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/*
 * Copyright (c) 2014 Badoo Trading Limited
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 * THE SOFTWARE.
 *
 * Portions of documentation in this code are modifications based on work created and
 * shared by Android Open Source Project and used according to terms described in the
 * Apache License, Version 2.0
 */
package com.lijinji.scan.util;

import android.os.Handler;
import android.os.Looper;
import android.os.Message;
import android.support.annotation.NonNull;
import android.support.annotation.Nullable;
import android.support.annotation.VisibleForTesting;

import java.lang.ref.WeakReference;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;

/**
 * Memory safer implementation of android.os.Handler
 * <p/>
 * Original implementation of Handlers always keeps hard reference to handler in queue of execution.
 * If you create anonymous handler and post delayed message into it, it will keep all parent class
 * for that time in memory even if it could be cleaned.
 * <p/>
 * This implementation is trickier, it will keep WeakReferences to runnables and messages,
 * and GC could collect them once WeakHandler instance is not referenced any more
 * <p/>
 *
 * @see Handler
 * <p/>
 * Created by Dmytro Voronkevych on 17/06/2014.
 */
public class WeakHandler {
    private final Handler.Callback mCallback; // hard reference to Callback. We need to keep callback in memory
    private final ExecHandler mExec;
    private Lock mLock = new ReentrantLock();
    @SuppressWarnings("ConstantConditions")
    @VisibleForTesting
    final ChainedRef mRunnables = new ChainedRef(mLock, null);

    /**
     * Default constructor associates this handler with the {@link Looper} for the
     * current thread.
     * <p/>
     * If this thread does not have a looper, this handler won't be able to receive messages
     * so an exception is thrown.
     */
    public WeakHandler() {
        mCallback = null;
        mExec = new ExecHandler();
    }

    /**
     * Constructor associates this handler with the {@link Looper} for the
     * current thread and takes a callback interface in which you can handle
     * messages.
     * <p/>
     * If this thread does not have a looper, this handler won't be able to receive messages
     * so an exception is thrown.
     *
     * @param callback The callback interface in which to handle messages, or null.
     */
    public WeakHandler(@Nullable Handler.Callback callback) {
        mCallback = callback; // Hard referencing body
        mExec = new ExecHandler(new WeakReference<>(callback)); // Weak referencing inside ExecHandler
    }

    /**
     * Use the provided {@link Looper} instead of the default one.
     *
     * @param looper The looper, must not be null.
     */
    public WeakHandler(@NonNull Looper looper) {
        mCallback = null;
        mExec = new ExecHandler(looper);
    }

    /**
     * Use the provided {@link Looper} instead of the default one and take a callback
     * interface in which to handle messages.
     *
     * @param looper   The looper, must not be null.
     * @param callback The callback interface in which to handle messages, or null.
     */
    public WeakHandler(@NonNull Looper looper, @NonNull Handler.Callback callback) {
        mCallback = callback;
        mExec = new ExecHandler(looper, new WeakReference<>(callback));
    }

    /**
     * Causes the Runnable r to be added to the message queue.
     * The runnable will be run on the thread to which this handler is
     * attached.
     *
     * @param r The Runnable that will be executed.
     * @return Returns true if the Runnable was successfully placed in to the
     * message queue.  Returns false on failure, usually because the
     * looper processing the message queue is exiting.
     */
    public final boolean post(@NonNull Runnable r) {
        return mExec.post(wrapRunnable(r));
    }

    /**
     * Causes the Runnable r to be added to the message queue, to be run
     * at a specific time given by <var>uptimeMillis</var>.
     * <b>The time-base is {@link android.os.SystemClock#uptimeMillis}.</b>
     * The runnable will be run on the thread to which this handler is attached.
     *
     * @param r            The Runnable that will be executed.
     * @param uptimeMillis The absolute time at which the callback should run,
     *                     using the {@link android.os.SystemClock#uptimeMillis} time-base.
     * @return Returns true if the Runnable was successfully placed in to the
     * message queue.  Returns false on failure, usually because the
     * looper processing the message queue is exiting.  Note that a
     * result of true does not mean the Runnable will be processed -- if
     * the looper is quit before the delivery time of the message
     * occurs then the message will be dropped.
     */
    public final boolean postAtTime(@NonNull Runnable r, long uptimeMillis) {
        return mExec.postAtTime(wrapRunnable(r), uptimeMillis);
    }

