Timer.java

/*
 * Copyright (C) 2013 The Android Open Source Project
 *
 * 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 com.google.android.glass.sample.timer;

import android.os.SystemClock;

/**
 * Model holding the Timer state.
 */
public class Timer {

    /**
     * Interface to listen for changes on the {@link Timer}.
     */
    public interface TimerListener {
        /** Timer has started. */
        public void onStart();
        /** Timer has been paused. */
        public void onPause();
        /** Timer has been reset */
        public void onReset();
    }

    private long mDurationMillis;
    private long mStartTimeMillis;
    private long mPauseTimeMillis;

    private TimerListener mListener;

    public Timer() {
        this(0);
    }

    public Timer(long durationMillis) {
        setDurationMillis(durationMillis);
    }

    /**
     * Sets the timer's duration in milliseconds.
     */
    public void setDurationMillis(long durationMillis) {
        mDurationMillis = durationMillis;
        if (mListener != null) {
            mListener.onReset();
        }
    }

    /**
     * Gets the timer's duration in milliseconds.
     */
    public long getDurationMillis() {
        return mDurationMillis;
    }

    /**
     * Returns whether or not the timer is running.
     */
    public boolean isRunning() {
        return mStartTimeMillis > 0 && mPauseTimeMillis == 0;
    }

    /**
     * Returns whether or not the timer has been started.
     */
    public boolean isStarted() {
        return mStartTimeMillis > 0;
    }

    /**
     * Gets the remaining time in milliseconds.
     */
    public long getRemainingTimeMillis() {
        long remainingTime = mDurationMillis;

        if (mPauseTimeMillis != 0) {
            remainingTime -= mPauseTimeMillis - mStartTimeMillis;
        } else if (mStartTimeMillis != 0) {
            remainingTime -= getElapsedRealtime() - mStartTimeMillis;
        }

        return remainingTime;
    }

    /**
     * Starts the timer.
     */
    public void start() {
        long elapsedTime = mPauseTimeMillis - mStartTimeMillis;

        mStartTimeMillis = getElapsedRealtime() - elapsedTime;
        mPauseTimeMillis = 0;
        if (mListener != null) {
            mListener.onStart();
        }
    }

    /**
     * Pauses the timer.
     */
    public void pause() {
        if (isStarted()) {
            mPauseTimeMillis = getElapsedRealtime();
            if (mListener != null) {
                mListener.onPause();
            }
        }
    }

    /**
     * Resets the timer.
     */
    public void reset() {
        mStartTimeMillis = 0;
        mPauseTimeMillis = 0;
        if (mListener != null) {
            mListener.onPause();
            mListener.onReset();
        }
    }

    /**
     * Sets a {@link TimerListener}.
     */
    public void setListener(TimerListener listener) {
        mListener = listener;
    }

    /**
     * Returns {@link SystemClock.elapsedRealtime()}, overridable for testing.
     */
    protected long getElapsedRealtime() {
        return SystemClock.elapsedRealtime();
    }
}