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Metrics is a light-weight Java library to measure the behavior of critical components in a production environment.
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/* Copyright (C) 2017 Maurits van der Schee
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in all
 * copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 * SOFTWARE.
 */
package com.tqdev.metrics.core;

import static java.util.Collections.emptySet;

import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.atomic.LongAdder;

/**
 * The Class MetricRegistry provides access to all metrics that are tracked.
 */
public class MetricRegistry {

	/**
	 * The values in the metric registry have a type and a key and are of type
	 * LongAdder or Gauge.
	 */
	protected volatile ConcurrentHashMap> values;

	/**
	 * Metrics enabled status.
	 */
	protected boolean enabled;

	/**
	 * Instantiates a new metric registry.
	 */
	public MetricRegistry() {
		values = new ConcurrentHashMap<>();
		enabled = true;
	}

	/**
	 * Instantiates a new metric registry.
	 */
	public MetricRegistry(boolean enabled) {
		values = new ConcurrentHashMap<>();
		this.enabled = enabled;
	}

	/**
	 * Resets the metric registry.
	 */
	public void reset() {
		for (Map.Entry> entry : values.entrySet()) {
			entry.getValue().clear();
		}
	}

	/**
	 * Checks if metrics are enabled.
	 *
	 * @return true, if metrics are enabled
	 */
	public boolean isEnabled() {
		return enabled;
	}

	/**
	 * Sets the metrics enabled status.
	 *
	 * @param enabled
	 *            the new metrics enabled status
	 */
	public void setEnabled(boolean enabled) {
		this.enabled = enabled;
	}

	/**
	 * Increment a metric for a given type and key.
	 *
	 * @param type
	 *            the type
	 * @param key
	 *            the key
	 * @return true, if successful
	 */
	public boolean increment(String type, String key) {
		Object o = values.computeIfAbsent(type, t -> new ConcurrentHashMap<>()).computeIfAbsent(key,
				k -> new LongAdder());
		if (o instanceof LongAdder) {
			((LongAdder) o).increment();
			return true;
		}
		return false;
	}

	/**
	 * Decrement a metric for a given type and key.
	 *
	 * @param type
	 *            the type
	 * @param key
	 *            the key
	 * @return true, if successful
	 */
	public boolean decrement(String type, String key) {
		Object o = values.computeIfAbsent(type, t -> new ConcurrentHashMap<>()).computeIfAbsent(key,
				k -> new LongAdder());
		if (o instanceof LongAdder) {
			((LongAdder) o).decrement();
			return true;
		}
		return false;
	}

	/**
	 * Adds a value to a metric for a given type and key.
	 *
	 * @param type
	 *            the type
	 * @param key
	 *            the key
	 * @param value
	 *            the value
	 * @return true, if successful
	 */
	public boolean add(String type, String key, long value) {
		Object o = values.computeIfAbsent(type, t -> new ConcurrentHashMap<>()).computeIfAbsent(key,
				k -> new LongAdder());
		if (o instanceof LongAdder) {
			((LongAdder) o).add(value);
			return true;
		}
		return false;
	}

	/**
	 * Sets the value of a metric for a given type and key.
	 *
	 * @param type
	 *            the type
	 * @param key
	 *            the key
	 * @param value
	 *            the value
	 */
	public void set(String type, String key, long value) {
		LongAdder adder = new LongAdder();
		adder.add(value);
		values.computeIfAbsent(type, t -> new ConcurrentHashMap<>()).put(key, adder);
	}

	/**
	 * Sets the Gauge (measure function) of a metric for a given type and key.
	 *
	 * @param type
	 *            the type
	 * @param key
	 *            the key
	 * @param value
	 *            the value
	 */
	public void set(String type, String key, Gauge value) {
		values.computeIfAbsent(type, t -> new ConcurrentHashMap<>()).put(key, value);
	}

	/**
	 * Gets the (unique) set of types of all registered metrics.
	 *
	 * @return the types
	 */
	public Iterable getTypes() {
		return values.keySet();
	}

	/**
	 * Gets the (unique) set of keys of all registered metrics of a given type.
	 *
	 * @param type
	 *            the type
	 * @return the keys
	 */
	public Iterable getKeys(String type) {
		ConcurrentHashMap map = values.get(type);
		if (map == null) {
			return emptySet();
		}
		return map.keySet();
	}

	/**
	 * Checks for existence of a metric for a given type and key.
	 *
	 * @param type
	 *            the type
	 * @param key
	 *            the key
	 * @return true, if successful
	 */
	public boolean has(String type, String key) {
		ConcurrentHashMap map = values.get(type);
		if (map == null) {
			return false;
		}
		return map.containsKey(key);
	}

	/**
	 * Checks for existence of a metric for a given type.
	 *
	 * @param type
	 *            the type
	 * @return true, if successful
	 */
	public boolean hasType(String type) {
		return values.containsKey(type);
	}

	/**
	 * Gets the value of a metric for a given type and key.
	 *
	 * @param type
	 *            the type
	 * @param key
	 *            the key
	 * @return the long
	 */
	public long get(String type, String key) {
		ConcurrentHashMap map = values.get(type);
		if (map != null) {
			Object o = map.get(key);
			if (o instanceof LongAdder) {
				return ((LongAdder) o).sum();
			} else if (o instanceof Gauge) {
				return ((Gauge) o).measure();
			}
		}
		return 0;
	}

	/**
	 * Gets the elapsed time in nanoseconds (from an arbitrary point in time,
	 * probably JVM start).
	 *
	 * @return the time
	 */
	public long getNanos() {
		return System.nanoTime();
	}

	/**
	 * Gets the current (wall clock) time in milliseconds (milliseconds elapsed
	 * since epoch).
	 *
	 * @return the time
	 */
	public long getMillis() {
		return System.currentTimeMillis();
	}

	// singleton pattern

	/** The single instance of Storage. */
	private static final MetricRegistry instance = new MetricRegistry();

	/**
	 * Gets the single instance of the Storage.
	 *
	 * @return single instance of Storage
	 */
	public static MetricRegistry getInstance() {
		return instance;
	}

}