'use strict';

const BaseError = require('../../errors/base-error');
const ConnectionError = require('../../errors/connection-error');

/**
 * Thrown when a connection to a database is closed while an operation is in progress
 */
class AsyncQueueError extends BaseError {
  constructor(message) {
    super(message);
    this.name = 'SequelizeAsyncQueueError';
  }
}

exports.AsyncQueueError = AsyncQueueError;

class AsyncQueue {
  constructor() {
    this.previous = Promise.resolve();
    this.closed = false;
    this.rejectCurrent = () => {};
  }
  close() {
    this.closed = true;
    this.rejectCurrent(new ConnectionError(new AsyncQueueError('the connection was closed before this query could finish executing')));
  }
  enqueue(asyncFunction) {
    // This outer promise might seems superflous since down below we return asyncFunction().then(resolve, reject).
    // However, this ensures that this.previous will never be a rejected promise so the queue will
    // always keep going, while still communicating rejection from asyncFunction to the user.
    return new Promise((resolve, reject) => {
      this.previous = this.previous.then(
        () => {
          this.rejectCurrent = reject;
          if (this.closed) {
            return reject(new ConnectionError(new AsyncQueueError('the connection was closed before this query could be executed')));
          }
          return asyncFunction().then(resolve, reject);
        }
      );
    });
  }
}

exports.default = AsyncQueue;