/**
 * js/api.js
 * Data layer for fetching measurement data (temperature & audio) from the backend API.
 *
 * @module api
 */

/**
 * Builds a query string from optional parameters.
 * @param {Object} [params={}] - Optional query parameters.
 * @returns {string} Query string starting with '?', or empty string if no params.
 */
function buildQueryString(params = {}) {
  const query = Object.entries(params)
    .filter(([_, v]) => v != null && v !== '')
    .map(([k, v]) => `${encodeURIComponent(k)}=${encodeURIComponent(v)}`)
    .join('&');
  return query ? `?${query}` : '';
}

/**
 * Fetches measurement data from the /data API endpoint.
 *
 * @async
 * @param {Object} [filters] - Optional filters, e.g. { sensorType: 'temperature', timeRange: '24h' }.
 * @returns {Promise<Object>} Resolves with parsed JSON { temperature: [...], audio: [...] }.
 * @throws Will throw an error if the fetch response is not OK or JSON is invalid.
 */
export async function fetchData(filters = {}) {
  const queryString = buildQueryString(filters);
  const url = `/data${queryString}`;

  try {
    const response = await fetch(url, { method: 'GET', headers: { 'Accept': 'application/json' } });

    if (!response.ok) {
      throw new Error(`Fetch error: ${response.status} ${response.statusText}`);
    }

    const data = await response.json();

    // Defensive checks
    if (!data || typeof data !== 'object' || !Array.isArray(data.temperature) || !Array.isArray(data.audio)) {
      throw new Error('Invalid data format from API');
    }

    return data;
  } catch (error) {
    console.error('Error fetching data:', error);
    throw error;
  }
}