Use local system time

[chdanielmueller]

Allow via option boolean useLocalTime to use the local system time instead of UTC for intervals.
Maybe does not solve the timezone/summertime issue for everyone but for me this should do it.
closes #8

To test you can use the following example and check the sleepUntil timestamp in the MongoDB. (Unless you are in a UTC timezone)

import { MongoClient } from 'mongodb';
import { MongoCron } from '../src';
import { promise as sleep } from 'es6-sleep';
import * as moment from 'moment';

(async function() {
  const mongo = await MongoClient.connect('mongodb://localhost:27017', { useNewUrlParser: true });
  const db = mongo.db('test');
  const collection = db.collection('jobs');

  const cron = new MongoCron({
    collection,
    onDocument: (doc) => console.log('onDocument', doc),
    onError: (err) => console.log(err),
    onStart: () => console.log('started ...'),
    onStop: () => console.log('stopped'),
    nextDelay: 1000,
    reprocessDelay: 1000,
    idleDelay: 10000,
    lockDuration: 600000,
    useLocalTime: true // New option
  });

  await collection.insertMany([
    { name: 'Job interval',
      sleepUntil: moment().toDate(),
      interval: '* * 20 * * *'
    }
  ]);

  cron.start();
  await sleep(30000);
  cron.stop();

})().catch(console.error);

[xpepermint]

Looks good ... let me do some more tests on this ...

[xpepermint]

@chdanielmueller can you please add tests for this new feature? I can merge then ...

[chdanielmueller]

@xpepermint what kind of tests would you like?
Do you want to duplicate the existing test suite and run them with the new setting?

[xpepermint]

We have to cover this feature with tests here https://github.com/xpepermint/mongodb-cron/blob/master/src/tests/cron.test.ts.

[chdanielmueller]

@xpepermint I'm a bit clueless at the moment how to write such a test.
What should the test do step by step?

[xpepermint]

Hum ... then I'll have to do it ;). Give me a few days. Use your branch until then.

[xpepermint]

OK, some more context ... when bunkat/later#95 is resolved, we will further upgrade this feature. For now, what you did is valid (exactly as stated in Later's docs).

[xpepermint]

Adding tests in another PR.