    /**
     * Causes the Runnable r to be added to the message queue, to be run
     * at a specific time given by <var>uptimeMillis</var>.
     * <b>The time-base is {@link android.os.SystemClock#uptimeMillis}.</b>
     * The runnable will be run on the thread to which this handler is attached.
     *
     * @param r            The Runnable that will be executed.
     * @param uptimeMillis The absolute time at which the callback should run,
     *                     using the {@link android.os.SystemClock#uptimeMillis} time-base.
     * @return Returns true if the Runnable was successfully placed in to the
     * message queue.  Returns false on failure, usually because the
     * looper processing the message queue is exiting.  Note that a
     * result of true does not mean the Runnable will be processed -- if
     * the looper is quit before the delivery time of the message
     * occurs then the message will be dropped.
     * @see android.os.SystemClock#uptimeMillis
     */
    public final boolean postAtTime(Runnable r, Object token, long uptimeMillis) {
        return mExec.postAtTime(wrapRunnable(r), token, uptimeMillis);
    }

    /**
     * Causes the Runnable r to be added to the message queue, to be run
     * after the specified amount of time elapses.
     * The runnable will be run on the thread to which this handler
     * is attached.
     *
     * @param r           The Runnable that will be executed.
     * @param delayMillis The delay (in milliseconds) until the Runnable
     *                    will be executed.
     * @return Returns true if the Runnable was successfully placed in to the
     * message queue.  Returns false on failure, usually because the
     * looper processing the message queue is exiting.  Note that a
     * result of true does not mean the Runnable will be processed --
     * if the looper is quit before the delivery time of the message
     * occurs then the message will be dropped.
     */
    public final boolean postDelayed(Runnable r, long delayMillis) {
        return mExec.postDelayed(wrapRunnable(r), delayMillis);
    }

    /**
     * Posts a message to an object that implements Runnable.
     * Causes the Runnable r to executed on the next iteration through the
     * message queue. The runnable will be run on the thread to which this
     * handler is attached.
     * <b>This method is only for use in very special circumstances -- it
     * can easily starve the message queue, cause ordering problems, or have
     * other unexpected side-effects.</b>
     *
     * @param r The Runnable that will be executed.
     * @return Returns true if the message was successfully placed in to the
     * message queue.  Returns false on failure, usually because the
     * looper processing the message queue is exiting.
     */
    public final boolean postAtFrontOfQueue(Runnable r) {
        return mExec.postAtFrontOfQueue(wrapRunnable(r));
    }

    /**
     * Remove any pending posts of Runnable r that are in the message queue.
     */
    public final void removeCallbacks(Runnable r) {
        final WeakRunnable runnable = mRunnables.remove(r);
        if (runnable != null) {
            mExec.removeCallbacks(runnable);
        }
    }

    /**
     * Remove any pending posts of Runnable <var>r</var> with Object
     * <var>TOKEN_KEY</var> that are in the message queue.  If <var>TOKEN_KEY</var> is null,
     * all callbacks will be removed.
     */
    public final void removeCallbacks(Runnable r, Object token) {
        final WeakRunnable runnable = mRunnables.remove(r);
        if (runnable != null) {
            mExec.removeCallbacks(runnable, token);
        }
    }

    /**
     * Pushes a message onto the end of the message queue after all pending messages
     * before the current time. It will be received in callback,
     * in the thread attached to this handler.
     *
     * @return Returns true if the message was successfully placed in to the
     * message queue.  Returns false on failure, usually because the
     * looper processing the message queue is exiting.
     */
    public final boolean sendMessage(Message msg) {
        return mExec.sendMessage(msg);
    }

