graphile-build/node8plus/callbackToAsyncIterator.js

Build a GraphQL schema from plugins

"use strict";

Object.defineProperty(exports, "__esModule", {
  value: true
});
exports.default = callbackToAsyncIterator;
var _iterall = require("iterall");
/* eslint-disable flowtype/no-weak-types */
// Turn a callback-based listener into an async iterator
// From https://raw.githubusercontent.com/withspectrum/callback-to-async-iterator/master/src/index.js
// License MIT (Copyright (c) 2017 Maximilian Stoiber)
// Based on https://github.com/apollographql/graphql-subscriptions/blob/master/src/event-emitter-to-async-iterator.ts
const defaultOnError = err => {
  throw err;
};
function callbackToAsyncIterator(listener, options = {}) {
  const {
    onError = defaultOnError,
    buffering = true,
    onClose
  } = options;
  let pullQueue = [];
  let pushQueue = [];
  let listening = true;
  let listenerReturnValue;
  function pushValue(value) {
    if (pullQueue.length !== 0) {
      pullQueue.shift()({
        value,
        done: false
      });
    } else if (buffering === true) {
      pushQueue.push(value);
    }
  }
  function pullValue() {
    return new Promise(resolve => {
      if (pushQueue.length !== 0) {
        resolve({
          value: pushQueue.shift(),
          done: false
        });
      } else {
        pullQueue.push(resolve);
      }
    });
  }
  function emptyQueue() {
    if (listening) {
      listening = false;
      pullQueue.forEach(resolve => resolve({
        value: undefined,
        done: true
      }));
      pullQueue = [];
      pushQueue = [];
      onClose && onClose(listenerReturnValue);
    }
  }
  try {
    // Start listener
    Promise.resolve(listener(value => pushValue(value))).then(a => {
      listenerReturnValue = a;
    }).catch(err => {
      onError(err);
    });
    return {
      next() {
        return listening ? pullValue() : this.return();
      },
      return() {
        emptyQueue();
        return Promise.resolve({
          value: undefined,
          done: true
        });
      },
      throw(error) {
        emptyQueue();
        onError(error);
        return Promise.reject(error);
      },
      [_iterall.$$asyncIterator]() {
        return this;
      }
    };
  } catch (err) {
    onError(err);
    return {
      next() {
        return Promise.reject(err);
      },
      return() {
        return Promise.reject(err);
      },
      throw(error) {
        return Promise.reject(error);
      },
      [_iterall.$$asyncIterator]() {
        return this;
      }
    };
  }
}
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