/**
 * Data layer module for retrieving retry statistics from the backend API.
 * Provides an async function to fetch retry stats relevant to Gate-V1 analysis.
 *
 * Expected API: /api/retry-stats
 * Supported parameters: stratum, policy_hash
 *
 * @module api
 */

/**
 * Constructs a query string from an object of parameters.
 * Empty or undefined values are omitted.
 * @param {Object} [params={}] - Key-value pairs for query parameters
 * @returns {string} Query string beginning with '?', or empty string if no params.
 */
const buildQueryString = (params = {}) => {
  const query = Object.entries(params)
    .filter(([, value]) => value !== undefined && value !== null && value !== '')
    .map(([key, value]) => `${encodeURIComponent(key)}=${encodeURIComponent(value)}`)
    .join('&');
  return query ? `?${query}` : '';
};

/**
 * Fetches retry statistics from the API endpoint.
 * @param {Object} [options] - Optional parameters for the query (e.g. stratum, policy_hash)
 * @returns {Promise<Object>} Promise resolving to the JSON response containing retry analysis report.
 * @throws Will throw an error if the network request fails or response is invalid.
 */
export async function fetchRetryStats(options = {}) {
  const query = buildQueryString(options);
  const endpoint = `/api/retry-stats${query}`;

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

    if (!response.ok) {
      const text = await response.text();
      throw new Error(`API request failed with status ${response.status}: ${text}`);
    }

    const data = await response.json();

    if (!data || typeof data !== 'object') {
      throw new Error('Invalid response: Expected JSON object');
    }

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

export default { fetchRetryStats };