include/tscpp/api/Stat.h

/**
  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.
 */
/**
 * @file Stat.h
 */

#pragma once

#include "ts/apidefs.h"
#include "tscpp/api/noncopyable.h"

#include <cstdint>
#include <string>

namespace atscppapi
{
/**
 * @brief A Stat is an atomic variable that can be used to store counters, averages, time averages, or summations.
 *
 * All stats are exposed through the traffic_ctl program included with Apache Traffic Server. Additionally,
 * if you've enabled HttpStats all Stats you define will be displayed there. Stats can be read via
 * traffic_ctl metric get stat_name.
 *
 * Stats are very easy to use, here is a simple example of how you can create a counter and increment its
 * value:
 * \code
 *  Stat stat;
 *  stat.init("stat_name");
    stat.inc();
 * \endcode
 *
 * A full example is available in examples/stat_example/.
 */
class Stat : noncopyable
{
public:
  /**
   * The available Stat types.
   */
  enum SyncType {
    SYNC_SUM = 0, /**< The stat will sum all values from a stat.inc(VAL) */
    SYNC_COUNT,   /**< The stat will count all calls to stat.inc(VAL) */
    SYNC_AVG,     /**< The stat will keep an average after call calls to stat.inc(VAL) */
    SYNC_TIMEAVG  /**< The stat will keep a time average of all calls to stat.inc(VAL) */
  };

  Stat();
  ~Stat();

  /**
   * You must initialize your Stat with a call to this init() method.
   *
   * @param name The string name of the stat, this will be visible via traffic_ctl, or through http stats.
   * @param type The SyncType of the Stat, this decides how TrafficServer will treat your inputs. The default
   *   value is SYNC_COUNT.
   * @param persistent This determines if your Stats will persist, the default value is false.
   * @return True if the stat was successfully created and false otherwise.
   *
   * @see SyncType
   */
  bool init(const std::string &name, Stat::SyncType type = SYNC_COUNT, bool persistent = false);

  /**
   * This method allows you to increment a stat by a certain amount.
   * @param amount the amount to increment the stat by the default value is 1.
   */
  void increment(int64_t amount = 1);

  /**
   * This method allows you to decrement a stat by a certain amount.
   * @param amount the amount to decrement the stat by the default value is 1.
   */
  void decrement(int64_t amount = 1);

  /**
   * This method returns the current value of the stat.
   * @return The value of the stat.
   */
  int64_t get() const;

  /** This method sets the value of the stat.
   * @param value the value to set the stat to.
   */
  void set(int64_t value);

private:
  int stat_id_ = TS_ERROR; /**< The internal stat ID */
};

} // namespace atscppapi