (ch === '"') {
        if (inQuotes && line[i + 1] === '"') {
          current += '"';
          i++;
        } else {
          inQuotes = !inQuotes;
        }
      } else if (ch === ',' && !inQuotes) {
        cols.push(current);
        current = '';
      } else {
        current += ch;
      }
    }
    cols.push(current);
    return cols;
  });
  return { headers, rows };
}

function renderCSVList(files) {
  const list = document.getElementById('csv-list');
  list.innerHTML = '';
  if (!files.length) {
    list.textContent = 'No CSV files listed in manifest.json yet.';
    return;
  }
  files.forEach(f => {
    const pill = document.createElement('div');
    pill.className = 'csv-pill';
    pill.textContent = f;
    list.appendChild(pill);
  });
}

function renderPreview(headers, rows) {
  const preview = document.getElementById('preview');
  if (!headers.length) {
    preview.textContent = 'No data loaded yet.';
    return;
  }
  const table = document.createElement('table');
  table.className = 'table';
  const thead = document.createElement('thead');
  const trh = document.createElement('tr');
  headers.forEach(h => {
    const th = document.createElement('th');
    th.textContent = h;
    trh.appendChild(th);
  });
  thead.appendChild(trh);
  table.appendChild(thead);

  const tbody = document.createElement('tbody');
  rows.slice(0, 10).forEach(r => {
    const tr = document.createElement('tr');
    r.forEach(cell => {
      const td = document.createElement('td');
      td.textContent = cell;
      tr.appendChild(td);
    });
    tbody.appendChild(tr);
  });
  table.appendChild(tbody);

  preview.innerHTML = '';
  preview.appendChild(table);
}

async function loadFirstCSV(files) {
  if (!files.length) return;
  const res = await fetch(`../data/${files[0]}`);
  if (!res.ok) throw new Error(`Failed to load ${files[0]}`);
  const text = await res.text();
  const { headers, rows } = parseCSV(text);
  renderPreview(headers, rows);
}

async function init() {
  try {
    const manifest = await loadManifest();
    const files = manifest.csvFiles || [];
    renderCSVList(files);
    await loadFirstCSV(files);
  } catch (err) {
    document.getElementById('csv-list').textContent = err.message;
    console.error(err);
  }
}

init();