import { ApolloLink, Operation, FetchResult, Observable } from 'apollo-link'
import { createClient, ClientOptions, Client } from 'graphql-ws'
import { print } from 'graphql'

// web socket generic apollo link
export class WebSocketLink extends ApolloLink {
  private client: Client

  constructor(options: ClientOptions) {
    super()
    this.client = createClient(options)
  }

  public request(operation: Operation): Observable<FetchResult> {
    return new Observable((sink) => {
      return this.client.subscribe<FetchResult>(
        { ...operation, query: print(operation.query) },
        {
          next: sink.next.bind(sink),
          complete: sink.complete.bind(sink),
          error: (err) => {
            if (Array.isArray(err))
              // GraphQLError[]
              return sink.error(
                new Error(err.map(({ message }) => message).join(', '))
              )

            if (err instanceof CloseEvent)
              return sink.error(
                new Error(
                  `Socket closed with event ${err.code} ${err.reason || ''}` // reason will be available on clean closes only
                )
              )

            return sink.error(err)
          },
        }
      )
    })
  }
}