/*
    * Copyright 2021 TiKV Project Authors.
    *
    * 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 org.tikv.common;
  
  import io.prometheus.client.exporter.HTTPServer;
  import io.prometheus.client.hotspot.DefaultExports;
  import org.slf4j.Logger;
  import org.slf4j.LoggerFactory;
  
  public class MetricsServer {
    private static final Logger logger = LoggerFactory.getLogger(MetricsServer.class);
  
    private static MetricsServer METRICS_SERVER_INSTANCE = null;
    private static int metricsServerRefCount = 0;
  
    private final int port;
    private final HTTPServer server;
  
    public static MetricsServer getInstance(TiConfiguration conf) {
      if (!conf.isMetricsEnable()) {
        return null;
      }
  
      synchronized (MetricsServer.class) {
        int port = conf.getMetricsPort();
        if (METRICS_SERVER_INSTANCE != null) {
          if (port != METRICS_SERVER_INSTANCE.port) {
            throw new IllegalArgumentException(
                String.format(
                    "Do dot support multiple tikv.metrics.port, which are %d and %d",
                    port, METRICS_SERVER_INSTANCE.port));
          }
        } else {
          METRICS_SERVER_INSTANCE = new MetricsServer(port);
        }
        metricsServerRefCount += 1;
        return METRICS_SERVER_INSTANCE;
      }
    }
  
    private MetricsServer(int port) {
      try {
        this.port = port;
        DefaultExports.initialize();
        this.server = new HTTPServer(port, true);
        logger.info("http server is up " + this.server.getPort());
      } catch (Exception e) {
        logger.error("http server not up");
        throw new RuntimeException(e);
      }
    }
  
    public void close() {
      synchronized (MetricsServer.class) {
        if (metricsServerRefCount == 1) {
          if (server != null) {
            server.stop();
            logger.info("Metrics server on " + server.getPort() + " is stopped");
          }
          METRICS_SERVER_INSTANCE = null;
        }
  
        if (metricsServerRefCount >= 1) {
          metricsServerRefCount -= 1;
        }
      }
    }
  }