    /**
     * Sends a Message containing only the what value.
     *
     * @return Returns true if the message was successfully placed in to the
     * message queue.  Returns false on failure, usually because the
     * looper processing the message queue is exiting.
     */
    public final boolean sendEmptyMessage(int what) {
        return mExec.sendEmptyMessage(what);
    }

    /**
     * Sends a Message containing only the what value, to be delivered
     * after the specified amount of time elapses.
     *
     * @return Returns true if the message was successfully placed in to the
     * message queue.  Returns false on failure, usually because the
     * looper processing the message queue is exiting.
     * @see #sendMessageDelayed(Message, long)
     */
    public final boolean sendEmptyMessageDelayed(int what, long delayMillis) {
        return mExec.sendEmptyMessageDelayed(what, delayMillis);
    }

    /**
     * Sends a Message containing only the what value, to be delivered
     * at a specific time.
     *
     * @return Returns true if the message was successfully placed in to the
     * message queue.  Returns false on failure, usually because the
     * looper processing the message queue is exiting.
     * @see #sendMessageAtTime(Message, long)
     */
    public final boolean sendEmptyMessageAtTime(int what, long uptimeMillis) {
        return mExec.sendEmptyMessageAtTime(what, uptimeMillis);
    }

    /**
     * Enqueue a message into the message queue after all pending messages
     * before (current time + delayMillis). You will receive it in
     * callback, in the thread attached to this handler.
     *
     * @return Returns true if the message was successfully placed in to the
     * message queue.  Returns false on failure, usually because the
     * looper processing the message queue is exiting.  Note that a
     * result of true does not mean the message will be processed -- if
     * the looper is quit before the delivery time of the message
     * occurs then the message will be dropped.
     */
    public final boolean sendMessageDelayed(Message msg, long delayMillis) {
        return mExec.sendMessageDelayed(msg, delayMillis);
    }

    /**
     * Enqueue a message into the message queue after all pending messages
     * before the absolute time (in milliseconds) <var>uptimeMillis</var>.
     * <b>The time-base is {@link android.os.SystemClock#uptimeMillis}.</b>
     * You will receive it in callback, in the thread attached
     * to this handler.
     *
     * @param uptimeMillis The absolute time at which the message should be
     *                     delivered, using the
     *                     {@link android.os.SystemClock#uptimeMillis} time-base.
     * @return Returns true if the message was successfully placed in to the
     * message queue.  Returns false on failure, usually because the
     * looper processing the message queue is exiting.  Note that a
     * result of true does not mean the message will be processed -- if
     * the looper is quit before the delivery time of the message
     * occurs then the message will be dropped.
     */
    public boolean sendMessageAtTime(Message msg, long uptimeMillis) {
        return mExec.sendMessageAtTime(msg, uptimeMillis);
    }

    /**
     * Enqueue a message at the front of the message queue, to be processed on
     * the next iteration of the message loop.  You will receive it in
     * callback, in the thread attached to this handler.
     * <b>This method is only for use in very special circumstances -- it
     * can easily starve the message queue, cause ordering problems, or have
     * other unexpected side-effects.</b>
     *
     * @return Returns true if the message was successfully placed in to the
     * message queue.  Returns false on failure, usually because the
     * looper processing the message queue is exiting.
     */
    public final boolean sendMessageAtFrontOfQueue(Message msg) {
        return mExec.sendMessageAtFrontOfQueue(msg);
    }

    /**
     * Remove any pending posts of messages with code 'what' that are in the
     * message queue.
     */
    public final void removeMessages(int what) {
        mExec.removeMessages(what);
    }

    /**
     * Remove any pending posts of messages with code 'what' and whose obj is
     * 'object' that are in the message queue.  If <var>object</var> is null,
     * all messages will be removed.
     */
    public final void removeMessages(int what, Object object) {
        mExec.removeMessages(what, object);
    }

