/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you 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.apache.beam.sdk.metrics;

import com.google.common.base.Joiner;
import org.apache.beam.sdk.annotations.Experimental;
import org.apache.beam.sdk.annotations.Experimental.Kind;

/**
 * Standard {@link org.apache.beam.sdk.io.Source} Metrics.
 */
@Experimental(Kind.METRICS)
public class SourceMetrics {

  private static final String SOURCE_NAMESPACE = "source";
  private static final String SOURCE_SPLITS_NAMESPACE = "source.splits";
  private static final String SEPARATOR = ".";

  private static final String ELEMENTS_READ = "elements_read";
  private static final String BYTES_READ = "bytes_read";
  private static final String BACKLOG_BYTES = "backlog_bytes";
  private static final String BACKLOG_ELEMENTS = "backlog_elements";

  private static final Counter ELEMENTS_READ_COUNTER =
      Metrics.counter(SOURCE_NAMESPACE, ELEMENTS_READ);
  private static final Counter BYTES_READ_COUNTER =
      Metrics.counter(SOURCE_NAMESPACE, BYTES_READ);
  private static final Gauge BACKLOG_BYTES_GAUGE =
      Metrics.gauge(SOURCE_NAMESPACE, BACKLOG_BYTES);
  private static final Gauge BACKLOG_ELEMENTS_GAUGE =
      Metrics.gauge(SOURCE_NAMESPACE, BACKLOG_ELEMENTS);

  /**
   * Counter of elements read by a source.
   */
  public static Counter elementsRead() {
    return ELEMENTS_READ_COUNTER;
  }

  /**
   * Counter of elements read by a source split.
   *
   * <p>Should only be used when there is a small, fixed set of split IDs so as not to overload
   * metrics backends.</p>
   */
  public static Counter elementsReadBySplit(String splitId) {
    return Metrics.counter(SOURCE_SPLITS_NAMESPACE, renderName(splitId, ELEMENTS_READ));
  }

  /**
   * Counter of bytes read by a source.
   */
  public static Counter bytesRead() {
    return BYTES_READ_COUNTER;
  }

  /**
   * Counter of bytes read by a source split.
   *
   * <p>Should only be used when there is a small, fixed set of split IDs so as not to overload
   * metrics backends.</p>
   */
  public static Counter bytesReadBySplit(String splitId) {
    return Metrics.counter(SOURCE_SPLITS_NAMESPACE, renderName(splitId, BYTES_READ));
  }

  /**
   * Gauge for source backlog in bytes.
   */
  public static Gauge backlogBytes() {
    return BACKLOG_BYTES_GAUGE;
  }

  /**
   * Gauge for source split backlog in bytes.
   *
   * <p>Should only be used when there is a small, fixed set of split IDs so as not to overload
   * metrics backends.</p>
   */
  public static Gauge backlogBytesOfSplit(String splitId) {
    return Metrics.gauge(SOURCE_SPLITS_NAMESPACE, renderName(splitId, BACKLOG_BYTES));
  }

  /**
   * Gauge for source backlog in elements.
   */
  public static Gauge backlogElements() {
    return BACKLOG_ELEMENTS_GAUGE;
  }

  /**
   * Gauge for source split backlog in elements.
   *
   * <p>Should only be used when there is a small, fixed set of split IDs so as not to overload
   * metrics backends.</p>
   */
  public static Gauge backlogElementsOfSplit(String splitId) {
    return Metrics.gauge(SOURCE_SPLITS_NAMESPACE, renderName(splitId, BACKLOG_ELEMENTS));
  }

  private static String renderName(String... nameParts) {
    return Joiner.on(SEPARATOR).join(nameParts);
  }
}