/***
 Copyright (c) 2008-2009 CommonsWare, LLC
 Portions (c) 2009 Google, Inc.

 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.irccloud.android;

import android.os.Handler;
import android.os.Message;
import android.os.Process;

import java.util.concurrent.Callable;
import java.util.concurrent.CancellationException;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.FutureTask;
import java.util.concurrent.LinkedBlockingQueue;
import java.util.concurrent.ThreadFactory;
import java.util.concurrent.ThreadPoolExecutor;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.TimeoutException;
import java.util.concurrent.atomic.AtomicInteger;

/**
 * <p>AsyncTaskEx enables proper and easy use of the UI thread. This class allows to
 * perform background operations and publish results on the UI thread without
 * having to manipulate threads and/or handlers.</p>
 * <p/>
 * <p>An asynchronous task is defined by a computation that runs on a background thread and
 * whose result is published on the UI thread. An asynchronous task is defined by 3 generic
 * types, called <code>Params</code>, <code>Progress</code> and <code>Result</code>,
 * and 4 steps, called <code>begin</code>, <code>doInBackground</code>,
 * <code>processProgress<code> and <code>end</code>.</p>
 * <p/>
 * <h2>Usage</h2>
 * <p>AsyncTaskEx must be subclassed to be used. The subclass will override at least
 * one method ({@link #doInBackground}), and most often will override a
 * second one ({@link #onPostExecute}.)</p>
 * <p/>
 * <p>Here is an example of subclassing:</p>
 * <pre class="prettyprint">
 * private class DownloadFilesTask extends AsyncTaskExEx&lt;URL, Integer, Long&gt; {
 * protected Long doInBackground(URL... urls) {
 * int count = urls.length;
 * long totalSize = 0;
 * for (int i = 0; i < count; i++) {
 * totalSize += Downloader.downloadFile(urls[i]);
 * publishProgress((int) ((i / (float) count) * 100));
 * }
 * return totalSize;
 * }
 * <p/>
 * protected void onProgressUpdate(Integer... progress) {
 * setProgressPercent(progress[0]);
 * }
 * <p/>
 * protected void onPostExecute(Long result) {
 * showDialog("Downloaded " + result + " bytes");
 * }
 * }
 * </pre>
 * <p/>
 * <p>Once created, a task is executed very simply:</p>
 * <pre class="prettyprint">
 * new DownloadFilesTask().execute(url1, url2, url3);
 * </pre>
 * <p/>
 * <h2>AsyncTaskEx's generic types</h2>
 * <p>The three types used by an asynchronous task are the following:</p>
 * <ol>
 * <li><code>Params</code>, the type of the parameters sent to the task upon
 * execution.</li>
 * <li><code>Progress</code>, the type of the progress units published during
 * the background computation.</li>
 * <li><code>Result</code>, the type of the result of the background
 * computation.</li>
 * </ol>
 * <p>Not all types are always used by am asynchronous task. To mark a type as unused,
 * simply use the type {@link Void}:</p>
 * <pre>
 * private class MyTask extends AsyncTaskExEx<Void, Void, Void) { ... }
 * </pre>
 * <p/>
 * <h2>The 4 steps</h2>
 * <p>When an asynchronous task is executed, the task goes through 4 steps:</p>
 * <ol>
 * <li>{@link #onPreExecute()}, invoked on the UI thread immediately after the task
 * is executed. This step is normally used to setup the task, for instance by
 * showing a progress bar in the user interface.</li>
 * <li>{@link #doInBackground}, invoked on the background thread
 * immediately after {@link #onPreExecute()} finishes executing. This step is used
 * to perform background computation that can take a long time. The parameters
 * of the asynchronous task are passed to this step. The result of the computation must
 * be returned by this step and will be passed back to the last step. This step
 * can also use {@link #publishProgress} to publish one or more units
 * of progress. These values are published on the UI thread, in the
 * {@link #onProgressUpdate} step.</li>
 * <li>{@link #onProgressUpdate}, invoked on the UI thread after a
 * call to {@link #publishProgress}. The timing of the execution is
 * undefined. This method is used to display any form of progress in the user
 * interface while the background computation is still executing. For instance,
 * it can be used to animate a progress bar or show logs in a text field.</li>
 * <li>{@link #onPostExecute}, invoked on the UI thread after the background
 * computation finishes. The result of the background computation is passed to
 * this step as a parameter.</li>
 * </ol>
 * <p/>
 * <h2>Threading rules</h2>
 * <p>There are a few threading rules that must be followed for this class to
 * work properly:</p>
 * <ul>
 * <li>The task instance must be created on the UI thread.</li>
 * <li>{@link #execute} must be invoked on the UI thread.</li>
 * <li>Do not call {@link #onPreExecute()}, {@link #onPostExecute},
 * {@link #doInBackground}, {@link #onProgressUpdate} manually.</li>
 * <li>The task can be executed only once (an exception will be thrown if
 * a second execution is attempted.)</li>
 * </ul>
 */
public abstract class AsyncTaskEx<Params, Progress, Result> {
    private static final String LOG_TAG = "AsyncTaskEx";

