/*
 * Timer.java November 2012
 *
 * Copyright (C) 2012, Niall Gallagher <niallg@users.sf.net>
 *
 * 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.simpleframework.http.core;

import static java.lang.System.currentTimeMillis;
import static java.util.concurrent.TimeUnit.MILLISECONDS;

import java.util.concurrent.TimeUnit;

/**
 * The <code>Timer<code> object is used to set the time a specific
 * event occurred at. The time can be set only once from that point 
 * on all attempts to set the time are ignored. This makes this 
 * timer useful when there is a desire to record when a certain
 * scenario was first encountered, for example when a request is
 * first read from the underlying transport.
 * 
 * @author Niall Gallagher
 */
class Timer {

    /**
     * This is the time unit that this timer provides the time in.
     */
    private TimeUnit unit;

    /**
     * This is the time in milliseconds used to record the event.
     */
    private volatile long time;

    /**
     * Constructor for the <code>Timer</code> object. This is used to record
     * when a specific event occurs. The provided time unit is used to determine
     * how the time is retrieved.
     * 
     * @param unit
     *            this time unit this timer will be using
     */
    public Timer(TimeUnit unit) {
        this.unit = unit;
        this.time = -1L;
    }

    /**
     * This is used to determine if the timer has been set. If the
     * <code>set</code> method has been called on this instance before then this
     * will return true, otherwise false.
     * 
     * @return this returns true if the timer has been set
     */
    public boolean isSet() {
        return this.time > 0;
    }

    /**
     * This is used to set the time for a specific event. Invoking this method
     * multiple times will have no effect as the time is set for the first
     * invocation only. Setting the time in this manner enables start times to
     * be recorded effectively.
     */
    public void set() {
        if (this.time < 0) {
            this.time = currentTimeMillis();
        }
    }

    /**
     * This is used to get the time for a specific event. The time returned by
     * this method is given in the time unit specified on construction of the
     * instance.
     * 
     * @return this returns the time recorded by the timer
     */
    public long get() {
        return this.unit.convert(this.time, MILLISECONDS);
    }
}