/*
 * Copyright (C) 2008 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 alt.android.os;

import android.os.Handler;
import android.os.Message;
import android.os.SystemClock;

/**
 * Schedule a countdown until a time in the future, with regular notifications on intervals along
 * the way.
 * 
 * Example of showing a 30 second countdown in a text field:
 * 
 * <pre class="prettyprint">
 * new CountdownTimer(30000, 1000) {
 * 
 *   public void onTick(long millisUntilFinished) {
 *     mTextField.setText("seconds remaining: " + millisUntilFinished / 1000);
 *   }
 * 
 *   public void onFinish() {
 *     mTextField.setText("done!");
 *   }
 * }.start();
 * </pre>
 * 
 * The calls to {@link #onTick(long)} are synchronized to this object so that one call to
 * {@link #onTick(long)} won't ever occur before the previous callback is complete. This is only
 * relevant when the implementation of {@link #onTick(long)} takes an amount of time to execute that
 * is significant compared to the countdown interval.
 */
// This modified implementation is required for all devices older Android 5.0
public abstract class CountDownTimer {

  /**
   * Millis since epoch when alarm should stop.
   */
  private final long mMillisInFuture;

  /**
   * The interval in millis that the user receives callbacks
   */
  private final long mCountdownInterval;

  private long mStopTimeInFuture;

  private boolean mCancelled = false;

  /**
   * @param millisInFuture The number of millis in the future from the call to {@link #start()}
   *        until the countdown is done and {@link #onFinish()} is called.
   * @param countDownInterval The interval along the way to receive {@link #onTick(long)} callbacks.
   */
  public CountDownTimer(long millisInFuture, long countDownInterval) {
    mMillisInFuture = millisInFuture;
    mCountdownInterval = countDownInterval;
  }

  /**
   * Cancel the countdown.
   * 
   * Do not call it from inside CountDownTimer threads
   */
  public final void cancel() {
    mHandler.removeMessages(MSG);
    mCancelled = true;
  }

  /**
   * Start the countdown.
   */
  public synchronized final CountDownTimer start() {
    if (mMillisInFuture <= 0) {
      onFinish();
      return this;
    }
    mStopTimeInFuture = SystemClock.elapsedRealtime() + mMillisInFuture;
    mHandler.sendMessage(mHandler.obtainMessage(MSG));
    mCancelled = false;
    return this;
  }


  /**
   * Callback fired on regular interval.
   * 
   * @param millisUntilFinished The amount of time until finished.
   */
  public abstract void onTick(long millisUntilFinished);

  /**
   * Callback fired when the time is up.
   */
  public abstract void onFinish();


  private static final int MSG = 1;


  // handles counting down
  private Handler mHandler = new Handler() {

    @Override
    public void handleMessage(Message msg) {

      synchronized (CountDownTimer.this) {
        final long millisLeft = mStopTimeInFuture - SystemClock.elapsedRealtime();

        if (millisLeft <= 0) {
          onFinish();
        } else if (millisLeft < mCountdownInterval) {
          // no tick, just delay until done
          sendMessageDelayed(obtainMessage(MSG), millisLeft);
        } else {
          long lastTickStart = SystemClock.elapsedRealtime();
          onTick(millisLeft);

          // take into account user's onTick taking time to execute
          long delay = lastTickStart + mCountdownInterval - SystemClock.elapsedRealtime();

          // special case: user's onTick took more than interval to
          // complete, skip to next interval
          while (delay < 0)
            delay += mCountdownInterval;

          if (!mCancelled) {
            sendMessageDelayed(obtainMessage(MSG), delay);
          }
        }
      }
    }
  };
}