    private static final int CORE_POOL_SIZE = 5;
    private static final int MAXIMUM_POOL_SIZE = 10;
    private static final int KEEP_ALIVE = 10;

    private static final LinkedBlockingQueue<Runnable> sWorkQueue =
            new LinkedBlockingQueue<Runnable>();

    private static final ThreadFactory sThreadFactory = new ThreadFactory() {
        private final AtomicInteger mCount = new AtomicInteger(1);

        public Thread newThread(Runnable r) {
            return new Thread(r, "AsyncTaskEx #" + mCount.getAndIncrement());
        }
    };

    private static final ThreadPoolExecutor sExecutor = new ThreadPoolExecutor(CORE_POOL_SIZE,
            MAXIMUM_POOL_SIZE, KEEP_ALIVE, TimeUnit.SECONDS, sWorkQueue, sThreadFactory);

    private static final int MESSAGE_POST_RESULT = 0x1;
    private static final int MESSAGE_POST_PROGRESS = 0x2;
    private static final int MESSAGE_POST_CANCEL = 0x3;

    private static final InternalHandler sHandler = new InternalHandler();

    private final WorkerRunnable<Params, Result> mWorker;
    private final FutureTask<Result> mFuture;

    private volatile Status mStatus = Status.PENDING;

    /**
     * Indicates the current status of the task. Each status will be set only once
     * during the lifetime of a task.
     */
    public enum Status {
        /**
         * Indicates that the task has not been executed yet.
         */
        PENDING,
        /**
         * Indicates that the task is running.
         */
        RUNNING,
        /**
         * Indicates that {@link AsyncTaskEx#onPostExecute} has finished.
         */
        FINISHED,
    }

    public static void clearQueue() {
        sWorkQueue.clear();
    }

    /**
     * Creates a new asynchronous task. This constructor must be invoked on the UI thread.
     */
    public AsyncTaskEx() {
        mWorker = new WorkerRunnable<Params, Result>() {
            public Result call() throws Exception {
                Process.setThreadPriority(Process.THREAD_PRIORITY_BACKGROUND);
                return doInBackground(mParams);
            }
        };

        mFuture = new FutureTask<Result>(mWorker) {
            @SuppressWarnings("unchecked")
            @Override
            protected void done() {
                Message message;
                Result result = null;

                try {
                    result = get();
                } catch (InterruptedException e) {
                    android.util.Log.w(LOG_TAG, e);
                } catch (ExecutionException e) {
                    throw new RuntimeException("An error occured while executing doInBackground()",
                            e.getCause());
                } catch (CancellationException e) {
                    message = sHandler.obtainMessage(MESSAGE_POST_CANCEL,
                            new AsyncTaskExResult<Result>(AsyncTaskEx.this, (Result[]) null));
                    message.sendToTarget();
                    return;
                } catch (Throwable t) {
                    throw new RuntimeException("An error occured while executing "
                            + "doInBackground()", t);
                }

                message = sHandler.obtainMessage(MESSAGE_POST_RESULT,
                        new AsyncTaskExResult<Result>(AsyncTaskEx.this, result));
                message.sendToTarget();
            }
        };
    }

    /**
     * Returns the current status of this task.
     *
     * @return The current status.
     */
    public final Status getStatus() {
        return mStatus;
    }

    /**
     * Override this method to perform a computation on a background thread. The
     * specified parameters are the parameters passed to {@link #execute}
     * by the caller of this task.
     * <p/>
     * This method can call {@link #publishProgress} to publish updates
     * on the UI thread.
     *
     * @param params The parameters of the task.
     * @return A result, defined by the subclass of this task.
     * @see #onPreExecute()
     * @see #onPostExecute
     * @see #publishProgress
     */
    protected abstract Result doInBackground(Params... params);

    /**
     * Runs on the UI thread before {@link #doInBackground}.
     *
     * @see #onPostExecute
     * @see #doInBackground
     */
    protected void onPreExecute() {
    }

    /**
     * Runs on the UI thread after {@link #doInBackground}. The
     * specified result is the value returned by {@link #doInBackground}
     * or null if the task was cancelled or an exception occured.
     *
     * @param result The result of the operation computed by {@link #doInBackground}.
     * @see #onPreExecute
     * @see #doInBackground
     */
    protected void onPostExecute(Result result) {
    }

    /**
     * Runs on the UI thread after {@link #publishProgress} is invoked.
     * The specified values are the values passed to {@link #publishProgress}.
     *
     * @param values The values indicating progress.
     * @see #publishProgress
     * @see #doInBackground
     */
    protected void onProgressUpdate(Progress... values) {
    }

    /**
     * Runs on the UI thread after {@link #cancel(boolean)} is invoked.
     *
     * @see #cancel(boolean)
     * @see #isCancelled()
     */
    protected void onCancelled() {
    }

