/**
 * CSV formatter
 * Produces a single CSV line: timestamp,measurement,field1=val1,field2=val2,...
 *
 * Values are escaped if they contain commas or quotes.
 *
 * @param {string} measurement - The measurement name (e.g. node name)
 * @param {object} metadata    - { fields, tags }
 *   - fields: key/value pairs of changed data points
 *   - tags:   flat key/value string pairs (included as columns)
 * @returns {string} CSV-formatted line
 */
function format(measurement, metadata) {
  const { fields, tags } = metadata;
  const timestamp = new Date().toISOString();
  const parts = [escapeCSV(timestamp), escapeCSV(measurement)];

  // Append tags first, then fields
  if (tags) {
    for (const key of Object.keys(tags).sort()) {
      parts.push(escapeCSV(`${key}=${tags[key]}`));
    }
  }

  for (const key of Object.keys(fields).sort()) {
    parts.push(escapeCSV(`${key}=${fields[key]}`));
  }

  return parts.join(',');
}

/**
 * Escapes a value for safe inclusion in a CSV field.
 * Wraps in double quotes if the value contains a comma, quote, or newline.
 */
function escapeCSV(value) {
  const str = String(value);
  if (str.includes(',') || str.includes('"') || str.includes('\n')) {
    return '"' + str.replace(/"/g, '""') + '"';
  }
  return str;
}

module.exports = { format };