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Maven plugin for generating graphql clients
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/**
 * Copyright (c) 2017-present, Facebook, Inc.
 *
 * This source code is licensed under the MIT license found in the
 * LICENSE file in the root directory of this source tree.
 *
 *  strict
 */

import { isAsyncIterable } from 'iterall';
import { GraphQLError } from '../error/GraphQLError';
import { locatedError } from '../error/locatedError';
import { addPath, assertValidExecutionArguments, buildExecutionContext, buildResolveInfo, collectFields, execute, getFieldDef, getOperationRootType, resolveFieldValueOrError, responsePathAsArray } from '../execution/execute';
import { GraphQLSchema } from '../type/schema';
import mapAsyncIterator from './mapAsyncIterator';

/**
 * Implements the "Subscribe" algorithm described in the GraphQL specification.
 *
 * Returns a Promise which resolves to either an AsyncIterator (if successful)
 * or an ExecutionResult (client error). The promise will be rejected if a
 * server error occurs.
 *
 * If the client-provided arguments to this function do not result in a
 * compliant subscription, a GraphQL Response (ExecutionResult) with
 * descriptive errors and no data will be returned.
 *
 * If the the source stream could not be created due to faulty subscription
 * resolver logic or underlying systems, the promise will resolve to a single
 * ExecutionResult containing `errors` and no `data`.
 *
 * If the operation succeeded, the promise resolves to an AsyncIterator, which
 * yields a stream of ExecutionResults representing the response stream.
 *
 * Accepts either an object with named arguments, or individual arguments.
 */

/* eslint-disable no-redeclare */

export function subscribe(argsOrSchema, document, rootValue, contextValue, variableValues, operationName, fieldResolver, subscribeFieldResolver) {
  /* eslint-enable no-redeclare */
  // Extract arguments from object args if provided.
  return arguments.length === 1 ? subscribeImpl(argsOrSchema.schema, argsOrSchema.document, argsOrSchema.rootValue, argsOrSchema.contextValue, argsOrSchema.variableValues, argsOrSchema.operationName, argsOrSchema.fieldResolver, argsOrSchema.subscribeFieldResolver) : subscribeImpl(argsOrSchema, document, rootValue, contextValue, variableValues, operationName, fieldResolver, subscribeFieldResolver);
}

/**
 * This function checks if the error is a GraphQLError. If it is, report it as
 * an ExecutionResult, containing only errors and no data. Otherwise treat the
 * error as a system-class error and re-throw it.
 */
function reportGraphQLError(error) {
  if (error instanceof GraphQLError) {
    return { errors: [error] };
  }
  throw error;
}

function subscribeImpl(schema, document, rootValue, contextValue, variableValues, operationName, fieldResolver, subscribeFieldResolver) {
  var sourcePromise = createSourceEventStream(schema, document, rootValue, contextValue, variableValues, operationName, subscribeFieldResolver);

  // For each payload yielded from a subscription, map it over the normal
  // GraphQL `execute` function, with `payload` as the rootValue.
  // This implements the "MapSourceToResponseEvent" algorithm described in
  // the GraphQL specification. The `execute` function provides the
  // "ExecuteSubscriptionEvent" algorithm, as it is nearly identical to the
  // "ExecuteQuery" algorithm, for which `execute` is also used.
  var mapSourceToResponse = function mapSourceToResponse(payload) {
    return execute(schema, document, payload, contextValue, variableValues, operationName, fieldResolver);
  };

  // Resolve the Source Stream, then map every source value to a
  // ExecutionResult value as described above.
  return sourcePromise.then(function (resultOrStream) {
    return (
      // Note: Flow can't refine isAsyncIterable, so explicit casts are used.
      isAsyncIterable(resultOrStream) ? mapAsyncIterator(resultOrStream, mapSourceToResponse, reportGraphQLError) : resultOrStream
    );
  }, reportGraphQLError);
}

/**
 * Implements the "CreateSourceEventStream" algorithm described in the
 * GraphQL specification, resolving the subscription source event stream.
 *
 * Returns a Promise.
 *
 * If the client-provided invalid arguments, the source stream could not be
 * created, or the resolver did not return an AsyncIterable, this function will
 * will throw an error, which should be caught and handled by the caller.
 *
 * A Source Event Stream represents a sequence of events, each of which triggers
 * a GraphQL execution for that event.
 *
 * This may be useful when hosting the stateful subscription service in a
 * different process or machine than the stateless GraphQL execution engine,
 * or otherwise separating these two steps. For more on this, see the
 * "Supporting Subscriptions at Scale" information in the GraphQL specification.
 */
export function createSourceEventStream(schema, document, rootValue, contextValue, variableValues, operationName, fieldResolver) {
  // If arguments are missing or incorrectly typed, this is an internal
  // developer mistake which should throw an early error.
  assertValidExecutionArguments(schema, document, variableValues);

  try {
    // If a valid context cannot be created due to incorrect arguments,
    // this will throw an error.
    var exeContext = buildExecutionContext(schema, document, rootValue, contextValue, variableValues, operationName, fieldResolver);

    // Return early errors if execution context failed.
    if (Array.isArray(exeContext)) {
      return Promise.resolve({ errors: exeContext });
    }

    var type = getOperationRootType(schema, exeContext.operation);
    var fields = collectFields(exeContext, type, exeContext.operation.selectionSet, Object.create(null), Object.create(null));
    var responseNames = Object.keys(fields);
    var responseName = responseNames[0];
    var fieldNodes = fields[responseName];
    var fieldNode = fieldNodes[0];
    var fieldName = fieldNode.name.value;
    var fieldDef = getFieldDef(schema, type, fieldName);

    if (!fieldDef) {
      throw new GraphQLError('The subscription field "' + fieldName + '" is not defined.', fieldNodes);
    }

    // Call the `subscribe()` resolver or the default resolver to produce an
    // AsyncIterable yielding raw payloads.
    var resolveFn = fieldDef.subscribe || exeContext.fieldResolver;

    var path = addPath(undefined, responseName);

    var info = buildResolveInfo(exeContext, fieldDef, fieldNodes, type, path);

    // resolveFieldValueOrError implements the "ResolveFieldEventStream"
    // algorithm from GraphQL specification. It differs from
    // "ResolveFieldValue" due to providing a different `resolveFn`.
    var result = resolveFieldValueOrError(exeContext, fieldDef, fieldNodes, resolveFn, rootValue, info);

    // Coerce to Promise for easier error handling and consistent return type.
    return Promise.resolve(result).then(function (eventStream) {
      // If eventStream is an Error, rethrow a located error.
      if (eventStream instanceof Error) {
        throw locatedError(eventStream, fieldNodes, responsePathAsArray(path));
      }

      // Assert field returned an event stream, otherwise yield an error.
      if (isAsyncIterable(eventStream)) {
        // Note: isAsyncIterable above ensures this will be correct.
        return eventStream;
      }
      throw new Error('Subscription field must return Async Iterable. Received: ' + String(eventStream));
    });
  } catch (error) {
    return Promise.reject(error);
  }
}