/*
 * Copyright (C) 2013 Brett Wooldridge
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package com.zaxxer.hikari.metrics.prometheus;

import com.zaxxer.hikari.metrics.IMetricsTracker;
import io.prometheus.client.CollectorRegistry;
import io.prometheus.client.Counter;
import io.prometheus.client.Histogram;

Alternative Prometheus metrics tracker using a Histogram instead of Summary
 This is an alternative metrics tracker that doesn't use a Summary. Summaries require heavy locks that might cause performance issues. Source: https://github.com/prometheus/client_java/issues/328 
See Also:
PrometheusMetricsTracker/**
 * Alternative Prometheus metrics tracker using a Histogram instead of Summary
 * <p>
 * This is an alternative metrics tracker that doesn't use a {@link io.prometheus.client.Summary}. Summaries require
 * heavy locks that might cause performance issues. Source: https://github.com/prometheus/client_java/issues/328
 *
 * @see PrometheusMetricsTracker
 */
class PrometheusHistogramMetricsTracker implements IMetricsTracker
{
   private static final Counter CONNECTION_TIMEOUT_COUNTER = Counter.build()
      .name("hikaricp_connection_timeout_total")
      .labelNames("pool")
      .help("Connection timeout total count")
      .create();

   private static final Histogram ELAPSED_ACQUIRED_HISTOGRAM =
      registerHistogram("hikaricp_connection_acquired_nanos", "Connection acquired time (ns)", 1_000);

   private static final Histogram ELAPSED_BORROWED_HISTOGRAM =
      registerHistogram("hikaricp_connection_usage_millis", "Connection usage (ms)", 1);

   private static final Histogram ELAPSED_CREATION_HISTOGRAM =
      registerHistogram("hikaricp_connection_creation_millis", "Connection creation (ms)", 1);

   private final Counter.Child connectionTimeoutCounterChild;

   private static Histogram registerHistogram(String name, String help, double bucketStart) {
      return Histogram.build()
         .name(name)
         .labelNames("pool")
         .help(help)
         .exponentialBuckets(bucketStart, 2.0, 11)
         .create();
   }

   private final Histogram.Child elapsedAcquiredHistogramChild;
   private final Histogram.Child elapsedBorrowedHistogramChild;
   private final Histogram.Child elapsedCreationHistogramChild;

   PrometheusHistogramMetricsTracker(String poolName, CollectorRegistry collectorRegistry) {
      registerMetrics(collectorRegistry);
      this.connectionTimeoutCounterChild = CONNECTION_TIMEOUT_COUNTER.labels(poolName);
      this.elapsedAcquiredHistogramChild = ELAPSED_ACQUIRED_HISTOGRAM.labels(poolName);
      this.elapsedBorrowedHistogramChild = ELAPSED_BORROWED_HISTOGRAM.labels(poolName);
      this.elapsedCreationHistogramChild = ELAPSED_CREATION_HISTOGRAM.labels(poolName);
   }

   private void registerMetrics(CollectorRegistry collectorRegistry) {
      CONNECTION_TIMEOUT_COUNTER.register(collectorRegistry);
      ELAPSED_ACQUIRED_HISTOGRAM.register(collectorRegistry);
      ELAPSED_BORROWED_HISTOGRAM.register(collectorRegistry);
      ELAPSED_CREATION_HISTOGRAM.register(collectorRegistry);
   }

   @Override
   public void recordConnectionAcquiredNanos(long elapsedAcquiredNanos) {
      elapsedAcquiredHistogramChild.observe(elapsedAcquiredNanos);
   }

   @Override
   public void recordConnectionUsageMillis(long elapsedBorrowedMillis) {
      elapsedBorrowedHistogramChild.observe(elapsedBorrowedMillis);
   }

   @Override
   public void recordConnectionCreatedMillis(long connectionCreatedMillis) {
      elapsedCreationHistogramChild.observe(connectionCreatedMillis);
   }

   @Override
   public void recordConnectionTimeout() {
      connectionTimeoutCounterChild.inc();
   }
}