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      1 /*
      2  * Copyright (C) 2015 The Android Open Source Project
      3  *
      4  * Licensed under the Apache License, Version 2.0 (the "License");
      5  * you may not use this file except in compliance with the License.
      6  * You may obtain a copy of the License at
      7  *
      8  *      http://www.apache.org/licenses/LICENSE-2.0
      9  *
     10  * Unless required by applicable law or agreed to in writing, software
     11  * distributed under the License is distributed on an "AS IS" BASIS,
     12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
     13  * See the License for the specific language governing permissions and
     14  * limitations under the License.
     15  */
     16 
     17 package com.android.deskclock.data;
     18 
     19 import android.os.SystemClock;
     20 
     21 import static com.android.deskclock.data.Stopwatch.State.PAUSED;
     22 import static com.android.deskclock.data.Stopwatch.State.RESET;
     23 import static com.android.deskclock.data.Stopwatch.State.RUNNING;
     24 
     25 /**
     26  * A read-only domain object representing a stopwatch.
     27  */
     28 public final class Stopwatch {
     29 
     30     public enum State { RESET, RUNNING, PAUSED }
     31 
     32     /** The single, immutable instance of a reset stopwatch. */
     33     private static final Stopwatch RESET_STOPWATCH = new Stopwatch(RESET, Long.MIN_VALUE, 0);
     34 
     35     /** Current state of this stopwatch. */
     36     private final State mState;
     37 
     38     /** Elapsed time in ms the stopwatch was last started; {@link Long#MIN_VALUE} if not running. */
     39     private final long mLastStartTime;
     40 
     41     /** Elapsed time in ms this stopwatch has accumulated while running. */
     42     private final long mAccumulatedTime;
     43 
     44     Stopwatch(State state, long lastStartTime, long accumulatedTime) {
     45         mState = state;
     46         mLastStartTime = lastStartTime;
     47         mAccumulatedTime = accumulatedTime;
     48     }
     49 
     50     public State getState() { return mState; }
     51     public long getLastStartTime() { return mLastStartTime; }
     52     public boolean isReset() { return mState == RESET; }
     53     public boolean isPaused() { return mState == PAUSED; }
     54     public boolean isRunning() { return mState == RUNNING; }
     55 
     56     /**
     57      * @return the total amount of time accumulated up to this moment
     58      */
     59     public long getTotalTime() {
     60         if (mState != RUNNING) {
     61             return mAccumulatedTime;
     62         }
     63 
     64         // In practice, "now" can be any value due to device reboots. When the real-time clock
     65         // is reset, there is no more guarantee that "now" falls after the last start time. To
     66         // ensure the stopwatch is monotonically increasing, normalize negative time segments to 0,
     67         final long timeSinceStart = now() - mLastStartTime;
     68         return mAccumulatedTime + Math.max(0, timeSinceStart);
     69     }
     70 
     71     /**
     72      * @return the amount of time accumulated up to the last time the stopwatch was started
     73      */
     74     long getAccumulatedTime() {
     75         return mAccumulatedTime;
     76     }
     77 
     78     /**
     79      * @return a copy of this stopwatch that is running
     80      */
     81     Stopwatch start() {
     82         if (mState == RUNNING) {
     83             return this;
     84         }
     85 
     86         return new Stopwatch(RUNNING, now(), getTotalTime());
     87     }
     88 
     89     /**
     90      * @return a copy of this stopwatch that is paused
     91      */
     92     Stopwatch pause() {
     93         if (mState != RUNNING) {
     94             return this;
     95         }
     96 
     97         return new Stopwatch(PAUSED, Long.MIN_VALUE, getTotalTime());
     98     }
     99 
    100     /**
    101      * @return a copy of this stopwatch that is reset
    102      */
    103     Stopwatch reset() {
    104         return RESET_STOPWATCH;
    105     }
    106 
    107     private static long now() {
    108         return SystemClock.elapsedRealtime();
    109     }
    110 }