    /**
     * Remove any pending posts of callbacks and sent messages whose
     * <var>obj</var> is <var>TOKEN_KEY</var>.  If <var>TOKEN_KEY</var> is null,
     * all callbacks and messages will be removed.
     */
    public final void removeCallbacksAndMessages(Object token) {
        mExec.removeCallbacksAndMessages(token);
    }

    /**
     * Check if there are any pending posts of messages with code 'what' in
     * the message queue.
     */
    public final boolean hasMessages(int what) {
        return mExec.hasMessages(what);
    }

    /**
     * Check if there are any pending posts of messages with code 'what' and
     * whose obj is 'object' in the message queue.
     */
    public final boolean hasMessages(int what, Object object) {
        return mExec.hasMessages(what, object);
    }

    public final Looper getLooper() {
        return mExec.getLooper();
    }

    private WeakRunnable wrapRunnable(@NonNull Runnable r) {
        //noinspection ConstantConditions
        if (r == null) {
            throw new NullPointerException("Runnable can't be null");
        }
        final ChainedRef hardRef = new ChainedRef(mLock, r);
        mRunnables.insertAfter(hardRef);
        return hardRef.wrapper;
    }

    private static class ExecHandler extends Handler {
        private final WeakReference<Callback> mCallback;

        ExecHandler() {
            mCallback = null;
        }

        ExecHandler(WeakReference<Callback> callback) {
            mCallback = callback;
        }

        ExecHandler(Looper looper) {
            super(looper);
            mCallback = null;
        }

        ExecHandler(Looper looper, WeakReference<Callback> callback) {
            super(looper);
            mCallback = callback;
        }

        @Override
        public void handleMessage(@NonNull Message msg) {
            if (mCallback == null) {
                return;
            }
            final Callback callback = mCallback.get();
            if (callback == null) { // Already disposed
                return;
            }
            callback.handleMessage(msg);
        }
    }

    static class WeakRunnable implements Runnable {
        private final WeakReference<Runnable> mDelegate;
        private final WeakReference<ChainedRef> mReference;

        WeakRunnable(WeakReference<Runnable> delegate, WeakReference<ChainedRef> reference) {
            mDelegate = delegate;
            mReference = reference;
        }

        @Override
        public void run() {
            final Runnable delegate = mDelegate.get();
            final ChainedRef reference = mReference.get();
            if (reference != null) {
                reference.remove();
            }
            if (delegate != null) {
                delegate.run();
            }
        }
    }

    static class ChainedRef {
        @Nullable
        ChainedRef next;
        @Nullable
        ChainedRef prev;
        @NonNull
        final Runnable runnable;
        @NonNull
        final WeakRunnable wrapper;

        @NonNull
        Lock lock;

        public ChainedRef(@NonNull Lock lock, @NonNull Runnable r) {
            this.runnable = r;
            this.lock = lock;
            this.wrapper = new WeakRunnable(new WeakReference<>(r), new WeakReference<>(this));
        }

        public WeakRunnable remove() {
            lock.lock();
            try {
                if (prev != null) {
                    prev.next = next;
                }
                if (next != null) {
                    next.prev = prev;
                }
                prev = null;
                next = null;
            } finally {
                lock.unlock();
            }
            return wrapper;
        }

        public void insertAfter(@NonNull ChainedRef candidate) {
            lock.lock();
            try {
                if (this.next != null) {
                    this.next.prev = candidate;
                }

                candidate.next = this.next;
                this.next = candidate;
                candidate.prev = this;
            } finally {
                lock.unlock();
            }
        }

        @Nullable
        public WeakRunnable remove(Runnable obj) {
            lock.lock();
            try {
                ChainedRef curr = this.next; // Skipping head
                while (curr != null) {
                    if (curr.runnable == obj) { // We do comparison exactly how Handler does inside
                        return curr.remove();
                    }
                    curr = curr.next;
                }
            } finally {
                lock.unlock();
            }
            return null;
        }
    }
}