/*
 * Copyright (C) 2006 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 android.os;

import android.util.AndroidRuntimeException;
import android.util.Log;

import java.util.ArrayList;

/**
 * Low-level class holding the list of messages to be dispatched by a
 * {@link Looper}.  Messages are not added directly to a MessageQueue,
 * but rather through {@link Handler} objects associated with the Looper.
 * 
 * <p>You can retrieve the MessageQueue for the current thread with
 * {@link Looper#myQueue() Looper.myQueue()}.
 */
public class MessageQueue {
    Message mMessages;
    private final ArrayList<IdleHandler> mIdleHandlers = new ArrayList<IdleHandler>();
    private IdleHandler[] mPendingIdleHandlers;
    private boolean mQuiting;
    boolean mQuitAllowed = true;

    // Indicates whether next() is blocked waiting in pollOnce() with a non-zero timeout.
    private boolean mBlocked;

    // Indicates the barrier nesting level.
    private int mBarrierNestCount;

    @SuppressWarnings("unused")
    private int mPtr; // used by native code
    
    private native void nativeInit();
    private native void nativeDestroy();
    private native void nativePollOnce(int ptr, int timeoutMillis);
    private native void nativeWake(int ptr);

    /**
     * Callback interface for discovering when a thread is going to block
     * waiting for more messages.
     */
    public static interface IdleHandler {
        /**
         * Called when the message queue has run out of messages and will now
         * wait for more.  Return true to keep your idle handler active, false
         * to have it removed.  This may be called if there are still messages
         * pending in the queue, but they are all scheduled to be dispatched
         * after the current time.
         */
        boolean queueIdle();
    }

    /**
     * Add a new {@link IdleHandler} to this message queue.  This may be
     * removed automatically for you by returning false from
     * {@link IdleHandler#queueIdle IdleHandler.queueIdle()} when it is
     * invoked, or explicitly removing it with {@link #removeIdleHandler}.
     * 
     * <p>This method is safe to call from any thread.
     * 
     * @param handler The IdleHandler to be added.
     */
    public final void addIdleHandler(IdleHandler handler) {
        if (handler == null) {
            throw new NullPointerException("Can't add a null IdleHandler");
        }
        synchronized (this) {
            mIdleHandlers.add(handler);
        }
    }

    /**
     * Remove an {@link IdleHandler} from the queue that was previously added
     * with {@link #addIdleHandler}.  If the given object is not currently
     * in the idle list, nothing is done.
     * 
     * @param handler The IdleHandler to be removed.
     */
    public final void removeIdleHandler(IdleHandler handler) {
        synchronized (this) {
            mIdleHandlers.remove(handler);
        }
    }

    /**
     * Acquires a synchronization barrier.
     *
     * While a synchronization barrier is active, only asynchronous messages are
     * permitted to execute.  Synchronous messages are retained but are not executed
     * until the synchronization barrier is released.
     *
     * This method is used to immediately postpone execution of all synchronous messages
     * until a condition is met that releases the barrier.  Asynchronous messages are
     * exempt from the barrier and continue to be executed as usual.
     *
     * This call nests and must be matched by an equal number of calls to
     * {@link #releaseSyncBarrier}.
     *
     * @hide
     */
    public final void acquireSyncBarrier() {
        synchronized (this) {
            mBarrierNestCount += 1;
        }
    }

    /**
     * Releases a synchronization barrier.
     *
     * This class undoes one invocation of {@link #acquireSyncBarrier}.
     *
     * @throws IllegalStateException if the barrier is not acquired.
     *
     * @hide
     */
    public final void releaseSyncBarrier() {
        synchronized (this) {
            if (mBarrierNestCount == 0) {
                throw new IllegalStateException("The message queue synchronization barrier "
                        + "has not been acquired.");
            }

            mBarrierNestCount -= 1;
            if (!mBlocked || mMessages == null) {
                return;
            }
        }
        nativeWake(mPtr);
    }

    MessageQueue() {
        nativeInit();
    }
    
    @Override
    protected void finalize() throws Throwable {
        try {
            nativeDestroy();
        } finally {
            super.finalize();
        }
    }

    final Message next() {
        int pendingIdleHandlerCount = -1; // -1 only during first iteration
        int nextPollTimeoutMillis = 0;

        for (;;) {
            if (nextPollTimeoutMillis != 0) {
                Binder.flushPendingCommands();
            }
            nativePollOnce(mPtr, nextPollTimeoutMillis);

            synchronized (this) {
                // Try to retrieve the next message.  Return if found.
                final long now = SystemClock.uptimeMillis();

                Message prevMsg = null;
                Message msg = mMessages;
                for (;;) {
                    if (msg == null) {
                        // No more messages.
                        nextPollTimeoutMillis = -1;
                        break;
                    }

                    final long when = msg.when;
                    if (now < when) {
                        // Next message is not ready.  Set a timeout to wake up when it is ready.
                        nextPollTimeoutMillis = (int) Math.min(when - now, Integer.MAX_VALUE);
                        break;
                    }

                    if (mBarrierNestCount == 0 || msg.isAsynchronous()) {
                        // Got a message.
                        mBlocked = false;
                        if (prevMsg != null) {
                            prevMsg.next = msg.next;
                        } else {
                            mMessages = msg.next;
                        }
                        msg.next = null;
                        if (false) Log.v("MessageQueue", "Returning message: " + msg);
                        msg.markInUse();
                        return msg;
                    }

                    // We have a message that we could return except that it is
                    // blocked by the sync barrier.  In particular, this means that
                    // we are not idle yet, so we do not want to run the idle handlers.
                    prevMsg = msg;
                    msg = msg.next;
                }

