import { Environment, Network, RecordSource, Store } from 'relay-runtime';

/**
 * Relay requires developers to configure a "fetch" function that tells Relay how to load
 * the results of GraphQL queries from your server (or other data source). See more at
 * https://relay.dev/docs/en/quick-start-guide#relay-environment.
 */
async function fetchRelay(params, variables, _cacheConfig) {
  // Check that the auth token is configured
  const REACT_APP_GITHUB_AUTH_TOKEN = process.env.REACT_APP_GITHUB_AUTH_TOKEN;
  if (
    REACT_APP_GITHUB_AUTH_TOKEN == null ||
    REACT_APP_GITHUB_AUTH_TOKEN === ''
  ) {
    throw new Error(
      'This app requires a GitHub authentication token to be configured. See readme.md for setup details.',
    );
  }

  // Fetch data from GitHub's GraphQL API:
  const response = await fetch('https://api.github.com/graphql', {
    method: 'POST',
    headers: {
      Authorization: `bearer ${REACT_APP_GITHUB_AUTH_TOKEN}`,
      'Content-Type': 'application/json',
    },
    body: JSON.stringify({
      query: params.text,
      variables,
    }),
  });

  // Get the response as JSON
  const json = await response.json();

  // GraphQL returns exceptions (for example, a missing required variable) in the "errors"
  // property of the response. If any exceptions occurred when processing the request,
  // throw an error to indicate to the developer what went wrong.
  if (Array.isArray(json.errors)) {
    console.log(json.errors);
    throw new Error(
      `Error fetching GraphQL query '${
        params.name
      }' with variables '${JSON.stringify(variables)}': ${JSON.stringify(
        json.errors,
      )}`,
    );
  }

  // Otherwise, return the full payload.
  return json;
}

// Export a singleton instance of Relay Environment configured with our network layer:
export default new Environment({
  network: Network.create(fetchRelay),
  store: new Store(new RecordSource(), {
    // This property tells Relay to not immediately clear its cache when the user
    // navigates around the app. Relay will hold onto the specified number of
    // query results, allowing the user to return to recently visited pages
    // and reusing cached data if its available/fresh.
    gcReleaseBufferSize: 10,
  }),
});