import {
  Environment,
  Network,
  RecordSource,
  Store,
  FetchFunction,
} 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.
 */
const fetchRelay: FetchFunction = async (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) {
    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 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.

    // TODO: RelayModernStore needs to be updated on @types/relay-runtime in order to allow new configuration options such as gcReleaseBufferSize
    // @ts-ignore
    gcReleaseBufferSize: 10,
  }),
})