const opentelemetry = require('@opentelemetry/api');
const { MeterProvider } = require('@opentelemetry/sdk-metrics');

// To create an instrument, you first need to initialize the Meter provider.
// NOTE: The default OpenTelemetry meter provider does not record any metric instruments.
//       Registering a working meter provider allows the API methods to record instruments.
opentelemetry.metrics.setGlobalMeterProvider(new MeterProvider());

// To record a metric event, we used the global singleton meter to create an instrument.
const counter = opentelemetry.metrics.getMeter('default').createCounter('foo');

// record a metric event.
counter.add(1, { attributeKey: 'attribute-value' });

// Creating an async instrument, similar to synchronous instruments
const observableCounter = opentelemetry.metrics.getMeter('default')
  .createObservableCounter('observable-counter');

// Register a single-instrument callback to the async instrument.
observableCounter.addCallback(async (observableResult) => {
  // ... do async stuff
  observableResult.observe(1, { attributeKey: 'attribute-value' });
});

// Register a multi-instrument callback and associate it with a set of async instruments.
opentelemetry.metrics.getMeter('default')
  .addBatchObservableCallback(batchObservableCallback, [ observableCounter ]);
async function batchObservableCallback(batchObservableResult) {
  // ... do async stuff
  batchObservableResult.observe(observableCounter, 1, { attributeKey: 'attribute-value' });
}

const meterProvider = new MeterProvider({
  views: [
    // override the bucket boundaries on `my.histogram` to [0, 50, 100]
    {
      aggregation: {
        type: AggregationType.EXPLICIT_BUCKET_HISTOGRAM,
        options: {
          boundaries: [0, 50, 100]
        }
      },
      instrumentName: 'my.histogram'
    },
    // rename 'my.counter' to 'my.renamed.counter'
    { name: 'my.renamed.counter', instrumentName: 'my.counter'}
  ]
})