                // If first time idle, then get the number of idlers to run.
                if (pendingIdleHandlerCount < 0 && msg == mMessages) {
                    pendingIdleHandlerCount = mIdleHandlers.size();
                }
                if (pendingIdleHandlerCount <= 0) {
                    // No idle handlers to run.  Loop and wait some more.
                    mBlocked = true;
                    continue;
                }

                if (mPendingIdleHandlers == null) {
                    mPendingIdleHandlers = new IdleHandler[Math.max(pendingIdleHandlerCount, 4)];
                }
                mPendingIdleHandlers = mIdleHandlers.toArray(mPendingIdleHandlers);
            }

            // Run the idle handlers.
            // We only ever reach this code block during the first iteration.
            for (int i = 0; i < pendingIdleHandlerCount; i++) {
                final IdleHandler idler = mPendingIdleHandlers[i];
                mPendingIdleHandlers[i] = null; // release the reference to the handler

                boolean keep = false;
                try {
                    keep = idler.queueIdle();
                } catch (Throwable t) {
                    Log.wtf("MessageQueue", "IdleHandler threw exception", t);
                }

                if (!keep) {
                    synchronized (this) {
                        mIdleHandlers.remove(idler);
                    }
                }
            }

            // Reset the idle handler count to 0 so we do not run them again.
            pendingIdleHandlerCount = 0;

            // While calling an idle handler, a new message could have been delivered
            // so go back and look again for a pending message without waiting.
            nextPollTimeoutMillis = 0;
        }
    }

    final boolean enqueueMessage(Message msg, long when) {
        if (msg.isInUse()) {
            throw new AndroidRuntimeException(msg
                    + " This message is already in use.");
        }
        if (msg.target == null && !mQuitAllowed) {
            throw new RuntimeException("Main thread not allowed to quit");
        }
        final boolean needWake;
        synchronized (this) {
            if (mQuiting) {
                RuntimeException e = new RuntimeException(
                    msg.target + " sending message to a Handler on a dead thread");
                Log.w("MessageQueue", e.getMessage(), e);
                return false;
            } else if (msg.target == null) {
                mQuiting = true;
            }

            msg.when = when;
            //Log.d("MessageQueue", "Enqueing: " + msg);
            Message p = mMessages;
            if (p == null || when == 0 || when < p.when) {
                // New head, wake up the event queue if blocked.
                msg.next = p;
                mMessages = msg;
                needWake = mBlocked;
            } else {
                // Inserted within the middle of the queue.  Usually we don't have to wake
                // up the event queue unless the message is asynchronous and it might be
                // possible for it to be returned out of sequence relative to an earlier
                // synchronous message at the head of the queue.
                Message prev = null;
                while (p != null && p.when <= when) {
                    prev = p;
                    p = p.next;
                }
                msg.next = prev.next;
                prev.next = msg;
                needWake = mBlocked && mBarrierNestCount != 0 && msg.isAsynchronous()
                        && !mMessages.isAsynchronous();
            }
        }
        if (needWake) {
            nativeWake(mPtr);
        }
        return true;
    }

    final boolean removeMessages(Handler h, int what, Object object,
            boolean doRemove) {
        synchronized (this) {
            Message p = mMessages;
            boolean found = false;

            // Remove all messages at front.
            while (p != null && p.target == h && p.what == what
                   && (object == null || p.obj == object)) {
                if (!doRemove) return true;
                found = true;
                Message n = p.next;
                mMessages = n;
                p.recycle();
                p = n;
            }

            // Remove all messages after front.
            while (p != null) {
                Message n = p.next;
                if (n != null) {
                    if (n.target == h && n.what == what
                        && (object == null || n.obj == object)) {
                        if (!doRemove) return true;
                        found = true;
                        Message nn = n.next;
                        n.recycle();
                        p.next = nn;
                        continue;
                    }
                }
                p = n;
            }
            
            return found;
        }
    }

    final void removeMessages(Handler h, Runnable r, Object object) {
        if (r == null) {
            return;
        }

        synchronized (this) {
            Message p = mMessages;

            // Remove all messages at front.
            while (p != null && p.target == h && p.callback == r
                   && (object == null || p.obj == object)) {
                Message n = p.next;
                mMessages = n;
                p.recycle();
                p = n;
            }

            // Remove all messages after front.
            while (p != null) {
                Message n = p.next;
                if (n != null) {
                    if (n.target == h && n.callback == r
                        && (object == null || n.obj == object)) {
                        Message nn = n.next;
                        n.recycle();
                        p.next = nn;
                        continue;
                    }
                }
                p = n;
            }
        }
    }

    final void removeCallbacksAndMessages(Handler h, Object object) {
        synchronized (this) {
            Message p = mMessages;

            // Remove all messages at front.
            while (p != null && p.target == h
                    && (object == null || p.obj == object)) {
                Message n = p.next;
                mMessages = n;
                p.recycle();
                p = n;
            }

            // Remove all messages after front.
            while (p != null) {
                Message n = p.next;
                if (n != null) {
                    if (n.target == h && (object == null || n.obj == object)) {
                        Message nn = n.next;
                        n.recycle();
                        p.next = nn;
                        continue;
                    }
                }
                p = n;
            }
        }
    }

    /*
    private void dumpQueue_l()
    {
        Message p = mMessages;
        System.out.println(this + "  queue is:");
        while (p != null) {
            System.out.println("            " + p);
            p = p.next;
        }
    }
    */
}