    /**
     * Returns <tt>true</tt> if this task was cancelled before it completed
     * normally.
     *
     * @return <tt>true</tt> if task was cancelled before it completed
     * @see #cancel(boolean)
     */
    public final boolean isCancelled() {
        return mFuture.isCancelled();
    }

    /**
     * Attempts to cancel execution of this task.  This attempt will
     * fail if the task has already completed, already been cancelled,
     * or could not be cancelled for some other reason. If successful,
     * and this task has not started when <tt>cancel</tt> is called,
     * this task should never run.  If the task has already started,
     * then the <tt>mayInterruptIfRunning</tt> parameter determines
     * whether the thread executing this task should be interrupted in
     * an attempt to stop the task.
     *
     * @param mayInterruptIfRunning <tt>true</tt> if the thread executing this
     *                              task should be interrupted; otherwise, in-progress tasks are allowed
     *                              to complete.
     * @return <tt>false</tt> if the task could not be cancelled,
     * typically because it has already completed normally;
     * <tt>true</tt> otherwise
     * @see #isCancelled()
     * @see #onCancelled()
     */
    public final boolean cancel(boolean mayInterruptIfRunning) {
        return mFuture.cancel(mayInterruptIfRunning);
    }

    /**
     * Waits if necessary for the computation to complete, and then
     * retrieves its result.
     *
     * @return The computed result.
     * @throws CancellationException If the computation was cancelled.
     * @throws ExecutionException    If the computation threw an exception.
     * @throws InterruptedException  If the current thread was interrupted
     *                               while waiting.
     */
    public final Result get() throws InterruptedException, ExecutionException {
        return mFuture.get();
    }

    /**
     * Waits if necessary for at most the given time for the computation
     * to complete, and then retrieves its result.
     *
     * @param timeout Time to wait before cancelling the operation.
     * @param unit    The time unit for the timeout.
     * @return The computed result.
     * @throws CancellationException If the computation was cancelled.
     * @throws ExecutionException    If the computation threw an exception.
     * @throws InterruptedException  If the current thread was interrupted
     *                               while waiting.
     * @throws TimeoutException      If the wait timed out.
     */
    public final Result get(long timeout, TimeUnit unit) throws InterruptedException,
            ExecutionException, TimeoutException {
        return mFuture.get(timeout, unit);
    }

    /**
     * Executes the task with the specified parameters. The task returns
     * itself (this) so that the caller can keep a reference to it.
     * <p/>
     * This method must be invoked on the UI thread.
     *
     * @param params The parameters of the task.
     * @return This instance of AsyncTaskEx.
     * @throws IllegalStateException If {@link #getStatus()} returns either
     *                               {@link AsyncTaskEx.Status#RUNNING} or {@link AsyncTaskEx.Status#FINISHED}.
     */
    public final AsyncTaskEx<Params, Progress, Result> execute(Params... params) {
        if (mStatus != Status.PENDING) {
            switch (mStatus) {
                case RUNNING:
                    throw new IllegalStateException("Cannot execute task:"
                            + " the task is already running.");
                case FINISHED:
                    throw new IllegalStateException("Cannot execute task:"
                            + " the task has already been executed "
                            + "(a task can be executed only once)");
            }
        }

        mStatus = Status.RUNNING;

        onPreExecute();

        mWorker.mParams = params;
        sExecutor.execute(mFuture);

        return this;
    }

    /**
     * This method can be invoked from {@link #doInBackground} to
     * publish updates on the UI thread while the background computation is
     * still running. Each call to this method will trigger the execution of
     * {@link #onProgressUpdate} on the UI thread.
     *
     * @param values The progress values to update the UI with.
     * @see #onProgressUpdate
     * @see #doInBackground
     */
    protected final void publishProgress(Progress... values) {
        sHandler.obtainMessage(MESSAGE_POST_PROGRESS,
                new AsyncTaskExResult<Progress>(this, values)).sendToTarget();
    }

    private void finish(Result result) {
        onPostExecute(result);
        mStatus = Status.FINISHED;
    }

    private static class InternalHandler extends Handler {
        @SuppressWarnings({"rawtypes", "unchecked"})
        @Override
        public void handleMessage(Message msg) {
            AsyncTaskExResult result = (AsyncTaskExResult) msg.obj;
            switch (msg.what) {
                case MESSAGE_POST_RESULT:
                    // There is only one result
                    result.mTask.finish(result.mData[0]);
                    break;
                case MESSAGE_POST_PROGRESS:
                    result.mTask.onProgressUpdate(result.mData);
                    break;
                case MESSAGE_POST_CANCEL:
                    result.mTask.onCancelled();
                    break;
            }
        }
    }

    private static abstract class WorkerRunnable<Params, Result> implements Callable<Result> {
        Params[] mParams;
    }

    private static class AsyncTaskExResult<Data> {
        @SuppressWarnings("rawtypes")
        final AsyncTaskEx mTask;
        final Data[] mData;

        @SuppressWarnings("rawtypes")
        AsyncTaskExResult(AsyncTaskEx task, Data... data) {
            mTask = task;
            mData = data;
        }
    }
}
