/*
 * Copyright (C) 2008 The Guava 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.glassfish.jersey.internal.guava;

import java.util.concurrent.TimeUnit;

import static org.glassfish.jersey.internal.guava.Preconditions.checkNotNull;
import static org.glassfish.jersey.internal.guava.Preconditions.checkState;

import static java.util.concurrent.TimeUnit.DAYS;
import static java.util.concurrent.TimeUnit.HOURS;
import static java.util.concurrent.TimeUnit.MICROSECONDS;
import static java.util.concurrent.TimeUnit.MILLISECONDS;
import static java.util.concurrent.TimeUnit.MINUTES;
import static java.util.concurrent.TimeUnit.NANOSECONDS;
import static java.util.concurrent.TimeUnit.SECONDS;

An object that measures elapsed time in nanoseconds. It is useful to measure elapsed time using this class instead of direct calls to System.nanoTime for a few reasons: 


An alternate time source can be substituted, for testing or performance
reasons.
As documented by nanoTime, the value returned has no absolute meaning, and can only be interpreted as relative to another timestamp returned by nanoTime at a different time. Stopwatch is a more effective abstraction because it exposes only these relative values, not the absolute ones. 

Basic usage:
 Stopwatch stopwatch = Stopwatch.createStarted(); doSomething(); stopwatch.stop(); // optional long millis = stopwatch.elapsed(MILLISECONDS); log.info("time: " + stopwatch); // formatted string like "12.3 ms"

Stopwatch methods are not idempotent; it is an error to start or stop a
stopwatch that is already in the desired state.

When testing code that uses this class, use createUnstarted(Ticker) or createStarted(Ticker) to supply a fake or mock ticker.  This allows you to
simulate any valid behavior of the stopwatch.

Note: This class is not thread-safe.
Author:
Kevin Bourrillion
Since:
10.0/**
 * An object that measures elapsed time in nanoseconds. It is useful to measure
 * elapsed time using this class instead of direct calls to {@link
 * System#nanoTime} for a few reasons:
 * <p>
 * <ul>
 * <li>An alternate time source can be substituted, for testing or performance
 * reasons.
 * <li>As documented by {@code nanoTime}, the value returned has no absolute
 * meaning, and can only be interpreted as relative to another timestamp
 * returned by {@code nanoTime} at a different time. {@code Stopwatch} is a
 * more effective abstraction because it exposes only these relative values,
 * not the absolute ones.
 * </ul>
 * <p>
 * <p>Basic usage:
 * <pre>
 *   Stopwatch stopwatch = Stopwatch.{@link #createStarted createStarted}();
 *   doSomething();
 *   stopwatch.{@link #stop stop}(); // optional
 *
 *   long millis = stopwatch.elapsed(MILLISECONDS);
 *
 *   log.info("time: " + stopwatch); // formatted string like "12.3 ms"</pre>
 * <p>
 * <p>Stopwatch methods are not idempotent; it is an error to start or stop a
 * stopwatch that is already in the desired state.
 * <p>
 * <p>When testing code that uses this class, use
 * {@link #createUnstarted(Ticker)} or {@link #createStarted(Ticker)} to
 * supply a fake or mock ticker.
 * <!-- TODO(kevinb): restore the "such as" --> This allows you to
 * simulate any valid behavior of the stopwatch.
 * <p>
 * <p><b>Note:</b> This class is not thread-safe.
 *
 * @author Kevin Bourrillion
 * @since 10.0
 */
public final class Stopwatch {
    private final Ticker ticker;
    private boolean isRunning;
    private long startTick;

    
Creates (but does not start) a new stopwatch using System.nanoTime as its time source. 
Deprecated:
Use createUnstarted() instead./**
     * Creates (but does not start) a new stopwatch using {@link System#nanoTime}
     * as its time source.
     *
     * @deprecated Use {@link Stopwatch#createUnstarted()} instead.
     */
    @Deprecated
    private Stopwatch() {
        this(Ticker.systemTicker());
    }

    
Creates (but does not start) a new stopwatch, using the specified time
source.
Deprecated:
Use createUnstarted(Ticker) instead./**
     * Creates (but does not start) a new stopwatch, using the specified time
     * source.
     *
     * @deprecated Use {@link Stopwatch#createUnstarted(Ticker)} instead.
     */
    @Deprecated
    private Stopwatch(Ticker ticker) {
        this.ticker = Preconditions.checkNotNull(ticker, "ticker");
    }

    
Creates (but does not start) a new stopwatch using System.nanoTime as its time source. 
Since:
15.0/**
     * Creates (but does not start) a new stopwatch using {@link System#nanoTime}
     * as its time source.
     *
     * @since 15.0
     */
    public static Stopwatch createUnstarted() {
        return new Stopwatch();
    }

    private static TimeUnit chooseUnit(long nanos) {
        if (DAYS.convert(nanos, NANOSECONDS) > 0) {
            return DAYS;
        }
        if (HOURS.convert(nanos, NANOSECONDS) > 0) {
            return HOURS;
        }
        if (MINUTES.convert(nanos, NANOSECONDS) > 0) {
            return MINUTES;
        }
        if (SECONDS.convert(nanos, NANOSECONDS) > 0) {
            return SECONDS;
        }
        if (MILLISECONDS.convert(nanos, NANOSECONDS) > 0) {
            return MILLISECONDS;
        }
        if (MICROSECONDS.convert(nanos, NANOSECONDS) > 0) {
            return MICROSECONDS;
        }
        return NANOSECONDS;
    }

    private static String abbreviate(TimeUnit unit) {
        switch (unit) {
            case NANOSECONDS:
                return "ns";
            case MICROSECONDS:
                return "\u03bcs"; // μs
            case MILLISECONDS:
                return "ms";
            case SECONDS:
                return "s";
            case MINUTES:
                return "min";
            case HOURS:
                return "h";
            case DAYS:
                return "d";
            default:
                throw new AssertionError();
        }
    }

    
Starts the stopwatch.
Throws:
IllegalStateException – if the stopwatch is already running.
Returns:
this Stopwatch instance/**
     * Starts the stopwatch.
     *
     * @return this {@code Stopwatch} instance
     * @throws IllegalStateException if the stopwatch is already running.
     */
    public Stopwatch start() {
        Preconditions.checkState(!isRunning, "This stopwatch is already running.");
        isRunning = true;
        startTick = ticker.read();
        return this;
    }

    private long elapsedNanos() {
        return isRunning ? ticker.read() - startTick : 0L;
    }

    
Returns a string representation of the current elapsed time.
/**
     * Returns a string representation of the current elapsed time.
     */
    @Override
    public String toString() {
        long nanos = elapsedNanos();

        TimeUnit unit = chooseUnit(nanos);
        double value = (double) nanos / NANOSECONDS.convert(1, unit);

        // Too bad this functionality is not exposed as a regular method call
        return String.format("%.4g %s", value, abbreviate(unit));
    }
}